MAX1617 ,Remote/Local Temperature Sensor with SMBus Serial InterfaceFeaturesThe MAX1617 is a precise digital thermometer that♦ Two Channels: Measures Both Remote and L ..
MAX1617AMEE ,Remote/Local Temperature Sensor with SMBus Serial InterfaceFeaturesThe MAX1617A (patents pending) is a precise digital ther-' Two Channels: Measures Both Remo ..
MAX1617AMEE+ ,Remote/Local Temperature Sensor with SMBus Serial InterfaceFeaturesThe MAX1617A is a precise digital thermometer that♦ Two Channels: Measures Both Remote and ..
MAX1617AMEE+T ,Remote/Local Temperature Sensor with SMBus Serial InterfaceELECTRICAL CHARACTERISTICS (continued)(V = +3.3V, T = 0°C to +85°C, unless otherwise noted.) (Note ..
MAX1617AMEE-T ,Remote/Local Temperature Sensor with SMBus Serial InterfaceEVALUATION KIT AVAILABLE MAX1617ARemote/Local Temperature Sensor with SMBus Serial Interface_______ ..
MAX1617AMEE-T ,Remote/Local Temperature Sensor with SMBus Serial InterfaceGeneral Description ________
MAX4327EUB+ ,Single/Dual/Quad, Low-Cost, UCSP/SOT23, Low-Power, Rail-to-Rail I/O Op AmpsELECTRICAL CHARACTERISTICS—T = +25°C A(V = 5.0V, V = 0V, V = 0V, V = V /2, SHDN = V R connected to ..
MAX4329ESD ,Single/Dual/Quad / Low-Cost / SOT23 / Low-Power / Rail-to-Rail I/O Op AmpsELECTRICAL CHARACTERISTICS—T = +25°C (continued)A(V = +5V, V = 0, V = 0, V = V / 2, SHDN = V R tied ..
MAX4329ESD ,Single/Dual/Quad / Low-Cost / SOT23 / Low-Power / Rail-to-Rail I/O Op AmpsApplications6 2DOUT AINMAX4322SERIALPin Configurations appear at end of data sheet.INTERFACE8 4SCLK ..
MAX4329ESD+ ,Single/Dual/Quad, Low-Cost, UCSP/SOT23, Low-Power, Rail-to-Rail I/O Op AmpsELECTRICAL CHARACTERISTICS—T = +25°C A(V = 5.0V, V = 0V, V = 0V, V = V /2, SHDN = V R connected to ..
MAX432CPA ,【15V Chopper-Stabilized Operational Amplifierapplications.
They offer input offset and drift specifications superior to
previous "precision" b ..
MAX4330EUK ,Single/Dual/Quad, Low-Power, Single-Supply, Rail-to-Rail I/O Op Amps with ShutdownApplications MAX4334ESD -40°C to +85°C 14 SO —Selector GuidePin ConfigurationsNO. OF AMPS SHUTDOWNP ..
MAX1617
Remote/Local Temperature Sensor with SMBus Serial Interface
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
________________General DescriptionThe MAX1617 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 tempera-
ture 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 for-
mat is 7 bits plus sign, with each bit corresponding to
1°C, in twos-complement format. Measurements can be
done automatically and autonomously, with the conver-
sion 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 MAX1617 is available in a small, 16-pin QSOP sur-
face-mount package.
________________________ApplicationsDesktop and NotebookCentral Office
ComputersTelecom Equipment
Smart Battery PacksTest and Measurement
LAN ServersMulti-Chip Modules
Industrial Controls
____________________________FeaturesTwo Channels: Measures Both Remote and Local
TemperaturesNo Calibration RequiredSMBus 2-Wire Serial InterfaceProgrammable Under/Overtemperature AlarmsSupports SMBus Alert ResponseAccuracy:
±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 Current70µA (max) Supply Current in Auto-Convert Mode+3V to +5.5V Supply RangeSmall, 16-Pin QSOP PackageMAX1617
SMBCLK
ADD0ADD1
VCCSTBY
GND
ALERT
SMBDATA
DXP
DXNINTERRUPT
TO μC
3V TO 5.5V
200Ω0.1μF
CLOCK
10k EACH
DATA
2N39042200pF
___________________Pin ConfigurationN.C.N.C.
STBY
SMBCLK
N.C.
SMBDATA
ALERT
ADD0
N.C.
TOP VIEW
MAX1617
QSOPVCC
DXP
ADD1
DXN
N.C.
GND
GND
__________Typical Operating Circuit
PARTMAX1617MEE+-55°C to +125°C
TEMP. RANGEPIN-PACKAGE16 QSOP
_______________Ordering Information+Denotes a lead(Pb)-free/RoHS-compliant package.
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VCC= +3.3V, TA
= 0°C to +85°C, unless otherwise noted.) (Note 1)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.
VCCto 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, STBYto GND...........-0.3V to +6V
SMBDATA, ALERTCurrent.................................-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
VCCinput, disables A/D conversion, rising edge
Auto-convert mode, average
measured over 4sec. Logic
inputs forced to VCCor GND.
CONDITIONS160Address Pin Bias Current0.7DXN Source Voltage81012100120Remote-Diode Source Current-2525Conversion Rate Timing Error94125156Conversion Time
Average Operating Supply Current2
Bits8Temperature Resolution (Note 2)
Standby Supply Current
31050POR Threshold Hysteresis1.01.72.5Power-On Reset Threshold-33
Initial Temperature Error,
Local Diode (Note 3)3.05.5Supply-Voltage Range2.602.802.95Undervoltage Lockout Threshold50Undervoltage Lockout Hysteresis
UNITSMINTYPMAXPARAMETERTR = +60°C to +100°C
TR = -55°C to +125°C3°C-55
Temperature Error, Remote Diode
(Notes 3 and 4)
Including long-term drift-2.52.5°C-3.53.5
Temperature Error, Local Diode
(Notes 2 and 3)
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 SUPPLYSMBus static
Hardware or software standby, SMB-
CLK at 10kHz
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
ELECTRICAL CHARACTERISTICS (continued)(VCC= +3.3V, TA
= 0°C to +85°C, unless otherwise noted.) (Note 1)STBY, SMBCLK, SMBDATA; VCC= 3V to 5.5V
tHIGH, 90% to 90% points
tLOW, 10% to 10% points
(Note 5)
SMBCLK, SMBDATA
Logic inputs forced to VCCor GND
ALERTforced to 5.5V
STBY, SMBCLK, SMBDATA; VCC= 3V to 5.5V
ALERT,SMBDATA forced to 0.4V
CONDITIONS4SMBCLK Clock High Time4.7SMBCLK Clock Low Time
kHzDC100SMBus Clock Frequency5SMBus Input Capacitance-11Logic Input Current1ALERTOutput High Leakage
Current2.2Logic Input High Voltage0.8Logic Input Low Voltage6Logic Output Low Sink Current
UNITSMINTYPMAXPARAMETERtSU: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% points800SMBus Data Valid to SMBCLK
Rising-Edge Time4SMBus Stop-Condition Setup Time4SMBus Start-Condition Hold Time500SMBus Repeated Start-Condition
Setup Time4.7SMBus Start-Condition Setup Time
tHD:DAT(Note 6)µs0SMBus Data-Hold Time
Master clocking in dataµs1SMBCLK Falling Edge to SMBus
Data-Valid Time
SMBus INTERFACE
ELECTRICAL CHARACTERISTICS (VCC= +3.3V, TA
= -55°C to +125°C, unless otherwise noted.) (Note 1)
CONDITIONSMonotonicity guaranteed= +60°C to +100°C
Bits8Temperature Resolution (Note 1)2= +60°C to +100°C= -55°C to +125°C°C-33
Initial Temperature Error,
Local Diode (Note 3)3.05.5Supply-Voltage Range
From stop bit to conversion complete (both channels)
Auto-convert mode94125156Conversion Time-2525Conversion Rate Timing Error3= -55°C to +125°C°C
UNITSMINTYPMAX5
PARAMETERTemperature Error, Remote Diode
(Notes 3 and 4)
ADC AND POWER SUPPLY
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX16175k500k50k5M50050M
TEMPERATURE ERROR vs.
POWER-SUPPLY NOISE FREQUENCYMAX1617TOC04
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
TEMPERATURE ERROR
vs. PCB RESISTANCE
MAX1617TOC01
LEAKAGE RESISTANCE (MΩ)
TEMPERATURE ERROR (
PATH = DXP TO VCC (5V)
PATH = DXP TO GND
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX1617TOC02
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
SAMSUNG KST3904
MOTOROLA MMBT3904
ZETEX FMMT3904
RANDOM
SAMPLES
__________________________________________Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
ELECTRICAL CHARACTERISTICS (continued)(VCC= +3.3V, TA
= -55°C to +125°C, unless otherwise noted.) (Note 1)
Note 1:All devices 100% production tested at TA= +85°C. Limits over temperature are guaranteed by design.
Note 2:Guaranteed but not 100% tested.
Note 3:Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1617 device tempera-
ture 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. See
Table 2.
Note 4:A remote diode is any diode-connected transistor from Table 1. TRis the junction temperature of the remote diode. See
Remote Diode Selectionfor remote diode forward voltage requirements.
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.
CONDITIONSUNITSMINTYPMAXPARAMETERSTBY, SMBCLK, SMBDATA2.2Logic Input High VoltageV2.4
STBY, SMBCLK, SMBDATA; VCC= 3V to 5.5VV0.8Logic Input Low Voltage
ALERTforced to 5.5VµA1ALERTOutput High Leakage
Current
Logic inputs forced to VCCor GNDµA-22Logic Input Current
VCC= 3V
VCC= 5.5V
ALERT,SMBDATA forced to 0.4VmA6Logic Output Low Sink Current
SMBus INTERFACE
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX16175k500k50k5M50050M
TEMPERATURE ERROR vs.
COMMON-MODE NOISE FREQUENCYMAX1617TOC05
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = SQUARE WAVE
AC COUPLED TO DXN
VIN = 100mVp-p
VIN = 50mVp-p
VIN = 25mVp-p5k500k50k5M50050M
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCYMAX1617TOC06
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = 10mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
TEMPERATURE ERROR vs.
DXP–DXN CAPACITANCE
MAX1617TOC07
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (°C)
VCC = 5V
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
MAX1617TOC10
CONVERSION RATE (Hz)
SUPPLY CURRENT (
VCC = 5V
AVERAGED MEASUREMENTS100k10k1000k
STANDBY SUPPLY CURRENT
vs. CLOCK FREQUENCYMAX1617TOC08
SMBCLK FREQUENCY (Hz)
SUPPLY CURRENT (
VCC = 5V
VCC = 3.3V
SMBCLK IS
DRIVEN RAIL-TO-RAIL
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX1617TOC09
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
ADD0,
ADD1
= GND
ADD0,
ADD1
= HIGH-Z
T = -2T = 8T = 0T = 4T = 2T = 6T = 10
RESPONSE TO THERMAL SHOCKMAX1617TOC11
TIME (sec)
TEMPERATURE (°C)
16-QSOP IMMERSED
IN +115°C FLUORINERT BATH
____________________________Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)5k500k50k5M50050M
TEMPERATURE ERROR vs.
DIFFERENTIAL-MODE NOISE FREQUENCYMAX1617TOC03
FREQUENCY (Hz)
TEMPERATURE ERROR (°C)
VIN = 3mVp-p SQUARE WAVE
APPLIED TO DXP-DXN
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
______________________________________________________________Pin Description
_______________Detailed DescriptionThe MAX1617 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 MAX1617
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 typical above ground
by an internal diode to set up the analog-to-digital (A/D)
inputs for a differential measurement. The typical
DXP–DXN differential input voltage range is 0.25V to
0.95V. To ensure proper operation over full temperature
range, ensure VDXP≤(0.78 x VCC- 1.1) volts.
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.
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.STBY15
SMBus Address Select pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance
(>50pF) at the address pins when unconnected may cause address-recognition problems.ADD16
GroundGND7, 8
SMBus Slave Address Select pinADD010
SMBus Alert (interrupt) Output, open drainALERT11
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 uncon-
nected; tie DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for
noise filtering.
DXP3
PINSupply 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.VCC2
No Connection. Not internally connected. May be used for PCB trace routing.N.C.1, 5, 9,
13, 16
FUNCTIONNAME
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617Figure 1. Functional Diagram
REMOTE
MUXLOCAL
REMOTE TEMPERATURE
DATA REGISTER
HIGH-TEMPERATURE THRESHOLD
(REMOTE T
HIGH
LOW-TEMPERATURE THRESHOLD
(REMOTE T
LOW
DIGITAL COMPARATOR
(REMOTE)
LOCAL TEMPERATURE
DATA REGISTER
HIGH-TEMPERATURE THRESHOLD
(LOCAL T
HIGH)
LOW-TEMPERATURE THRESHOLD
(LOCAL T
LOW
DIGITAL COMPARATOR
(LOCAL)
COMMAND BYTE
(INDEX) REGISTER
SMBDATA
SMBCLK
ADDRESSDECODERREAD
WRITE
CONTROL
LOGIC
SMBUSADD1
ADD0
STBY
STATUS BYTE REGISTER
CONFIGURATION
BYTE REGISTER
CONVERSION RATE
REGISTER
ALERT RESPONSE
ADDRESS REGISTER
SELECTED VIASLAVE ADD = 0001 100
ADCDIODEFAULT
DXPDXNGND+--8
ALERT
MAX1617
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
A/D Conversion SequenceIf 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 SelectionTemperature accuracy depends on having a good-qual-
ity, diode-connected small-signal transistor. See Table 1
for a recommended list of diode-connected small-signal
transistors. The MAX1617 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 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 (VDXP- VDXN) must be less than 0.95V
at 100µA; additionally, ensure the maximum VDXP(DXP
voltage) ≤(0.78 x VCC- 1.1) volts over your expected
range of temperature. 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 manufac-
turer has good process controls and that the devices
have consistent VBE characteristics.
For heat-sink 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-HeatingThermal mass can seriously degrade the MAX1617’s
effective accuracy. The thermal time constant of the
QSOP-16 package is about 140sec in still air. For the
MAX1617 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 ALERToutput. For example, at an 8Hz rate
and with ALERTsinking 1mA, the typical power dissi-
pation is VCCx 450µA plus 0.4V x 1mA. Package theta
J-A is about 150°C/W, so with VCC= 5V and no copper
PCB heat-sinking, the resulting temperature rise is:
dT = 2.7mW x 150°C/W = 0.4°C
Even with these contrived circumstances, it is difficult
to introduce significant self-heating errors.
ADC Noise FilteringThe ADC is an integrating type with inherently good
noise rejection, especially of low-frequency signals such
as 60Hz/120Hz power-supply hum. Micropower opera-
tion places constraints on high-frequency noise rejec-
tion; therefore, careful PCB 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. 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).
CMPT3904Central Semiconductor (USA)
MMBT3904Motorola (USA)
MMBT3904
SST3904Rohm Semiconductor (Japan)
KST3904-TFSamsung (Korea)
FMMT3904CT-NDZetex (England)
MANUFACTURERMODEL NUMBERSMBT3904Siemens (Germany)
Table 1. Remote-Sensor Transistor
ManufacturersNote: Transistors must be diode-connected (base shorted to
collector).
National Semiconductor (USA)
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617
PCB LayoutPlace the MAX1617 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.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.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 PCB contamination must be dealt with careful-
ly, since a 20MΩleakage path from DXP to ground
causes about +1°C error.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.Route through as few vias and crossunders as possi-
ble to minimize copper/solder thermocouple effects.When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. In general, PCB-induced thermo-
couples 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 ther-
mocouple errors are swamped out.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.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.
PCB Layout ChecklistPlace the MAX1617 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 VCCbypass
capacitors close to the MAX1617.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, 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;series resistance introduces about +1/2°C error.
Low-Power Standby ModeStandby mode disables the ADC and reduces the sup-
ply-current drain to less than 10µA. Enter standby
mode by forcing the STBYpin 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,
MINIMUM
10MILS
Figure 2. Recommended DXP/DXN PC Traces
Remote/Local Temperature Sensor
with SMBus Serial Interface
MAX1617the MAX1617 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 con-
nected to the system SUSTAT# suspend-state signal.
The STBYpin 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). In 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 InterfaceFrom a software perspective, the MAX1617 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 MAX1617 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 twos-com-
plement form for each channel, with each data bit repre-
senting 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.
MAX1617
ACK7 bits
ADDRESSACKWR8 bits
DATAACK8 bits
COMMAND
Write Byte Format
Read Byte Format
Send Byte FormatReceive Byte FormatSlave 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)
ACK7 bits
ADDRESSACKWRSACK8 bits
DATA7 bits
ADDRESSRD8 bits
///PSCOMMANDSlave 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
ACK7 bits
ADDRESSWR8 bits
COMMANDACKPSACK7 bits
ADDRESSRD8 bits
DATA///PSCommand 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 conditionShaded = Slave transmission
P = Stop condition/// = Not acknowledged
Figure 3. SMBus Protocols
