AMC6821-Q1
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INTELLIGENT TEMPERATURE MONITOR AND PWM FAN CONTROLLER
FEATURES
1
• Qualified for Automotive Applications
• Remote Temperature Sensor:
±3°C Accuracy, 0.250°C Resolution
• Local Temperature Sensor:
±3°C Accuracy, 0.250°C Resolution
• PWM Controller
• PWM Frequency: 10Hz to 40kHz
• Duty Cycle: 0% to 100%, 8 Bits
234
•
•
•
•
•
•
Automatic Fan Speed Control Loops
SMBus Interface
Power: 2.7 V to 5.5 V
Package (Green): SSOP-16 (4mm × 5mm)
RoHS Compliant
Latch-Up Exceeds 100 mA
per JESD78B - Class I
DESCRIPTION
The AMC6821 is an intelligent temperature monitor and pulse-width modulation (PWM) fan controller. It is
designed for noise-sensitive or power-sensitive applications that require active system cooling. Using either a
low-frequency or a high-frequency PWM signal, this device can simultaneously drive a fan, monitor remote
sensor diode temperatures, and measure and control the fan speed so that it operates with minimal acoustic
noise at the lowest possible speed.
The AMC6821 has three fan control modes: Auto Temperature-Fan mode, Software-RPM mode, and
Software-DCY mode. Each mode controls the fan speed by changing the duty cycle of a PWM output. Auto
Temperature-Fan mode is an intelligent, closed-loop control that optimizes fan speed according to user-defined
parameters. This mode allows the AMC6821 to run as a stand-alone device without CPU intervention; the fan
can continue to be controlled (based on temperature measurements) even if the CPU or system locks up.
Software-RPM mode is a second closed-loop control. In this mode, the AMC6821 adjusts the PWM output to
maintain a consistent fan speed at a user-specified target value; that is, the device functions as a fan speed
regulator. Software-RPM mode can also be used to allow the AMC6821 to operate as a stand-alone device. The
third mode, Software-DCY, is open-loop. In Software-DCY mode, the PWM duty cycle is set directly by the value
written to the device.
The AMC6821 has a programmable SMBALERT output to indicate error conditions and a dedicated FAN-FAULT
output to indicate fan failure. The THERM pin is a fail-safe output for over-temperature conditions that can be
used to throttle a CPU clock. Additionally, the OVR pin indicates the over-temperature limit as well. All of the
alarm thresholds are set through the device registers. The AMC6821 is available in a SSOP-16 package.
ORDERING INFORMATION (1)
PACKAGE (2)
TA
–40°C to 125°C
(1)
(2)
SSOP – DBQ
Reel of 2500
ORDERABLE PART NUMBER
AMC6821SQDBQRQ1
TOP-SIDE MARKING
AMC6821Q
For the most current package and ordering information, see the Package Option Addendum at the end of this document, or see the TI
web site at www.ti.com.
Package drawings, thermal data, and symbolization are available at www.ti.com/packaging.
1
2
3
4
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Pentium M, Pentium-IV are trademarks of Intel.
JMC is a trademark of JMC Products.
I2C is a trademark of Philips International, Inc.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2009, Texas Instruments Incorporated
AMC6821-Q1
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This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
Functional Block Diagram
VDD
GND
AMC6821
SMBALERT
SDA
FAN-FAULT
THERM
Alarm
Detectors
SMBus
2
IC
Interface
Temperature
Data
TACH-DATA
OVR
SCLK
A1
A0
IN+
IN-
TACH COUNTER
ADC
(11-Bit)
MUX
TACH
PWM-Out
PWM
Driver
On-Chip
Temperature Sensor
PWM-MODE
Ref
Remote
Temperature
Sensing
Auto Fan Speed
Controller
NOTE: Patents 7, 083,328 and 7,098,617
ABSOLUTE MAXIMUM RATINGS (1)
over operating free-air temperature range (unless otherwise noted)
VDD to GND
–0.3 V to 6.5 V
Digital input voltage to GND
–0.3 V to 6.5 V
Input current
10 mA
Select pins A0, A1, PWM-MODE to GND
–0.3 V to VDD + 0.3 V
Analog input voltage to GND
–0.3 V to VDD + 0.3 V
Operating temperature range
–40°C to 125°C
Storage temperature range
–65°C to 150°C
Junction temperature (TJ Max)
(1)
150°C
Stresses above these ratings may cause permanent damage. Exposure to absolute maximum conditions for extended periods may
degrade device reliability. These are stress ratings only, and functional operation of the device at these or any other conditions beyond
those specified is not implied.
RECOMMENDED OPERATING CONDITIONS
MIN
NOM
MAX
Operating VDD
2.7
5
5.5
V
Specified VDD
3
5
V
–40
125
°C
Operating temperature
2
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ELECTRICAL CHARACTERISTICS
TA = –40°C to 100°C and VDD = 3 V or 5 V (unless otherwise noted)
AMC6821
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNIT
TA = 0°C to 90°C
±0.5
±3.0
°C
TA = –25°C to 100°C
±1.0
±4.0
°C
TR = 50°C to 100°C
±0.5
±3.0
°C
±1.0
±4.0
°C
TEMPERATURE MEASUREMENT
Local sensor accuracy
Remote sensor accuracy (1)
TR = –40°C to 125°C
Sensor resolution
Both channels
0.125
°C
Conversion time
Two channels
62.5
ms
PWM CONTROLLER
PWM frequency range (programmable) (2)
PWM frequency accuracy
TA = 25°C to 100°C
Duty cycle (2)
Programmable
Duty cycle resolution
8-bit
10
40k
Hz
–6
+7
%
0
100
%
0.39
%/bit
FAN RPM-TO-DIGITAL CONVERTER
Accuracy
Full-scale count
TA = 25°C to 100°C
–6
+7
(2)
%
65535
Nominal input RPM (2)
100
Internal clock frequency for RPM measurement
23000
100
RPM
kHz
DIGITAL INPUT/OUTPUT
VOL
Open-drain output low voltage
IOH
Open-drain high-level output leakage current
Sink current 6 mA, VDD = 3 V
VIH
Input high voltage
VIL
Input low voltage
IIH
Input high current
IIL
Input low current
0
0.1
0.4
V
1
µA
2.1
V
0.8
1
Input capacitance
V
µA
–1
5
µA
pF
POWER SUPPLY
Current
VDD = 5
Power dissipation
(1)
(2)
1.1
2.0
5
mA
mW
The remote temperature sensor is optimized for the Pentium M™ thermal diode with diode ideality n = 1.0022 and TA = 0°C to 100°C.
Not production tested. Specified by design.
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SDA
tLOW
tF
tSU:DAT
tF
tHD:STA
tF
tBUF
tR
SCLK
S
tHD:STA
tSU:STA
tHD:DAT
tHIGH
tSU:STO
Sr
P
S
Figure 1. Timing Specification
TIMING REQUIREMENTS
At VDD = 3 V or +5V, and TA = –40°C to +125°C, unless otherwise noted.
AMC6821
PARAMETER
MIN
TYP
MAX
UNIT
100
kHz
fSCLK
Clock frequency
tBUF
Bus free time
4.7
µs
tSU:STA
Start setup time
4.7
µs
tHD:STA
Start hold time
4.0
µs
tSU:STO
Stop condition setup time
4.0
µs
tLOW
SCLK low time
4.7
µs
tHIGH
SCLK high time
4.0
tR
SCLK, SDA rise time
tF
SCLK, SDA fall time
tSU:DAT
Data setup time
350
ns
tHD:DAT
Data hold time
350
ns
tPOR
Time from software reset command or power-on to normal operation. During this period,
I2C™ communication is not recognized.
4
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µs
1000
ns
300
ns
1.5
ms
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DEVICE INFORMATION
SSOP-16
(body size: 5mm x 4mm)
PWM-OUT
1
16 SCLK
TACH
2
15 SDA
OVR
3
14 SMBALERT
NC
4
GND
5
12 A1
VDD
6
11 PWM-MODE
THERM
7
10 IN+
FAN-FAULT
8
9
AMC6821
13 A0
IN-
Table 1. TERMINAL FUNCTIONS
NAME
NO.
DESCRIPTION
PWM-OUT
1
Digital output, open-drain. PWM output to control fan speed.
TACH
2
Digital input. Fan tachometer input to measure the fan speed.
OVR
3
Digital output, open-drain, active low. Goes low when temperature reaches the critical shutdown
threshold or remote temperature sensor failed. (See the Interrupt section for details.)
NC
4
Not connected. Reserved for manufacturer's testing.
GND
5
System ground
VDD
6
Power supply, 3 V to 5 V
THERM
7
Digital input/output (open-drain). As an output, an active low output indicates the temperature over the
THERM temperature limit. As an input, the pin provides an external fan control. When the pin is pulled
low by external signal, the THERM-IN bit is set, and the fan is set to full-speed.
FAN-FAULT
8
Digital open-drain output. Goes low when a fan failure is detected.
IN–
9
Negative analog differential input. Connected to cathode of external temperature-sensing diode.
IN+
10
Positive analog differential input. Connected to anode of external temperature-sensing diode
Pentium-IV™ substrate transistor or general-purpose 2N3904 type transistor.
PWM-MODE
11
PWM mode selection. When tied low (GND), the high PWM frequency range (1 kHz to 40 kHz) is
selected. When tied to VDD or floated, the low PWM frequency range (10 Hz to 94 Hz) is selected.
Checked only on power-up or reset.
A1
12
Device slave address selection pin (see the SMB Interface section for details). Checked only on
power-up or reset.
A0
13
Device slave address selection pin (see the SMB Interface section for details). Checked only on
power-up or reset.
SMBALERT
14
Digital output, open-drain, SMBALERT, active low. Requires a pull-up resistor (2.2 kΩ typical).
SDA
15
Bi-directional digital I/O pin, SMBus data, open-drain. Requires a pull-up resistor (2.2 kΩ typical).
SCLK
16
Digital input, SMBus clock. Requires a pull-up resistor (2.2 kΩ typical).
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TYPICAL CHARACTERISTICS
TA = 25°C, VDD = 5 V (unless otherwise noted)
REMOTE CHANNEL ERROR vs REMOTE TEMPERATURE
LOCAL CHANNEL ERROR FROM CALIBRATED BATH
3
2
Local Channel Error (°C)
Remote Channel Error (°C)
3
Remote Error, VDD = 3V
1
0
-1
Remote Error, VDD = 5V
2
VDD = 5V
1
0
VDD = 3V
-1
-2
-2
-3
-3
0
-20
-40
20
40
60
80
100
120
-40
0
-20
Remote Temperature (°C)
40
60
80
Figure 2.
Figure 3.
TEMPERATURE ERROR vs
POWER-SUPPLY NOISE FREQUENCY
TEMPERATURE ERROR vs
COMMON-MODE NOISE FREQUENCY
20
100
5
4
15
250mVPP
10
Remote Channel Error (°C)
Remote Channel Error (°C)
20
Local Temperature (°C)
5
0
-5
100mVPP
-10
-15
3
50mVPP
2
1
0
-1
20mVPP
-2
-3
-4
-20
-5
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
100k
10k
1M
10M
100M
Frequency (Hz)
Frequency (MHz)
Figure 4.
Figure 5.
SUPPLY CURRENT vs VDD
SUPPLY CURRENT vs TEMPERATURE
2.0
1.4
IDD 5V (mA)
1.8
1.2
Supply CUrrent (mA)
Supply Current (mA)
1.6
1.4
1.2
1.0
0.8
0.6
1.0
0.8
IDD 3V (mA)
0.6
0.4
0.4
0.2
0.2
0
0
2.7
6
3.3
3.9
4.5
5.1
-40
-20
0
20
40
60
VDD (V)
Temperature (°C)
Figure 6.
Figure 7.
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80
100
120
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TYPICAL CHARACTERISTICS (continued)
TA = 25°C, VDD = 5 V (unless otherwise noted)
TEMPERATURE ERROR vs DIFFERENTIAL MODE NOISE
FREQUENCY
TEMPERATURE ERROR vs CAPACITANCE
BETWEEN IN+ AND IN–
5
4
Remote Channel Error (°C)
Remote Channel Error (°C)
5
20mVPP
3
2
1
10mVPP
0
0
-5
-10
-15
-1
10k
100k
1M
10M
0.1
0
100M
1.0
10.0
Capacitance IN+ to IN- (nF)
Frequency (Hz)
Figure 8.
Figure 9.
PWM FREQUENCY ERROR vs TEMPERATURE
10
8
Frequency Error (%)
6
4
VDD = 5V
2
0
-2
VDD = 3V
-4
-6
-8
-10
0
20
40
60
80
100
DUT Temperature (°C)
Figure 10.
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SMBUS INTERFACE
The AMC6821 communicates through the serial system management bus (SMBus). The AMC6821 is connected
to this bus as a slave device, under the control of a bus master. The AMC6821 has a 7-bit serial bus address
that is programmable by properly connecting the address pins A0 and A1. Table 2 shows the selection of the
AMC6821 slave address. The address selection pins should be either tied directly to VDD or GND. For the NC
condition, they should be unconnected with minimum trace capacitance. Note that the address is checked only
on a reset or power-up condition.
Table 2. AMC6821 Address Select (1)
(1)
A0
A1
ADDRESS
GND
GND
0011000
NC
GND
0011010
VDD
GND
0011001
GND
NC
0101100
NC
NC
0101110
VDD
NC
0101101
GND
VDD
1001100
NC
VDD
1001110
VDD
VDD
1001101
NC = No connection.
Communication Protocols
The AMC6821 employs four standard SMBus protocols: the send byte, receive byte, write byte, and read byte.
All other operations result in undefined results. Repeated start is not allowed during the read bit.
Table 3. Send Byte
S
SLAVE ADDRESS
WR
ACK
COMMAND
7-bit AMC6821 slave address
ACK
P
8-bit register address
S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0).
Table 4. Receive Byte
S
SLAVE ADDRESS
RD
ACK
DATA
NACK
P
8-bit data from the register selected
previously
7-bit AMC6821 slave address
S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; RD = read (bit value of 1); NACK = not
acknowledged.
Table 5. Write Byte
S
SLAVE ADDRESS
WR
7-bit AMC6821 slave address
ACK
COMMAND
ACK
8-bit register address
DATA
ACK
P
8-bit data written to register
S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0).
8
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Table 6. Write Multiple Bytes
S
SLAVE ADDRESS
WR
ACK
COMMAND
7-bit AMC6821 slave
address
ACK
8-bit register address of
first register to be written
DATA
ACK
DATA
ACK
First 8-bit data written
first register
...
DATA
DATA
Third 8-bit data written third register
ACK
Second 8-bit data written
second register
ACK
P
Last 8-bit data
S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0).
The first register is the one to which the first data byte is written. The next register is the second register. If the
bus master continues to transfer data into the AMC6821 after writing the last location, all data are ignored until
the operation stops.
Table 7. Read Byte
S
SLAVE ADDRESS
WR
ACK
7-bit AMC6821 slave
address
COMMAND
ACK
Sr
SLAVE ADDRESS
RD
ACK
DATA
7-bit AMC6821 slave
address
8-bit register address
NACK
P
8-bit data from
register
S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0); RD = read (bit
value of 1);
NACK = not acknowledged; Sr = repeated start condition.
Table 8. Read Multiple Bytes
S
SLAVE ADDRESS
WR
7-bit AMC6821 slave
address
DATA
ACK
COMMAND
ACK
Address of first
register to be read
ACK
Sr
SLAVE ADDRESS
RD
ACK
7-bit AMC6821 slave
address
...
DATA
DATA
8-bit data from second register
ACK
8-bit data from first
register
NACK
P
Last 8-bit data
S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; WR = write (bit value of 0); RD = read (bit
value of 1);
NACK = not acknowledged; Sr = repeated start condition.
The first register is the one from which the first data byte is transmitted. The next register is the second register.
If the bus master continues clocking data out after reading the last location (0x3F), the value 0x00 is sent out
until the operation stops.
The AMC6821 is entirely controlled by the registers. All registers are 8-bit. The AMC6821 has an address pointer
register; the value of the address pointer register determines the register to be written to or read from. To write
data to the device register or read data from it, the address pointer register must be set properly. Data can then
be written into or read from that register. The command issued by the bus master always contains the initial
value of the address pointer register. The command is constructed as shown in Table 9.
Table 9. Command Format (1)
Bit 7 (MSB)
0
Bit 6
0
Bit 5
ADDR5
Bit 4
ADDR4
Bit 3
ADDR3
Bit 2
ADDR2
Bit 1
ADDR1
Bit 0 (LSB)
ADDR0
In the send byte operation, the bus master writes the address of a specified device register into the address
pointer register.
In the receive byte operation, the bus master reads the data back from the device register addressed by the
address point register.
In the write byte operation, the bus master sets the address pointer register to the address of a specified device
register, then writes 8-bit data into it. In the read byte operation, the SMBus master sets the address pointer
register to the address of a specified device register first, then reads 8-bit data back from it.
(1)
ADDR[5:0] is the address of the register that is accessed first. The register address is stored in the address pointer register.
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In the write multiple bytes operation, the address pointer of the AMC6821 increments by '1' after the data are
written, until it reaches the last register address (0x3F). If the host continues to transfer data into the AMC6821
after writing the last location, all data are ignored until the operation stops. When reading multiple bytes, the
address pointer of the AMC6821 increments by '1' after transmitting the data until it reaches the last register
address (0x3F). If the host continues clocking data out after reading the last location, the value 0x00 is sent out
until the operation stops.
SMBus ALERT RESPONSE ADDRESS (ARA)
The alert response address is a feature of SMBus devices that allows an interrupting device to identify itself to
the host when multiple devices issue simultaneous interrupts. The SMBALERT pin is an open-drain interrupt
output pin. When the AMC6821 issues an interrupt request, the following procedure occurs:
1. SMBALERT is pulled low.
2. The bus master sends an alert response address or ARA (ARA = 0001100), and initiates a read operation,
as shown in Table 10.
3. The AMC6821 responds to the ARA by sending its slave address back. The 7-bit device slave address is
placed in the seven most significant bits of the byte; the last bit is '0'.
4. The master receives the AMC6821 slave address and starts the interrupt service.
5. If more than one device pulls the SMBus low, the highest priority (lowest slave address) device wins the
communication right via standard arbitration during the slave address transfer (refer to the SMBus
specification version 2.0 for details).
6. To service the interrupt request of the AMC6821, the master must read the status register. Most interrupt
source bits in the status registers are cleared after reading the status register, and are reasserted if the error
condition still exists on the next monitoring cycle. The SMBALERT only clears if the interrupt has been
resolved.
Table 10. ARA Operation
S
ALERT RESPONSE ADDRESS
RD
ACK
0001100
DATA
NACK
P
7-bit MSB: slave address of AMC6821 LSB = 0
S = start condition; P = stop condition; shaded = slave to master; unshaded = master to slave; RD = read (bit value of 1); NACK = not
acknowledged.
POWER-ON RESET AND START OPERATION
After power-on, all registers are set to the power-on default values. The device does not perform any monitoring
functions until the START bit of Configuration Register 1 is set ('1'). No detections are executed until the first
monitoring cycle is completed, and all measurement data registers (such as remote and local temp-data registers
and the TACH data register) are updated with the new measured value. No interrupt signals are generated until
the first cycle of monitoring and detection is completed. This process avoids any false alarms caused by the
power-on default setting.
After power-on, the fan spin-up process is performed. At the end of spin-up, the duty cycle of the PWM driver is
adjusted to 33%. (Refer to the Fan Spin-Up section for details). Device status after software reset is similar to
power-on reset.
10
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FUNCTIONAL BLOCK DIAGRAM
VDD
GND
A0
A1
AMC6821
THERM
2
SCLK
SMBus/I C
Interface
THERM
Control
Temperature Threshold
Registers
FAN-FAULT
Chip Registers
Control Logic
Limit
Comparator
OVR
Local/Remote
Temperature Registers
SMBALERT
TACH Data
+V
IN+
IN-
Mux
Remote
Sensing
Transistor
SDA
ADC
TACH
Signal Conditioning
Fan Speed Counter
mP
PWM
Control
On-Chip Diode
Temperature Sensor
PWM Output
+5V
Ref
Current Source
(I1; I0)
PWM-MODE
Automatic Fan Speed
Controller
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APPLICATION INFORMATION
ADC CONVERTER
The AMC6821 has an 11-bit, on-chip analog-to-digital converter (ADC), as shown in Figure 11. This ADC
converts the analog input into digital format. The analog input is passed through front-end signal conditioning
circuitry to remove the noise. The resulting signal is then converted by the ADC. To further reduce the effects of
noise, digital filtering is performed by averaging the results of 32 measurement cycles. After digital filtering, the
newest result is stored in the temperature data register (low byte and high byte) in two’s complement format. The
ADC stops when the START bit of Configuration Register 1 is cleared ('0') and runs when START = 1.
Mux
LPF and
Signal Conditioning
ADC
Digital
Filter
Data
Registers
60kHz
Figure 11. On-Chip Analog-to-Digital Converter
TEMPERATURE SENSOR
The AMC6821 has an integrated temperature sensor (shown in Figure 12) to measure the ambient temperature,
and one remote diode sensor (such as a Pentium thermal diode) input to measure external (CPU) temperature.
The measurement relies on the characteristics of a semiconductor junction operation at a fixed current level. The
forward voltage of the diode (VBE) depends on the current through it and the ambient temperature. The change in
VBE when the diode is operated at two different currents, I1 and I2, is shown in Equation 1:
DV BE + KT
In(N)
q
(1)
Where:
k — is Boltzmann’s constant,
q —
is the charge of the carrier,
T —
is the absolute temperature in degrees Kelvin, and
N —
is the ratio of the two currents.
I1
SW2
Mux
SW1
I2
LPF and
Signal Conditioning
ADC and
Signal
Processing
Local
Temperature
Registers
Diode
Temperature
Sensor
Figure 12. Integrated Local Temperature Sensor
12
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The remote sensing transistor can be a substrate transistor built within the microprocessor (as in a Pentium-IV),
or a discrete small-signal type transistor. This architecture is shown in Figure 13. The internal bias diode biases
the IN– terminal above ground to prevent the ground noise from interfering with the measurement. An external
capacitor (up to 1000pF) may be placed between IN+ and IN– to further reduce the noise from interfering.
Remote
Temperature
Registers
I2
I1
SW1
SW2
Mux
IN+
Substrate
Sensing
Transistor
IN-
LPF and
Signal Conditioning
ADC and
Signal
Processing
IBIAS
uP
Bias Diode
Figure 13. Remote Temperature Sensor
The analog sensing signal is pre-processed by a low-pass filter and signal conditioning circuitry, then digitized by
the ADC. The resulting digital signal is further processed by the digital filter and processing unit. The final result
is stored in the local temperature data register and remote temperature data register, respectively. The eight
MSBs are stored in the corresponding Temp-DATA-HByte register, and the three LSBs are stored in the
Temp-DATA-LByte register. Refer to the Temperature Data Registers section for details.
The format of the final result is in two’s complement; see Table 11. It should be noted that the device measures
the temperature from –40°C to +125°C, although the code represents temperature from –128°C to +127°C.
Series Resistance Cancellation
Parasitic resistance (seen in series with the remote diode) to the IN+ and IN– inputs to the AMC6821 is caused
by a variety of factors, including printed circuit board (PCB) trace resistance and trace length. This series
resistance appears as a temperature offset in the remote sensor temperature measurement, and causes more
than 0.45°C error per ohm. The AMC6821 is implemented with a TI-patented technology to automatically cancel
out the effect of this series resistance, giving a more accurate result without the need for user characterization of
this resistance. With this technology, the AMC6821 is able to reduce the effects of series resistance to typically
less than 0.0025°C per ohm.
Reading Temperature Data
It is important to note that temperature can be read by an 8-bit value (with 1°C of resolution) from the
Temp-DATA-HByte register, or as an 11-bit value (with 0.125°C of resolution) from the Temp-DATA-LByte and
Temp-DATA-HByte registers. If only 1°C of resolution is required, the temperature readings can be read back at
any time and in no particular order. If reading the 11-bit measurement is required, the process involves a
two-register read for each measurement. To get an 11-bit result of the remote sensor, the controller must read
the Temp-DATA-LByte register (0x06) first, and then the Remote-Temp-DATA-HByte register (0x0B) to complete
the reading. However, to get bit 11 of the local sensor only, or to get both local and remote sensors, the
controller
must
read
Temp-DATA-LByte
first,
Local-Temp-DATA-HByte
(0x0A)
second,
and
Remote-Temp-DATA-HByte third. This method causes all associated temperature data registers to be frozen
until the Remote-Temp-DATA-HByte register has been read. This process also prevents the high byte data from
being updated while the three LSBs are being read, and vice-versa.
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Table 11. Temperature Data Format
TEMPERATURE (°C)
BINARY DIGITAL CODE (11 bits)
+127
01111111000
+125
01111101000
+100
01100100000
+75
01001011000
+50
00110010000
+25
00011001000
+10
00001010000
+1
00000001000
0
00000000000
–1
11111111000
–25
11100111000
–50
11001110000
–75
10110101000
–100
10011100000
–125
10000011000
–128
10000000000
Temperature Out-of-Range Detection
The AMC6821 has the following temperature limitation detections:
1. High and Low Temperature Limit: The value of the High-Temp-Limit and Low-Temp-Limit registers specify
the remote or local temperature ranges of normal operation. When the local or remote temperatures are
equal to or above the value of the corresponding High-Temp-Limit register, the LTH or RTH bits in the status
register are set ('1'). Likewise, when the local or remote temperatures are less than or equal to the
corresponding Low-Temp-Limit register, the LTL or RTL bits in the status register are set ('1').
When the local temperature is out-of-range (LTH = 1 or LTL = 1), the local temperature out-of-range event
occurs. The LTO bit in the status register is set ('1'), and the LTO interrupt is generated via the SMBALERT
pin if it is enabled (the LTOIE bit of Configuration Register 2 is set). Similarly, when the remote temperature
is out-of range (RTH = 1 or RTL = 1), the remote temperature out-of-range event occurs. The RTO bit in the
status register is set ('1'), and the RTO interrupt is generated via the SMBALERT pin if it is enabled (that is,
the RTOIE bit of Configuration Register 2 is set).
2. Critical Limit: Critical temperature limit is the highest allowed of remote or local temperature. When the
temperature is greater than or equal to the corresponding critical temperature, the LTCT or RTCT bit of the
status register is set ('1'), the output of the OVR pin goes low, and a non-maskable interrupt is generated
through the SMBALERT pin (low).
3. Passive Cooling Temperature (PSV) Limit: This limit defines the passive cooling threshold. In the auto
remote-temperature-fan control mode, the system enters a passive cooling condition when the remote
temperature is equal to or below this limit, and the fan stops. In the maximum fast speed calculated control
mode, the fan stops and the system enters a passive cooling condition when both the remote and local
temperatures are equal to or below this limit. In passive cooling, the LPSV bit of Status Register 2 (0x03) is
set ('1'), and a PSV interrupt is generated on the SMBALERT pin if enabled (PSVIE = 1). Note that reading
the Status Register clears the LPSV bit. After reading, if the active control temperature remains equal to or
below the PSV temperature, this bit reasserts on next monitoring cycle.
14
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4. THERM Limit: This limit is an additional fail-safe threshold. When the local or remote temperature is equal to
or above this limit, the corresponding L-THERM or R-THERM bit is set ('1'), and the THERM pin is asserted
low, which can be used to throttle the CPU clock. Furthermore, the THERM interrupt is generated on the
SMBALERT pin if enabled (THERMOVIE = 1). Reading Status Register 1 clears the R-THERM and
L-THERM bits. Once cleared, these bits are not reasserted until the temperature falls 5°C below the THERM
limit, even if the THERM condition persists. If the THERM-FAN-EN bit of Configuration Register 3 is set ('1'),
L-THERM = 1 or R-THERM = 1 forces the fan to run at full speed. When THERM-FAN-EN = 0, the status of
the L-THERM and R-THERM bits do not affect the fan speed directly. Note that the THERM limit can be
lower or higher than other temperature limits. For example, if the THERM limit is lower than the PSV
temperature limit, then the CPU clock can be throttled while the cooling fan is off.
Local-High-Temp-Limit
LTH
LTO
LTO Interrupt
SMBALERT Pin Low
Local Temperature
LTL
Local-Low-Temp-Limit
Remote-High-Temp-Limit
LTOIE
RTH
RTO
RTO Interrupt
SMBALERT Pin Low
Remote Temperature
RTL
Remote-Low-Temp-Limit
Local-Critical-Temp
RTOIE
LTC Bit in Status Register 2
OVR Pin Low
Local Temperature
SMBALERT Pin Low
Remote-Critical-Temp
RTC Bit in Status Register 2
OVR Pin Low
Remote Temperature
SMBALERT Pin Low
Active Control Temperature
LPSV Bit in Status Register 2
PSV Interrupt
SMBALERT Pin Low
PSV-Temp
PSVIE
Assert THERM Pin Low
L-THERM Limit
Local Temperature
Force Fan to Full Speed
THERM-FAN-EN
L-THERM Bit in Status Register 2
Local Therm Interrupt
SMBALERT Pin Low
THERMOVIE
Assert THERM Pin Low
R-THERM Limit
Remote Temperature
Force Fan to Full Speed
THERM-FAN-EN
R-THERM Bit in Status Register 1
Remote Therm Interrupt
SMBALERT Pin Low
THERMOVIE
Figure 14. Temperature Out-of-Range Detection
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Remote Temperature Sensor Failure Detection
The remote temperature sensor failure detection determines whether the remote sensor diode has an
open-circuit condition, a short-circuit to ground, or a short-circuit (IN+) to (IN–) condition. This fault detection is
based on the analog input voltage and is not checked until the first monitoring cycle is completed after power-on.
Reading the fault sensor returns a value of –128°C (0x80). Since the power-on default value of the temperature
data registers is 0x80 (–128°C), a reading of 0x80 from the temperature data register immediately after power-on
does not indicate a diode fault condition. The remote temperature sensor failure is only checked after the first
monitoring cycle has been completed after power-on or reset.
When a remote sensor failure occurs, the remote sensor failure bit (RTF in the Status Register) is set to '1', the
OVR pin is forced low, and if the interrupt is enabled (RTFIE = 1), the RTF interrupt is generated through the
SMBALERT pin. Once this interrupt is generated, the RTF bit remains '1' and the OVR pin stays low until a
power-on reset or software reset is issued, whether or not the failure condition persists.
PWM Output
The PWM-Out pin is an open-drain output. When PWM-EN of Configuration Register 2 is cleared ('0'), the
PWM-Out pin is disabled and goes into a high-impedance status. When PWM-EN is set ('1'), the PWM-Out pin is
enabled to drive the fan. When enabled, the status of the PWM-Out pin is determined by the PWM duty cycle
and phase bits (PWMINV of Configuration Register 1). When PWMINV = 0 (default), the PWM-Out pin goes low
for 100% duty cycle (suitable for driving the fan using a PMOS FET). Setting PWMINV to '1' makes the PWM-Out
pin go high (with an external pull-up resistor) for a 100% duty cycle. This setting is used to drive an NMOS-power
FET.
+5V
+5V
AMC6821
PWMINV = 0
AMC6821
PWM-Out
PWM
Control
PWM-Out
PWM
Control
ON
PWM-EN
ON
PWM-EN
PWMINV = 1 for driving the NMOS.
PWMINV = 0 (default) for driving the PMOS.
Figure 15. PWM Output
PWM WAVEFORM SETTING
PWM frequency and duty cycle are programmable. The value of the DCY Register defines the duty cycle: it has
8-bit resolution, 1LSB corresponding to 1/255 (0.392%). Writing 0x00 sets the duty cycle to 0%; writing 0xFF sets
the duty cycle to 100%.
PWM frequency has two ranges: the high range is from 1kHz to 40kHz, and the low range is from 10Hz to 94Hz.
The PWM-MODE pin status determines which range is selected. When the PWM-MODE pin is tied to ground,
the high range is selected. Otherwise, the low range is selected. Bits [PWM2:PWM0] in the Fan Characteristics
Register define the frequency; see Table 12. The resolution of the PWM waveform period is 0.312µs,
corresponding to a 3.2MHz clock. The default value after power-on is 30Hz when the low range is selected, or
25kHz when the high range is selected.
ON
RPM reduces as the
duty cycle decreases.
OFF
Period
Figure 16. PWM Waveform (PWMINV = 1)
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Table 12. PWM Frequency
PWM2
PWM1
PWM0
PWM FREQUENCY
When the PWM-MODE Pin is Floating or Tied to VDD
0
0
0
10Hz
0
0
1
15Hz
0
1
0
23Hz
0
1
1
30Hz (default)
1
0
0
38Hz
1
0
1
47Hz
1
1
0
62Hz
1
1
1
94Hz
When the PWM-MODE Pin is Tied to GND
0
0
0
1kHz
0
0
1
10kHz
0
1
0
20kHz
0
1
1
25kHz (default)
1
0
0
30kHz
1
0
1
40kHz
1
1
0
40kHz
1
1
1
40kHz
FAN SPEED MEASUREMENT
The AMC6821 monitors the fan speed (RPM) via the TACH pin, as illustrated in Figure 17. The TACH-EN bit of
Configuration Register 2 (bit 2, 0x01) enables the fan speed measurement. When TACH-EN is cleared ('0'), the
measurement is disabled. The measurement is enabled when the TACH-EN bit is set to '1'. This section
describes the device behavior when TACH-EN is set ('1').
The on-chip fan-speed counter does not count the fan tach output pulses directly because of the low RPM of the
fan. Instead, the period of the fan revolution is measured by gating an on-chip clock (100kHz). The result is
stored in the TACH-DATA Register that contains two bytes (16 bits total). RPM monitoring is disabled when the
START bit of Configuration Register 1 or the TACH-EN bit of Configuration Register 2 is cleared ('0'), and is
enabled when START = 1 and TACH-EN = 1.
If the TACH-MODE bit is cleared, RPM monitoring stops and the TACH-DATA register is not updated when the
duty cycle is less than 7% for the software duty cycle mode and auto-temperature-fan control modes. In
software-RPM mode, RPM monitoring is always performed and updated after each monitoring. If the TACH
mode = '1' the RPM monitoring is always performed, and the TACH data are always updated after each
monitoring.
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TACH-DATA Register
Two fan tach pulse periods (PSPR = 0) or four tach pulse periods (PSPR = 1) are measured and the result is
stored in the TACH-DATA Register, as shown in Figure 17. Counting stops if the counter is over-range; the
measurement cycle repeats until monitoring is disabled, and the fan speed (RPM) can be calculated as shown in
Equation 2:
RPM =
(100,000 x 60)
(Value of TACH-DATA Register)
(2)
Reading the TACH Data Register
To read the fan speed, both TACH-DATA-LByte and TACH-DATA-HByte must be read. TACH-DATA-LByte must
be read first. This reading causes TACH-DATA-HByte to be frozen until both the high and low byte registers
have been read from, preventing TACH reading errors.
RPM Measurement Rate
The TACH-FAST bit of Configuration Register 4 determines the rate. When TACH-FAST = 1, the TACH-DATA
Register is updated every 250ms (fast monitoring). When TACH-FAST = 0 (default), the reading is updated every
second (standard monitoring period).
Select Number of Pulses/Revolution
The speed sensor of most common fans provides two or four TACH pulses per revolution. The PSPR bit of
Configuration Register 4 specifies how many pulses per revolution are generated. PSPR = 1 indicates four
pulses/revolution and PSPR = 0 (default) indicates two pulses/revolution.
TACH Mode Selection
The TACH-MODE bit of Configuration Register 2 specifies the TACH pulse output mode of the fan. Some fans
(such as three- and two-wire) are powered directly by the PWM, and must be PWM-On to provide a TACH pulse
output. When the PWM-Out pin switches these fans ON/OFF directly, the PWM-Out must be kept ON to power
the fan during the measurement. In this case, the TACH-MODE bit of Configuration Register 2 must be cleared
('0'). When TACH-MODE = 0, the PWM-Out pin is kept ON during the critical tach edges of the measurement
period. Clearing the TACH mode ('0') also enables the internal correction circuitry to correct the error caused by
the extra duty cycle applied in the measurement period. The power-on default value of the PWM mode is '0'.
Clock
PWM
TACH Pulse
Measurement Period
for 2 Pulses/Revolution
+5V
TACH Data
Signal Conditioning
FAN Speed Counter
START
PWM
Control
Measurement Period for
4 Pulses Per Revolution
TACH
RPM Measurement for TACH-MODE = 0
TACH
Output
+5V
PWM-Out
TACH-EN
AMC6821
Clock
TACH Pulse
Measurement
Starts
Measurement Period
for 2 Pulses/Revolution
Measurement Period for 4 Pulses Per Revolution
RPM Measurement for TACH-MODE = 1
a) Block Diagram of Fan Speed Monitoring
b) Measuring the Period of TACH Pulses to Determine the Fan Speed
Figure 17. Fan Speed Measurement
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Some fans (such as the JMC™ four-wire fan) are powered directly by dc power, instead of being powered by the
PWM. In this case, the TACH mode must be set to '1'. When TACH-MODE = 1, the PWM-Out pin is not forced
ON; instead, the status is controlled completely by the DCY register, just as in normal operation. Setting
TACH-MODE to '1' also disables the internal correction circuit because no extra duty cycle is applied. Setting the
TACH mode to '1' allows TACH reading continuously, regardless of the status of the PWM-Out pin.
The selection of the TACH mode affects the RPM monitoring and control. When the TACH-MODE bit is equal to
'1', the duty cycle of the PWM-Out pin is always determined by the calculated value; the TACH data are always
updated at every RPM monitoring. However, when the TACH-MODE bit is equal to '0', in the Software-RPM
Control mode the PWM-Out pin is forced to 30% if the calculated duty cycle is less than 30%; in other modes,
the PWM-Out pin is forced to 0% and the TACH data are not updated if the calculated duty cycle is less than 7%.
FAN RPM Out-of-Range Detection
The larger value of the TACH data corresponds to a slower speed. When the TACH data are larger than the
TACH-Low-Limit, the fan runs at a speed below the predefined minimum RPM, and the FANS bit in Status
Register 1 is set to '1'. Note that no FANS (fan-slow) detections are made during spin-up. The FANS bit is
cleared ('0') only after reading this register and reasserted ('1') in the next monitoring if a fan-slow is detected.
After spin-up, FANS is set ('1') even if the TACH data are less than the TACH-Low-Limit until the register is read.
When the TACH data are less than the TACH-High-Limit, the fan runs at a speed above the predefined
maximum RPM, and the RPM-ALARM bit in Status Register 1 is set ('1'). Note that the RPM-ALARM bit is
cleared when reading the register. Once cleared, this bit is not reasserted in the next monitoring cycle even if the
condition persists. This bit may be reasserted only if the RPM drops below the allowed maximum speed.
When FANS = 1 or RPM-ALARM = 1, there is a fan-out-of-range interrupt and FAN-ORN is generated if the
FANIE bit in Configuration Register 1 is set ('1'). This interrupt makes the SMBALERT pin go low.
RPM Alarm (TACH is less than the high limit)
FANS (TACH is greater than the low limit)
(RPM out-of-range)
FANIE
(FAN-TACH interrupt enabled)
FAN-ORN Interrupt
Figure 18. RPM Out-of-Range Detection
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FAN FAILURE DETECTION
When the TACH data are larger than the TACH low limit, the fan runs at a speed below the predefined minimum
RPM. When this condition occurs, a spin-up process is applied to start the fan again when spin-up is enabled.
Bits [STIME2:STIME0] of the Fan Characteristics Register define this time period. Figure 19 shows the function
of the fan failure detection. Refer to the Fan Spin-Up section.
The fan speed is measured immediately after spin-up; the TACH-FAST bit of Configuration Register 4
determines the monitoring rate. If the fan does not return to a normal range after five consecutive spin-ups, a
FAN-FAILURE occurs; the FAN-FAULT pin goes low when it is enabled (the FAN-FAULT-EN bit of Configuration
Register 1 is set), and the spin-up process continues. If the fan returns to a normal speed range before the fifth
spin-up, the FAN-FAULT pin does not go low even though the FANS bit is still set to '1'. No FANS (fan-slow)
detections are performed during spin-up. After the FAN-FAULT pin goes low, spin-up is performed indefinitely
until the RPM reading returns to within normal range or the spin-up is disabled.
Normal Operation of Fan Failure
Detection and Spin-Up
Yes
Bit FANS = 0
During Spin-Up Process
Clear Spin-Up
Time Counter
No
Measure RPM
TACH Data > Low Limit
No
Yes
Bit FANS = 1
Fan failure,
FAN-FAULT pin
goes low.
Yes
Spin-Up Time Count ³ 5
No
Spin-Up Time Count +1
Spin-Up Disabled?
No Spin-Up if Disabled
Yes
No
Spin-Up Process
Measure the RPM continuously once every 0.25s (TACH-FAST bit = 1) or 1s (TACH-FAST = 0),
even after a fan failure. However, there are no FANS detections during spin-up.
The FAN-FAULT pin is negated if the fan returns to a normal RPM range.
Figure 19. Fan Failure Detection and Spin-Up
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The SMBALERT pin continues to generate interrupts after the assertion of the FAN-FAULT pin because the tach
measurement continues even after a fan failure. Should the fan recover from the failure condition, the
FAN-FAULT pin signal is negated and the fan returns to normal operating speed. Figure 20 shows the operation
of a FANS interrupt.
PWM_OUT
2s
2s
2s
Full-Speed
TACH
Fifth TACH
Failure
Fourth TACH Failure
Third TACH Failure
INT
Status Register Read to Clear Interrupt
Continuing
TACH Failure
FAN_FAULT
INT is a Fan-Slow (FANS) Interrupt Through the SMBALERT Pin
Figure 20. Operation of the FAN-FAULT Pin with a Spin-Up Time = 2 Seconds
FAN-FAULT PIN
The FAN-FAULT pin is an open-drain output pin, as shown in Figure 21. When the FAN-FAULT-EN bit of
Configuration Register 1 is cleared ('0'), this pin is disabled and is always in a high-impedance status. When
FAN-FAULT-EN = 1, the pin is enabled and the status indicates a fan-failure. The pin asserts low when a fan
failure occurs. FAN-FAULT is negated when the fan returns to normal speed.
+V
AMC6821
10kW
Fan Failure
(below minimum speed
after fifth spin-up)
FAN-FAULT
Pin is Enabled
(FAN-FAULT-EN bit = 1)
Figure 21. FAN-FAULT Pin
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FAN CONTROL
THERM Pin and External Hardware Control
The THERM pin is a bi-directional I/O, as shown in Figure 22.
THERM Pin As An Output
As an open-drain output, the THERM pin is the indicator of temperature over the THERM limit. When the remote
temperature exceeds the Remote-THERM-Limit, or when the local temperature is greater than the
Local-THERM-Limit, the THERM pin goes low and remains low until the measured temperature falls 5°C below
the exceeded THERM limit.
THERM-FAN-EN
Drive Fan at Full Speed
L-THERM Bit
(Set to ‘1’ when the local temperature is
greater than the Local-THERM-Limit.)
Local temperature is less than (Local-THERM-Limit - 5°C)
R-THERM Bit
(Set to ‘1’ when the remote temperature is
greater than the Remote-THERM-Limit.)
Remote temperature is less than (Remote-THERM-Limit - 5°C)
Latch
Set
Output
Reset
THERM
Latch
Set
Output
Reset
THERM-IN bit
(Drive fan at full speed when THERM-IN = 1)
Figure 22. Structure of the THERM Pin
22
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When the THERM limit is exceeded, the corresponding status flag bit (R-THERM or L-THERM of Status Register
1 or Status Register 2) is set to '1', and the THERM interrupt through the SMBALERT pin is generated if it is
enabled (THERMOVIE of bit Configuration Register 1 is set to '1'). This interrupt forces the SMBALERT pin low.
Note that the THERM pin is always forced to low when R-THERM = 1 or L-THERM = 1, no matter what the
status of THERMOVIE is. Reading the status registers clears the flag bit (R-THERM and L-THERM). Clearing the
flag bit makes the SMBALERT pin go back to high, but does not negate the THERM pin. It remains low until the
temperature falls 5＝C below the exceeded THERM limit. After this bit is cleared, the active flag bit (R-THERM
for remote temperature or L-THERM for local temperature) and the THERM interrupt are not re-armed until the
temperature falls 5°C below the exceeded THERM limit. This procedure is shown in Figure 23.
THERM Limit
5°
Temperature
THERM
INT via SMBALERT
INT via SMBALERT
Status Register Read
Figure 23. Operation of the THERM Interrupt and the THERM Pin
When working as an output, the status of the THERM pin affects the RPM fan. If the THERM-FAN-EN bit is set
('1'), the fan goes to full-speed (that is, the duty cycle is 100%) when the THERM pin goes low. However, when
THERM-FAN-EN = 0, the status of the THERM pin does not affect the fan speed.
THERM Pin As An Input
When this pin works as input, it is the input of the external hardware control signal; the THERM-IN bit of Status
Register 2 reflects the input. When the THERM pin is pulled low as an input, THERM-IN is set ('1') and the fan is
driven at full speed (that is, the duty cycle is 100%), no matter what THERM-FAN-EN is. The THERM-FAN-EN
bit has no effect when the THERM pin works as an input.
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Fan Spin-Up
The PWM duty cycle controls the cooling fan speed. To spin up a fan from a stopped state or under-speed
status, the spin-up process is applied to overcome the fan inertia. During the first third of spin-up, the duty cycle
of the PWM gradually increases from 33.3% to 100%, and then maintains at 100% through the rest of the
process. At the end of the spin-up process, the duty cycle is adjusted to 33.3%. After starting, the fan speed is
controlled normally. The spin-up process is shown in Figure 24. The bits [STIME2:STIME0] (bits 2:0 of 0x20)
define the spin-up time, from 0.2 seconds to 8 seconds, as shown in Table 13. Fan speed is monitored
immediately after the spin-up process.
Spin-up is disabled by setting the FSPD bit of the Fan Characteristics Register to '1'. If disabled, the spin-up
process is not applied when the fan stops or an RPM is detected below the minimum speed. The TACH low limit
register defines the minimum speed. After power-on or reset, the FSPD bit is cleared and the spin-up is always
performed, regardless of the state of the FANS bit (bit 1 of 0x02).
Note that no FANS (fan-slow) detections are performed during spin-up. This bit is cleared ('0') only after reading
it, and reasserts '1' in the next monitoring if a fan-slow condition is detected. After spin-up, FANS is set ('1') even
if the TACH data are less than the TACH low limit until the flag is read.
DCY
100%
Normal
Control
33.3%
0
TSPIN-UP/3
TSPIN-UP
Figure 24. Spin-Up Process
Table 13. Spin-Up Time
24
STIME2
STIME1
STIME0
SPIN-UP TIME (seconds)
0
0
0
0.2
0
0
1
0.4
0
1
0
0.6
0
1
1
0.8
1
0
0
1
1
0
1
2 (default)
1
1
0
4
1
1
1
8
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Normal Fan Speed Control
The fan speed is controlled by four different modes:
• software DCY control;
• software RPM control,
• auto remote temperature fan control;
• maximum fast-speed calculated control.
The Auto Temperature-Fan Control mode consists of auto remote temperature-fan control and maximum
fast-speed calculated control. It is an intelligent closed-loop control. In this mode, the fan speed is controlled
either by the remote temperature (Auto-Remote Temperature-Fan Control) or by maximum speed calculated for
internal and remote temperature. This control mode optimizes fan speed for a given temperature to intelligently
manage the system thermals/acoustics. The user writes the proper registers to define the linear feedback control
algorithm parameters. After programming, the AMC6821 runs stand-alone, even without the intervention of the
micro-controller. It ensures that if the controller or system locks up, the fan can still be controlled based on
temperature measurements, and the fan speed adjusted to correct any changes in system temperature.
Software-RPM works as a fan speed regulator to maintain the speed at a programmable target value. It is a
closed-loop mode and can run stand-alone as well. The Software-DCY mode is an open-loop mode; the PWM
output duty cycle changes to the target value immediately after the user writes the desired duty cycle to the
device registers.
Bits FDRC1 and FDRC0 in Configuration Register 1 determine the operation mode.
Software DCY Control Mode
When the bits [FDRC1:FDRC0] = [00], the fan works in the software DCY control mode. The host writes the
desired duty cycle value corresponding to the required RPM into the DCY register. The duty cycle changes to the
new value immediately after the writing. In this mode, if the TACH measurement is enabled (bit 2 of 0x01 = 1)
and the TACH-MODE bit (bit 1 of 0x01) is cleared ('0'), the duty cycle from the PWM-OUT pin is forced to 0%
when the value in the DCY register is less than 7%. However, if the TACH measurement is disabled (bit 2 of
0x01 is cleared) or the TACH mode is set ('1'), the DCY register always keeps the programmed value written by
the host and is not forced to '0' even when the programmed value is less than 7%.
Software-RPM Control Mode (Fan Speed Regulator)
This mode works as a fan speed regulator that maintains the speed at a programmable target value. It works
only when the TACH measurement is enabled (bit 2 of 0x02 = 1). When the bits [FDRC1:FDRC0] = [01], the fan
works in the software RPM control mode, as shown in Figure 25. The host writes the proper value into the TACH
Setting Register to set the target fan speed. The actual fan speed is monitored by an on-chip fan speed counter,
and the result is stored in the TACH-DATA Register (refer to the Fan Speed Measurement section for more
details). The actual speed is compared with the setting value. If there is a difference, the duty cycle is adjusted.
+V
AMC6821
TACH Data
+
TACH Setting
Register
-
DCY
Adjustment
Fan Speed
Counter
PWM
Control
The PWM duty cycle increases if the TACH data is above
the setting value, decreases if the TACH data is below
the setting, and does not change if the TACH data is
equal to the setting (with a tolerance of 0x000A).
TACH
+3V/+5V
PWM-Out
NOTE: The tach resistor network is
used to limit the TACH input voltage to 5.5V max.
Figure 25. Software RPM Control
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The monitoring and adjustment is made once every second, or once every 250ms, as determined by the
TACH-FAST bit of Configuration Register 4 (bit 5, 0x04). Bits [STEP1:STEP0] of the DCY-RAMP Register define
the allowed amount of each adjustment. When the difference between the values of the TACH-DATA and TACH
Setting Registers are equal to or less than 0x000A, the adjustment finishes. 0x000A corresponds to about 1.8%
tolerance for 10,000RPMs, or 0.9% for 5000RPMs. This measurement architecture is illustrated in Figure 26.
In practice, the selected target speed must be not too low to operate the fan. When the TACH-MODE bit (bit 1 of
0x02) is cleared ('0'), the duty cycle of PWM-Out is forced to 30% when the calculated desired value of duty
cycle is less than 30%. Therefore, the TACH setting must be not greater than the value corresponding to the
RPM for 30% duty cycle. When TACH mode = '1', the TACH setting must not be greater than the value
corresponding to the allowed minimum RPM at which the fan runs properly.
Measure RPM and adjust DCY once every second (TACH-FAST = 0)
or once every 250ms (TACH-FAST = 1).
(TACH-DATA Register) - TACH-SETTING Register)
No
|Error| > 0x000A
Yes
(TACH-DATA) >
(TACH-SETTING)
Yes
Increase DCY
by one STEP
No
Decrease DCY
by one STEP
Figure 26. RPM Fan DCY Loop
26
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Auto Temperature Fan Mode
The Auto Temperature-Fan mode is a closed-loop control that optimizes fan speed for a given temperature to
intelligently manage the system thermals/acoustics. It runs stand-alone even without the intervention of a
controller. The AMC6821 has two auto temperature fan control modes. When the bits [FDRC1:FDRC0] = [10]
(default), the fan is in the Auto Remote Temperature-Fan Speed control mode. The temperature reading from the
remote temperature sensor is the active control temperature that controls the PWM duty cycle. When the bits
[FDRC1:FDRC0] = [11], the fan is in the maximum fast-speed calculated control mode. The local temperature
and the remote temperature have independently-programmed control loops with different parameters. In the
maximum fast-speed calculated control mode, the required fan speed is calculated for the remote and local
channels, respectively. Whichever control loop calculates the fastest speed based on the measured temperature
drives the fan. After the monitor starts, the PWM duty cycle is determined by the actual control temperature.
When the temperature is above the low temperature and below the high temperature, the internal control loop
automatically adjusts the duty cycle to a proper value according to the measured temperature. When the
temperature rises, the duty cycle increases to a higher value; when the temperature drops, the duty cycle
reduces. This architecture makes the fan always run at an optimal speed. This adjustment is based on the
control-loop parameters defined in the Local TEMP-FAN Control Register, Remote TEMP-FAN Control Register,
and the DCY-RAMP Register. Changing the parameters changes the desired value of the duty cycle and the fan
speed.
+V
The DCY-RAMP Register temperature determines
the speed of adjustment.
Temperature-to-DCY
Adjustment
Actual Temperature
Temperature
Channel
PWM Control
AMC6821
Figure 27. Auto Fan Temperature Loop
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The bits [R-TEMP4:R-TEMP0] of the Remote TEMP-FAN Control Register and the bits [L-TEMP4:L-TEMP0] of
the Local TEMP-FAN Control Register are the low temperature bits that define the low temperature of the control
loops. Bits [SPL2:SPL0] of these registers are the slope bits that define the increment of the duty cycle when the
temprature increases 1°C. The bits [RATE2:RATE0] of the DCY-RAMP Register (bits [4:1], 0x23) specify the
updating rate of the duty cycle in the temp-fan control mode, and the bits [STEP1:STEP0] define how much the
duty cycle is adjusted by each updating. The target duty cycle for temperature T1 and the HIGH-TEMP (high
temperature) can be calculated by Equation 3:
Target DCY at T1 = DCY-LOW-TEMP + (T1 - LOW-TEMP) ´ SLOPE;
HIGH-TEMP = (LOW-TEMP) +
(100 - DCY-LOW-TEMP)
(3)
SLOPE
100%
Low-Temp-Limit
LOW-TEMP (Low Temperature)
PSV-Temp
(Passive Cooling Temperature)
Critical-Temp
RPM = 0
0%
THERM-Limit
DCY increases when the temperature rises.
DCY decreases when the temperature reduces.
High-Temp-Limit
DCY-LOW-TEMP
(DCY at Low Temperature,
Default is 33%)
HIGH-TEMP
(High Temperature)
Duty Cycle
Temperature-to-DCY Adjustment Range
Actual Temperature
Out-of-Range
Out-of-Range
Normal Range
Figure 28. Active Control Temperature—PWM Duty Cycle
When the active control temperature is equal to or below the corresponding low temperature, the duty cycle is
equal to the value of the DCY-LOW-TEMP Register and the fan runs at a predefined minimum speed. When the
control temperature is equal to or higher than the corresponding high temperature, the PWM duty cycle is set to
100% and the fan runs at full speed. When the active control temperature is equal to or below the corresponding
value of the PSV-Temp Register (the predefined passive cooling temperature), the fan stops and the PWM duty
cycle is set to 0.
28
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When the actual duty cycle is different from the desired value, the duty cycle is adjusted automatically. When the
RAMPE bit of the DCY-RAMP Register is cleared ('0'), the duty cycle changes to the desired value immediately
after being calculated. When the RAMPE bit is '1', the duty cycle changes to the new value gradually.
The DCY-RAMP Register specifies how quickly the duty cycle changes. The duty cycle can be checked every
0.0625 second to every eight seconds, depending on the bits [RATE2:RATE0] bits. It changes 1/255(0.392%) to
4/255 (1.57%) each time, depending on the bits [STEP1:STEP0] bits. When the difference between the actual
value and the target value is equal to or less than the adjustment threshold (as defined by the bits
[THRE1:THRE0] bits), the adjustment finishes. See the DCY-RAMP Register for details. When the TACH
monitoring is enabled (TACH-EN bit, bit 2 of 0x02, is set to '1') and the TACH-MODE bit (bit 1 of 0x02) is cleared
('0'), the duty cycle is forced to 0% when the calculated value is less than 7%. If the TACH monitoring is disabled
(TACH-EN = 0) or the TACH-MODE bit is set ('1'), the duty cycle is always set to the calculated value even if the
value is less than 7%.
(Update DCY with the rate defined by the
bits [RATE2:RATE0] of the DCY ramp register.
Read Local
Temperature
Temperature ³
Local-High-Temp-Limit
Read Remote
Temperature
Yes
LTH = 1,
LTO = 1
Yes
Temperature ³
Remote-High-Temp-Limit
No
No
Temperature ³
Local-Critical-Temp
No
Temperature ³
Remote-Critical-Temp
Yes
Yes
No
Yes
LTC = 1,
OVR is Low
LTL = 1,
LTO = 1
RTH = 1,
RTO = 1
RTC = 1,
OVR is Low
Temperature £
Local-Low-Temp-Limit
Temperature £
Remote-Low-Temp-Limit
No
Yes
RTL = 1,
RTO = 1
No
No
Update DCY?
The temperature updating rate may be faster than the DCY updating rate.
Yes
Remote Fan Temperature Control Mode
No
(Maximum fast speed calculated control)
Yes
(Remote Fan Temperature Control)
Calculate New DCY for the Remote
Fan Temperature Control
Calculate DCY for the remote fan temperature control
and local fan temperature control, respectively.
Use the larger one as the new DCY.
Update DCY
Figure 29. Temperature Monitoring Flow Chart
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INTERRUPT
The AMC6821 provides two interrupt output pins, OVR and SMBALERT.
OVR Pin
OVR is an open-drain output pin that works as an over-critical temperature limit (shutdown threshold) indicator
and remote sensor failure indicator. This architecture is shown in Figure 30. Setting the OVREN bit of
Configuration Register 4 to '1' enables this pin; clearing OVREN ('0') disables it. When disabled, the OVR pin is
in a high-impedance status. When enabled, the status is controlled by the over-critical temperature flag and
remote sensor failure flag bits of the Status Registers.
When the temperature is over the critical limit (shutdown threshold), the corresponding over-critical limit flag of
the Status Register (RTC for the remote channel and LTC for the local channel) is set ('1'). This flag is cleared
('0') when reading the Status Registers. Once cleared, this bit is not reasserted until the temperature falls 5°C
below the exceeded critical limit, even if the over-critical limit condition persists. When the temperature is equal to
or above the critical temperature limit, the OVR pin is asserted (active low) to indicate this critical condition. As
the over-critical temperature limit indicator, the OVR pin remains low once asserted until the measured
temperature falls 5°C below the exceeded critical limit.
Latch
LTC Bit
(Local temperature reaches the critcal shutdown threshold.)
AMC6821
Set
+V
Output
Local Temperature < (Local-Critical-Temp - 5°C)
Reset
OVR
Latch
RTC Bit
(Remote temperature reaches the critcal shutdown threshold.)
Set
Output
Remote Temperature < (Remote-Critical-Temp - 5°C)
Reset
RTF
(Remote Temperature Sensor Failure)
OVREN
Figure 30. OVR Pin
When a remote temperature sensor failure condition is detected (either short-circuit or open-circuit), the remote
temperature sensor failure bit (RTF) in Status Register 1 (bit 5, 0x02) is set ('1') and the OVR pin is forced low no
matter what the status of RTFIE is. This value indicates a remote sensor failure condition. Once this condition
occurs, the RTF bit remains '1' and the OVR pin stays low until a power-on reset or software reset is issued,
regardless if the failure condition continues thereafter. RTF = 1 also generates an RTF interrupt through the
SMBALERT pin when RTFIE = 1.
SMBALERT Pin
The SMBALERT pin is a standard interrupt output defined by SMBus specification revision 2.0. This pin is an
open-drain output pin and is illustrated in Figure 33.
SMBALERT Interrupt Behavior
When an out-of-limit event occurs, the proper flag bits in the status registers are set ('1'), and the corresponding
interrupts are generated, if enabled. When an interrupt is generated, the SMBALERT pin asserts low. The host
can poll the device status registers to get the information, or give a response to the SMBALERT interrupt signal.
It is important to note how the SMBALERT output and status bits behave when writing interrupt-handler software.
Figure 31 shows how the SMBALERT output and status bits behave.
30
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Once a limit is exceeded, the corresponding status bit is set to '1'. The status bit remains set until the error
condition subsides and the status register gets read. The status bits are referred to as being sticky because they
remain set until read by software. This design ensures that out-of-limit events cannot be missed if the software is
polling the device periodically. The SMBALERT output remains low for the entire duration that the reading is out
of limits and remains low until the status register has been read. This architecture has implications on how
software handles the interrupt.
High Limit
Temperature
Cleared on Read
(Temperature below limit)
Status Bit
Temperature Back in Limit
(status bit stays set)
SMBALERT
Figure 31. SMBALERT Pin and Status Bits Behavior
HANDLING SMBALERT INTERRUPTS
To prevent the system from being tied up while servicing interrupts, it is recommend to handle the SMBALERT
interrupt in this manner:
1. Detect the SMBALERT assertion.
2. Enter the interrupt handler.
3. Read the status registers to identify the interrupt source.
4. Disable the interrupt source by clearing the appropriate enable bit in the configuration registers.
5. Take the appropriate action for a given interrupt source.
6. Exit the interrupt handler.
7. Periodically poll the status registers. If the interrupt source bit has cleared, reset the corresponding interrupt
enable bit to '1'. This reset makes the SMBALERT output and status bits behave as shown in Figure 32.
High Limit
Temperature
Cleared on Read
(temperature below limit)
Sticky Status Bit
Temperature Back in Limit
(status bit stays set)
SMBALERT
Interrupt Disabled
Interrupt Enabled
(SMBALERT Rearmed)
Figure 32. How Masking the Interrupt Source Affects SMBALERT
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Individual interrupts can be masked by clearing the corresponding interrupt enable bit in the configuration
registers to prevent SMBALERT interrupts. Note that masking an interrupt source only prevents the SMBALERT
pin output from being asserted; the appropriate status bit gets set as normal.
LTL Bit (Local Temperature £ Local-Low-Temp-Limit)
AMC6821
(local temperature out-of-range)
(Local Temperature Out-of-Range Interrupt)
LTH Bit (Local Temperature ³ Local-High-Temp-Limit)
LTOIE Bit
(local temperature interrupt enabled)
RTL Bit (Remote Temperature £ Remote-Low-Temp-Limit)
RTH Bit (Remote Temperature ³ Remote-High-Temp-Limit)
(remote temperature out-of-range)
(Remote Temperature Out-of-Range Interrupt)
RTOIE Bit
(remote temperature interrupt enabled)
RPM-ALARM Bit (TACH < TACH-High-Limit)
FANS Bit (TACH > TACH-Low-Limit)
(RPM out-of-range)
(FAN-ORN interrupt)
+V
FANIE Bit
(FAN-TACH interrupt enabled)
LPSV Bit (PSV interrupt)
SMBALERT
PSVIE Bit
L-THERM Bit (over local THERM interrupt)
THERMOVIE Bit
R-THERM Bit (over remote THERM interrupt)
THERMOVIE Bit
INT-EN
RTF = 1 (remote sensor failure)
RTFIE Bit
RTC Bit (remote temperature reaches critical temperature)
LTC Bit (local temperature reaches critical temperature)
Figure 33. SMBALERT
32
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REGISTER MAP
All registers are 8-bit. Table 14 shows the memory map. Locations that are marked Reserved read back 0x0000
if they are read by the host. Writing to these locations has no effect.
Table 14. Memory Map
ADDR
NAME
R/W
DEFAULT
R
0x21
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
1
0
0
0
0
1
0
0
1
0
0
1
FDRC0
FAN-FaultEN
PWMINV
FANIE
INT-EN
START
FAN-Fault
Pin EN
PWM Invert
RPM Int EN
Global Int
EN
Start Monitor
LTOIE
RTFIE
TACH-EN
TACHMODE
PWM-EN
TACH EN
TACH Mode
PWM-Out
EN
0
1
0
IDENTIFICATION REGISTERS
0x3D
Device ID Register
Device identification number. Always read '0x21'.
0
0x3E
Company ID Register
R
1
0x49
Company identification number.
CONFIGURATION REGISTERS
THERMOVIE
0x00
Configuration Register 1
R/W
THERM INT
Enable
RST
0x01
0x3F
Configuration Register 2
Configuration Register 3
R/W
R/W
FDRC1
0xD4
Fan Control Mode
PSVIE
RTOIE
0x3D
Reset
LPSV Int EN
RT Int EN
LT Int EN
Remote
Failure Int
EN
THERM-FANEN
0
0
0
0
0x82
THERM-Fan
Control
0x04
0x02
0x03
Configuration Register 4
Status Register 1
Status Register 2
R/W
R
R
Part Revision Number
For Future
Use
PSPR
TACH-FAST
OVREN
Must be
rewritten to '1'.
Pulse
Number
TACH
Reading
Fast
OVR Pin EN
LTL
LTH
RTF
R-THERM
RTL
LT Low
LT High
RT Failure
RT Over
Therm
0x08
1
0
0
0
RTH
FANS
RPMALARM
RT Low
RT High
Fan Slow
Fan Fast
0
0
0
Reserved
0x00
THERM-IN
L-THERM
LPSV
LTC
RTC
Therm Input
LT Over
Therm
LT Below
Therm
LT Over
Critical
RT Over
Critical
LT2
LT1
LT0
0
0
0x00
Reserved
TEMPERATURE MONITORING
0x06
Temp-DATA-LByte
R
3 LSBs of Local Reading
LT10 (MSB)
0x0A
Local-Temp-DATA-HByte
R
RT2
RT1
RT0
0x00
LT9
Reserved
LT8
LT7
3 LSBs of Remote Reading
LT6
LT5
LT4
LT3
RT5
RT4
RT3
LT-H5
LT-H4
LT-H3
0x80
The 8 MSBs of newest reading of local temperature sensor. Default = –128°C.
RT10 (MSB)
0x0B
Remote-Temp-DATA-HByte
R
RT9
RT8
RT7
RT6
0x80
The 8 MSBs of newest reading of remote temperature sensor. Default = –128°C.
LT-H10
0x14
Local-High-Temp-Limit
R/W
LT-H9
LT-H8
LT-H7
LT-H6
0x3C
8 MSBs of upper-bound threshold of out-of-range detection of Local-Temp. 3 LSBs are '0'. Default = +60°C.
LT-L10
0x15
Local-Low-Temp-Limit
R/W
LT-L9
LT-L8
LT-L7
LT-L6
LT-L5
LT-L4
LT-L3
0x00
8 MSBs of lower-bound threshold of the out-of-range detection of Local-Temp. 3 LSBs are '0'. Default = 0°C.
LT-T10
0x16
Local-THERM-Limit
R/W
0x46
0x18
Remote-High-Temp-Limit
R/W
0x50
LT-T9
LT-T8
LT-T7
LT-T6
LT-T5
LT-T4
LT-T3
8 MSBs of local THERM temperature limit. 3 LSBs are '0'. When local temperature is equal to or above this limit,
L-THERM is detected. Default = +70°C.
RT-H10
RT-H9
RT-H8
RT-H7
RT-H6
RT-H5
RT-H4
RT-H3
The 8 MSBs of the upper-bound threshold of the out-of-range detection of Remote-Temp. 3 LSBs are '0'. Default = +80°C.
RT-L10
0x19
Remote-Low-Temp-Limit
R/W
RT-L9
RT-L8
RT-L7
RT-L6
RT-L5
RT-L4
RT-L3
0x00
The 8 MSBs of the lower-bound threshold of the out-of-range detection of Remote-Temp. 3 LSBs are '0'. Default = 0°C.
RT-T10
RT-T9
RT-T8
RT-T7
RT-T6
RT-T5
RT-T4
RT-T3
0x1A
Remote-THERM-Limit
R/W
0x64
8 MSBs of Remote THERM temperature limit. 3 LSBs are '0'. When remote temperature is equal to or above this limit,
R-THERM is detected. Default = +100°C.
0x1B
Local-Critical-Temp
R/W
0x50
The 8 MSBs of Local Critical temperature shutdown threshold. 3 LSBs are '0'. When the Local-Temp is equal to or above
this limit, the LTC interrupt occurs and OVR goes low. Default = +80°C.
LT-C10
LT-C9
LT-C8
LT-C7
LT-C6
LT-C5
LT-C4
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Table 14. Memory Map (continued)
ADDR
NAME
R/W
DEFAULT
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
0
0
PSV8
PSV7
PSV6
PSV5
PSV4
PSV3
TEMPERATURE MONITORING (continued)
0x1C
PSV-Temp
R/W
0x00
Passive Cooling Temperature threshold. 3 LSBs and two MSBs are '0'. For details, refer to the passive cooling
temperature limit in the Temperature Out-of-Range Detection section. Default = 0°C.
0x1D
Remote-Critical-Temp
R/W
0x69
The 8 MSBs of Remote Critical temperature shutdown threshold. 3 LSBs are '0'. When the Remote-Temp is equal to or
above this limit, an RCRT interrupt occurs and OVR goes low. Default = +105°C.
R/W
0x1D
RT-C10
RT-C9
RT-C8
RT-C7
RT-C6
RT-C5
RT-C4
RT-C3
PWM CONTROLLER
FSPD
0x20
FAN-Characteristics
0
PWM2
Spin Dis
L-DCY7
0x21
DCY-Low-Temp
R/W
0x55
DCY (Duty Cycle)
R/W
0x55
0x23
DCY-RAMP
R/W
0x52
L-DCY6
DCY5
STEP1
STEP0
DCY Adjustment Step in
Auto Fan Control
L-TEMP4
R/W
L-DCY5
DCY6
Ramp Enable
Local Temp-Fan Control (1)
L-DCY4
R/W
STIME0
L-DCY3
L-DCY2
L-DCY1
L-DCY0
DCY4
DCY3
DCY2
DCY1
DCY0
L-TEMP3
L-TEMP2
RATE2
RATE1
RATE0
DCY Update Rate in Auto Temp-Fan
Control
L-TEMP1
L-TEMP0
L-SLP2
THRE1
THRE0
Adjustment Threshold in
Auto Temp-Fan Control
L-SLP1
L-SLP0
0x41
R-TEMP4
Remote Temp-Fan Control
STIME1
Spin-Up Time Setting
Low-Temp in Auto Local Temp-Fan control.
0x25
STIME2
Actual Duty cycle of PWM output. The duty cycle changes immediately after new data are written into this register. 8-bit,
0.39%/bit, range 0%-100%. Default = 33%.
In read operation, the returned data are the actual DCY value driving the PWM-Out pin with two exceptions. Refer to the
DCY Register section.
In write operation, the data written are the actual DCY value driving the PWM-Out pin in Software-DCY control mode.
In all other control modes, the data are not used to drive the PWM. Instead, they are stored in a temporary register, and
used to control the PWM immediately after the control mode is changed to software-DCY control.
RAMPE
0x24
PWM0
The duty cycle of PWM when the temperature is equal to or below Low-Temp in Auto Temp-Fan Control mode.
Default = 0x55, 33.2%.
DCY7 (MSB)
0x22
PWM1
PWM Frequency Setting
R-TEMP3
R-TEMP2
R-TEMP1
Slope in Auto Local Temp-Fan control.
R-TEMP0
R-SLP2
R-SLP1
R-SLP0
0x61
Low-Temp in Auto Remote Temp-Fan control.
Slope in Auto Remote Temp-Fan control.
TACH (RPM) MEASUREMENT
0x08
TACH-DATA-LByte
R
0x00
TACHDATA7
TACHDATA6
TACHDATA5
TACHDATA4
TACHDATA3
TACHDATA2
TACHDATA1
TACHDATA0
TACHDATA13
TACHDATA12
TACHDATA11
TACHDATA10
TACHDATA9
TACHDATA8
TACH-LowLimit5
TACH-LowLimit4
TACH-LowLimit3
TACH-LowLimit2
TACH-LowLimit1
TACH-LowLimit0
Low byte of TACH measurement.
0x09
TACH-DATA-HByte
R
0x00
TACHDATA15
TACHDATA14
High byte of TACH measurement.
TACH-LowLimit7
0x10
TACH-Low-Limit-LByte
R/W
0xFF
0x11
TACH-Low-Limit-HByte
R/W
0xFF
TACH-LowLimit6
Low byte of TACH count limit corresponding to minimum allowed RPM. Since the TACH circuit counts between TACH
pulses, a slow fan results in a larger measured value. When the measured value is larger than TACH-Low-Limit, the fan
runs below the allowed minimum speed limit.
TACH-LowLimit15
TACH-LowLimit14
TACH-LowLimit13
TACH-LowLimit12
TACH-LowLimit11
TACH-LowLimit10
TACH-LowLimit9
TACH-LowLimit8
TACH-HighLimit2
TACH-HighLimit1
TACH-HighLimit0
High byte of TACH Limit corresponding to minimum allowed RPM.
TACH-HighLimit7
0x12
TACH-High-Limit-LByte
R/W
0x00
0x13
TACH-High-Limit-HByte
R/W
0x00
TACH-HighLimit6
TACH-HighLimit5
TACH-HighLimit4
TACH-HighLimit3
Low byte of TACH count Limit corresponding to maximum allowed RPM. Since the TACH circuit counts between TACH
pulses, a fast fan results in a small measured value. When the measurement is less than this limit, the fan runs above the
allowed maximum speed limit.
TACH-HighLimit15
TACH-HighLimit14
TACH-HighLimit13
TACH-HighLimit12
TACH-HighLimit11
TACH-HighLimit10
TACH-HighLimit9
TACH-HighLimit8
TACHSETTING2
TACHSETTING1
TACHSETTING0
High byte of TACH limit corresponding to maximum allowed RPM.
TACHSETTING7
0x1E
TACH-SETTING-LByte
R/W
TACHSETTING6
TACHSETTING5
TACHSETTING4
TACHSETTING3
0xFF
Low byte of TACH value corresponding to the predetermined target fan speed. TACH-SETTING must be not greater than
the value corresponding to the RPM for 30% duty cycle when the TACH-MODE bit is cleared ('0').
TACHSETTING15
0x1F
TACH-SETTING-HByte
R/W
TACHSETTING14
TACHSETTING13
TACHSETTING12
TACHSETTING11
TACHSETTING10
TACHSETTING9
TACHSETTING8
0xFF
High byte of TACH value corresponding to the predetermined fan speed. TACH-SETTING must be not greater than the
value corresponding to the RPM for 30% duty cycle when the TACH-MODE bit is cleared ('0').
0x3A
Reserved
R
0x00
Always read '0'.
0x3B
Reserved
R
0x00
Always read '0'.
(1)
34
Used to calculate the target PWM duty cycle for local temperature in maximum fast-speed calculated control.
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REGISTER DESCRIPTION
In this section, all interrupts are the interrupt signal through the SMBALERT pin, unless otherwise noted.
DEVICE CONFIGURATION REGISTERS
Configuration Register 1 (Address 0x00, Value After Power-On Reset = 0xD4)
BIT
NAME
R/W
DEFAULT
DESCRIPTION
7
THERMOVIE
R/W
1
THERM interrupt enable. When this bit is set, the THERM interrupt is enabled.
L-THERM = 1 or R-THERM = 1 causes an interrupt. When this bit is cleared ('0'), the
THERM interrupt is disabled. When disabled, L-THERM = 1 or R-THERM = 1 does not
assert the SMBALERT pin, but forces the THERM pin low. Power-on default = 1.
6
FDRC1
R/W
1
Fan driver control bit 1. Power-on default = 1. Refer to Table 15.
5
FDRC0
R/W
0
Fan driver control bit 0. Power-on default = 0. Refer to Table 15.
4
FAN-Fault-EN
R/W
1
Setting this pin to '1' enables the FAN-FAULT pin. Clearing this pin ('0') disables the
FAN-FAULT pin (always in Hi-Z). Power-on default = 1.
0
PWM invert bit. When PWMINV = 0 (default), the PWM-Out pin goes low for 100% duty
cycle (suitable for driving the fan using a PMOS device). Setting PWMINV to '1' makes
the PWM-Out pin go high (with an external pull-up resistor) for 100% duty cycle (suitable
for driving the fan using a NMOS device). Power-on default = 0.
3
PWMINV
R/W
2
FANIE
R/W
1
Fan RPM interrupt enable bit. Power-on default = 1. When FANIE = 1, the FAN-RPM
interrupt is enabled. FANS = 1 or RPM-ALARM = 1 generates a FANORN interrupt,
making the SMBALERT pin go low. When FANIE = 0, a FAN-RPM interrupt is disabled.
Fan out-of-range = 1 does not generate an interrupt.
1
INT-EN
R/W
0
Setting this bit to '1' enables the interrupt from the SMBALERT pin. Clearing this bit ('0')
disables the interrupt. Power-on default = 0.
0
START
R/W
0
Temperature monitoring and fan speed monitoring. When START = 0 , only
software-DCY control mode works; software-RPM and auto temperature control modes
do not work.
Table 15. Fan Driver Control Bits
FDRC1
36
FDRC0
FUNCTION
1
1
Maximum speed calculated control. The required duty cycle for remote temperature and
local temperature is calculated respectively. The larger value is used to control the fan.
1
0
Auto remote-temperature-fan control. The PWM duty cycle is controlled by the remote
temperature. Power-on default mode.
0
0
Software DCY control. Host writes DCY register to set the PWM duty cycle directly.
0
1
Software RPM control. Host writes the TACH setting register with the value corresponding
to the desired RPM. The device measures the actual RPM and adjusts the PWM duty cycle
to maintain the fan speed to the target value.
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Configuration Register 2 (Address 0x01, Value After Power-On Reset = 0x3D)
BIT
NAME
R/W
DEFAULT
DESCRIPTION
7
RST
R/W
0
Reset bits. RST = 1 resets the device. Self-clears after reset. Always read '0'. Power-on
default = 0. Reset is immediate on rising edge of SCLK of data LSB with no
acknowledge.
6
PSVIE
R/W
0
LPSV enable bit. Power-on default = 0. When LPSVIE = 1, the LPSV interrupt is enabled
and an interrupt is generated when LPSV = 1. When LPSVIE = 0, LPSV is disabled and
LPSV = 1 does not cause an interrupt.
5
RTOIE
R/W
1
Remote temperature interrupt enable bit. When RTIE = 1, the remote temperature
interrupt is enabled and RTO = 1 causes an interrupt. When RTIE = 0, the remote
temperature interrupt is disabled and RTO = 1 does not generate an interrupt. Power-on
default = 1, except when a remote sensor failure is detected at power-on.
4
LTOIE
R/W
1
Local temperature interrupt enable bit. Power-on default = 1. When LTIE = 1, the local
temperature interrupt is enabled and LTO = 1 causes an interrupt. When LTIE = 0, the
local temperature interrupt is disabled and LTO = 1 does not generate an interrupt.
3
RTFIE
R/W
1
Remote sensor failure interrupt enable bit. Power-on default = 1. When RTFIE = 1, the
remote sensor failure interrupt is enabled and RTF = 1 causes an interrupt through the
SMBALERT pin. When RTFIE = 0, the remote sensor failure interrupt is disabled and
RTF = 1 does not generate an interrupt through the SMBALERT pin.
2
TACH-EN
R/W
1
Setting this bit to '1' enables the TACH input. Clearing ('0') disables the TACH input and
freezes the counter. Power-on default = 1. If TACH-EN is cleared, TACH-MODE must be
set ('1').
1
TACH-MODE
R/W
0
When the TACH-MODE bit is cleared ('0'), the PWM-Out pin is forced ON during RPM
measurement, and internal correction circuitry is enabled to correct the error caused by
this extra duty cycle. Making TACH-MODE = 0 for the fans that are switched ON/OFF
directly by the PWM requires PWM ON to provide TACH pulses. In the software RPM
mode, the PWM-Out is forced to 30% duty cycle if the calculated duty cycle is less than
30% when TACH-MODE = 0. In all other modes the PWM-Out is forced to 0% if the
calculated duty cycle is less than 7%. When the TACH mode is set ('1'), the internal
correction circuit is disabled and PWM-Out is not forced ON. Instead, the PWM-Out pin
is completely controlled by the value of the DCY register, just as in normal operation.
Setting the TACH-MODE bit ('1') when the fans can provide TACH pulses output
regardless the status of the PWM-Out pin. The TACH mode must be '1' for any fan
which is powered directly by dc power, such as a four-wire fan. Power-on default = 0.
(See the TACH-DATA Register section for details.)
0
PWM-EN
R/W
1
Setting this bit to '1' enables the PWM-Out pin. Clearing ('0') disables the PWM-Out pin
(H-Z). Power-on default = 1.
Configuration Register 3 (Address 0x3F, Value After Power-On Reset = 0x82)
BIT
NAME
R/W
DEFAULT
DESCRIPTION
7
THERM-FAN-EN
R/W
1
Setting this bit to '1' enables the fan to run at full-speed when the THERM pin as
an output) is asserted low. This configuration allows the system to be run in
performance mode. Clearing this bit to '0' disables the fan from running at
full-speed whenever the THERM pin (as an output) is asserted low. This
configuration allows the system to run in silent mode. Note that this bit has no
effect whenever THERM is pulled low as an input. The fan always runs at full
speed when the THERM pin is pulled low as an input. Power-on default = 1.
6
Reserved
R
0
Read-back '0'.
5
Reserved
R
0
Read-back '0'.
4
Reserved
R
0
Read-back '0'.
3
Part Revision Number
R
0
0, bit 3 (MSB) of 4-bit revision number.
2
Part Revision Number
R
0
0, bit 2 of revision number.
1
Part Revision Number
R
1
0, bit 1 of revision number.
0
Part Revision Number
R
0
0, bit 0 (LSB) of revision number.
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Configuration Register 4 (Address 0x04, Value After Power-On Reset = 0x08)
BIT
NAME
R/W
DEFAULT
DESCRIPTION
7
MODE
R/W
0
Required configure bit: User must write a 1 to this location.
6
PSPR
R/W
0
Number of pulses per revolution of the fan. Power-on default = 0. PLSPR = 0 for two
pulses/revolution (default), PLSPR = 1 for four pulses per revolution.
5
TACH-FAST
R/W
0
When TACH-FAST = 1, the TACH data reading is updated every 250ms. This monitor is
the fast RPM monitor. When TACH-FAST = 0, the TACH data reading is updated every
second. Default = 0, power-on default = 0.
4
OVREN
R/W
0
Setting this bit to '1' enables the OVR pin. Clearing this bit ('0') disables the OVR pin
(high-impedance). Default = 0.
3
Reserved
R
1
Read back '1'.
2
Reserved
R
0
Read-back '0'.
1
Reserved
R
0
Read-back '0'.
0
Reserved
R
0
Read-back '0'.
Writing the reserved bit has no effect.
38
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DEVICE STATUS REGISTERS
Reading the status registers clears the appropriate status bit. Status register bits are sticky (except the RTF bit).
Whenever a status bit is set, indicating an out-of-limit condition, it remains set until the event that caused it is
resolved and the status register is read. The status bit can only be cleared by reading the status register after the
event is resolved. All bits are cleared when reading the register, and all bits are reasserted if the out-of limit
condition still exists on the next monitoring cycle, unless otherwise noted.
Status Register 1 (Address 0x02, Value After Power-On or Reset = 0x00)
BIT
NAME
R/W
DEFAULT
DESCRIPTION
7
LTL
R
0
LTL = 1 when the local temperature is less than or equal to the value of the
Local-Low-Temp-Limit register. Otherwise, LTL = 0. If the local temperature is still
outside the local temperature low limit, this bit reasserts on the next monitoring cycle.
6
LTH
R
0
LTH = 1 when the local temperature is greater than or equal to the value of the
Local-High-Temp-Limit register. Otherwise, LTH = 0. If the local temperature is still
outside the local temperature high limit, this bit reasserts on the next monitoring cycle.
0
Remote sensor-failure interrupt. RTF = 1 when the remote temperature sensor fails
(short- or open-circuit). RTF = 0 when the remote sensor is in normal condition. When
RTF = 1, the OVR pin is asserted and the remote temperature data register is set to
–128°C.
RTF = 1 also generates an interrupt through the SMBALERT pin if an interrupt is
enabled (RTFIE = 1). Once RTF is set ('1'), it always remains ('1') until power-on reset or
software reset occurs, whether or not the failure condition continues. Reading the status
register does not clear the RTF bit.
5
RTF
R
4
R-THERM
R
0
Remote temperature over the remote THERM limit flag. R-THERM = 1 when the
temperature is greater than the value of the Remote-THERM-Limit register. Otherwise,
R-THERM = 0. When R-THERM = 1, the THERM pin goes low. It also generates a
THERM interrupt if THERMOVIE = 1. This bit is cleared on a read of Status Register 1.
Once cleared, this bit is not reasserted until the remote temperature falls 5°C below this
THERM limit, even if the THERM condition persists. Refer to the THERM Pin and
External Hardware Control section.
3
RTL
R
0
RTL = 1 when the remote temperature is less than or equal to the value of the
Remote-Low-Temp-Limit register. Otherwise, RTL = 0. If the remote temperature is still
beyond the remote temperature low limit, this bit reasserts on the next monitoring cycle.
2
RTH
R
0
RTH = 1 when the remote temperature is greater than or equal to the value of
Remote-High-Temp-Limit register. Otherwise, RTH = 0. If the remote temperature is still
beyond the remote temperature high limit, this bit reasserts on the next monitoring cycle.
0
Fan-slow flag. FANS = 1 if the TACH data are greater than or equal to the value of the
TACH-Low-Limit register. This bit indicates if the fan becomes stuck or goes under the
minimum speed. FANS = 0 if the TACH data are smaller than the TACH low limit. This
bit is cleared ('0') only after reading this register, and reasserts '1' in the next monitoring
if a fan-slow is detected. After spin-up, FANS is set ('1') even if the TACH data are less
than the TACH low limit until the register is read. FANS = 1 generates a fan out-of-range
interrupt through the SMBALERT pin if fan out-of-range is enabled (FANIE = 1). Five
consecutive fan-slow events result in a FAN FAILURE status; which asserts the
FAN-FAULT pin low. See the FAN-FAULT PIN section for details. Note that a FANS
(fan-slow) detection is not performed during spin-up.
0
RPM-ALARM = 1 when the TACH data are less than or equal to the value of the
TACH-High-Limit register. This means the RPM is over the maximum limit defined by the
TACH high limit. Otherwise, RPM-ALARM = 0. This bit is cleared when reading this
register. Once cleared, this bit is not reasserted on the next monitoring cycle even if the
condition still persists. This bit may be reasserted only if the RPM drops below the
allowed maximum speed. RPM-ALARM = 1 generates a fan out-of-range interrupt
through the SMBALERT pin if fan out-of-range is enabled (FANIE = 1), but does not
cause an interrupt through the FAN-FAULT pin.
1
0
FANS
RPM-ALARM
R
R
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Status Register 2 (Address 0x03, Value After Power-On or Reset = 0x00)
BIT
NAME
R/W
DEFAULT
DESCRIPTION
7
THERM-IN
R
0
Status of the THERM pin as an input. When this input is pulled low, THERM-IN = 1, and
the fan is driven at full speed. This bit is cleared when reading this register and be
written to '1' if the pin persists "pulled-low".
0
Local temperature over the local THERM limit flag. L-THERM = 1 when the local
temperature is greater than the value of the Local-THERM-Limit register. Otherwise,
L-THERM = 0. When L-THERM is set to 1, the THERM pin goes low. It also generates a
THERM interrupt through the SMBALERT pin, if enabled (THERMOVIE = 1). This bit is
cleared on a read of Status Register 1. Once cleared, this bit is not reasserted until the
temperature falls 5°C below the THERM limit, even if the THERM condition persists.
Refer to the THERM Pin and External Hardware Control section.
0
Active control temperature below the PSV (passive cooling) temperature flag. This bit is
set to '1' when the active control temperature is equal to or below the PSV temperature.
Otherwise, this bit is cleared ('0'). LPSV = 1 generates a PSV interrupt on SMBALERT, if
enabled (PSVIE = 1). This bit is cleared when reading this register. If the active control
temperature remains equal to or below the PSV temperature, this bit reasserts on the
next monitoring cycle.
0
Local temperature over the local critical temperature flag. This bit is set ('1') when the
local temperature is equal to or above the local critical temperature. LTC = 0 if the local
critical temperature is below this value. LTC = 1 asserts the OVR pin low and generates
an LTC interrupt (non-maskable) though the SMBALERT pin. This bit is cleared when
reading this register. If the over-critical limit condition persists, this bit reasserts on the
next monitoring cycle.
6
L-THERM
5
LPSV
4
LTC
R
R
R
3
RTC
R
0
Remote temperature over the remote critical temperature flag. This bit is set to '1' when
the remote temperature is equal to or above the remote critical temperature. RTC = 0 if
the remote critical temperature is below this value. RTC = 1 asserts the OVR pin low and
generates an RTC interrupt (non-maskable) though the SMBALERT pin. This bit is
cleared when reading this register. If the over-critical limit condition persists, this bit
reasserts on next monitoring cycle.
2
Reserved
R
0
Reserved. Reading returns '0'.
1
Reserved
R
0
Reserved. Reading returns '0'.
0
Reserved
R
0
Reserved. Reading returns '0'.
FAN CONTROLLER REGISTERS
DCY (Duty Cycle) Register (Address 0x22, Value After Power-On or Reset = 0x55)
BIT
NAME
DEFAULT
DESCRIPTION
7 (MSB)
DCY7 (MSB)
0
DCY CODE
6
DCY6
1
0x00
0%
5
DCY5
0
0x01
0.392%
4
DCY4
1
... ...
... ...
3
DCY3
0
0x40
25%
2
DCY2
1
... ...
... ...
1
DCY1
0
0x80
50%
0
DCY0
1
... ...
... ...
0xFF
100%
DUTY CYCLE
The DCY register stores the value of the PWM duty cycle, 0x00 corresponds to 0%, and 0xFF to 100%. 1LSB
corresponds to 0.392%. Power-on default = 0x55, 33.2%.
In a read operation, with the two following exceptions, the returned data are the actual duty cycle (DCY) value
driving the PWM-Out pin:
1. When TACH-MODE = 0 and the system is in software-RPM control mode, if the calculated duty cycle is less
than 30%, the returned value is the calculated value, not the actual PWM-OUT pin duty cycle which is forced
to 30%.
2. When TACH-MODE = 0 and the system is in software DCY-control mode or Auto Temperature-Fan mode, if
the calculated duty cycle is less than 7%, the returned value is the calculated value, not the actual
PWM-OUT pin duty cycle which is forced to 0%.
40
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In a write operation, the data written are the actual DCY driving the PWM-Out pin in the software DCY control
mode. However, in all other control modes, the data being written are not used to drive the PWM. Instead, it is
stored in a temporary register, and controls the PWM immediately after the control mode is changed to the
software DCY control mode.
Fan Characteristics Register (Address 0x20, Value After Power-On or Reset = 0x1D)
BIT
NAME
DEFAULT
DESCRIPTION
7
FSPD
0
Fan Spin Disable Bit
When FSPD = 1, the fan spin-up process is disabled.
When FSPD = 0, the fan spin-up process is enabled.
6
0
0
Reserved
5
PWM2
0
4
PWM1
1
3
PWM0
1
PWM Frequency Bits
PWM2
PWM1
PWM0
PWM Frequency
When PWM-MODE pin is floating or tied to VDD
0
0
0
10Hz
0
0
1
15Hz
0
1
0
23Hz
0
1
1
30Hz (Default)
1
0
0
38Hz
1
0
1
47Hz
1
1
0
62Hz
1
1
94Hz
1
When PWM-MODE pin is tied to GND
2
STIME2
1
1
STIME1
0
0
STIME0
1
0
0
0
1kHz
0
0
1
10kHz
0
1
0
20kHz
0
1
1
25kHz (Default)
1
0
0
30kHz
1
0
1
40kHz
1
1
0
40kHz
1
1
1
40kHz
Spin-Up Time Bit
STIME2
STIME1
STIME0
Spin-Up Time
(in Seconds)
0
0
0
0.2
0
0
1
0.4
0
1
0
0.6
0
1
1
0.8
1
0
0
1
1
0
1
2 (Default)
1
1
0
4
1
1
1
8
This register specifies the PWM frequency and the fan spin-up functions.
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Fan Spin Disable Bit: FSPD
This bit enables or disables the spin-up function.
PWM Frequency Bits: [PWM2:PWM0]
These bits specify the PWM frequency; the high range (1kHz–40kHz) has a default value of 25kHz, and the low
range (10Hz–94Hz) has a default value of 30Hz. The clock frequency is 3.2MHz. The PWM-MODE pin
determines which range is selected. When the PWM mode is tied to ground, the high range is selected;
otherwise, the low range is selected.
Spin-Up Time Bits: [STIME2:STIME0]
These bits specify a predetermined time period, or spin-up time, during which the 100% duty cycle is applied to
start the fan spinning. These bits are ignored when FSPD = 1.
DCY-LOW-TEMP Register (Address 0x21, Value After Power-On or Reset = 0x55, 33.2%)
Bit 7 (MSB)
L-DCY 7
Bit 6
L-DCY 6
Bit 5
L-DCY 5
Bit 4
L-DCY 4
Bit 3
L-DCY 3
Bit 2
L-DCY 2
Bit 1
L-DCY 1
Bit 0 (LSB)
L-DCY 0
This register specifies the duty cycle in Auto Temp-Fan Control mode when the control temperature is less than
or equal to the value of the Low-Temp bits in the TEMP-FAN Control Regsiter.
Local TEMP-FAN Control Register (Address 0x24, Value After Power-On or Reset = 0x41)
BIT
NAME
DEFAULT
DESCRIPTION
7
L-TEMP4
0
Low Temperature Bit of Local Sensor
6
L-TEMP3
1
L-TEMP4
L-TEMP3
L-TEMP2
L-TEMP1
L-TEMP0
Low Temp
5
L-TEMP2
0
0
0
0
0
0
0°C
4
L-TEMP1
0
0
0
0
0
1
4°C
3
L-TEMP0
0
0
0
0
1
0
8°C
0
0
0
1
1
12°C
...
...
...
...
...
...
0
1
0
0
0
32°C (Default)
...
...
...
...
...
...
1
1
1
1
0
120°C
1
1
1
1
1
124°C
Temp Range in °C
(DCY 33.3% to 100%)
2
L-SLP2
0
1
L-SLP1
0
0
L-SLP0
1
Slope Bits of Local Sensor
Slope
L-SLP2
L-SLP1
L-SLP0
LSB/°C
%/°C
0
0
0
32
12.55
5.31
0
0
1
16
6.27
10.62 (default)
0
1
0
8
3.14
21.25
0
1
1
4
1.57
42.5
1
0
0
2
0.78
85
This register specifies the parameters of the local Temperature-Fan Control mode.
Low Temperature Bits: [L-TEMP4:L-TEMP0]
These bits specify the low temperature of the local temperature fan control loop. The calculated duty cycle is
equal to the value of the DCY-LOW-TEMP register when the local temperature is less than or equal to the value
defined by bits [L-TEMP4:L-TEMP0]. Refer to the Auto Temperature Fan Mode section for details.
Slope Bits: [L-SLP2:L-SLP0]
These bits define the increment of the duty cycle when the local temperature rises every 1°C in the auto local
temperature-fan control.
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Remote TEMP-FAN Control Register (Address 0x25, Value After Power-On or Reset = 0x61)
BIT
NAME
DEFAULT
7
R-TEMP4
0
6
R-TEMP3
1
R-TEMP4
R-TEMP3
R-TEMP2
R-TEMP1
R-TEMP0
Low Temp
5
R-TEMP2
1
0
0
0
0
0
0°C
4
R-TEMP1
0
0
0
0
0
1
4°C
3
R-TEMP0
0
0
0
0
1
0
8°C
0
0
0
1
1
12°C
...
...
...
...
...
...
48°C (Default)
2
R-SLP2
0
1
R-SLP1
0
0
R-SLP0
1
DESCRIPTION
Low Temperature Bit of Remote Sensor
0
1
1
0
0
...
...
...
...
...
...
1
1
1
1
0
120°C
1
1
1
1
1
124°C
Slope Bits of Remote Sensor
Slope
Temp Range in °C
(DCY 33.3% to 100%)
R-SLP2
R-SLP1
R-SLP0
LSB/°C
%/°C
0
0
0
32
12.55
5.31
0
0
1
16
6.27
10.62 (default)
0
1
0
8
3.14
21.25
0
1
1
4
1.57
42.5
1
0
0
2
0.78
85
This register specifies the parameters of the Remote Temperature-Fan Control mode.
Low Temperature Bits: [R-TEMP 4:R-TEMP0]
These bits specify the low temperature of the auto remote temperature-fan control. In this control mode, the duty
cycle is equal to the value of the DCY-LOW-TEMP register when the remote temperature is less than or equal to
the value defined by bits [R-TEMP4:R-TEMP0].
Slope Bits: [R-SLP2:R-SLP0]
These bits define the increment of the duty cycle when the remote temperature rises every 1°C in the auto
remote temperature-fan control.
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DCY-RAMP Register (Address 0x23, Value After Power-On or Reset = 0x52)
BIT
NAME
DEFAULT
DESCRIPTION
7
RAMPE
0
Ramp Enable Bit. Ignored in software-RPM control.
When RAMPE = 1, Ramp is enabled. The DCY changes to the desired value gradually according
to STEP bits and RATE bits.
When RAMPE = 0, Ramp is disabled. DCY changes to the desired target value immediately.
Default = 0.
6
STEP1
1
5
STEP0
0
4
RATE2
1
3
RATE1
0
2
RATE0
0
1
THRE1
1
0
THRE0
0
Adjustment Step Bits.
STEP1
STEP0
Max Adjustment
0
0
1/256
0
1
2/256
1
0
4/256 (Default)
1
1
8/256
DCY Updating Rate Bits in Auto Temp-Fan Control Mode.
RATE2
RATE1
RATE0
DCY Updates/Sec
(Auto Temp-Fan CTR)
0
0
0
0.0625
0
0
1
0.125
0
1
0
0.25
0
1
1
0.5
1
0
0
1 (Default)
1
0
1
2
1
1
0
4
1
1
1
8
Adjustment Threshold Bits in Auto Temp-Fan Control Mode.
THRE1
THRE0
Threshold
0
0
1/256
0
1
2/256
1
0
3/256 (Default)
1
1
4/256
This register is ignored in the software DCY control mode. This register determines how fast the PWM duty cycle
is adjusted to the desired value when the temperature changes in the automatic temperature-fan control, or when
the fan speed varies from the predetermined value in the software RPM control mode.
RAMPE: Ramp Enable bit.
This bit is ignored in the software RPM control mode. The duty cycle always gradually ramps to the target value
in Software-RPM mode.
Adjustment Step Bits: [STEP1:STEP0]
In the software RPM control, these bits specify the amount that duty cycle changes each time.
In the auto fan temperature control mode, these bits are ignored when RAMPE = 0. When RAMPE = 1, these
bits define the maximum amount that the duty cycle can change each time if the duty cycle needs to be adjusted.
For example, if the current value of the duty cycle is 50% and the desired value is 75%, the total required
increment is 25%. If the step is 1/256 (bits [STEP1:STEP0] = '00'), then the duty cycle increases by 1/256
(0.39%) each time the duty cycle is updated, and the duty cycle reaches the desired value (75%) after 64
updates. This takes eight seconds if the update rate is 8/sec (bits [RATE2:RATE0] = '111'), and takes 64
seconds if the update rate is 1/sec. (bits [RATE2:RATE0] = '100'). However, if the step is 2/256, then the time
reduces to half. If the required adjustment is less than the value specified by step bits, the actual required value
is used. For example, if the current duty cycle is 50%, the required value is 73%, and the step is 4/256, a total of
15 updates are needed. The duty cycle increases 21.875% after the first 14 updates, and increases 1.125% in
the last update.
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Updating Rate Bits: [RATE2:RATE0]
These bits define the rate (time/sec) that the duty cycle is recalculated in the auto temp-fan control mode. The
value of [RATE2:RATE0] does not affect the ADC conversion rate. Both external and local temperature readings
are updated continuously, even if the DCY is updated slowly.
The RPM monitoring rate and DCY updating rate in the software RPM control mode are specified by the
TACH-FAST bit of Configuration Register 3. The [RATE2:RATE0] bits are ignored in this mode.
Adjustment Threshold Bits: [THRE1:THRE0]
These bits determine the threshold of the duty cycle adjustment in the auto temp-fan control mode, and are
ignored in all other modes. When the auto fan temperature control loop is active, the duty cycle is not adjusted if
the required adjustment is less than or equal to the threshold defined by bits [THRE1:THRE0]. This provides a
hysteresis to improve the control stability. For example, if the current duty cycle is 50% and the desired value is
71%, the total required increment is 21%. If the step is 4/256 and the threshold is 2/256 (0.78%), the duty cycle
reaches 70.31% after 13 updates, 0.6875% less than the desired value. This difference is less than the threshold
(0.78%); therefore, the adjustment stops. However, if the threshold is 1/256 (0.39%), then one more update
occurs, and the duty cycle increases by 0.39% (1LSB) because 0.39% (1LSB) < 0.6875% < 0.78% (2LSB).
Finally, the duty cycle reaches 70.7%, 0.3% less than the desired value because of the limitation of 8-bit
resolution.
Note that bits [THRE1:THRE0] are ignored in the software RPM control. In this mode, the DCY adjustment stops
when the difference between the TACH data and TACH setting is less than or equal to 0x000A.
TEMPERATURE DATA REGISTERS
Local Temperature Data Register Bits: [LT10:LT0]
Bits [LT10:LT0] are the newest local temperature reading.
Remote Temperature Register Bits: [RT10:RT0]
Bits [RT10:RT0] are the newest remote temperature reading.
Temp-DATA-LByte Register (Address 0x06, Value After Power-On or Reset = 0x00)
Bit 7 (MSB)
LT2
Bit 6
LT1
Bit 5
LT0 (LSB)
Bit 4
0
Bit 3
0
Bit 2
RT2
Bit 1
RT1
Bit 0 (LSB)
RT0
Bits [LT2:LT0] are the three LSBs of the newest local temperature reading.
Bits [RT2:RT0] are the three LSBs of the newest remote temperature reading.
Local-Temp-DATA-HByte Register (Address 0x0A, Value After Power-On or Reset = 0x80, –128°C)
Bit 7 (MSB)
LT10 (MSB)
Bit 6
LT9
Bit 5
LT8
Bit 4
LT7
Bit 3
LT6
Bit 2
LT5
Bit 1
LT4
Bit 0 (LSB)
LT3
Bits [LT10:LT3] are the eight MSBs of the newest local temperature reading.
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Remote-Temp-DATA-HByte Register (Address 0x0B, Value After Power-On or Reset = 0x80, –128°C)
Bit 7 (MSB)
RT10 (MSB)
Bit 6
RT9
Bit 5
RT8
Bit 4
RT7
Bit 3
RT6
Bit 2
RT5
Bit 1
RT4
Bit 0 (LSB)
RT3
Bits [RT10:RT3] are the eight MSBs of the newest remote temperature reading.
It is important to note that temperature can be read as an 8-bit value (with 1°C resolution) from the
Temp-DATA-Hbyte register, or as an 11-bit value (with 0.125°C resolution) from the Temp-DATA-LByte and
Temp-DATA-HByte registers. If only 1°C resolution is required, the temperature readings can be read back at
any time and in no particular order. If the 11-bit measurement is required, this involves a two-register read for
each measurement. The Temp-DATA-LByte register (0x06) should be read first. This condition causes all
temperature reading registers to be frozen until the Remote-Temp-DATA-HByte Register (0x0B) is read. This
architecture also prevents an MSB reading from being updated while the 3LSBs are being read, and vice versa.
See the Reading Temperature Data section for details.
TEMPERATURE LIMIT REGISTERS
All temperature limits are 11 bits with three LSBs always '0'. Only eight MSBs need to be set in one register for
each limit.
Local-High-Temp-Limit Register (Address 0x14, Value After Power-On or Reset = 0x3C, +60°C)
Bit 7 (MSB)
LT-H10 (MSB)
Bit 6
LT-H9
Bit 5
LT-H8
Bit 4
LT-H7
Bit 3
LT-H6
Bit 2
LT-H5
Bit 1
LT-H4
Bit 0 (LSB)
LT-H3
These bits are the upper bounds of the local temperature.
Local-Low-Temp-Limit Register (Address 0x15, Value After Power-On or Reset = 0x00, 0°C)
Bit 7 (MSB)
LT-L10 (MSB)
Bit 6
LT-L9
Bit 5
LT-L8
Bit 4
LT-L7
Bit 3
LT-L6
Bit 2
LT-L5
Bit 1
LT-L4
Bit 0 (LSB)
LT-L3
These bits are the lower bounds of the local temperature.
Local-THERM-Limit Register (Address 0x16, Value After Power-On or Reset = 0x46, +70°C)
Bit 7 (MSB)
LT-T10 (MSB)
Bit 6
LT-T9
Bit 5
LT-T8
Bit 4
LT-T7
Bit 3
LT-T6
Bit 2
LT-T5
Bit 1
LT-T4
Bit 0 (LSB)
LT-T3
These bits are the thermal threshold of the local temperature.
Remote-High-Temp-Limit Register (Address 0x18, Value After Power-On or Reset = 0x50, +80°C)
Bit 7 (MSB)
RT-H10 (MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
RT-H9
RT-H8
RT-H7
RT-H6
RT-H5
RT-H4
Bit 0 (LSB)
RT-H3
These bits are the upper bounds of the remote temperature.
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Remote-Low-Temp-Limit Register (Address 0x19, Value After Power-On or Reset = 0x00, 0°C)
Bit 7 (MSB)
RT-L10 (MSB)
Bit 6
RT-L9
Bit 5
RT-L8
Bit 4
RT-L7
Bit 3
RT-L6
Bit 2
RT-L5
Bit 1
RT-L4
Bit 0 (LSB)
RT-L3
These bits are the lower bounds of the remote temperature.
Remote-THERM-Limit Register (Address 0x1A, Value After Power-On or Reset = 0x64, +100°C)
Bit 7 (MSB)
RT-T10 (MSB)
Bit 6
RT-T9
Bit 5
RT-T8
Bit 4
RT-T7
Bit 3
RT-T6
Bit 2
RT-T5
Bit 1
RT-T4
Bit 0 (LSB)
RT-T3
These bits are the thermal threshold of the remote temperature.
Local-Critical-Temp Register (Address 0x1B, Value After Power-On or Reset = 0x50, +80°C)
Bit 7 (MSB)
LT-C10
Bit 6
LT-C9
Bit 5
LT-C8
Bit 4
LT-C7
Bit 3
LT-C6
Bit 2
LT-C5
Bit 1
LT-C4
Bit 0 (LSB)
LT-C3
These bits are the critical threshold of the local temperature.
PSV-Temp Register (Address 0x1C, Value After Power-On or Reset = 0x00, 0°C)
Bit 7 (MSB)
0
Bit 6
0
Bit 5
PSV8
Bit 4
PSV7
Bit 3
PSV6
Bit 2
PSV5
Bit 1
PSV4
Bit 0 (LSB)
PSV3
Bits [PSV10:PSV0] are the passive cooling temperature threshold. Bits PSV10, PSV9, and [PSV2:PSV0] are
always '0'. The PSV ranges from 0°C to +64°C.
In the auto fan temperature loop, the fan stops and the duty cycle is forced to 0% when the active temperature is
equal to or below the PSV temperature.
Remote-Critical-Temp Register (Address 0x1D, Value After Power-On or Reset = 0x69, +105°C)
Bit 7 (MSB)
RT-C10
Bit 6
RT-C9
Bit 5
RT-C8
Bit 4
RT-C7
Bit 3
RT-C6
Bit 2
RT-C5
Bit 1
RT-C4
Bit 0 (LSB)
RT-C3
Bits [RT-C10:RT-C0] are the critical threshold of the remote temperature.
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TACH-DATA Register
TACH-DATA-LByte Register (Address 0x08, Power-On Default = 0x00)
Bit 7 (MSB)
TACH-DATA7
Bit 6
TACH-DATA6
Bit 5
TACH-DATA5
Bit 4
TACH-DATA4
Bit 3
TACH-DATA3
Bit 2
TACH-DATA2
Bit 1
TACH-DATA1
Bit 0 (LSB)
TACH-DATA0
TACH-DATA-HByte Register (Address 0x09, Power-On Default = 0x00)
Bit 7 (MSB)
TACH-DATA15
Bit 6
TACH-DATA14
Bit 5
TACH-DATA13
Bit 4
TACH-DATA12
Bit 3
TACH-DATA11
Bit 2
TACH-DATA10
Bit 1
TACH-DATA9
Bit 0 (LSB)
TACH-DATA8
Bits [TACH-DATA15:TACH-DATA0] are the number of clock pulses counted during one fan revolution and
represents the period of the fan revolution (refer to the Fan Speed Measurement section). Reading the TACH
data register involves a two-register read. The low byte should be read first. This method causes the high byte to
be frozen until both the high and low byte registers have been read from, preventing erroneous TACH readings.
TACH Setting Register
TACH-SETTING-LByte Register (Address 0x1E, Power-On Default = 0xFF)
Bit 7 (MSB)
TACHSETTING7
Bit 6
TACHSETTING6
Bit 5
TACHSETTING5
Bit 4
TACHSETTING4
Bit 3
TACHSETTING3
Bit 2
TACHSETTING2
Bit 1
TACHSETTING1
Bit 0 (LSB)
TACHSETTING0
TACH-SETTING-HByte Register (Address 0x1F, Power-On Default = 0xFF)
Bit 7 (MSB)
TACHSETTING15
Bit 6
TACHSETTING14
Bit 5
TACHSETTING13
Bit 4
TACHSETTING12
Bit 3
TACHSETTING11
Bit 2
TACHSETTING10
Bit 1
TACHSETTING9
Bit 0 (LSB)
TACHSETTING8
Bits [TACH-SETTING15:TACH-SETTING0] represent the period of the fan revolution (in the number of clock
pulses counted during one revolution), which is equal to the reciprocal of the target fan speed. Refer to the Fan
Speed Measurement section. Software writes this register to set the target RPM in the Software-RPM Control
mode. When the TACH-MODE bit (bit 1, 0x02) is cleared ('0'), the TACH setting must be not greater than the
value corresponding to the RPM for a 30% duty cycle. When the TACH mode is equal to '1', the TACH setting
must be not greater than the value corresponding to the allowed minimum RPM at which the fan properly runs.
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TACH Low Limit Register
TACH-Low-Limit-LByte Register (Address 0x10, Power-On Default = 0xFF)
Bit 7 (MSB)
TACH-LowLimit7
Bit 6
TACH-LowLimit6
Bit 5
TACH-LowLimit5
Bit 4
TACH-LowLimit4
Bit 3
TACH-LowLimit3
Bit 2
TACH-LowLimit2
Bit 1
TACH-LowLimit1
Bit 0 (LSB)
TACH-LowLimit0
TACH-Low-Limit-HByte Register (Address 0x11, Power-On Default = 0xFF)
Bit 7 (MSB)
TACH-LowLimit15
Bit 6
TACH-LowLimit14
Bit 5
TACH-LowLimit13
Bit 4
TACH-LowLimit12
Bit 3
TACH-LowLimit11
Bit 2
TACH-LowLimit10
Bit 1
TACH-LowLimit9
Bit 0 (LSB)
TACH-LowLimit8
Bits [TACH-Low-Limit15:TACH-Low-Limit0] are the value that corresponds to the predetermined minimum
allowable fan speed (RPM). If the value of the TACH data register is greater than this bound, the fan speed is
below the minimum allowed RPM.
TACH High Limit Register
TACH-High-Limit-LByte Register (Address 0x12, Power-On Default = 0x00)
Bit 7 (MSB)
TACH-HighLimit7
Bit 6
TACH-HighLimit6
Bit 5
TACH-HighLimit5
Bit 4
TACH-HighLimit4
Bit 3
TACH-HighLimit3
Bit 2
TACH-HighLimit2
Bit 1
TACH-HighLimit1
Bit 0 (LSB)
TACH-HighLimit0
TACH-High-Limit-HByte Register (Address 0x13, Power-On Default = 0x00)
Bit 7 (MSB)
TACH-HighLimit15
Bit 6
TACH-HighLimit14
Bit 5
TACH-HighLimit13
Bit 4
TACH-HighLimit12
Bit 3
TACH-HighLimit11
Bit 2
TACH-HighLimit10
Bit 1
TACH-HighLimit9
Bit 0 (LSB)
TACH-HighLimit8
Bits [TACH-High-Limit15:TACH-High-Limit0] are the value that corresponds to the predetermined maximum
allowable fan speed (RPM). If the value of the TACH data register is smaller than this bound, the fan speed is
above the maximum allowed RPM.
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
AMC6821SQDBQRQ1
ACTIVE
SSOP
DBQ
16
2500
RoHS & Green
NIPDAU
Level-3-260C-168 HR
-40 to 125
C6821Q
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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