________________General Description
The MAX1617A 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 ther-
mocouples. Remote accuracy is ±3°C for multiple transis-
tor 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 MAX1617A is nearly identical to the popular MAX1617,
but has improved SMBus timing specifications, improved
bus collision immunity, software manufacturer and device
identification available via the serial interface, and a power-
on reset function that can force a reset of the slave address
via the serial interface.
________________________Applications
Desktop and Notebook Central Office
Computers Telecom Equipment
Smart Battery Packs Test and Measurement
LAN Servers Multichip Modules
Industrial Controls
____________________________Features
♦Two Channels: Measures Both Remote and Local
Temperatures
♦No Calibration Required
♦SMBus 2-Wire Serial Interface
♦Programmable Under/Overtemperature Alarms
♦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
♦Small 16-Pin QSOP Package
MAX1617 A
Remote/Local Temperature Sensor
with SMBus Serial Interface
________________________________________________________________ Maxim Integrated Products 1
MAX1617A
SMBCLK
ADD0 ADD1
VCC STBY
GND
ALERT
SMBDATA
DXP
DXN INTERRUPT
TO µC
3V TO 5.5V
200Ω
0.1µF
CLOCK
10k EACH
DATA
2N3904 2200pF
___________________Pin Configuration
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
N.C. N.C.
STBY
SMBCLK
N.C.
SMBDATA
ALERT
ADD0
N.C.
TOP VIEW
MAX1617A
QSOP
VCC
DXP
ADD1
DXN
N.C.
GND
GND
Typical Operating Circuit
19-4508; Rev 0; 1/99
PART
MAX1617AMEE -55°C to +125°C
TEMP. RANGE PIN-PACKAGE
16 QSOP
EVALUATION KIT MANUAL
FOLLOWS DATA SHEET
Ordering Information
SMBus is a trademark of Intel Corp.
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.
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = +3.3V, TA= 0°C to +85°C, unless otherwise noted.)
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.
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, STBY to GND...........-0.3V to +6V
SMBDATA, ALERT Current.................................-1mA to +50mA
DXN Current .......................................................................±1mA
ESD Protection (SMBCLK, SMBDATA,
ALERT, Human Body Model)......................................... 4000V
ESD Protection (other 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 +165°C
Lead Temperature (soldering, 10sec).............................+300°C
TA = +60°C to +100°C
Monotonicity guaranteed
ADD0, ADD1; momentary upon power-on reset
DXP forced to 1.5V
Logic inputs
forced to VCC
or GND
Auto-convert mode
From stop bit to conversion complete (both channels)
VCC, falling edge
TA = 0°C to +85°C
VCC input, disables A/D conversion, rising edge
Auto-convert mode, average
measured over 4sec. Logic
inputs forced to VCC or GND.
CONDITIONS
µA160Address Pin Bias Current V0.7DXN Source Voltage
µA
81012
80 100 120
Remote-Diode Source Current
%-25 25Conversion Rate Timing Error ms94 125 156Conversion Time
µA
120 180
35 70
Average Operating Supply Current
-2 2 Bits8Temperature Resolution (Note 1)
µA
4
Standby Supply Current 310
mV50POR Threshold Hysteresis V1.0 1.7 2.5Power-On Reset Threshold
°C
-3 3
Initial Temperature Error,
Local Diode (Note 2)
V3.0 5.5Supply-Voltage Range V2.60 2.80 2.95Undervoltage Lockout Threshold mV50Undervoltage Lockout Hysteresis
UNITSMIN TYP MAXPARAMETER
TR = +60°C to +100°C
TR = -55°C to +125°C -3 3 °C
-5 5
Temperature Error, Remote Diode
(Notes 2 and 3)
Including long-term drift -2.5 2.5 °C
-3.5 3.5
Temperature Error, Local Diode
(Notes 1 and 2)
0.25 conv/sec
2.0 conv/sec
TA = +60°C to +100°C
TA = 0°C to +85°C
High level
Low level
ADC AND POWER SUPPLY
SMBus static
Hardware or software standby,
SMBCLK at 10kHz
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.3V, TA= 0°C to +85°C, unless otherwise noted.)
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
tHIGH, 90% to 90% points
tLOW, 10% to 10% points
(Note 4)
SMBCLK, SMBDATA
Logic inputs forced to VCC or GND
ALERT forced to 5.5V
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V
ALERT, SMBDATA forced to 0.4V
CONDITIONS
µs4SMBCLK Clock High Time µs4.7SMBCLK Clock Low Time kHzDC 100SMBus Clock Frequency pF5SMBus Input Capacitance µA-1 1Logic Input Current
µA1
ALERT Output High Leakage
Current
V2.2Logic Input High Voltage
V0.8Logic Input Low Voltage
mA6Logic Output Low Sink Current
UNITSMIN TYP MAXPARAMETER
tSU:DAT, 10% or 90% of SMBDATA to 10% of SMBCLK
tSU:STO, 90% of SMBCLK to 10% of SMBDATA
tHD:STA, 10% of SMBDATA to 90% of SMBCLK
tSU:STA, 90% to 90% points
ns250
SMBus Data Valid to SMBCLK
Rising-Edge Time
µs4SMBus Stop-Condition Setup Time µs4SMBus Start-Condition Hold Time
ns500
SMBus Repeated Start-Condition
Setup Time
µs4.7SMBus Start-Condition Setup Time
tHD:DAT (Note 5) µs0SMBus Data-Hold Time
Master clocking in data µs1
SMBCLK Falling Edge to SMBus
Data-Valid Time
SMBus INTERFACE
ELECTRICAL CHARACTERISTICS
(VCC = +3.3V, TA= -55°C to +125°C, unless otherwise noted.) (Note 6)
CONDITIONS
Monotonicity guaranteed
TA= +60°C to +100°C Bits8Temperature Resolution (Note 1) -2 2
TR= +60°C to +100°C
TA= -55°C to +125°C °C
-3 3
Initial Temperature Error,
Local Diode (Note 2)
V3.0 5.5Supply-Voltage Range From stop bit to conversion complete (both channels)
Auto-convert mode ms94 125 156Conversion Time %-25 25Conversion Rate Timing Error
-3 3
TR= -55°C to +125°C °C
UNITSMIN TYP MAX
-5 5
PARAMETER
Temperature Error, Remote Diode
(Notes 2 and 3)
ADC AND POWER SUPPLY
0
6
3
9
12
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
POWER-SUPPLY NOISE FREQUENCY
MAX1617ATOC04
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE APPLIED TO
VCC WITH NO 0.1µF VCC CAPACITOR
VIN = 250mVp-p
REMOTE DIODE
VIN = 250mVp-p
LOCAL DIODE
VIN = 100mVp-p
REMOTE DIODE
-20
-10
0
10
20
110303 100
TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
MAX1617ATOC01
LEAKAGE RESISTANCE (MΩ)
TEMPERATURE ERROR (°C)
PATH = DXP TO VCC (5V)
PATH = DXP TO GND
-2
-1
0
1
2
-50 50 1000 150
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX1617ATOC02
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
SAMSUNG KST3904
MOTOROLA MMBT3904
ZETEX FMMT3904
RANDOM
SAMPLES
__________________________________________Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.3V, TA= -55°C to +125°C, unless otherwise noted.) (Note 6)
Note 1: Guaranteed but not 100% tested.
Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1617A device temper-
ature 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. TRis the junction temperature of the remote diode. See
Remote Diode Selection
for remote diode forward voltage requirements.
Note 4: 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 5: 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.
Note 6: Specifications from -55°C to +125°C are guaranteed by design, not production tested.
CONDITIONS UNITSMIN TYP MAXPARAMETER
STBY, SMBCLK, SMBDATA 2.2
Logic Input High Voltage V
2.4
STBY, SMBCLK, SMBDATA; VCC = 3V to 5.5V V0.8Logic Input Low Voltage
ALERT forced to 5.5V µA1
ALERT Output High Leakage
Current
Logic inputs forced to VCC or GND µA-2 2Logic Input Current
VCC = 3V
VCC = 5.5V
ALERT, SMBDATA forced to 0.4V mA6Logic Output Low Sink Current
SMBus INTERFACE
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
_______________________________________________________________________________________
5
0
10
20
30
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
COMMON-MODE NOISE FREQUENCY
MAX1617ATOC05
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE
AC COUPLED TO DXN
VIN = 100mVp-p
VIN = 50mVp-p
VIN = 25mVp-p
-5
5
0
10
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCY
MAX1617ATOC06
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = 10mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
0
10
20
04060
80
20 100
TEMPERATURE ERROR vs.
DXP–DXN CAPACITANCE
MAX1617ATOC07
DXP–DXN CAPACITANCE (nF)
TEMPERATURE ERROR (°C)
VCC = 5V
0
5
15
25
10
20
30
35
1k 100k10k 1000k
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCY
MAX1617ATOC08
SMBCLK FREQUENCY (Hz)
SUPPLY CURRENT (µA)
VCC = 5V
VCC = 3.3V
SMBCLK IS
DRIVEN RAIL-TO-RAIL®
0
3
60
6
20
100
031425
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1617ATOC09
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
ADD0, ADD1
= GND
ADD0, ADD1
= HIGH-Z
0
25
100
50
75
125
-2 8 042610
RESPONSE TO THERMAL SHOCK
MAX1617ATOC11
TIME (sec)
TEMPERATURE (°C)
16-QSOP IMMERSED
IN +115°C FLUORINERT BATH
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
-5
0
5
50 5k 500k50k 5M500 50M
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCY
MAX1617ATOC03
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = 3mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
Rail-to Rail is a registered trademark of Nippon Motorola, Ltd.
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
6 _______________________________________________________________________________________
Pin Description
General Description
The MAX1617A is a temperature sensor designed to
work in conjunction with an external microcontroller
(µC) or other intelligence in thermostatic, process-con-
trol, or monitoring applications. The µC is typically a
power-management or keyboard controller, generating
SMBus serial commands by “bit-banging” general-pur-
pose input/output (GPIO) pins or via a dedicated
SMBus interface block.
Essentially an 8-bit serial analog-to-digital converter
(ADC) with a sophisticated front end, the MAX1617A
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, where it is automatically com-
pared with data previously stored in four over/under-
temperature alarm registers.
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. If the remote diode channel is unused, tie DXP
to DXN rather than leaving the pins open.
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.
SMBus Serial-Data Input/Output, Open DrainSMBDATA12
SMBus Serial-Clock InputSMBCLK14
Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode.
Low = standby mode, high = operate mode.
STBY
15
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.
ADD16
GroundGND7, 8
SMBus Slave Address Select PinADD010
SMBus Alert (interrupt) Output, Open Drain
ALERT
11
Combined Current Sink and A/D Negative Input. DXN is normally biased to a diode voltage above
ground.
DXN4
Combined Current Source and A/D Positive Input for Remote-Diode Channel. Do not leave DXP floating;
tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise fil-
tering.
DXP3
PIN
Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ωseries resistor is recom-
mended but not required for additional noise filtering.
VCC
2
No Connection. Not internally connected. May be used for PC board trace routing.N.C.
1, 5, 9,
13, 16
FUNCTIONNAME
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
_______________________________________________________________________________________ 7
Figure 1. Functional Diagram
REMOTE
MUX
LOCAL
REMOTE TEMPERATURE
DATA REGISTER
HIGH-TEMPERATURE THRESHOLD
(REMOTE THIGH)
LOW-TEMPERATURE THRESHOLD
(REMOTE TLOW)
DIGITAL COMPARATOR
(REMOTE)
LOCAL TEMPERATURE
DATA REGISTER
HIGH-TEMPERATURE THRESHOLD
(LOCAL THIGH)
LOW-TEMPERATURE THRESHOLD
(LOCAL TLOW)
DIGITAL COMPARATOR
(LOCAL)
COMMAND BYTE
(INDEX) REGISTER
SMBDATA
SMBCLK
ADDRESS
DECODER
READ WRITE
CONTROL
LOGIC SMBUS
ADD1ADD0STBY
STATUS BYTE REGISTER
CONFIGURATION
BYTE REGISTER
CONVERSION RATE
REGISTER
ALERT RESPONSE
ADDRESS REGISTER
SELECTED VIA
SLAVE ADD = 0001 100
ADC
+
DIODE
FAULT
DXP
DXN
GND
VCC
-
+
-
+
-
8
8
8
8
8
8
88
27
ALERT
QS
R
MAX1617A
Excess resistance in series with the remote diode caus-
es about +1/2°C error per ohm. Likewise, 200µV of off-
set voltage forced on DXP–DXN causes about 1°C error.
A/D Conversion Sequence
If a Start command is written (or generated automatical-
ly 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-qual-
ity, diode-connected small-signal transistor. Accuracy
has been experimentally verified for all of the devices
listed in Table 1. The MAX1617A can also directly mea-
sure 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 rela-
tively 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 tem-
perature. Large power transistors don’t work at all. 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 MAX1617A’s
effective accuracy. The thermal time constant of the
QSOP-16 package is about 140sec in still air. For the
MAX1617A junction temperature to settle to within +1°C
after a sudden +100°C change requires about five time
constants or 12 minutes. The use of smaller packages
for remote sensors, such as SOT23s, improves the situ-
ation. 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
worst-case error occurs when auto-converting at the
fastest rate and simultaneously sinking maximum cur-
rent at the ALERT output. For example, at an 8Hz rate
and with ALERT sinking 1mA, the typical power dissi-
pation is VCC ·450µA plus 0.4V ·1mA. Package theta
J-A is about 150°C/W, so with VCC = 5V and no copper
PC board heatsinking, the resulting temperature rise is:
dT = 2.7mW ·150°C/W = 0.4°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 environ-
ments.
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. Higher capacitance than 3300pF intro-
duces errors due to the rise time of the switched cur-
rent source.
Nearly all noise sources tested cause the ADC measure-
ments to be higher than the actual temperature, typically
by +1°C to +10°C, depending on the frequency and
amplitude (see
Typical Operating Characteristics
).
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
8 _______________________________________________________________________________________
CMPT3904Central Semiconductor (USA)
MMBT3904Motorola (USA)
MMBT3904
SST3904Rohm Semiconductor (Japan)
KST3904-TFSamsung (Korea)
FMMT3904CT-NDZetex (England)
MANUFACTURER MODEL NUMBER
SMBT3904Siemens (Germany)
Table 1. Remote-Sensor Transistor
Manufacturers
Note: Transistors must be diode-connected (base shorted to
collector).
National Semiconductor (USA)
·
PC Board Layout
1) Place the MAX1617A as close as practical to the
remote diode. In a noisy environment, such as a
computer motherboard, this distance can be 4 in. to
8 in. (typical) or more as long as the worst noise
sources (such as CRTs, clock generators, memory
buses, and ISA/PCI buses) are avoided.
2) Do not route the DXP–DXN lines next to the deflec-
tion coils of a CRT. Also, do not route the traces
across a fast memory bus, which can easily intro-
duce +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 high-
voltage traces such as +12VDC. Leakage currents
from PC board contamination must be dealt with
carefully, since a 20MΩleakage 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 possi-
ble 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 ther-
mocouples are not a serious problem. A copper-sol-
der 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 ther-
mocouple 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 MAX1617A 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.
• Use guard traces flanking DXP and DXN and con-
necting to GND.
• Place the noise filter and the 0.1µF VCC bypass
capacitors close to the MAX1617A.
• Add a 200Ωresistor in series with VCC for best noise
filtering (see
Typical Operating Circuit
).
Twisted Pair and Shielded Cables
For remote-sensor distances longer than 8 in., or in par-
ticularly noisy environments, a twisted pair is recom-
mended. 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
for distances up to 100 feet in a noisy environment.
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 sen-
sor distances (see
Typical Operating Characteristics
).
For very long cable runs, the cable’s parasitic capaci-
tance often provides noise filtering, so the 2200pF
capacitor can often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy;
1Ωseries resistance introduces about +1/2°C error.
Low-Power Standby Mode
Standby mode disables the ADC and reduces the sup-
ply-current drain to less than 10µA. 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 differ-
ence 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,
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
_______________________________________________________________________________________ 9
MINIMUM
10 MILS
10 MILS
10 MILS
10 MILS
GND
DXN
DXP
GND
Figure 2. Recommended DXP/DXN PC Traces
the MAX1617A can be forced to perform A/D conver-
sions 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 con-
nected 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 previ-
ous data is not changed and remains available.
Supply-current drain during the 125ms conversion peri-
od is always about 450µA. Slowing down the conver-
sion rate reduces the average supply current (see
Typical Operating Characteristics
). Between conver-
sions, 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.
SMBus Digital Interface
From a software perspective, the MAX1617A 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 tempera-
ture 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 MAX1617A 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 systems,
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 rep-
resenting 1°C (Table 2), transmitted MSB first. Measure-
ments are offset by +1/2°C to minimize internal rounding
errors; for example, +99.6°C is reported as +100°C.
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
10 ______________________________________________________________________________________
ACK
7 bits
ADDRESS ACKWR
8 bits
DATA ACK
1
P
8 bits
S COMMAND
Write Byte Format
Read Byte Format
Send Byte Format Receive Byte Format
Slave Address: equiva-
lent to chip-select line of
a 3-wire interface
Command Byte: selects which
register you are writing to Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
ACK
7 bits
ADDRESS ACKWR S ACK
8 bits
DATA
7 bits
ADDRESS RD
8 bits
/// PS COMMAND
Slave Address: equiva-
lent to chip-select line Command Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in data-
flow direction
Data Byte: reads from
the register set by the
command byte
ACK
7 bits
ADDRESS WR
8 bits
COMMAND ACK PS ACK
7 bits
ADDRESS RD
8 bits
DATA /// PS
Command Byte: sends com-
mand with no data, usually
used for one-shot command
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
S = Start condition Shaded = Slave transmission
P = Stop condition /// = Not acknowledged
Figure 3. SMBus Protocols
Alarm Threshold Registers
Four registers store alarm threshold data, with high-
temperature (THIGH) and low-temperature (TLOW) reg-
isters for each 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 both THIGH registers
is full scale (0111 1111, or +127°C). The POR state of
both TLOW registers is 1100 1001 or -55°C.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
whether the remote diode has an open-circuit condi-
tion. 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 VCC - 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 immedi-
ately after power-on reset the status byte indicates no
fault is present, even if the diode path is broken.
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 THIGH or TLOW 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 indi-
cate 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 device alarms.
AALLEERRTT
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 disconnect-
ed (for continuity fault detection). The interrupt does not
halt automatic conversions; new temperature data con-
tinues 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 inter-
rupt is valid by reading the current temperature.
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).
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
______________________________________________________________________________________ 11
DIGITAL OUTPUT
DATA BITS
0 111 1111+127+127.00 0 111 1111
0 111 1110+126+126.00 +127+126.50
0 001 1001
0 000 0001+1+0.50 0 000 0000
0 000 000000.00
ROUNDED
TEMP.
(°C)
TEMP.
(°C)
0+0.25
+25+25.25
0 000 0000
0 000 00000-0.50 1 111 1111
1 111 1111-1-1.00 -1-0.75
1 110 0111
1 110 0110-26-25.50 1 100 1001
1 100 1001-55-55.00
0-0.25
-55-54.75
-25-25.00
1 011 1111
1 011 1111-65-70.00 -65-65.00
Table 2. Data Format (Two’s Complement) Table 3. Read Format for Alert Response
Address (0001100)
ADD66 Provide the current MAX1617A
slave address that was latched at
POR (Table 8)
FUNCTION
ADD55 ADD44 ADD33 ADD22 ADD11
ADD7
7
(MSB)
1
0
(LSB) Logic 1
BIT NAME
SIGN MSB LSB
0 111 1111+127+130.00
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 gener-
ate 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 various other registers within the
MAX1617A. The register’s POR state is 0000 0000, so
that a Receive Byte transmission (a protocol that lacks
the command byte) that occurs immediately after POR
returns the current local temperature data.
The one-shot command immediately forces a new conver-
sion 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 con-
versions, 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 and to put the device in soft-
ware standby mode. The lower six bits are internally set
to (XX1111), making them “don’t care” bits. Write zeros
to these bits. This register’s contents can be read back
over the serial interface.
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 convert-
ing and whether there is an open circuit in the remote
diode DXP–DXN path. After POR, the normal state of all
the flag bits is zero, assuming none of the alarm condi-
tions are present. The status byte is cleared by any
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
12 ______________________________________________________________________________________
Table 4. Command-Byte Bit Assignments
*
If the device is in hardware standby mode at POR, both temperature registers read 0°C.
Read remote temperature: returns latest temperatureRRTE 01h
00h
COMMAND
0000 0000*
0000 0000*
POR STATE
Read configuration byteRCL 03h
02h 0000 0000
N/A Read status byte (flags, busy signal)RSL
Read local THIGH limitRLHN 05h
Read local temperature: returns latest temperatureRLTS
04h 0111 1111
0000 0010
Read remote THIGH limitRRHI 07h
06h 0111 1111
1100 1001 Read local TLOW limitRLLI
Read conversion rate byte
REGISTER
RCRA
Write configuration byteWCA 09h
08h N/A
1100 1001
FUNCTION
Write local THIGH limitWLHO 0Bh
0Ah N/A
N/A Write conversion rate byteWCRW
Write remote THIGH limitWRHA 0Dh
Read remote TLOW limitRRLS
0Ch N/A
N/A
One-shot command (use send-byte format)OSHT 0Fh
0Eh N/A
N/A Write remote TLOW limitWRLN
Write local TLOW limitWLLM
Write software PORSPOR FCh N/A
Read device ID codeDEVID FFh
FEh 00000001
0100 1101 Read manufacturer ID codeMFGID
I2C is a trademark of Phillips Corp.
successful read of the status byte, unless the fault per-
sists. Note that the ALERT interrupt latch is not auto-
matically cleared when the status flag bit is cleared.
When auto-converting, if the THIGH and TLOW limits are
close together, it’s possible for both high-temp and low-
temp 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 rever-
sals in long-term temperature changes and instead use
a current temperature reading to establish the trend
direction.
Conversion Rate Byte
The conversion rate register (Table 7) programs the time
interval between conversions in free-running auto-convert
mode. This variable rate control reduces the supply cur-
rent in portable-equipment applications. The conversion
rate byte’s POR state is 02h (0.25Hz). The MAX1617A
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 avail-
able one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conver-
sion 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 01h, indicating a MAX1617A
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 signifi-
cant byte contains 00h in both cases.
Slave Addresses
The MAX1617A appears to the SMBus as one device
having a common address for both ADC channels. The
device address can be set to one of nine different val-
ues by pin-strapping ADD0 and ADD1 so that more
than one MAX1617A can reside on the same bus with-
out address conflicts (Table 9).
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
______________________________________________________________________________________ 13
RUN/
STOP
6 0
0
POR
STATE
Standby mode control
bit. If high, the device
immediately stops con-
verting and enters stand-
by mode. If low, the
device converts in either
one-shot or timer mode.
Masks all ALERT inter-
rupts when high.
FUNCTION
RFU5–0 0 Reserved for future use
MASK7 (MSB)
BIT NAME
Table 5. Configuration-Byte Bit
Assignments Table 7. Conversion-Rate Control Byte
Table 6. Status-Byte Bit Assignments
*
These flags stay high until cleared by POR, or until the status
byte register is read.
LHIGH*6 A high indicates that the local high-
temperature alarm has activated.
A high indicates that the ADC is busy
converting.
FUNCTION
LLOW*5 A high indicates that the local low-
temperature alarm has activated.
RHIGH*4 A high indicates that the remote high-
temperature alarm has activated.
RLOW*3 A high indicates that the remote low-
temperature alarm has activated.
OPEN*2 A high indicates a remote-diode conti-
nuity (open-circuit) fault.
RFU1
BUSY
7
(MSB)
Reserved for future use (returns 0)
RFU
0
(LSB) Reserved for future use (returns 0)
BIT NAME
0.12501h 33
30
0.2502h 35
0.503h 48
104h 70
205h 128
406h
0.062500h
225
807h 425
RFU
08h to
FFh —
DATA CONVERSION
RATE
(Hz)
AVERAGE SUPPLY
CURRENT
(µA typ, at VCC = 3.3V)
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
14 ______________________________________________________________________________________
The address pin states are checked at POR and SPOR
only, and the address data stays latched to reduce qui-
escent supply current due to the bias current needed
for high-Z state detection.
The MAX1617A also responds to the SMBus Alert
Response slave address (see the
Alert Response
Address
section).
POR and UVLO
The MAX1617A has a volatile memory. To prevent ambig-
uous 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 MAX1617A 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 MAX1617A “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 00h to facilitate quick
remote Receive Byte queries.
•THIGH and TLOW registers are set to max and min
limits, respectively.
Table 8. RLTS and RRTE Temp Register Update Timing Chart
n/a (0.25Hz)
NEW CONVERSION RATE
(CHANGED VIA WRITE TO
WCRW)
Power-on resetAuto-Convert
OPERATING MODE CONVERSION INITIATED BY:
156ms max
TIME UNTIL RLTS AND RRTE
ARE UPDATED
156ms maxn/a
1-shot command, while idling
between automatic conversions
Auto-Convert
When current conversion is
complete (1-shot is ignored)
20sec
n/a
0.0625HzRate timerAuto-Convert
1-shot command that occurs
during a conversion
Auto-Convert
10sec
5sec
0.125Hz
0.25HzRate timerAuto-Convert 2.5sec
1.25sec
0.5Hz
1HzRate timerAuto-Convert Rate timerAuto-Convert
Rate timerAuto-Convert
625ms
312.5ms
2Hz
4HzRate timerAuto-Convert 237.5ms
156ms
8Hz
n/a
STBY pin
Hardware Standby Rate timerAuto-Convert
Rate timerAuto-Convert
156ms
156ms
n/a
n/a1-shot commandSoftware Standby RUN/STOP bitSoftware Standby
Table 9. Slave Address Decoding (ADD0
and ADD1)
Note: High-Z means that the pin is left unconnected and floating.
0011 001High-ZGND 0011 000
ADDRESS
0101 001GNDHigh-Z 0011 010VCC
GND
0101 011VCC
High-Z 0101 010
1001 101High-ZVCC
1001 100
GNDGND
GNDVCC
High-ZHigh-Z
1001 110VCC
VCC
ADD0 ADD1
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
______________________________________________________________________________________ 15
Figure 5. SMBus Read Timing Diagram
Figure 4. SMBus Write Timing Diagram
SMBCLK
AB CD
EFG H
IJK
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tHD:DAT tSU:STO tBUF
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
LM
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
J = ACKNOWLEDGE CLOCKED INTO MASTER
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION, DATA EXECUTED BY SLAVE
M = NEW START CONDITION
SMBCLK
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
AB CD
EFG H
IJ
SMBDATA
tSU:STA tHD:STA
tLOW tHIGH
tSU:DAT tSU:STO tBUF
K
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
I = ACKNOWLEDGE CLOCK PULSE
J = STOP CONDITION
K = NEW START CONDITION
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
16 ______________________________________________________________________________________
Listing 1. Pseudocode Example
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
______________________________________________________________________________________ 17
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
via 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
MAX1617A 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 look-
up table contained in the microcontroller code.
Note: Thermal management decisions should be made
based on the latest temperature obtained from the
MAX1617A rather than the value of the Status Byte. The
MAX1617A responds very quickly to changes in its
environment due to its sensitivity and its small thermal
mass. High and low alarm conditions can exist in the
Status Byte due to the MAX1617A correctly reporting
environmental changes around it.
MAX1617A
Remote/Local Temperature Sensor
with SMBus Serial Interface
18 ______________________________________________________________________________________
Listing 1. Pseudocode Example (continued)