ADT7483A
Dual Channel Temperature
Sensor and Over
Temperature Alarm
The ADT7483A is a three-channel digital thermometer and
under/over temperature alarm, intended for use in PCs and thermal
management systems. It can measure the temperature in two remote
locations, for example, the remote thermal diode in a CPU or GPU, or
a discrete diode connected transistor. It can also measure its own
ambient temperature. The temperature of the remote thermal diode
and ambient temperature can be accurately measured to 1C. The
temperature measurement range defaults to 0C to 127C, compatible
with ADM1032, but can be switched to a wider measurement range,
from −64C to +191C.
The ADT7483A communicates over a 2-wire serial interface
compatible with system management bus (SMBus) standards. The
SMBus address is set by the ADD0 and ADD1 pins. As many as nine
different SMBus addresses are possible.
An ALERT output signals when the on-chip or remote temperature
is outside the programmed limits. The THERM output is a comparator
output that allows, for example, on/off control of a cooling fan. The
ALERT output can be reconfigured as a second THERM output, if
required.
Features
1 Local and 2 Remote Temperature Sensors
0.25C Resolution/1C Accuracy on Remote Channels
1C Resolution/1C Accuracy on Local Channel
Extended, Switchable Temperature Measurement Range
0C to 127C (Default) or –64C to +191C
2-wire SMBus Serial Interface with SMBus Alert Support
Programmable Over/Under Temperature Limits
Offset Registers for System Calibration
Up to 2 Overtemperature Fail-safe THERM Outputs
Small 16-lead QSOP Package
240 mA Operating Current, 5 mA Standby Current
This Device is Pb-Free, Halogen Free and is RoHS Compliant
Applications
July, 2012 − Rev. 2
QSOP−16
CASE 492
PIN ASSIGNMENT
ADD1
1
16
ADD0
VDD
2
15
SCLK
D1+
3
14
D1−
4
ADT7483A
13
THERM
5
(Top View)
GND
6
11
D2−
NC
7
10
NC
NC
8
9
NC
SDATA
ALERT/
THERM2
12 D2+
NC = No Connect
MARKING DIAGRAM
ADT7483
AARQZ
#YYWW
ADT7483AARQZ = Specific Device Code
#
= Pb-Free Package
YYWW
= Date Code
ORDERING INFORMATION
Desktop and Notebook Computers
Industrial Controllers
Smart Batteries
Automotive
Embedded Systems
Burn-in Applications
Instrumentation
Semiconductor Components Industries, LLC, 2012
http://onsemi.com
See detailed ordering and shipping information in the package
dimensions section on page 19 of this data sheet.
1
Publication Order Number:
ADT7483A/D
ADT7483A
ADDRESS POINTER
REGISTER
3
D1−
4
D2+
12
D2−
11
ONE-SHOT
REGISTER
LOCAL TEMPERATURE
VALUE REGISTER
LOCAL TEMPERATURE
THERM LIMIT REGISTER
11-BIT A-TO-D
CONVERTER
ANALOG
MUX
BUSY
RUN/STANDBY
LOCAL TEMPERATURE
LOW LIMIT REGISTER
LIMIT COMPARATOR
D1+
CONVERSION RATE
REGISTER
DIGITAL MUX
ON-CHIP
TEMPERATURE
SENSOR
REMOTE 1 & 2 TEMP
VALUE REGISTERS
LOCAL TEMPERATURE
HIGH LIMIT REGISTER
REMOTE 1 & 2 TEMP.
THERM LIMIT REG.
REMOTE 1 & 2 TEMP.
LOW LIMIT REGISTERS
REMOTE 1 & 2 TEMP
OFFSET REGISTERS
REMOTE 1 & 2 TEMP.
HIGH LIMIT REGISTERS
CONFIGURATION
REGISTER
EXTERNAL DIODE OPEN-CIRCUIT
INTERRUPT
MASKING
STATUS REGISTERS
ADT7483A
SMBUS INTERFACE
2
6
16
1
14
15
5
VDD
GND
ADD0
ADD1
SDATA
SCLK
THERM
13
ALERT/THERM2
Figure 1. Functional Block Diagram
Table 1. PIN ASSIGNMENT
Pin No.
Mnemonic
1
ADD1
2
VDD
3
D1+
Positive Connection. Connects to the first remote temperature sensor.
4
D1−
Negative Connection. Connects to the first remote temperature sensor.
5
THERM
6
GND
7
NC
No Connect.
8
NC
No Connect.
9
NC
No Connect.
10
NC
No Connect.
11
D2−
Negative Connection. Connects to the second remote temperature sensor.
12
D2+
Positive Connection. Connects to the second remote temperature sensor.
13
ALERT/THERM2
14
SDATA
Logic Input/Output, SMBus Serial Data. Open-drain output. Requires a pull-up resistor.
15
SCLK
Logic Input, SMBus Serial Clock. Requires a pull-up resistor.
16
ADD0
Address 0 Pin. Tri-state input to set the SMBus address.
B
Description
Address 1 Pin. Tri-state input to set the SMBus address.
Positive Supply, 3 V to 3.6 V.
Open-drain Output. Turns a fan on/off, or throttles a CPU clock in the event of an overtemperature
condition.
Supply Ground Connection.
Open-drain Logic Output. Used as interrupt or SMBus alert. This may also be configured as a second
THERM output. Requires a pull-up resistor.
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2
ADT7483A
Table 2. ABSOLUTE MAXIMUM RATINGS
Parameter
Positive Supply Voltage (VDD) to GND
D+
Rating
Unit
−0.3, +3.6
V
−0.3 to VDD + 0.3
V
D− to GND
−0.3 to +0.6
V
SCLK, SDATA, ALERT, THERM
−0.3 to +3.6
V
Input Current, SDATA, THERM
−1, +50
mA
1
mA
Input Current, D−
ESD Rating, All Pins (Human Body Model)
1,500
V
150
C
Storage Temperature Range
−65 to +150
C
IR Reflow Peak Temperature
220
C
IR Reflow Peak Temperature Pb-Free
260
C
Lead Temperature (Soldering 10 sec)
300
C
Maximum Junction Temperature (TJ MAX)
Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the
Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect
device reliability.
NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.
Table 3. THERMAL CHARACTERISTICS
Package Type
16-lead QSOP
qJA
qJC
Unit
150
38.8
C/W
Table 4. SMBus TIMING SPECIFICATIONS (Note 1)
1.
2.
3.
4.
Parameter
Limit at TMIN and TMAX
Unit
fSCLK
400
kHz max
tLOW
4.7
ms min
Clock Low Period, between 10% Points
tHIGH
4.0
ms min
Clock High Period, between 90% Points
tR
1.0
ms max
Clock/Data Rise Time
Description
tF
300
ns max
Clock/Data Fall Time
tSU; STA
4.7
ms min
Start Condition Setup Time
tHD; STA
(Note 2)
4.0
ms min
Start Condition Hold Time
tSU; DAT
(Note 3)
250
ns min
Data Setup Time
tSU; STO
(Note 4)
4.0
ms min
Stop Condition Setup Time
tBUF
4.7
ms min
Bus Free Time between Stop and Start Conditions
Guaranteed by design, not production tested.
Time from 10% of SDATA to 90% of SCLK.
Time for 10% or 90% of SDATA to 10% of SCLK.
Time for 90% of SCLK to 10% of SDATA.
t LOW
tF
t HD; STA
tR
SCLK
t HD; STA
t HD; DAT
t HIGH
t SU; STA
t SU; DAT
t SU; STO
SDATA
t BUF
STOP START
START
Figure 2. Serial Bus Timing
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3
STOP
ADT7483A
Table 5. ELECTRICAL CHARACTERISTICS (TA = −40C to +125C, VDD = 3 V to 3.6 V, unless otherwise noted) (Note 1)
Parameter
Test Conditions
Min
Typ
Max
Unit
Power Supply
3.0
3.3
3.6
V
Average Operating Supply Current, IDD
0.0625 Conversions/sec Rate (Note 1)
Standby Mode
−
−
240
5
350
30
mA
Undervoltage Lockout Threshold
VDD Input, Disables ADC, Rising Edge
−
2.55
−
V
1
−
2.5
V
0C TA 70C
0C TA 85C
−40C TA +100C
−
−
−
−
−
−
−
1
1
1.5
2.5
−
C
0C TA 70C, −55C TD 150C (Note 3)
0C TA 85C, −55C TD 150C (Note 3)
−40C TA +125C, −55C TD 150C
(Note 3)
−
−
−
−
−
−
1
1.5
2.5
C
−
0.25
−
Remote Sensor Source Current (Note 3)
High Level
Low Level
−
−
233
14
−
−
mA
Conversion Time
from Stop Bit to Conversion Complete
(All Channels), One-shot Mode with Averaging
Switched On
One-shot Mode with Averaging Off,
(Conversion Rate = 16, 32, or 64
Conversions/sec)
−
73
94
ms
−
11
14
Supply Voltage, VDD
Power-On-Reset Threshold
Temperature-to-Digital Converter (Note 2)
Local Sensor Accuracy
Resolution
Remote Diode Sensor Accuracy
Resolution
Open-drain Digital Outputs (THERM, ALERT/THERM2)
Output Low Voltage, VOL
IOUT = −6.0 mA
−
−
0.4
V
High Level Output Current, IOH
VOUT = VDD
−
0.1
1
mA
Logic Input High Voltage, VIH, SCLK, SDATA
2.1
−
−
V
Logic Input Low Voltage, VIL, SCLK, SDATA
−
−
0.8
V
Hysteresis
−
500
−
mV
SMBus Interface (Notes 3 and 4)
SDA Output Low Voltage, VOL
1.
2.
3.
4.
5.
−
−
0.4
V
Logic Input Current, IIH, IIL
IOUT = −6.0 mA
−1
−
+1
mA
SMBus Input Capacitance, SCLK, SDATA
−
5
−
pF
SMBus Clock Frequency
−
−
400
kHz
SMBus Timeout (Note 5)
User Programmable
−
25
32
ms
SCLK Falling Edge to SDATA Valid Time
Master Clocking in Data
−
−
1
ms
See Table 11 for information on other conversion rates.
Averaging enabled.
Guaranteed by design, not production tested.
See SMBus Timing Specifications section for more information.
Disabled by default. See the Serial Bus Interface section for details to enable it.
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4
ADT7483A
TYPICAL PERFORMANCE CHARACTERISTICS
3.5
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
3.0
2.5
2.0
DEV 8
DEV 9
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
DEV 15
DEV 16
MEAN
HIGH 4S
LOW 4S
1.5
1.0
0.5
0
−0.5
−1.0
−50
0
50
100
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
3.0
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
3.5
2.5
2.0
1.0
0.5
0
−0.5
−1.0
−50
150
3.0
2.5
2.0
1.0
0.5
0
−0.5
0
5
50
100
0
−5
−10
D+ To VDD
−15
−20
−25
150
10
1
100
LEAKAGE RESISTANCE (MW)
Figure 5. Remote 2 Temperature Error
vs. Temperature
Figure 6. Temperature Error vs. D+/D− Leakage
Resistance
0
1000
−2
900
−4
800
DEV 2BC
700
−6
IDD (mA)
TEMPERATURE ERROR (C)
150
D+ To GND
TEMPERATURE (C)
−8
−10
DEV 3
−12
500
DEV 4BC
400
DEV 3BC
200
DEV 4
−16
600
300
DEV 2
−14
−18
100
10
DEV 15
DEV 16
MEAN
HIGH 4S
LOW 4S
1.5
−1.0
−50
50
Figure 4. Remote 1 Temperature Error
vs. Temperature
TEMPERATURE ERROR (C)
TEMPERATURE ERROR (C)
DEV 8
DEV 9
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
0
TEMPERATURE (C)
Figure 3. Local Temperature Error vs. Temperature
DEV 1
DEV 2
DEV 3
DEV 4
DEV 5
DEV 6
DEV 7
DEV 15
DEV 16
HIGH 4S
LOW 4S
1.5
TEMPERATURE (C)
3.5
DEV 8
DEV 9
DEV 10
DEV 11
DEV 12
DEV 13
DEV 14
100
0
5
10
15
20
0
0.01
25
CAPACITANCE (nF)
0.1
1
10
CONVERTION RATE (Hz)
Figure 7. Temperature Error vs. D+/D− Capacitance
Figure 8. Operating Supply Current
vs. Conversion Rate
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5
100
ADT7483A
422
4.4
420
4.2
DEV 2BC
418
4.0
416
3.8
414
IDD (mA)
IDD (mA)
TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)
DEV 3BC
DEV 4BC
412
DEV 2
DEV 3
DEV 4
3.6
3.4
3.2
410
408
3.0
3.1
3.2
3.3
3.4
3.5
3.0
3.0
3.6
3.1
3.2
Figure 9. Operating Supply Current vs. Voltage
TEMPERATURE ERROR (C)
15
10
5
10
100
20
100 mV
15
10
50 mV
5
0
1000
20 mV
0
100
200
300
400
500
600
NOISE FREQUENCY (MHz)
FSCL (kHz)
Figure 11. Standby Supply Current vs. SCLK
Frequency
Figure 12. Temperature Error vs. Common-Mode
Noise Frequency
80
TEMPERATURE ERROR (C)
ISTBY (mA)
20
1
3.6
25
25
0
3.5
Figure 10. Standby Supply Current vs. Voltage
DEV 2BC
DEV 3BC
DEV 4BC
30
3.4
VDD (V)
VDD (V)
35
3.3
70
60
100 mV
50
40
30
50 mV
20
10
20 mV
0
−10
0
100
200
300
400
500
600
NOISE FREQUENCY (MHz)
Figure 13. Temperature Error vs. Differential Mode Noise Frequency
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ADT7483A
Theory of Operation
The ADT7483A is a local and 2 remote temperature
sensor and over/under temperature alarm. When the
ADT7483A is operating normally, the on-board ADC
operates in a freerunning mode. The analog input
multiplexer alternately selects either the on-chip
temperature sensor or one of the remote temperature sensors
to measure its local temperature. The ADC digitizes these
signals, and the results are stored in the local, Remote 1, and
Remote 2 temperature value registers.
The local and remote measurement results are compared
with the corresponding high, low, and THERM temperature
limits stored in on-chip registers. Out-of-limit comparisons
generate flags that are stored in the status register. A result
that exceeds the high temperature limit, the low temperature
limit, or a remote diode open circuit causes the ALERT
output to assert low. Likewise, exceeding THERM
temperature limits causes the THERM output to assert low.
The ALERT output can be reprogrammed as a second
THERM output.
The limit registers can be programmed, and the device
controlled and configured, via the serial SMBus. The
contents of any register can also be read back via the SMBus.
Control and configuration functions consist of:
Switching the Device between Normal Operation and
Standby Mode
Selecting the Temperature Measurement Scale
Masking or Enabling the ALERT Output
Switching Pin 13 between ALERT and THERM2
Selecting the Conversion Rate
the baseemitter voltage (VBE) of a transistor, operated at
constant current. Unfortunately, this technique requires
calibration to null the effect of the absolute value of VBE,
which varies from device to device. The technique used in
the ADT7483A is to measure the change in VBE when the
device is operated at two different currents.
Figure 14 shows the input signal conditioning used to
measure the output of a remote temperature sensor. This
figure shows the remote sensor as a substrate transistor, but
it could equally be a discrete transistor. If a discrete
transistor is used, the collector is not grounded and should
be linked to the base. To prevent ground noise interfering
with the measurement, the more negative terminal of the
sensor is not referenced to ground but is biased above ground
by an internal diode at the D− input. C1 can be optionally
added as a noise filter (recommended maximum value
1,000 pF).
To measure DVBE, the operating current through the sensor
is switched among two related currents, I and N I. The
currents through the temperature diode are switched
between I and N I, giving DVBE. The temperature is then
calculated using the DVBE measurement.
The resulting DVBE waveforms pass through a 65 kHz
low-pass filter to remove noise and then to a
chopper-stabilized amplifier. This amplifies and rectifies the
waveform to produce a dc voltage proportional to DVBE.
The ADC digitizes this voltage and produces a temperature
measurement. To reduce the effects of noise, digital filtering
is performed by averaging the results of 16 measurement
cycles for low conversion rates. At rates of 16, 32, and
64 conversions/second, no digital averaging takes place.
Signal conditioning and measurement of the local
temperature sensor is performed in the same manner.
Temperature Measurement Method
A simple method of measuring temperature is to exploit
the negative temperature coefficient of a diode, measuring
I
NI
IBIAS
VDD
D+
REMOTE
SENSING
TRANSISTOR
VOUT+
To ADC
C1*
D−
VOUT−
BIAS
DIODE
LOW-PASS FILTER
fC = 65 kHz
*CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 1,000 pF MAX
Figure 14. Input Signal Conditioning
Temperature Measurement Results
The local temperature measurement is an 8-bit
measurement with 1C resolution. The remote temperature
measurements are 10-bit measurements, with eight MSBs
stored in one register and two LSBs stored in another
register. Table 6 lists the temperature measurement registers.
The results of the local and remote temperature
measurements are stored in the local and remote temperature
value registers and are compared with limits programmed
into the local and remote high and low limit registers.
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ADT7483A
registers themselves can have values from −64C to +191C.
However, most temperature sensing diodes have a
maximum temperature range of −55C to +150C.
Note that although both local and remote temperature
measurements can be made while the part is in extended
temperature mode, the ADT7483A should not be exposed to
temperatures greater than those specified in theAbsolute
Maximum Ratings section. Further, the device is only
guaranteed to operate as specified at ambient temperatures
from −40C to +120C.
Table 6. REGISTER ADDRESS FOR
THE TEMPERATURE VALUES
Temperature
Channel
Register Address,
MSBs
Register Address,
LSBs
Local
0x00
N/A
Remote 1
0x01
0x10 (2 MSBs)
Remote 2
0x30
0x33 (2 MSBs)
By setting Bit 3 of the Configuration 1 Register to 1, the
Remote 2 temperature values can be read from the following
register addresses:
Remote 2, MSBs = 0x01
Remote 2, LSBs = 0x10
Temperature Data Format
The ADT7483A has two temperature data formats. When
the temperature measurement range is from 0C to 127C
(default), the temperature data format for both local and
remote temperature results is binary. When the
measurement range is in extended mode, an offset binary
data format is used for both local and remote results.
Temperature values in the offset binary data format are
offset by +64. Examples of temperatures in both data
formats are shown in Table 8.
The above is true only when Bit 3 of the Configuration 1
register is set. To read the Remote 1 temperatures, this bit
needs to be switched back to 0.
Only the two MSBs in the remote temperature low byte
are used. This gives the remote temperature measurement a
resolution of 0.25C. Table 7 shows the data format for the
remote temperature low byte.
Table 8. TEMPERATURE DATA FORMAT
(LOCAL AND REMOTE TEMPERATURE HIGH BYTE)
Table 7. EXTENDED TEMPERATURE RESOLUTION
(REMOTE TEMPERATURE LOW BYTE)
Offset Binary
(Note 1)
Extended Resolution
Remote Temperature
Low Byte
0.00C
0 000 0000
0.25C
0 100 0000
0C
0 000 0000
0 100 0000
0.50C
1 000 0000
+1C
0 000 0001
0 100 0001
0.75C
1 100 0000
+10C
0 000 1010
0 100 1010
+25C
0 001 1001
0 101 1001
+50C
0 011 0010
0 111 0010
+75C
0 100 1011
1 000 1011
+100C
0 110 0100
1 010 0100
+125C
0 111 1101
1 011 1101
+127C
0 111 1111
1 011 1111
+150C
0 111 1111
(Note 3)
1 101 0110
When reading the full remote temperature value, both the
high and low byte, the two registers should be read LSB first
and then the MSB. This is because reading the LSB will
cause the MSB to be locked until it is read, guaranteeing that
the two values read are a result of the same temperature
measurement.
Temperature Measurement Range
The temperature measurement range for both local and
remote measurements is, by default, 0C to 127C.
However, the ADT7483A can be operated using an
extended temperature range from −64C to +191C. This
means, the ADT7483A can measure the full temperature
range of a remote thermal diode, from −55C to +150C. The
user can switch between these two temperature ranges by
setting or clearing Bit 2 in the Configuration 1 register. A
valid result is available in the next measurement cycle after
changing the temperature range.
In extended temperature mode, the upper and lower
temperatures that can be measured by the ADT7483A are
limited by the remote diode selection. The temperature
Temperature
Binary
−55C
0 000 0000
(Note 2)
0 000 1001
1. Offset binary scale temperature values are offset by +64.
2. Binary scale temperature measurement returns 0 for all
temperatures < 0C.
3. Binary scale temperature measurement returns 127 for all
temperatures > 127C.
The user may switch between measurement ranges at any
time. Switching the range also switches the data format. The
next temperature result following the switching is reported
back to the register in the new format. However, the contents
of the limit registers do not change. It is up to the user to
ensure that when the data format changes, the limit registers
are reprogrammed as necessary (for more information, see
the Limit Registers section).
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ADT7483A
Registers
The registers in the ADT7483A are eight bits wide. These
registers are used to store the results of remote and local
temperature measurements, and high and low temperature
limits, and to configure and control the device. A description
of these registers is provided in this section.
Temperature Value Registers
The ADT7483A has five registers to store the results of
local and remote temperature measurements. These
registers can only be written to by the ADC and can be read
by the user over the SMBus.
The local temperature value register is at Address 0x00
The Remote 1 temperature value high byte register is at
Address 0x01, with the Remote 1 low byte register at
Address 0x10
The Remote 2 temperature value high byte register is at
Address 0x30, with the Remote 2 low byte register at
Address 0x33
The Remote 2 temperature values can be read from
Address 0x01 for the high byte and Address 0x10 for
the low byte if Bit 3 of Configuration Register 1 is set
to 1
To read the Remote 1 temperature values, Bit 3 of
Configuration Register 1 should be set to 0
The power-on default for all five registers is 0x00
Address Pointer Register
The address pointer register does not have, nor does it
require, an address because the first byte of every write
operation is automatically written to this register. The data
in this first byte always contains the address of another
register on the ADT7483A, which is stored in the address
pointer register. It is to this other register address that the
second byte of a write operation is written, or to which a
subsequent read operation is performed.
The power-on default value of the address pointer register
is 0x00, so if a read operation is performed immediately after
power-on without first writing to the address pointer, the
value of the local temperature will be returned, since its
register address is 0x00.
Table 9. CONFIGURATION 1 REGISTER (READ ADDRESS = 0x03, WRITE ADDRESS = 0x09)
Bit
Mnemonic
Function
7
Mask
6
Mon/STBY
5
AL/TH
4
Reserved
Reserved for future use.
3
Remote 1/
Remote 2
Setting this bit to 1 enables the user to read the Remote 2 values from the Remote 1 registers.
Default = 0 = Remote 1 temperature values and limits are read from these registers. This bit is not lockable.
2
Temp
Range
1
Mask R1
Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit. Default = 0.
0
Mask R2
Setting this bit to 1 masks ALERTs due to the Remote 2 temperature exceeding a programmed limit. Default = 0.
Setting this bit to 1 masks all ALERTs on the ALERT pin. Default = 0 = ALERT enabled. This applies only if
Pin 13 is configured as ALERT, otherwise it has no effect.
Setting this bit to 1 places the ADT7483A in standby mode, that is, suspends all temperature measurements
(ADC). The SMBus remains active and values can be written to, and read from, the registers. THERM and
ALERT are also active in standby mode. Changes made to the limit registers in standby mode that affect the
THERM or ALERT outputs will cause these signals to be updated. Default = 0 = temperature monitoring
enabled.
This bit selects the function of Pin 13. Default = 0 = ALERT. Setting this bit to 1 configures Pin 13 as the
THERM2 pin.
Setting this bit to 1 enables the extended temperature measurement range (−50C to +150C).
Default = 0 = 0C to +127C.
Table 10. CONFIGURATION 2 REGISTER (ADDRESS = 0x24)
Bit
Mnemonic
7
Lock Bit
Res
Function
Setting this bit to 1 locks all lockable registers to their current values. This prevents settings being tampered
with until the device is powered down. Default = 0.
Reserved for future use.
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ADT7483A
Conversion Rate/Channel Selector Register
This register can be written to and read back over the
SMBus. The default value of this register is 0x07, giving a
rate of 8 conversions/second.
Bit 7 in this register can be used to disable averaging of the
temperature measurements. The ADT7483A can be
configured to take temperature measurements of either a
single temperature channel or all temperature channels.
Bit 5 and Bit 4 can be used to specify which temperature
channel or channels are measured.
The conversion rate/channel selector register is at
Address 0x04 for reads, and Address 0x0A for writes. The
four LSBs of this register are used to program the conversion
times from 15.5 ms (Code 0x0A) to 16 seconds
(Code 0x00). To program the ADT7483A to perform
continuous measurements, set the conversion rate register to
0x0B. For example, a conversion rate of 8 conversions/
second means that beginning at 125 ms intervals, the device
performs a conversion on the local and the remote
temperature channels.
Table 11. CONVERSION RATE/CHANNEL SELECTOR REGISTER
Bit
Mnemonic
Function
7
Averaging
Setting this bit to 1 disables averaging of the temperature measurements at the slower conversion
rates (averaging cannot take place at the three faster rates, so setting this bit has no effect). When
default = 0, averaging is enabled.
Reserved for future use. Do not write to this bit.
6
Reserved
Channel Selector
These bits are used to select the temperature measurement channels:
00 = Round Robin = Default = All Channels
01 = Local Temperature
10 = Remote 1 Temperature
11 = Remote 2 Temperature
Conversion Rates
These bits set how often the ADT7483A measures each temperature channel.
Conversions/second
Time
0000 = 0.0625
0001 = 0.125
0010 = 0.25
0011 = 0.5
0100 = 1
0101 = 2
0110 = 4
0111 = 8 = Default
1000 = 16
1001 = 32
1010 = Continuous Measurements
Limit Registers
16 s
8s
4s
2s
1s
500 ms
250 ms
125 ms
62.5 ms
31.25 ms
provided that applies to both THERM channels. This
hysteresis value may be reprogrammed to any value after
power-up using Register Address 0x21.
It is important to remember that the data format for
temperature limits is the same as the temperature
measurement data format. Thus, if the temperature
measurement uses the default (binary), then the temperature
limits also use the binary scale. If the temperature
measurement scale is switched, however, the temperature
limits do not automatically switch. The user must reprogram
the limit registers to the desired value in the correct data
format. For example, if the remote low limit is set at 10C
and the default binary scale is being used, the limit register
value should be 0000 1010b. If the scale is switched to offset
binary, the value in the low temperature limit register should
be reprogrammed to be 0100 1010b.
The ADT7483A has three limits for each temperature
channel: high, low, and THERM temperature limits for
local, Remote 1, and Remote 2 temperature measurements.
The remote temperature high and low limits span two
registers each to contain an upper and lower byte for each
limit. There is also a THERM hysteresis register. All limit
registers can be written to and read back over the SMBus.
See Table 16 for details of the limit registers’ addresses and
their power-on default values.
When Pin 13 is configured as an ALERT output, the high
limit registers perform a > comparison while the low limit
registers perform a comparison. For example, if the high
limit register is programmed with 80C, then measuring
81C will result in an out-of-limit condition, setting a flag in
the status register. If the low limit register is programmed
with 0C, measuring 0C or lower will result in an
out-of-limit condition.
Exceeding either the local or remote THERM limit asserts
THERM low. When Pin 13 is configured as THERM2,
exceeding either the local limit or remote high limit asserts
THERM2 low. A default hysteresis value of 10C is
Status Registers
The status registers are read-only registers, at
Address 0x02 (Status Register 1) and Address 0x23 (Status
Register 2). They contain status information for the
ADT7483A.
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ADT7483A
serviced by the master reading the device address, provided
the error condition has gone away and the status register flag
bits have been reset.
When Flag 1 and/or Flag 0 of Status Register 1, or Flag 1
of Status Register 2 are set, the THERM output goes low to
indicate that the temperature measurements are outside the
programmed limits. The THERM output does not need to be
reset, unlike the ALERT output. Once the measurements are
within the limits, the corresponding status register bits are
automatically reset and the THERM output goes high. The
user may add hysteresis by programming Register 0x21.
The THERM output will be reset only when the temperature
falls below the THERM limit minus hysteresis.
When Pin 13 is configured as THERM2, only the high
temperature limits are relevant. If Flag 6, Flag 4 of Status
Register 1, or Flag 4 of Status Register 2 are set, the
THERM2 output goes low to indicate that the temperature
measurements are outside the programmed limits. Flag 5
and Flag 3 of Status Register 1, and Flag 3 of Status
Register 2 have no effect on THERM2. The behavior of
THERM2 is otherwise the same as THERM.
Bit 0 of Status Register 2 is set whenever the ALERT
output of the ADT7483A is asserted low. This means that the
user need only read Status Register 2 to determine if the
ADT7483A is responsible for the ALERT. Bit 0 of Status
Register 2 is reset when the ALERT output is reset. If the
ALERT output is masked, then this bit is not set.
Table 12. STATUS REGISTER 1 BIT ASSIGNMENTS
Bit
Mnemonic
7
BUSY
6
Function
ALERT
1 when ADC Converting
No
LHIGH
(Note 1)
1 when Local High
Temperature Limit Tripped
Yes
5
LLOW
(Note 1)
1 when Local Low
Temperature Limit Tripped
Yes
4
R1HIGH
(Note 1)
1 when Remote 1 High
Temperature Limit Tripped
Yes
3
R1LOW
(Note 1)
1 when Remote 1 Low
Temperature Limit Tripped
Yes
2
D1 OPEN
(Note 1)
1 when Remote 1 Sensor
Open Circuit
Yes
1
R1THRM1
1 when Remote1 THERM
Limit Tripped
No
0
LTHRM1
1 when Local THERM Limit
Tripped
No
1. These flags stay high until the status register is read, or they are
reset by POR.
Table 13. STATUS REGISTER 2 BIT ASSIGNMENTS
Bit
Mnemonic
Function
ALERT
7
Res
Reserved for Future Use
No
6
Res
Reserved for Future Use
No
5
Res
Reserved for Future Use
No
4
R2HIGH
(Note 1)
1 when Remote 2 High
Temperature Limit Tripped
Yes
3
R2LOW
(Note 1)
1 when Remote 2 Low
Temperature Limit Tripped
Yes
2
D2 OPEN
(Note 1)
1 when Remote 2 Sensor
Open Circuit
Yes
1
R2THRM1
1 when Remote 2 THERM
Limit Tripped
No
0
ALERT
1 when ALERT Condition
Exists
No
Offset Register
Offset errors may be introduced into the remote
temperature measurement by clock noise or by the thermal
diode being located away from the hot spot. To achieve the
specified accuracy on this channel, these offsets must be
removed.
The offset values are stored as 10-bit, twos complement
values:
The Remote 1 offset MSBs are stored in Register 0x11,
and the LSBs are stored 0x12 (low byte, left justified).
The Remote 2 offset MSBs are stored in Register 0x34,
and the LSBs are stored 0x35 (low byte, left justified).
The Remote 2 offset can be written to, or read from, the
Remote 1 offset registers if Bit 3 of the Configuration 1
register is set to 1. This bit should be set to 0 (default)
to read the Remote 1 offset values.
1. These flags stay high until the status register is read, or they are
reset by POR.
The eight flags that can generate an ALERT are NOR’d
together, so if any of them are high, the ALERT interrupt
latch is set and the ALERT output goes low (provided they
are not masked out).
Reading the Status 1 register will clear the five flags, Bit 6
to Bit 2 in Status Register 1, provided the error conditions
that caused the flags to be set have gone away. Reading the
Status 2 register will clear the three flags, Bit 4 to Bit 2 in
Status Register 2, provided the error conditions that caused
the flags to be set have gone away. A flag bit can only be reset
if the corresponding value register contains an in-limit
measurement or if the sensor is good.
The ALERT interrupt latch is not reset by reading the
status register. It is reset when the ALERT output has been
Only the upper 2 bits of the LSB registers are used. The
MSB of the MSB offset registers is the sign bit. The
minimum offset that can be programmed is −128C, and the
maximum is +127.75C.
The value in the offset register is added or subtracted to the
measured value of the remote temperature.
The offset register powers up with a default value of 0C
and will have no effect unless the user writes a different
value to it.
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ADT7483A
Consecutive ALERT Register
Table 14. SAMPLE OFFSET REGISTER CODES
Offset Value
0x11/0x34
0x12/0x35
−128C
1000 0000
00 00 0000
−4C
1111 1100
00 00 0000
−1C
1111 1111
00 000000
−0.25C
1111 1111
10 00 0000
0C
0000 0000
00 00 0000
+0.25C
0000 0000
01 00 0000
+1C
0000 0001
00 00 0000
+4C
0000 0100
00 00 0000
+127.75C
0111 1111
11 00 0000
The value written to this register determines how many
out-of-limit measurements must occur before an ALERT is
generated. The default value is that one out-of-limit
measurement generates an ALERT. The maximum value
that can be chosen is 4. The purpose of this register is to
allow the user to perform some filtering of the output. This
is particularly useful at the fastest three conversion rates,
where no averaging takes place. This register is at
Address 0x22.
Table 15. CONSECUTIVE ALERT REGISTER BIT
Register Value
Amount of Out-of-Limit
Measurements Required
One-shot Register
yzax 000x
1
The one-shot register is used to initiate a conversion and
comparison cycle when the ADT7483A is in standby mode,
after which the device returns to standby. Writing to the
one-shot register address (0x0F) causes the ADT7483A to
perform a conversion and comparison on both the local and
the remote temperature channels. This is not a data register
as such, and it is the write operation to Address 0x0F that
causes the one-shot conversion. The data written to this
address is irrelevant and is not stored.
yzax 001x
2
yzax 011x
3
yzax 111x
4
NOTES: y = SMBus SCL timeout bit. Default = 0. See the Serial
Bus Interface section for more information.
z = SMBus SDA timeout bit. Default = 0. See the Serial
Bus Interface section for more information.
a = Mask Internal ALERTs.
x = Don’t care bit.
Table 16. LIST OF REGISTERS
Read
Address
(Hex)
Write
Address
(Hex)
N/A
N/A
Address Pointer
Undefined
00
N/A
Local Temperature Value
0000 0000 (0x00)
01
N/A
Remote 1 Temperature Value High Byte
0000 0000 (0x00)
Bit 3 Conf. Reg. = 0
No
01
N/A
Remote 2 Temperature Value High Byte
0000 0000 (0x00)
Bit 3 Conf. Reg. = 1
No
02
N/A
Status Register 1
Undefined
No
03
09
Configuration Register 1
0000 0000 (0x00)
Yes
04
0A
Conversion Rate
0000 0111 (0x07)
Yes
05
0B
Local Temperature High Limit
0101 0101 (0x55) (85C)
Yes
06
0C
Local Temperature Low Limit
0000 0000 (0x00) (0C)
Yes
07
0D
Remote 1 Temperature High Limit High Byte
0101 0101 (0x55) (85C)
Bit 3 Conf. Reg. = 0
Yes
07
0D
Remote 2 Temperature High Limit High Byte
0101 0101 (0x55) (85C)
Bit 3 Conf. Reg. = 1
Yes
08
0E
Remote 1 Temperature Low Limit High Byte
0000 0000 (0x00) (0C)
Bit 3 Conf. Reg. = 0
Yes
08
0E
Remote 2 Temperature Low Limit High Byte
0000 0000 (0x00) (0C)
Bit 3 Conf. Reg. = 1
N/A
0F
(Note 1)
10
N/A
Remote 1 Temperature Value Low Byte
0000 0000
Bit 3 Conf. Reg. = 0
10
N/A
Remote 2 Temperature Value Low Byte
0000 0000
Bit 3 Conf. Reg. = 1
No
11
11
Remote 1 Temperature Offset High Byte
0000 0000
Bit 3 Conf. Reg. = 0
Yes
11
11
Remote 2 Temperature Offset High Byte
0000 0000
Bit 3 Conf. Reg. = 1
Yes
12
12
Remote 1 Temperature Offset Low Byte
0000 0000
Bit 3 Conf. Reg. = 0
Yes
12
12
Remote 2 Temperature Offset Low Byte
0000 0000
Bit 3 Conf. Reg. = 1
Yes
13
13
Remote 1 Temperature High Limit Low Byte
0000 0000
Bit 3 Conf. Reg. = 0
Yes
13
13
Remote 2 Temperature High Limit Low Byte
0000 0000
Bit 3 Conf. Reg. = 1
Yes
14
14
Remote 1 Temperature Low Limit Low Byte
0000 0000
Bit 3 Conf. Reg. = 0
Yes
Mnemonic
Power-On Default
Comment
Lock
No
No
One Shot
Yes
N/A
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No
ADT7483A
Table 16. LIST OF REGISTERS (continued)
Read
Address
(Hex)
Write
Address
(Hex)
Comment
Lock
14
14
Remote 2 Temperature Low Limit Low Byte
0000 0000
Bit 3 Conf. Reg. = 1
Yes
19
19
Remote 1 THERM Limit
0101 0101 (0x55) (85C)
Bit 3 Conf. Reg. = 0
Yes
19
19
Remote 2 THERM Limit
0101 0101 (0x55) (85C)
Bit 3 Conf. Reg. = 1
Yes
20
20
Local THERM Limit
0101 0101 (0x55) (85C)
Yes
21
21
THERM Hysteresis
0000 1010 (0x0A) (10C)
Yes
22
22
Consecutive ALERT
0000 0001 (0x01)
Yes
23
N/A
Status Register 2
0000 0000 (0x00)
No
24
24
Configuration 2 Register
0000 0000 (0x00)
Yes
30
N/A
Remote 2 Temperature Value High Byte
0000 0000 (0x00)
No
31
31
Remote 2 Temperature High Limit High Byte
0101 0101 (0x55) (85C)
Yes
32
32
Remote 2 Temperature Low Limit High Byte
0000 0000 (0x00) (0C)
Yes
33
N/A
Remote 2 Temperature Value Low Byte
0000 0000 (0x00)
No
34
34
Remote 2 Temperature Offset High Byte
0000 0000 (0x00)
Yes
35
35
Remote 2 Temperature Offset Low Byte
0000 0000 (0x00)
Yes
36
36
Remote 2 Temperature High Limit Low Byte
0000 0000 (0x00) (0C)
Yes
37
37
Remote 2 Temperature Low Limit Low Byte
0000 0000 (0x00) (0C)
Yes
Mnemonic
Power-On Default
39
39
Remote 2 THERM Limit
0101 0101 (0x55) (85C)
Yes
FE
N/A
Manufacturer ID
0100 0001 (0x41)
N/A
FF
N/A
Die Revision Code
1001 0100 (0x94)
N/A
1. Writing to address 0F causes the ADT7482 to perform a single measurement. It is not a data register as such and it does not matter what
data is written to it.
Serial Bus Interface
The ADT7483A has two address pins, ADD0 and ADD1, to
allow selection of the device address, so that several
ADT7483As can be used on the same bus, and/or to avoid
conflict with other devices.
Although only two address pins are provided, these are
threestate, and can be grounded, left unconnected, or tied to
VDD, so that a total of nine different addresses are possible,
as shown in Table 17. It should be noted that the state of the
address pins is only sampled at power-up, so changing them
after power-up has no effect.
Control of the ADT7483A is carried out via the serial bus.
The ADT7483A is connected to the serial bus as a slave
device, under the control of a master device.
The ADT7483A has an SMBus timeout feature. When
this is enabled, the SMBus typically times out after 25 ms of
no activity. However, this feature is not enabled by default.
Bit 7 (SCL timeout bit) of the consecutive ALERT register
(Address = 0x22) should be set to enable the SCL timeout.
Bit 6 (SDA timeout bit) of the consecutive ALERT register
(Address = 0x22) should be set to enable the SDA timeout.
The ADT7483A supports packet error checking (PEC)
and its use is optional. It is triggered by supplying the extra
clock for the PEC byte. The PEC byte is calculated using
CRC−8. The frame check sequence (FCS) conforms to
CRC−8 by the polynomial:
C(x) + x 8 ) x 2 ) x 1 ) 1
Consult the SMBus 1.1 specification
information (www.smbus.org).
Table 17. SAMPLE OFFSET REGISTER CODES
(eq. 1)
for
more
Addressing the Device
In general, every SMBus device has a 7-bit device address
(except for some devices that have extended, 10-bit
addresses). When the master device sends a device address
over the bus, the slave device with that address will respond.
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13
ADD1
ADD0
Device Address
0
0
0011 000
0
NC
0011 001
0
1
0011 010
NC
0
0101 001
NC
NC
0101 010
NC
1
0101 011
1
0
1001 100
1
NC
1001 101
1
1
1001 110
ADT7483A
3. When all data bytes have been read or written,
stop conditions are established. In write mode, the
master will pull the data line high during the tenth
clock pulse to assert a stop condition. In read
mode, the master device will override the
acknowledge bit by pulling the data line high
during the low period before the ninth clock pulse.
This is known as no acknowledge. The master will
then take the data line low during the low period
before the tenth clock pulse, then high during the
tenth clock pulse to assert a stop condition.
The serial bus protocol operates as follows:
1. The master initiates data transfer by establishing a
start condition, defined as a high-to-low transition
on the serial data line (SDATA), while the serial
clock line (SCLK) remains high. This indicates
that an address/data stream follows. All slave
peripherals connected to the serial bus respond to
the start condition and shift in the next eight bits,
consisting of a 7-bit address (MSB first) plus an
R/W bit, which determines the direction of the
data transfer, that is, whether data will be written
to, or read from, the slave device. The peripheral
whose address corresponds to the transmitted
address responds by pulling the data line low
during the low period before the ninth clock pulse,
known as the acknowledge bit. All other devices
on the bus now remain idle while the selected
device waits for data to be read from or written to
it. If the R/W bit is a 0, the master writes to the
slave device. If the R/W bit is a 1, the master reads
from the slave device.
2. Data is sent over the serial bus in a sequence of
nine clock pulses, eight bits of data followed by an
acknowledge bit from the slave device. Transitions
on the data line must occur during the low period
of the clock signal and remain stable during the
high period, since a low-to-high transition when
the clock is high may be interpreted as a stop
signal. The number of data bytes that can be
transmitted over the serial bus in a single read or
write operation is limited only by what the master
and slave devices can handle.
1
Any number of bytes of data may be transferred over the
serial bus in one operation, but it is not possible to mix read
and write in one operation because the type of operation is
determined at the beginning and cannot subsequently be
changed without starting a new operation. For the
ADT7483A, write operations contain either one or two
bytes, while read operations contain one byte.
To write data to one of the device data registers, or to read
data from it, the address pointer register must be set so that
the correct data register is addressed. The first byte of a write
operation always contains a valid address that is stored in the
address pointer register. If data is to be written to the device,
the write operation contains a second data byte that is written
to the register selected by the address pointer register (see
Figure 15).
The device address is sent over the bus followed by R/W
set to 0. This is followed by two data bytes. The first data
byte is the address of the internal data register to be written
to, which is stored in the address pointer register. The second
data byte is the data to be written to the internal data register.
9
9
1
SCLK
SDATA
START BY
MASTER
1
0
0
1
1
0
1
FRAME 1
SERIAL BUS ADDRESS BYTE
R/W
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADT7483A
FRAME 2
ADDRESS POINTER REGISTER BYTE
ACK. BY
ADT7483A
1
9
SCLK (CONTINUED)
SDATA (CONTINUED)
D7
D6
D5
D4
D3
D2
FRAME 3
DATA BYTE
D1
D0
ACK. BY STOP BY
ADT7483A MASTER
Figure 15. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
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14
ADT7483A
1
9
9
1
SCLK
SDATA
1
START BY
MASTER
0
0
1
1
0
1
FRAME 1
SERIAL BUS ADDRESS BYTE
D7
R/W
ACK. BY
ADT7483A
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADT7483A
FRAME 2
ADDRESS POINTER REGISTER BYTE
STOP BY
MASTER
Figure 16. Writing to the Address Pointer Register Only
9
1
1
9
SCLK
SDATA
START BY
MASTER
1
0
0
1
1
0
1
FRAME 1
SERIAL BUS ADDRESS BYTE
R/W
D7
D6
ACK. BY
ADT7483A
D5
D4
D3
D2
D1
FRAME 2
DATA BYTE FROM ADT7483A
D0
ACK. BY
MASTER
STOP BY
MASTER
Figure 17. Reading Data from a Previously Selected Register
be wire-OR’ed together, so that the common line will go low
if one or more of the ALERT outputs goes low.
The ALERT output can be used as an interrupt signal to a
processor, or it can be used as an SMBALERT. Slave devices
on the SMBus cannot normally signal to the bus master that
they want to talk, but the SMBALERT function allows them
to do so.
One or more ALERT outputs can be connected to a
common SMBALERT line connected to the master. When
the SMBALERT line is pulled low by one of the devices, the
following procedure occurs, as shown in Figure 18.
When reading data from a register there are two
possibilities:
1. If the address pointer register value of the
ADT7483A is unknown or not the desired value, it
is first necessary to set it to the correct value
before data can be read from the desired data
register. This is done by performing a write to the
ADT7483A as before, but only the data byte
containing the register read address is sent, as data
is not to be written to the register (see Figure 16).
A read operation is then performed consisting of
the serial bus address, R/W bit set to 1, followed
by the data byte read from the data register (see
Figure 17).
2. If the address pointer register is known to be
already at the desired address, data can be read
from the corresponding data register without first
writing to the address pointer register and the bus
transaction shown in Figure 16 can be omitted.
MASTER
RECEIVES
SMBALERT
START
ALERT RESPONSE
ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
RD ACK
DEVICE
ADDRESS
NO
STOP
ACK
DEVICE SENDS
ITS ADDRESS
Figure 18. Use of SMBALERT
1. SMBALERT is pulled low.
2. Master initiates a read operation and sends the
alert response address (ARA = 0001 100). This is
a general call address that must not be used as a
specific device address.
3. The device whose ALERT output is low responds
to the alert response address, and the master reads
its device address. The device address is seven
bits, so an LSB of 1 is added. The address of the
device is now known and it can be interrogated in
the usual way.
4. If more than one device’s ALERT output is low,
the one with the lowest device address will have
priority, in accordance with normal SMBus
arbitration.
5. Once the ADT7483A has responded to the alert
response address, it will reset its ALERT output,
provided that the error condition that caused the
ALERT no longer exists. If the SMBALERT line
NOTES:It is possible to read a data byte from a data register without
first writing to the address pointer register. However, if the
address pointer register is already at the correct value, it is
not possible to write data to a register without writing to the
address pointer register because the first data byte of a write
is always written to the address pointer register.
Remember that some of the ADT7483A registers have
different addresses for read and write operations. The write
address of a register must be written to the address pointer
if data is to be written to that register, but it may not be
possible to read data from that address. The read address
of a register must be written to the address pointer before
data can be read from that register.
ALERT Output
This is applicable when Pin 13 is configured as an ALERT
output. The ALERT output goes low whenever an
out-of-limit measurement is detected, or if the remote
temperature sensor is open circuit. It is an open-drain output
and requires a pull-up to VDD. Several ALERT outputs can
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15
ADT7483A
together to prevent the OPEN flag from being continuously
set.
Most temperature sensing diodes have an operating
temperature range of −55C to +150C. Above 150C, they
lose their semiconductor characteristics and approximate
conductors instead. This results in a diode short, setting the
OPEN flag. The remote diode in this case no longer gives an
accurate temperature measurement. A read of the
temperature result register will give the last good
temperature measurement. The user should be aware that,
while the diode fault is triggered, the temperature
measurement on the remote channels may not be accurate.
remains low, the master will send the ARA again,
and so on, until all devices whose ALERT outputs
were low have responded.
Masking the ALERT Output
The ALERT output can be masked for local, Remote 1,
Remote 2, or all three channels. This is done by setting the
appropriate mask bits in either the Configuration 1 register
(read address = 0x03, write address = 0x09) or in the
consecutive ALERT register (address = 0x22)
To mask ALERTs due to local temperature, set Bit 5 of the
consecutive ALERT register to 1. Default = 0.
To mask ALERTs due to Remote 1 temperature, set Bit 1 of
the Configuration 1 register to 1. Default = 0.
To mask ALERTs due to Remote 2 temperature, set Bit 0 of
the Configuration 1 register to 1. Default = 0.
To mask ALERTs due to any channel, set Bit 7 of the
Configuration 1 register to 1. Default = 0.
Interrupt System
The ADT7483A has two interrupt outputs, ALERT and
THERM. Both outputs have different functions and
behavior. ALERT is maskable and responds to violations of
software programmed temperature limits or an open-circuit
fault on the remote diode. THERM is intended as a fail-safe
interrupt output that cannot be masked.
If the Remote 1, Remote 2, or local temperature exceeds
the programmed high temperature limits, or equals or
exceeds the low temperature limits, the ALERT output is
asserted low. An open-circuit fault on the remote diode also
causes ALERT to assert. ALERT is reset when serviced by
a master reading its device address, provided the error
condition has gone away and the status register has been
reset.
Similarly, the THERM output asserts low if the Remote 1,
Remote 2, or local temperature exceeds the programmed
THERM limits. The THERM temperature limits should
normally be equal to or greater than the high temperature
limits. THERM is automatically reset when the temperature
falls back within the (THERM − Hysteresis) limit. The local
and remote THERM limits are set by default to 85C. An
hysteresis value can be programmed, in which case,
THERM resets when the temperature falls to the limit value
minus the hysteresis value. This applies to both local and
remote measurement channels. The power-on hysteresis
default value is 10C, but this may be reprogrammed to any
value after power-up.
The hysteresis loop on the THERM outputs is useful when
THERM is used for on/off control of a fan. The user’s
system can be set up so that when THERM asserts, a fan can
be switched on to cool the system. When THERM goes high
again, the fan can be switched off. Programming an
hysteresis value protects from fan jitter, wherein the
temperature hovers around the THERM limit and the fan is
constantly being switched.
Low Power Standby Mode
The ADT7483A can be put into low power standby mode
by setting Bit 6 (Mon/STBY bit) of the Configuration 1
register (read address = 0x03, write address = 0x09) to 1.
When Bit 6 is 0, the ADT7483A operates normally. When
Bit 6 is 1, the ADC is inhibited, and any conversion in
progress is terminated without writing the result to the
corresponding value register.
The SMBus is still enabled. Power consumption in the
standby mode is reduced to less than 5 mA.
When the device is in standby mode, it is still possible to
initiate a one-shot conversion of both channels by writing to
the oneshot register (Address 0x0F), after which the device
will return to standby. It does not matter what is written to
the one-shot register, all data written to it is ignored.
It is also possible to write new values to the limit register
while in standby mode. If the values stored in the
temperature value registers are now outside the new limits,
an ALERT is generated, even though the ADT7483A is still
in standby.
Sensor Fault Detection
The ADT7483A has internal sensor fault detection
circuitry located at its D+ input. This circuit can detect
situations where a remote diode is not connected, or is
incorrectly connected, to the ADT7483A. A simple voltage
comparator trips if the voltage at D+ exceeds VDD − 1 V
(typical), signifying an open circuit between D+ and D−.
The output of this comparator is checked when a conversion
is initiated. Bit 2 (D1 OPEN flag) of the Status Register 1
(Address 0x02) is set if a fault is detected on the Remote 1
channel. Bit 2 (D2 OPEN flag) of the Status Register 2
(Address 0x23) is set if a fault is detected on the Remote 2
channel. If the ALERT pin is enabled, setting this flag will
cause ALERT to assert low.
If a remote sensor is not used with the ADT7483A, then
the D+ and D− inputs of the ADT7483A need to be tied
Table 18. THERM HYSTERESIS
THERM Hysteresis
Binary Representation
0C
0 000 0000
1C
0 000 0001
10C
0 000 1010
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16
ADT7483A
Figure 19 shows how the THERM and ALERT outputs
operate. The ALERT output can be used as an SMBALERT
to signal to the host via the SMBus that the temperature has
risen. If the temperature continues to increase, the THERM
output can be used to turn on a fan to cool the system. This
method ensures that there is a fail-safe mechanism to cool
the system, without the need for host intervention.
programmed local and/or remote high temperature limits. It
is reset in the same manner as THERM, and it is not
maskable. The programmed hysteresis value also applies to
THERM2. Figure 20 shows how THERM and THERM2
might operate together to implement two methods of cooling
the system. In this example, the THERM2 limits are set
lower than the THERM limits. The THERM2 output can be
used to turn on a fan. If the temperature continues to rise and
exceeds the THERM limits, the THERM output can provide
additional cooling by throttling the CPU.
TEMPERATURE
1005C
905C
THERM LIMIT
805C
TEMPERATURE
THERM LIMIT − HYSTERESIS
705C
905C
HIGH TEMP LIMIT
605C
705C
505C
605C
405C
RESET BY MASTER
ALERT
1
405C
4
305C
2
3
Figure 19. Operation of the ALERT and THERM
Interrupts
THERM2
THERM
If the measured temperature exceeds the high
THERM2 LIMIT
505C
THERM
THERM LIMIT
805C
1
4
2
3
Figure 20. Operation of the THERM and THERM2
Interrupts
temperature limit, the ALERT output asserts low.
If the temperature continues to increase and exceeds the
THERM limit, the THERM output asserts low. This can
be used to throttle the CPU clock or switch on a fan.
The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis. In
Figure 19, the default hysteresis value of 10C is
shown.
The ALERT output deasserts only when the
temperature has fallen below the high temperature
limit, and the master has read the device address and
cleared the status register.
When the THERM2 limit is exceeded, the THERM2
signal asserts low.
If the temperature continues to increase and exceeds the
Pin 13 on the ADT7483A can be configured as either an
ALERT output or as an additional THERM output.
THERM2 will assert low when the temperature exceeds the
THERM limit, the THERM output asserts low.
The THERM output deasserts (goes high) when the
temperature falls to THERM limit minus hysteresis. In
Figure 20, there is no hysteresis value shown.
As the system cools further, and the temperature falls
below the THERM2 limit, the THERM2 signal resets.
Again, no hysteresis value is shown for THERM2.
The temperature measurement can be either the local or
the remote temperature measurement.
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17
ADT7483A
Applications
Base resistance less than 100 W.
Small variation in hFE (50 to 150) that indicates tight
Noise Filtering
control of VBE characteristics.
For temperature sensors operating in noisy environments,
previous practice was to place a capacitor across the D+ and
D− pins to help combat the effects of noise. However, large
capacitances affect the accuracy of the temperature
measurement, leading to a recommended maximum
capacitor value of 1,000 pF.
Transistors such as 2N3904, 2N3906, or equivalents in
SOT−23 packages, are suitable devices to use.
Thermal Inertia and Self-heating
Accuracy depends on the temperature of the remote
sensing diode and/or the local temperature sensor being at
the same temperature as that being measured. A number of
factors can affect this. Ideally, the sensor should be in good
thermal contact with the part of the system being measured.
If it is not, the thermal inertia caused by the sensor’s mass
causes a lag in the response of the sensor to a temperature
change. In the case of the remote sensor, this should not be
a problem, since it will either be a substrate transistor in the
processor or a small package device, such as SOT−23,
placed in close proximity to it.
The on-chip sensor, however, is often remote from the
processor and only monitors the general ambient
temperature around the package. In practice, the
ADT7483A package will be in electrical, and hence thermal,
contact with a PCB and may also be in a forced airflow. How
accurately the temperature of the board and/or the forced
airflow reflects the temperature to be measured will also
affect the accuracy. Self-heating, due to the power dissipated
in the ADT7483A or the remote sensor, causes the chip
temperature of the device or remote sensor to rise above
ambient. However, the current forced through the remote
sensor is so small that self-heating is negligible. In the case
of the ADT7483A, the worst-case condition occurs when the
device is converting at 64 conversions per second while
sinking the maximum current of 1 mA at the ALERT and
THERM output. In this case, the total power dissipation in
the device is about 4.5 mW. The thermal resistance, qJA, of
the QSOP−16 package is about 150C/W.
Factors Affecting Diode Accuracy
Remote Sensing Diode
The ADT7483A is designed to work with substrate
transistors built into processors or with discrete transistors.
Substrate transistors will generally be PNP types with the
collector connected to the substrate. Discrete types can be
either a PNP or NPN transistor connected as a diode (base
shorted to collector). If an NPN transistor is used, the
collector and base are connected to D+ and the emitter to D−.
If a PNP transistor is used, the collector and base are
connected to D− and the emitter to D+.
To reduce the error due to variations in both substrate and
discrete transistors, the following factors should be taken
into consideration:
The ideality factor, nf , of the transistor is a measure of
the deviation of the thermal diode from ideal behavior.
The ADT7483A is trimmed for an nf value of 1.008.
Use the following equation to calculate the error
introduced at a temperature,T (C) when using a
transistor whose nf does not equal 1.008. Consult the
processor data sheet for the nf values.
DT + ǒn f * 1.008Ǔń1.008
ǒ273.15 Kelvin ) TǓ
(eq. 2)
To factor this in, write the DT value to the offset register.
It is then automatically added to, or subtracted from, the
temperature measurement by the ADT7483A.
Some CPU manufacturers specify the high and low
current levels of the substrate transistors. The high
current level of the ADT7483A, IHIGH, is 200 mA, and
the low level current, ILOW, is 12 mA. If the ADT7483A
current levels do not match the current levels specified
by the CPU manufacturer, it may be necessary to
remove an offset. Refer to the CPU data sheet to
determine whether this offset needs to be removed and
how to calculate it. This offset is programmed to the
offset register. It is important to note that if more than
one offset must be considered, program the algebraic
sum of these offsets to the offset register.
Layout Considerations
Digital boards can be electrically noisy environments, and
the ADT7483A measures very small voltages from the
remote sensor, so care must be taken to minimize noise
induced at the sensor inputs. Follow these precautions:
1. Place the ADT7483A as close as possible to the
remote sensing diode. Provided that the worst
noise sources such as clock generators,
data/address buses, and CRTs are avoided, this
distance can be 4 inches to 8 inches.
2. Route the D+ and D– tracks close together, in
parallel, with grounded guard tracks on each side.
To minimize inductance and reduce noise pickup,
a 5 mil track width and spacing is recommended.
Provide a ground plane under the tracks, if
possible.
If a discrete transistor is used with the ADT7483A, the
best accuracy is obtained by choosing devices according to
the following criteria:
Base-emitter voltage greater than 0.25 V at 6 mA, at the
highest operating temperature.
Base-emitter voltage less than 0.95 V at 100 mA, at the
lowest operating temperature.
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18
ADT7483A
GND
to ensure that any capacitance seen at D+ and D−
is a maximum of 1,000 pF. This maximum value
includes the filter capacitance, plus any cable or
stray capacitance between the pins and the sensor
diode.
5. If the distance to the remote sensor is more than
8 inches, the use of twisted pair cable is
recommended. A total of 6 feet to 12 feet is
needed.
6. For very long distances (up to 100 feet), use
shielded twisted pair, such as Belden No. 8451
microphone cable. Connect the twisted pair to D+
and D−, and the shield to GND close to the
ADT7483A. Leave the remote end of the shield
unconnected to avoid ground loops.
5 MIL
5 MIL
D+
5 MIL
5 MIL
5 MIL
D−
5 MIL
GND
5 MIL
Figure 21. Typical Arrangement of Signal Tracks
3. Minimize the number of copper/solder joints that
can cause thermocouple effects. Where
copper/solder joints are used, make sure that they
are in both the D+ and D− path and at the same
temperature.
Thermocouple effects should not be a major
problem as 1C corresponds to approximately
200 mV, and thermocouple voltages are about
3 mV/C of temperature difference. Unless there
are two thermocouples with a large temperature
differential between them, thermocouple voltages
should be much less than 200 mV.
4. Place a 0.1 mF bypass capacitor close to the VDD
pin. In extremely noisy environments, place an
input filter capacitor across D+ and D− close to the
ADT7483A. This capacitance can effect the
temperature measurement, so care must be taken
Because the measurement technique uses switched
current sources, excessive cable or filter capacitance can
affect the measurement. When using long cables, the filter
capacitance can be reduced or removed.
Application Circuit
Figure 22 shows a typical application circuit for the
ADT7483A, using discrete sensor transistors. The pull-ups
on SCLK, SDATA, and ALERT are required only if they are
not already provided elsewhere in the system.
The SCLK and SDATA pins of the ADT7483A can be
interfaced directly to the SMBus of an I/O controller, such
as the Intel 820 chipset.
VDD
ADT7483A
D1+
2N3904/06
or
CPU THERMAL
DIODE
D1−
D2+
3.0 V to 3.6 V
0.1 mF
TYP 10 kW
SCLK
SMBUS
CONTROLLER
SDATA
ALERT
D2−
VDD
ADD0
5.0 V or 12 V
THERM
TYP 10 kW
ADD1
GND
FAN ENABLE
FAN
CONTROL
CIRCUIT
Figure 22. Typical Application Circuit
Table 19. ORDERING INFORMATION
Device Number*
ADT7483AARQZ−RL
Temperature Range
Package Type
Package Option
Shipping†
−40C to +125C
16-lead QSOP
RQ−16
2,500 Tape & Reel
†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.
*The “Z’’ suffix indicates Pb-Free part.
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19
MECHANICAL CASE OUTLINE
PACKAGE DIMENSIONS
QSOP16
CASE 492−01
ISSUE A
DATE 23 MAR 2011
2X
SCALE 2:1
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME
Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b DOES NOT INCLUDE DAMBAR
PROTRUSION.
4. DIMENSION D DOES NOT INCLUDE MOLD FLASH,
PROTRUSIONS, OR GATE BURRS. MOLD FLASH,
PROTRUSIONS, OR GATE BURRS SHALL NOT EX
CEED 0.005 PER SIDE. DIMENSION E1 DOES NOT
INCLUDE INTERLEAD FLASH OR PROTRUSION. IN
TERLEAD FLASH OR PROTRUSION SHALL NOT EX
CEED 0.005 PER SIDE. D AND E1 ARE DETERMINED
AT DATUM H.
5. DATUMS A AND B ARE DETERMINED AT DATUM H.
0.20 C D
D
16
L2
D
A
9
GAUGE
PLANE
SEATING
PLANE
E
E1
C
L
C
DETAIL A
2X
2X 10 TIPS
0.20 C D
1
8
16X
e
B
b
0.25
A2
0.10 C
0.10 C
A1
16X
C
0.25 C D
M
C A-B D
h x 45 _
A
SEATING
PLANE
M
1.12
9
XXXXXXX
XXXXXXX
YYWWG
6.40
1
8
0.635
PITCH
DOCUMENT NUMBER:
DESCRIPTION:
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
1.24
---0.20
0.30
0.19
0.25
4.89 BSC
6.00 BSC
3.90 BSC
0.635 BSC
0.22
0.50
0.40
1.27
0.25 BSC
0_
8_
16X
0.42
16
DETAIL A
INCHES
MIN
MAX
0.053
0.069
0.004
0.010
0.049
---0.008
0.012
0.007
0.010
0.193 BSC
0.237 BSC
0.154 BSC
0.025 BSC
0.009
0.020
0.016
0.050
0.010 BSC
0_
8_
GENERIC
MARKING DIAGRAM*
SOLDERING FOOTPRINT
16X
H
DIM
A
A1
A2
b
c
D
E
E1
e
h
L
L2
M
XXXXX
YY
WW
G
= Specific Device Code
= Year
= Work Week
= Pb−Free Package
*This information is generic. Please refer
to device data sheet for actual part
marking. Pb−Free indicator, “G”, may
or not be present.
DIMENSIONS: MILLIMETERS
98AON04472D
QSOP16
Electronic versions are uncontrolled except when accessed directly from the Document Repository.
Printed versions are uncontrolled except when stamped “CONTROLLED COPY” in red.
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