19-1483; Rev 0; 4/99
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
____________________________Features
The MAX1619 is a precise digital thermometer that reports
the temperature of both a remote sensor and its own
package. The remote sensor is a diode-connected transistor—typically a low-cost, easily mounted 2N3904 NPN
type—that replaces conventional thermistors or thermocouples. Remote accuracy is ±3°C for multiple transistor
manufacturers, with no calibration needed. The remote
channel can also measure the die temperature of other
ICs, such as microprocessors, that contain an on-chip,
diode-connected transistor.
The 2-wire serial interface accepts standard System
Management Bus (SMBus®) Write Byte, Read Byte, Send
Byte, and Receive Byte commands to program the alarm
thresholds and to read temperature data. The data format
is 7 bits plus sign, with each bit corresponding to 1°C, in
two’s complement format. Measurements can be done
automatically and autonomously, with the conversion rate
programmed by the user or programmed to operate in a
single-shot mode. The adjustable rate allows the user to
control the supply-current drain.
The MAX1619 is nearly identical to the popular MAX1617A,
with the additional feature of an overtemperature alarm output (OVERT) that responds to the remote temperature; this
is optimal for fan control.
♦ Two Channels Measure Both Remote and Local
Temperatures
♦ No Calibration Required
♦ SMBus 2-Wire Serial Interface
♦ Programmable Under/Overtemperature Alarms
♦ OVERT Output for Fan Control
♦ Supports SMBus Alert Response
♦ Supports Manufacturer and Device ID Codes
♦ Accuracy
±2°C (+60°C to +100°C, local)
±3°C (-40°C to +125°C, local)
±3°C (+60°C to +100°C, remote)
♦ 3µA (typ) Standby Supply Current
♦ 70µA (max) Supply Current in Auto-Convert Mode
♦ +3V to +5.5V Supply Range
♦ Write-Once Protection
♦ Small 16-Pin QSOP Package
Ordering Information
________________________Applications
Desktop and Notebook
Computers
Central Office
Telecom Equipment
Smart Battery Packs
LAN Servers
Test and Measurement
Multichip Modules
PART
MAX1619MEE
TEMP. RANGE
-55°C to +125°C
PIN-PACKAGE
16 QSOP
Typical Operating Circuit
Industrial Controls
+3V TO +5.5V
200Ω
0.1µF
___________________Pin Configuration
TOP VIEW
VCC
VCC 1
16 N.C.
GND 2
15 STBY
DXN 4
14 SMBCLK
MAX1619
ADD1 6
11 ALERT
GND 7
10 ADD0
GND 8
9
SMBCLK
SMBDATA
13 N.C.
12 SMBDATA
N.C. 5
10k EACH
MAX1619
DXP
DXP 3
STBY
2N3904
DXN
2200pF
ALERT
OVERT
CLOCK
DATA
INTERRUPT
TO µC
FAN
CONTROL
ADD0 ADD1 GND
OVERT
QSOP
SMBus is a registered trademark of Intel Corp.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAX1619
________________General Description
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
ABSOLUTE MAXIMUM RATINGS
VCC to GND ..............................................................-0.3V to +6V
DXP, ADD_ to GND ....................................-0.3V to (VCC + 0.3V)
DXN to GND ..........................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERT, OVERT,
STBY to GND............................................................-0.3V to +6V
SMBDATA, ALERT, OVERT Current....................-1mA to +50mA
DXN Current .......................................................................±1mA
ESD Protection (all pins, Human Body Model) ..................2000V
Continuous Power Dissipation (TA = +70°C)
QSOP (derate 8.30mW/°C above +70°C) .....................667mW
Operating Temperature Range .........................-55°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +3.3V, TA = 0°C to +85°C, configuration byte = XCh, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ADC AND POWER SUPPLY
Temperature Resolution (Note 1)
Monotonicity guaranteed
8
Initial Temperature Error,
Local Diode (Note 2)
TA = +60°C to +100°C
-2
2
TA = 0°C to +85°C
-3
3
TR = +60°C to +100°C
-3
3
TR = -55°C to +125°C (Note 4)
-5
5
TA = +60°C to +100°C
-2.5
2.5
TA = 0°C to +85°C
-3.5
3.5
3.0
5.5
Temperature Error, Remote Diode
(Notes 2, 3)
Temperature Error, Local Diode
(Notes 1, 2)
Including long-term drift
Supply Voltage Range
Undervoltage Lockout Threshold
VCC input, disables A/D conversion, rising edge
2.60
Undervoltage Lockout Hysteresis
Power-On Reset Threshold
Average Operating Supply Current
VCC, falling edge
1.0
Logic inputs
forced to VCC
or GND
1.7
SMBus static
3
Hardware or software standby,
SMBCLK at 10kHz
5
Autoconvert mode, average
measured over 4sec. Logic
inputs forced to VCC or GND.
°C
°C
°C
V
V
mV
2.5
V
mV
10
µA
0.25 conv/sec
35
70
2.0 conv/sec
120
180
125
156
ms
25
%
µA
From stop bit to conversion complete (both channels)
94
Conversion Rate Timing Error
Auto-convert mode
-25
Remote-Diode Source Current
DXP forced to 1.5V
High level
80
100
120
Low level
8
10
12
DXN Source Voltage
2
2.95
50
Conversion Time
Address Pin Bias Current
2.80
50
POR Threshold Hysteresis
Standby Supply Current
Bits
ADD0, ADD1; momentary upon power-on reset
µA
0.7
V
160
µA
_______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
(VCC = +3.3V, TA = 0°C to +85°C, configuration byte = XCh, unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus INTERFACE
Logic Input High Voltage
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
Logic Input Low Voltage
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
Logic Output Low Sink Current
ALERT, OVERT, SMBDATA forced to 0.4V
ALERT, OVERT Output High
Leakage Current
ALERT, OVERT, forced to 5.5V
Logic Input Current
Logic inputs forced to VCC or GND
SMBus Input Capacitance
SMBCLK, SMBDATA
SMBus Clock Frequency
(Note 5)
DC
SMBCLK Clock Low Time
tLOW, 10% to 10% points
4.7
µs
SMBCLK Clock High Time
tHIGH, 90% to 90% points
4
µs
4.7
µs
500
ns
SMBus Start-Condition Setup Time
2.2
V
0.8
6
V
mA
-1
1
µA
1
µA
100
kHz
5
pF
SMBus Repeated Start-Condition
Setup Time
tSU:STA, 90% to 90% points
SMBus Start-Condition Hold Time
tHD:STA, 10% of SMBDATA to 90% of SMBCLK
4
µs
SMBus Stop-Condition Setup Time
tSU:STO, 90% of SMBCLK to 10% of SMBDATA
4
µs
SMBus Data Valid to SMBCLK
Rising-Edge Time
tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK
250
ns
SMBus Data-Hold Time
tHD:DAT (Note 6)
0
µs
SMBCLK Falling Edge to SMBus
Data-Valid Time
Master clocking in data
1
µs
MAX
UNITS
ELECTRICAL CHARACTERISTICS
(VCC = +3.3V, TA = -55°C to +125°C, configuration byte = XCh, unless otherwise noted.) (Note 4)
PARAMETER
CONDITIONS
MIN
TYP
ADC AND POWER SUPPLY
Temperature Resolution (Note 1)
Monotonicity guaranteed
8
Initial Temperature Error,
Local Diode (Note 2)
TA = +60°C to +100°C
-2
2
TA = -55°C to +125°C
-3
3
Temperature Error, Remote Diode
(Notes 2, 3)
TR = +60°C to +100°C
-3
3
TR = -55°C to +125°C
-5
5
Supply Voltage Range
Bits
3.0
Conversion Time
From stop bit to conversion complete (both channels)
94
Conversion Rate Timing Error
Autoconvert mode
-25
125
°C
°C
5.5
V
156
ms
25
%
_______________________________________________________________________________________
3
MAX1619
ELECTRICAL CHARACTERISTICS (continued)
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.3V, TA = -55°C to +125°C, configuration byte = XCh, unless otherwise noted.) (Note 4)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus INTERFACE
VCC = 3V
2.2
VCC = 5.5V
2.4
Logic Input High Voltage
STBY, SMBCLK, SMBDATA
Logic Input Low Voltage
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
Logic Output Low Sink Current
ALERT, OVERT, SMBDATA forced to 0.4V
ALERT, OVERT Output High
Leakage Current
ALERT, OVERT forced to 5.5V
Logic Input Current
Logic inputs forced to VCC or GND
V
0.8
V
6
mA
-2
1
µA
2
µA
Note 1: Guaranteed but not 100% tested.
Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1619 device temperature is exactly +66.7°C, the ADC may report +66°C, +67°C, or +68°C (due to the quantization error plus the +1/2°C offset
used for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to +100°C temperature range
(Table 2).
Note 3: A remote diode is any diode-connected transistor from Table 1. TR is the junction temperature of the remote diode. See
Remote Diode Selection for remote diode forward voltage requirements.
Note 4: Specifications from -55°C to +125°C are guaranteed by design, not production tested.
Note 5: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it
violates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus.
Note 6: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of
SMBCLK’s falling edge.
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
10
PATH = DXP TO GND
5
0
-5
PATH = DXP TO VCC (5V)
-10
1
ZETEX FMMT3904
0
MOTOROLA MMBT3904
-1
VIN = SQUARE WAVE APPLIED TO
VCC WITH NO 0.1µF VCC CAPACITOR
VIN = 250mVp-p
REMOTE DIODE
9
VIN = 100mVp-p
LOCAL DIODE
6
VIN = 100mVp-p
REMOTE DIODE
3
RANDOM
SAMPLES
-15
-20
0
-2
1
10
LEAKAGE RESISTANCE (MΩ)
4
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
15
12
MAX1619-02
2
MAX1619-01
20
TEMPERATURE ERROR vs.
POWER-SUPPLY NOISE FREQUENCY
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX1619-03
TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
TEMPERATURE ERROR (°C)
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
100
-50
0
50
TEMPERATURE (°C)
100
150
50
500
5k
50k
500k
FREQUENCY (Hz)
_______________________________________________________________________________________
5M
50M
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
VIN = 100mVp-p
4
VIN = 50mVp-p
VIN = 25mVp-p
40
10
2
30
VCC = 5V
20
VCC = 3.3V
10
0
0
0
0.1
1
10
0
100
20
40
80
60
1
100
10
100
1000
FREQUENCY (MHz)
DXP–DXN CAPACITANCE (nF)
SMBCLK FREQUENCY (kHz)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
INTERNAL DIODE
RESPONSE TO THERMAL SHOCK
VCC = 5V
AVERAGED MEASUREMENTS
125
400
ADD0, ADD1 = HIGH-Z
6
100
TEMPERATURE (°C)
20
SUPPLY CURRENT (µA)
60
300
200
100
3
MAX1619-11
ADD0, ADD1 = GND
MAX1619-10
500
MAX1619-09
100
SUPPLY CURRENT (µA)
MAX1619-08
MAX1619-07
50
SUPPLY CURRENT (µA)
8
VCC = 5V
TEMPERATURE ERROR (°C)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE
AC-COUPLED TO DXN
6
20
MAX1619-04
10
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
TEMPERATURE ERROR vs.
DXP–DXN CAPACITANCE
TEMPERATURE ERROR vs.
COMMON-MODE NOISE FREQUENCY
75
50
25
16-QSOP IMMERSED
IN +115°C FLUORINERT BATH
0
0
0
1
2
3
SUPPLY VOLTAGE (V)
4
5
0
0 0.0625 0.125 0.25
0.5
1
2
CONVERSION RATE (Hz)
4
8
-2
0
2
4
6
8
10
TIME (sec)
_______________________________________________________________________________________
5
MAX1619
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
MAX1619
Pin Description
PIN
NAME
FUNCTION
1
VCC
Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series resistor is recommended but not required for additional noise filtering.
2
GND
Not internally connected. Connect to GND to act against leakage paths from VCC to DXP.
3
DXP
Combined Current Source and A/D Positive Input for Remote-Diode Channel. Do not leave DXP floating;
connect DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for
noise filtering.
4
DXN
Combined Current Sink and A/D Negative Input. DXN is normally internally biased to a diode voltage
above ground.
5, 13,
16
N.C.
No Connection. Not internally connected. May be used for PC board trace routing.
6
ADD1
SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance
(>50pF) at the address pins when floating may cause address-recognition problems.
7, 8
GND
Ground
9
OVERT
Overtemperature Alarm Output, Open Drain. This is an unlatched alarm output that responds only to the
remote diode temperature.
10
ADD0
SMBus Slave Address Select Pin
11
ALERT
SMBus Alert (interrupt) Output, Open Drain
12
SMBDATA
14
SMBCLK
15
STBY
SMBus Serial-Data Input/Output, Open Drain
SMBus Serial-Clock Input
Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.
Low = standby mode, high = operate mode.
Detailed Description
The MAX1619 is a temperature sensor designed to work
in conjunction with an external microcontroller (µC) or
other intelligence in thermostatic, process-control, or
monitoring applications. The µC is typically a powermanagement or keyboard controller, generating SMBus
serial commands either by “bit-banging” general-purpose input/output (GPIO) pins or through a dedicated
SMBus interface block.
Essentially an 8-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the MAX1619
contains a switched current source, a multiplexer, an
ADC, an SMBus interface, and associated control logic
(Figure 1). Temperature data from the ADC is loaded
into two data registers (local and remote). The remote
temperature data is automatically compared with data
previously stored in four temperature-alarm threshold
registers. One pair of alarm-threshold registers is used
to provide hysteretic fan control; the other pair is used
for alarm interrupt. The local temperature data is available for monitoring.
6
ADC and Multiplexer
The ADC is an averaging type that integrates over a
60ms period (each channel, typical) with excellent
noise rejection.
The multiplexer automatically steers bias currents
through the remote and local diodes, measures their
forward voltages, and computes their temperatures.
Both channels are automatically converted once the
conversion process has started, either in free-running
or single-shot mode. If one of the two channels is not
used, the device still performs both measurements, and
the user can simply ignore the results of the unused
channel.
The DXN input is biased at 0.65V above ground by an
internal diode to set up the analog-to-digital (A/D)
inputs for a differential measurement. The worst-case
DXP–DXN differential input voltage range is 0.25V to
0.95V.
Excess resistance in series with the remote diode causes about +1/2°C error per ohm. Likewise, 200µV of offset voltage forced on DXP–DXN causes about 1°C error.
_______________________________________________________________________________________
OVERT
ALERT
GND
DXN
DXP
REMOTE TEMPERATURE
DATA REGISTER
DIODE
FAULT
LOCAL
REMOTE
-
+
Q
Q
POL
R
R
S
S
DIGITAL COMPARATOR
(REMOTE)
8
LOW-TEMPERATURE THRESHOLD
(REMOTE TLOW)
8 HIGH-TEMPERATURE THRESHOLD
(REMOTE THIGH)
8
-
+
-
+
MUX
ADC
SELECTED VIA
SLAVE ADD = 0001 100
DIGITAL COMPARATOR
(REMOTE OVERTEMP)
ALERT RESPONSE
ADDRESS REGISTER
CONVERSION RATE
REGISTER
CONFIGURATION
BYTE REGISTER
HYSTERESIS THRESHOLD
(REMOTE THYST)
8
STATUS BYTE REGISTER
8
WRITE
HIGH-TEMPERATURE THRESHOLD 8
(REMOTE TMAX)
8
READ
SMBus
COMMAND BYTE
(INDEX) REGISTER
CONTROL
LOGIC
7
ADD1
ADDRESS
DECODER
ADD0
LOCAL TEMPERATURE
DATA REGISTER
MAX1619
2
STBY
SMBCLK
SMBDATA
MAX1619
VCC
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
Figure 1. Functional Diagram
_______________________________________________________________________________________
7
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
A/D Conversion Sequence
If a Start command is written (or generated automatically in the free-running auto-convert mode), both channels
are converted, and the results of both measurements
are available after the end of conversion. A BUSY status
bit in the status byte shows that the device is actually
performing a new conversion; however, even if the ADC
is busy, the results of the previous conversion are
always available.
Remote-Diode Selection
Temperature accuracy depends on having a good-quality, diode-connected small-signal transistor. Accuracy
has been experimentally verified for all the devices listed in Table 1. The MAX1619 can also directly measure
the die temperature of CPUs and other integrated circuits having on-board temperature-sensing diodes.
The transistor must be a small-signal type with a relatively high forward voltage; otherwise, the A/D input
voltage range can be violated. The forward voltage
must be greater than 0.25V at 10µA; check to ensure
this is true at the highest expected temperature. The
forward voltage must be less than 0.95V at 100µA;
check to ensure this is true at the lowest expected
temperature. Large power transistors don’t work. Also,
ensure that the base resistance is less than 100Ω. Tight
specifications for forward-current gain (+50 to +150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
VBE characteristics.
For heatsink mounting, the 500-32BT02-000 thermal
sensor from Fenwal Electronics is a good choice. This
device consists of a diode-connected transistor, an
aluminum plate with screw hole, and twisted-pair cable
(Fenwal Inc., Milford, MA, 508-478-6000).
Thermal Mass and Self-Heating
Thermal mass can seriously degrade the MAX1619’s
effective accuracy. The thermal time constant of the
QSOP-16 package is about 4sec in still air. To settle to
within +1°C after a sudden +100°C change, the
MAX1619 junction temperature requires about five time
constants. The use of smaller packages for remote sensors, such as SOT23s, improves the situation. Take
care to account for thermal gradients between the heat
source and the sensor, and ensure that stray air currents across the sensor package do not interfere with
measurement accuracy.
Self-heating does not significantly affect measurement
accuracy. Remote-sensor self-heating due to the diode
current source is negligible. For the local diode, the
8
Table 1. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
MODEL NUMBER
Central Semiconductor (USA)
CMPT3904
Fairchild Semiconductor (USA)
MMBT3904
Motorola (USA)
MMBT3904
Rohm Semiconductor (Japan)
SST3904
Siemens (Germany)
SMBT3904
Zetex (England)
FMMT3904CT-ND
Note: Transistors must be diode-connected (base shorted to
collector).
worst-case error occurs when auto-converting at the
fastest rate and simultaneously sinking maximum current at the ALERT and OVERT outputs. For example, at
an 8Hz rate and with ALERT and OVERT each sinking
1mA, the typical power dissipation is:
(VCC)(450µA) + 2(0.4V)(1mA)
Package θJA is about 120°C/W, so with VCC = 5V and
no copper PC board heatsinking, the resulting temperature rise is:
∆T = 3.1mW(120°C/W) = 0.36°C
Even with these contrived circumstances, it is difficult
to introduce significant self-heating errors.
ADC Noise Filtering
The ADC is an integrating type with inherently good
noise rejection, especially of low-frequency signals such
as 60Hz/120Hz power-supply hum. Micropower operation places constraints on high-frequency noise rejection;
therefore, careful PC board layout and proper external
noise filtering are required for high-accuracy remote
measurements in electrically noisy environments.
High-frequency EMI is best filtered at DXP and DXN
with an external 2200pF capacitor. This value can be
increased to about 3300pF (max), including cable
capacitance. Capacitance higher than 3300pF introduces errors due to the rise time of the switched current source.
Nearly all noise sources tested cause the ADC measurements to be higher than the actual temperature, typically
by +1°C to +10°C, depending on the frequency and
amplitude (see Typical Operating Characteristics).
_______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
2) Do not route the DXP–DXN lines next to the deflection coils of a CRT. Also, do not route the traces
across a fast memory bus, which can easily introduce +30°C error, even with good filtering.
Otherwise, most noise sources are fairly benign.
3) Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any highvoltage traces such as +12VDC. Leakage currents
from PC board contamination must be dealt with
carefully, since a 10MΩ leakage path from DXP to
ground causes about +1°C error.
4) Connect guard traces to GND on either side of the
DXP–DXN traces (Figure 2). With guard traces in
place, routing near high-voltage traces is no longer
an issue.
5) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple effects.
6) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. In general, PC board-induced thermocouples are not a serious problem. A copper-solder thermocouple exhibits 3µV/°C, and it takes
about 200µV of voltage error at DXP–DXN to cause
a +1°C measurement error. So, most parasitic thermocouple errors are swamped out.
7) Use wide traces. Narrow ones are more inductive
and tend to pick up radiated noise. The 10 mil
widths and spacings recommended in Figure 2
aren’t absolutely necessary (as they offer only a
minor improvement in leakage and noise), but try to
use them where practical.
8) Keep in mind that copper can’t be used as an EMI
shield, and only ferrous materials, such as steel, work
well. Placing a copper ground plane between the
DXP-DXN traces and traces carrying high-frequency
noise signals does not help reduce EMI.
PC Board Layout Checklist
• Place the MAX1619 close to a remote diode.
• Keep traces away from high voltages (+12V bus).
• Keep traces away from fast data buses and CRTs.
• Use recommended trace widths and spacings.
• Place a ground plane under the traces.
MAX1619
PC Board Layout
1) Place the MAX1619 as close as practical to the
remote diode. In a noisy environment, such as a
computer motherboard, this distance can be 4 inches to 8 inches (typical) or more as long as the worst
noise sources (such as CRTs, clock generators,
memory buses, and ISA/PCI buses) are avoided.
GND
10 MILS
10 MILS
DXP
MINIMUM
10 MILS
DXN
10 MILS
GND
Figure 2. Recommended DXP/DXN PC Traces
• Use guard traces flanking DXP and DXN and connecting to GND.
• Place the noise filter and the 0.1µF V CC bypass
capacitors close to the MAX1619.
• Add a 200Ω resistor in series with VCC for best noise
filtering (see Typical Operating Circuit).
Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8 inches, or in
particularly noisy environments, a twisted pair is recommended. Its practical length is 6 feet to 12 feet (typical)
before noise becomes a problem, as tested in a noisy
electronics laboratory. For longer distances, the best
solution is a shielded twisted pair like that used for audio
microphones. For example, the Belden 8451 works well
in a noisy environment for distances up to 100 feet.
Connect the twisted pair to DXP and DXN and the shield
to GND, and leave the shield’s remote end unterminated.
Excess capacitance at DX_ limits practical remote sensor distances (see Typical Operating Characteristics).
For very long cable runs, the cable’s parasitic capacitance often provides noise filtering, so the 2200pF
capacitor can often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy;
1Ω series resistance introduces about +1/2°C error.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the supply-current drain to 3µA (typical). Enter standby mode
by forcing the STBY pin low or via the RUN/STOP bit in
the configuration byte register. Hardware and software
standby modes behave almost identically: all data is
retained in memory, and the SMB interface is alive and
listening for reads and writes. The only difference is
that in hardware standby mode, the one-shot command
does not initiate a conversion.
Standby mode is not a shutdown mode. With activity on
the SMBus, extra supply current is drawn (see Typical
Operating Characteristics). In software standby mode,
_______________________________________________________________________________________
9
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
Operating Characteristics). Between conversions, the
instantaneous supply current is about 25µA due to the
current consumed by the conversion rate timer. In
standby mode, supply current drops to about 3µA. At
very low supply voltages (under the power-on-reset
threshold), the supply current is higher due to the
address pin bias currents. It can be as high as 100µA,
depending on ADD0 and ADD1 settings.
the MAX1619 can be forced to perform A/D conversions
via the one-shot command, despite the RUN/STOP bit
being high.
Activate hardware standby mode by forcing the STBY
pin low. In a notebook computer, this line may be connected to the system SUSTAT# suspend-state signal.
The STBY pin low state overrides any software conversion
command. If a hardware or software standby command
is received while a conversion is in progress, the conversion cycle is truncated, and the data from that conversion
is not latched into either temperature reading register.
The previous data is not changed and remains available.
SMBus Digital Interface
From a software perspective, the MAX1619 appears as a
set of byte-wide registers that contain temperature data,
alarm threshold values, or control bits. A standard
SMBus 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data.
Each A/D channel within the device responds to the
same SMBus slave address for normal reads and writes.
The MAX1619 employs four standard SMBus protocols:
Write Byte, Read Byte, Send Byte, and Receive Byte
(Figure 3). The shorter Receive Byte protocol allows
quicker transfers, provided that the correct data register
was previously selected by a Read Byte instruction. Use
caution with the shorter protocols in multi-master sys-
The OVERT output continues to function in both hardware and software standby modes. If the overtemp limits are adjusted while in standby mode, the digital
comparator checks the new values and puts the OVERT
pin in the correct state based on the last valid ADC conversion. The last valid ADC conversion may include a
conversion performed using the one-shot command.
Supply-current drain during the 125ms conversion period is always about 450µA. Slowing down the conversion
rate reduces the average supply current (see Typical
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
7 bits
ACK
DATA
8 bits
Slave Address:
equivalent to chip-select
line of a 3-wire interface
ACK
P
8 bits
Command Byte: selects
which register you are
writing to
1
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Read Byte Format
S
ADDRESS
WR
ACK
7 bits
COMMAND
ACK
ACK
Command Byte: selects
which register you are
reading from
DATA
WR
ACK
COMMAND
ACK
P
8 bits
Command Byte: sends command with no data; usually
used for one-shot command
P
8 bits
Slave Address: repeated
due to change in dataflow direction
Data Byte: reads from
the register set by the
command byte
Shaded = Slave transmission
/// = Not acknowledged
S
ADDRESS
7 bits
RD
ACK
DATA
///
P
8 bits
Data Byte: reads data from
the register commanded
by the last Read Byte or
Write Byte transmission;
also used for SMBus Alert
Response return address
Figure 3. SMBus Protocols
10
///
Receive Byte Format
7 bits
S = Start condition
P = Stop condition
RD
7 bits
Send Byte Format
ADDRESS
ADDRESS
8 bits
Slave Address:
equivalent to
chip-select line
S
S
______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
Alarm Threshold Registers
Two registers store ALERT threshold limits, with hightemperature (THIGH) and low-temperature (TLOW) registers for the remote A/D channel. There are no
comparison registers for the local A/D channel. If either
measured temperature equals or exceeds the corresponding alarm threshold value, an ALERT interrupt is
asserted. The power-on-reset (POR) state of the THIGH
register is full scale (0111 1111, or +127°C). The POR
state of the TLOW register is 1100 1001 or -55°C.
Two additional alarm threshold registers control the
OVERT output (see OVERT Alarm Output section), TMAX
and T HYST . The POR state of T MAX is +100°C, and
THYST is +95°C.
OVERT Alarm Output for Fan Control
The OVERT output is an unlatched open-drain output that
behaves as a thermostat to control a fan (Figure 4). When
using the SMBus interface, the polarity of the OVERT pin
(active-low at POR) can be inverted via bit 5 in the configuration byte. OVERT’s current state can be read in the
status byte.
OVERT can also be used to control a fan without system
intervention. OVERT goes low when the remote temperature rises above TMAX and won’t go high again until the
temperature drops below THYST. The power-up default
settings for T MAX and T HYST (+100°C and +95°C,
respectively) allow the MAX1619 to be used in standalone thermostat applications where connection to an
SMBus serial bus isn’t required.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
whether the remote diode has an open-circuit condition. At the beginning of each conversion, the diode
fault is checked, and the status byte is updated. This
fault detector is a simple voltage detector; if DXP rises
above V CC - 1V (typical) due to the diode current
source, a fault is detected. Note that the diode fault
isn’t checked until a conversion is initiated, so immediately after power-on reset the status byte indicates no
fault is present, even if the diode path is broken.
Table 2. Data Format (Two’s Complement)
DIGITAL OUTPUT
DATA BITS
ROUNDED
TEMP.
(°C)
SIGN
MSB
LSB
+130.00
+127
0
111
1111
+127.00
+127
0
111
1111
+126.50
+127
0
111
1111
+126.00
+126
0
111
1110
+25.25
+25
0
001
1001
+0.50
+1
0
000
0001
+0.25
0
0
000
0000
0.00
0
0
000
0000
-0.25
0
0
000
0000
-0.50
0
0
000
0000
-0.75
-1
1
111
1111
TEMP.
(°C)
-1.00
-1
1
111
1111
-25.00
-25
1
110
0111
-25.50
-25
1
110
0111
-54.75
-55
1
100
1001
-55.00
-55
1
100
1001
-65.00
-65
1
011
1111
-70.00
-65
1
011
1111
+3V TO +5.5V
+12V
STBY
VCC
MAX1619
SMBUS
SERIAL
INTERFACE
(TO HOST)
SMBCLK
SMBDATA
ALERT
DXP
2N3904
DXN
OVERT
ADD0
ADD1
GND
PGND
Figure 4. Fan Control Application
______________________________________________________________________________________
11
MAX1619
tems, since a second master could overwrite the command byte without informing the first master.
The temperature data format is 7 bits plus sign in two’s
complement form for each channel, with each data bit representing 1°C (Table 2), transmitted MSB first. Measurements are offset by +1/2°C to minimize internal rounding
errors; for example, +99.6°C is reported as +100°C.
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
If the remote channel is shorted (DXP to DXN or DXP to
GND), the ADC reads 0000 0000 so as not to trip either
the T HIGH or T LOW alarms at their POR settings. In
applications that are never subjected to 0°C in normal
operation, a 0000 0000 result can be checked to indicate a fault condition in which DXP is accidentally short
circuited. Similarly, if DXP is short circuited to VCC, the
ADC reads +127°C for both remote and local channels,
and the ALERT and OVERT outputs are activated.
ALERT Interrupts
The ALERT interrupt output signal is latched and can
only be cleared by reading the Alert Response address.
Interrupts are generated in response to THIGH and TLOW
comparisons and when the remote diode is disconnected (for continuity fault detection). The interrupt does not
halt automatic conversions; new temperature data continues to be available over the SMBus interface after
ALERT is asserted. The interrupt output pin is open-drain
so that devices can share a common interrupt line. The
interrupt rate can never exceed the conversion rate.
The interface responds to the SMBus Alert Response
address, an interrupt pointer return-address feature
(see Alert Response Address section). Prior to taking
corrective action, always check to ensure that an interrupt is valid by reading the current temperature.
To prevent reoccurring interrupts, the MAX1619 asserts
ALERT only once per crossing of a given temperature
threshold. To enable a new interrupt, the value in the
limit register that triggered the interrupt must be rewritten. Note that other interrupt conditions can be caused
by crossing the opposite temperature threshold, or a
diode fault can still cause an interrupt.
Example: the remote temperature reading crosses
T HIGH, activating ALERT. The host responds to the
Table 3. Read Format for Alert Response
Address (0001100)
BIT
7
(MSB)
6
5
4
3
2
1
0
(LSB)
NAME
FUNCTION
ADD7
ADD6
ADD5
ADD4
ADD3
ADD2
ADD1
1
Provide the current MAX1619
slave address
Logic 1
I2C is a trademark of Philips Corp.
12
interrupt and reads the Alert Response address, clearing the interrupt. The system may also read the status
byte at this time. The condition that caused the interrupt
persists, but no new ALERT interrupt is issued. Finally,
the host writes a new value to THIGH. This enables the
device to generate a new THIGH interrupt if the alert
condition still exists.
Alert Response Address
The SMBus Alert Response interrupt pointer provides
quick fault identification for simple slave devices that lack
the complex, expensive logic needed to be a bus master.
Upon receiving an ALERT interrupt signal, the host master can broadcast a Receive Byte transmission to the
Alert Response slave address (0001 100). Then any slave
device that generated an interrupt attempts to identify
itself by putting its own address on the bus (Table 3).
The Alert Response can activate several different slave
devices simultaneously, similar to the I2C™ General
Call. If more than one slave attempts to respond, bus
arbitration rules apply, and the device with the lower
address code wins. The losing device does not generate an acknowledge and continues to hold the ALERT
line low until serviced (implies that the host interrupt
input is level-sensitive). Successful reading of the alert
response address clears the interrupt latch.
Command Byte Functions
The 8-bit command byte register (Table 4) is the master
index that points to the other registers within the
MAX1619. The register’s POR state is 0000 0001 so
that a Receive Byte transmission (a protocol that lacks
the command byte) that occurs immediately after POR
returns the current remote temperature data.
The one-shot command immediately forces a new conversion cycle to begin. In software standby mode
(RUN/STOP bit = high), a new conversion is begun, after
which the device returns to standby mode. If a conversion
is in progress when a one-shot command is received, the
command is ignored. If a one-shot command is received
in auto-convert mode (RUN/STOP bit = low) between conversions, a new conversion begins, the conversion rate
timer is reset, and the next automatic conversion takes
place after a full delay elapses.
Configuration Byte Functions
The configuration byte register (Table 5) is used to
mask (disable) interrupts, to put the device in software
standby mode, to change the polarity of the OVERT
output, and to enable the write-once protection. The
lowest two bits are internally set to zeros, making them
“don’t care” bits. This register’s contents can be read
back over the serial interface.
______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
MAX1619
Table 4. Command-Byte Bit Assignments
REGISTER
COMMAND
POR STATE
FUNCTION
RLTS
00h
0000 0000*
Read local temperature: returns latest temperature
RRTE
01h
0000 0000*
Read remote temperature: returns latest temperature
RSL
02h
N/A
Read status byte (flags, busy signal)
RCL
03h
0000 1100
Read configuration byte
RCRA
04h
0000 0010
Read conversion rate byte
RRTM
10h
01100100
Read remote TMAX limit
RRTH
11h
01011111
Read remote THYST limit
RRHI
07h
0111 1111
Read remote THIGH limit
RRLS
08h
1100 1001
Read remote TLOW limit
WCA
09h
N/A
Write configuration byte
WCRW
0Ah
N/A
Write conversion rate byte
WRTM
12h
N/A
Write remote TMAX limit
WRTH
13h
N/A
Write remote THYST limit
WRHA
0Dh
N/A
Write remote THIGH limit
WRLN
0Eh
N/A
Write remote TLOW limit
OSHT
0Fh
N/A
One-shot command
SPOR
FCh
N/A
Write software POR
Write address
WADD
FDh
N/A
MFG ID
FEh
0100 1101
Read manufacturer ID code
DEV ID
FFh
0000 0100
Read device ID code
*If the device is in hardware standby mode at POR, both temperature registers read 0°C.
Table 5. Configuration-Byte Bit Assignments
BIT
NAME
POR STATE
FUNCTION
7 (MSB)
MASK
0
Masks all ALERT interrupts when high.
6
RUN/
STOP
0
Standby mode control bit. If high, the device immediately stops converting and
enters standby mode. If low, the device converts in either one-shot or timer
mode.
5
POL
0
Determines the polarity of the OVERT output:
0 = active low (low when overtemp)
1 = active high
4
PROT
0
When asserted high, locks out all subsequent writes to:
[] Configuration register bits 6, 5, 4, 3, 2 (RUN/STOP, POL, PROT, ID1, ID2)
[] TMAX register
[] THYST register
[] Conversion rate register
[] Diode Current
3
ID1
1
Reduces the diode current by 5µA when set low.
2
ID2
1
Reduces the diode current by 2.5µA when set low.
1–0
RFU
0
Reserved for future use.
______________________________________________________________________________________
13
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
Table 6. Status-Byte Bit Assignments
BIT
NAME
FUNCTION
7
(MSB)
BUSY
A high indicates that the ADC is busy
converting.
6
RFU
Reserved for future use.
5
RFU
4
RHIGH*
DATA
CONVERSION
FREQUENCY
(Hz)
AVERAGE SUPPLY
CURRENT
(µA typ, at VCC = 3.3V)
Reserved for future use.
00h
0.0625
30
A high indicates that the remote hightemperature alarm has activated.
01h
0.125
33
02h
0.25
35
03h
0.5
48
04h
1
70
05h
2
128
06h
4
225
07h
8
425
08h to
FFh
RFU
—
3
RLOW*
A high indicates that the remote lowtemperature alarm has activated.
2
OPEN*
A high indicates a remote-diode continuity (open-circuit) fault.
1
OVER
This bit follows the state of the OVERT
pin exactly, in real time (unlatched).
0
(LSB)
RFU
Reserved for future use.
*The HIGH and LOW temperature alarm flags stay high until
cleared by POR or until status register is read.
Write-Once Protection
Write-once protection allows the host BIOS code to
configure the MAX1619 in a particular way, and then
protect that configuration against data corruption in the
host that might cause spurious writes to the MAX1619.
In particular, write protection allows a foolproof overtemperature override that forces the fan on 100% via
OVERT independent of the host system. The write-protection bit (bit 4), once set high, can’t be reset to low
except by a hardware power-on reset. A SPOR (software POR) will not reset this bit.
Status Byte Functions
The status byte register (Table 6) indicates which (if
any) temperature thresholds have been exceeded. This
byte also indicates whether or not the ADC is converting
and whether there is an open circuit in the remote diode
DXP–DXN path. The status byte is cleared by any successful read of the status byte, unless the fault persists.
The status of bit1 (OVER) follows the state of OVERT
exactly. Note that the ALERT interrupt latch is not automatically cleared when the status flag bit is cleared.
When autoconverting, if the THIGH and TLOW limits are
close together, it’s possible for both high-temp and lowtemp status bits to be set, depending on the amount of
time between status read operations (especially when
converting at the fastest rate). In these circumstances, it’s
best not to rely on the status bits to indicate reversals in
long-term temperature changes. Instead, use a current
temperature reading to establish the trend direction.
14
Table 7. Conversion-Frequency Control
Byte
Conversion Rate Byte
The conversion rate register (Table 7) programs the time
interval between conversions in free-running autoconvert
mode. This variable rate control reduces the supply current in portable-equipment applications. The conversion
rate byte’s POR state is 02h (0.25Hz). The MAX1619
looks only at the 3 LSB bits of this register, so the upper 5
bits are “don’t care” bits, which should be set to zero. The
conversion rate tolerance is ±25% at any rate setting.
Valid A/D conversion results for both channels are available one total conversion period (125ms nominal, 156ms
maximum) after initiating a conversion, whether conversion is initiated via the RUN/STOP bit, hardware STBY
pin, one-shot command, or initial power-up. Changing the
conversion rate can also affect the delay until new results
are available (Table 8).
Manufacturer and Device ID Codes
Two ROM registers provide manufacturer and device ID
codes (Table 4). Reading the manufacturer ID returns
4Dh, which is the ASCII code “M” (for Maxim). Reading
the device ID returns 04h, indicating a MAX1619 device.
If READ WORD 16-bit SMBus protocol is employed
(rather than the 8-bit READ BYTE), the least significant
byte contains the data and the most significant byte contains 00h in both cases.
Slave Addresses
The MAX1619 appears to the SMBus as one device
having a common address for both ADC channels. The
device address can initially be set to one of nine different values by pin-strapping ADD0 and ADD1 so that
more than one MAX1619 can reside on the same bus
without address conflicts (Table 9).
______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
OPERATING MODE
CONVERSION INITIATED BY:
NEW CONVERSION
FREQUENCY (CHANGED VIA
WRITE TO WCRW)
TIME UNTIL RLTS AND RRTE
ARE UPDATED
Autoconvert
Power-on reset
n/a (0.25Hz)
156ms max
Autoconvert
One-shot command, while idling
between automatic conversions
n/a
156ms max
Autoconvert
One-shot command that occurs
during a conversion
n/a
When current conversion is
complete (1-shot is ignored)
Autoconvert
Rate timer
0.0625Hz
20sec
Autoconvert
Rate timer
0.125Hz
10sec
Autoconvert
Rate timer
0.25Hz
5sec
Autoconvert
Rate timer
0.5Hz
2.5sec
Autoconvert
Rate timer
1Hz
1.25sec
Autoconvert
Rate timer
2Hz
625ms
Autoconvert
Rate timer
4Hz
312.5ms
Autoconvert
Rate timer
8Hz
237.5ms
Hardware Standby
STBY pin
n/a
156ms
Software Standby
RUN/STOP bit
n/a
156ms
Software Standby
One-shot command
n/a
156ms
Table 9. POR Slave Address Decoding
(ADD0 and ADD1)
ADD0
GND
GND
GND
High-Z
High-Z
High-Z
VCC
VCC
VCC
ADD1
GND
High-Z
VCC
GND
High-Z
VCC
GND
High-Z
VCC
ADDRESS
0011 000
0011 001
0011 010
0101 001
0101 010
0101 011
1001 100
1001 101
1001 110
Note: High-Z means that the pin is left unconnected and floating.
The address pin states are checked at POR and SPOR
only, and the address data stays latched to reduce quiescent supply current due to the bias current needed
for high-Z state detection. A new device address can be
written using the Write Address Command FDh.
The MAX1619 also responds to the SMBus Alert Response
slave address (see the Alert Response Address section).
POR and UVLO
The MAX1619 has a volatile memory. To prevent ambiguous power-supply conditions from corrupting the data in
memory and causing erratic behavior, a POR voltage
detector monitors VCC and clears the memory if VCC falls
below 1.7V (typical, see Electrical Characteristics table).
When power is first applied and VCC rises above 1.75V
(typical), the logic blocks begin operating, although reads
and writes at VCC levels below 3V are not recommended.
A second VCC comparator, the ADC UVLO comparator,
prevents the ADC from converting until there is sufficient
headroom (VCC = 2.8V typical).
The SPOR software POR command can force a power-on
reset of the MAX1619 registers via the serial interface. Use
the SEND BYTE protocol with COMMAND = FCh. This is
most commonly used to reconfigure the slave address of
the MAX1619 “on the fly,” where external hardware has
forced new states at the ADD0 and ADD1 address pins
prior to the software POR. The new address takes effect
less than 100µs after the SPOR transmission stop condition.
Power-Up Defaults:
• Interrupt latch is cleared.
• Address select pins are sampled.
• ADC begins auto-converting at a 0.25Hz rate.
• Command byte is set to 01h to facilitate quick
remote Receive Byte queries.
• THIGH and TLOW registers are set to +127°C and
-55°C, respectively.
• T MAX and T HYST are set to +100°C and +95°C,
respectively.
• OVERT polarity is active low.
______________________________________________________________________________________
15
MAX1619
Table 8. RLTS and RRTE Temperature Register Update Timing Chart
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
A
B
tLOW
C
D
E
F
G
H
J
I
tHIGH
K
SMBCLK
SMBDATA
tSU:STA tHD:STA
tSU:STO
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
tBUF
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
Figure 5. SMBus Write Timing Diagram
A
tLOW
B
tHIGH
C
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
tSU:DAT
tHD:DAT
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = SLAVE PULLS SMBDATA LINE LOW
tSU:STO tBUF
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
Figure 6. SMBus Read Timing Diagram
16
______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
MAX1619
Listing 1. Pseudocode Example
______________________________________________________________________________________
17
MAX1619
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
Listing 1. Pseudocode Example (continued)
18
______________________________________________________________________________________
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
MAX1619
Listing 1. Pseudocode Example (continued)
Programming Example:
Clock-Throttling Control for CPUs
Listing 1 gives an untested example of pseudocode for
proportional temperature control of Intel mobile CPUs
through a power-management microcontroller. This
program consists of two main parts: an initialization routine and an interrupt handler. The initialization routine
checks for SMBus communications problems and sets
up the MAX1619 configuration and conversion rate. The
interrupt handler responds to ALERT signals by reading
the current temperature and setting a CPU clock duty
factor proportional to that temperature. The relationship
between clock duty and temperature is fixed in a lookup table contained in the microcontroller code.
Note: Thermal management decisions should be made
based on the latest external temperature obtained from
the MAX1619 rather than the value of the Status Byte.
The MAX1619 responds very quickly to changes in its
environment due to its sensitivity. High and low alarm
conditions can exist at the same time in the Status Byte
due to the MAX1619 correctly reporting environmental
changes around it.
Chip Information
TRANSISTOR COUNT: 11,487
______________________________________________________________________________________
19
Remote/Local Temperature Sensor with DualAlarm Outputs and SMBus Serial Interface
QSOP.EPS
MAX1619
Package Information
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
20 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1999 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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