MAX6680MEE+ ,±1°C Fail-Safe Remote/Local Temperature Sensors with SMBus InterfaceFeaturesThe MAX6680/MAX6681 are precise, two-channel digi-♦ Two Alarm Outputs: ALERT and OVERTtal t ..
MAX6682MUA ,Thermistor-to-Digital ConverterApplications3.3VHVAC0.1μFMedical DevicesBattery Packs/Chargers VCCHome AppliancesR+REXTMAX6682R-Pin ..
MAX6682MUA+ ,Thermistor-to-Digital ConverterFeaturesThe MAX6682 converts an external thermistor’s temper-♦ Converts Thermistor Temperature to D ..
MAX6682MUA+ ,Thermistor-to-Digital ConverterMAX668219-2219; Rev 0; 2/02Thermistor-to-Digital Converter
MAX6682MUA+T ,Thermistor-to-Digital ConverterFeaturesThe MAX6682 converts an external thermistor’s temper-♦ Converts Thermistor Temperature to D ..
MAX6684ESA ,Fan-Failure Detector with Integrated Power SwitchELECTRICAL CHARACTERISTICS(V = 3.0 to 5.5V, OFF = V , T = -40°C to +85°C, unless otherwise noted. T ..
MB3771P ,Power Supply MonitorFUJITSU SEMICONDUCTORDS04-27400-7EDATA SHEETASSP For power supply
MB3771PF ,Power Supply MonitorFUJITSU SEMICONDUCTORDS04-27400-7EDATA SHEETASSP For power supply
MB3771PF. ,Power Supply MonitorapplicationsBIPOLARPower Supply MonitorMB3771nnnn DESCRIPTIONThe Fujitsu MB3771 is designed to moni ..
MB3771PF-G-BND-JNE1 , ASSP For power supply applications BIPOLAR Power Supply Monitor
MB3771PS ,Power Supply MonitorFUJITSU SEMICONDUCTORDS04-27400-7EDATA SHEETASSP For power supply
MB3771PS ,Power Supply MonitorFUJITSU SEMICONDUCTORDS04-27400-7EDATA SHEETASSP For power supply
MAX6680MEE+
±1°C Fail-Safe Remote/Local Temperature Sensors with SMBus Interface
General DescriptionThe MAX6680/MAX6681 are precise, two-channel digi-
tal thermometers. Each accurately measures the tem-
perature of its own die and one remote PN junction and
reports the temperature on a 2-wire serial interface. The
remote junction can be a diode-connected transistor
like the low-cost NPN type 2N3904 or PNP type
2N3906. The remote junction can also be a common-
collector PNP, such as a substrate PNP of a micro-
processor.
The MAX6680/MAX6681 include pin-programmable
default temperature thresholds for the OVERToutput,
which provides fail-safe clock throttling or system shut-
down. In addition, the devices are pin programmable to
select whether the OVERToutput responds to either the
local, remote, or both temperatures.
The 2-wire serial interface accepts standard System
Management Bus (SMBus)™ commands such as Write
Byte, Read Byte, Send Byte, and Receive Byte to read
the temperature data and program the alarm thresholds
and conversion rate. The MAX6680/MAX6681 can func-
tion autonomously with a programmable conversion
rate, which allows the control of supply current and
temperature update rate to match system needs. For
conversion rates of 4Hz or less, the remote sensor tem-
perature can be represented in extended mode as 10
bits + sign with a resolution of 0.125°C. When the con-
version rate is 8Hz, output data is 7 bits + sign with a
resolution of 1°C. The MAX6680/MAX6681 also include
an SMBus timeout feature to enhance system reliability.
The MAX6681 is an upgrade to the MAX6654. The
MAX6680/MAX6681 remote accuracy is ±1°C with no
calibration needed. They are available in a 16-pin
QSOP package and operate throughout the -55°C to
+125°C temperature range.
Applications
FeaturesTwo Alarm Outputs: ALERTand OVERTPin-Programmable Threshold for OVERTLimitProgrammable Under/Overtemperature ALERT
LimitDual Channel: Measures Remote and Local
Temperature11-Bit, 0.125°C Resolution for Remote Temperature
MeasurementsHigh Accuracy ±1°C (max) from +60°C to +100°C
(Remote)No Calibration RequiredSMBus/I2C™-Compatible InterfaceSMBus Timeout Prevents SMBus LockupMAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus InterfaceCLOCK
DATA
TO SYSTEM
SHUTDOWN
STBY
CRIT1CRIT0GND
OVERT
SMBCLK
RESET
SMBDATA
VCC
INTERRUPT
TO µP
0.1µF
2200pF
DXN
MICROPROCESSOR
DXP
200Ω
10kΩ
EACH
ALERT
3.3V
INT_SEL
SENS_SEL
ADD1
ADD0
MAX6680
MAX6681
Typical Operating Circuit
Ordering Information19-2305; Rev 1; 1/05
PARTTEMP RANGEPIN-PACKAGE
MAX6680MEE-55°C to +125°C16 QSOP
MAX6681MEE-55°C to +125°C16 QSOP
SMBus is a trademark of Intel Corp.
I2C is a trademark of Philips Corp.
Pin Configurations appear at end of data sheet.Desktop Computers
Notebook
Computers
Servers
Thin Clients
Workstations
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(Circuit of Typical Operating Circuit, VCC= 3.0V to 5.5V, TA= -25°C to +125°C, unless otherwise specified. Typical values are at VCC
= 3.3V and TA= +25°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.
VCC...........................................................................-0.3V to +6V
DXP.............................................................-0.3V to (VCC+ 0.3V)
DXN ......................................................................-0.3V to +0.8V
SMBCLK, SMBDATA, ALERT, OVERT.....................-0.3V to +6V
RESET, INT_SEL, STBY, ADD0, ADD1.....................-0.3V to +6V
CRIT1, CRIT0, SENS_SEL........................................-0.3V to +6V
SMBDATA, ALERT, OVERT, Current ..................-1mA to +50mA
DXN Current ......................................................................±1mA
Continuous Power Dissipation (TA= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C) ..........664mW
Junction Temperature .....................................................+150°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS1°CTemperature Resolution,
Legacy Mode8Bits
0.125°CTemperature Resolution,
Extended Mode11Bits
TRJ = +60°C to +100°C, VCC = 3.3V-1.0+1.0
TRJ = +50°C to +120°C, VCC = 3.3V-2.0+2.0Rem ote Tem p er atur e E r r or ( N ote 1)
TRJ = -55°C to +125°C, VCC = 3.3V-3.0+3.0
TA = +60°C to +100°C, VCC = 3.3V-1.5+1.5
TA = 0°C to +125°C, VCC = 3.3V-3.0+3.0Local Temperature Error
TA = -55°C to +125°C, VCC = 3.3V (Note 2)-5.0+5.0
Line Regulation3.0V ≤ VCC ≤ 5.5V0.20.6m°C/V
Supply Voltage RangeVCC3.05.5V
Undervoltage Lockout ThresholdUVLOFalling edge of VCC disables ADC2.602.802.95V
Undervoltage Lockout Hysteresis90mV
Power-On Reset (POR)
ThresholdVCC, falling edge1.52.02.5V
POR Threshold Hysteresis90mV
Legacy62.5Conversion TimeExtended125ms
Standby Supply CurrentSMBus static310µA
Operating CurrentDuring conversion0.551.0mA
0.25 conversions/s3570Average Operating Current
(Note 3)2 conversions/s120180µA
DXP and DXN Leakage CurrentIn standby mode2µA
High level80100120Remote-Diode Source CurrentIRJLow level81012µA
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
ELECTRICAL CHARACTERISTICS (continued)(Circuit of Typical Operating Circuit, VCC= 3.0V to 5.5V, TA= -25°C to +125°C, unless otherwise specified. Typical values are at VCC
= 3.3V and TA= +25°C.)
Note 1:TA= +25°C to +85°C.
Note 2:If both the local and the remote junction are below TA= -20°C, then VCC> 3.15V.
Note 3:Conversions done in extended mode. For legacy mode, current is approximately half.
Note 4:Timing specifications guaranteed by design.
Note 5:The serial interface resets when SMBCLK or SMBDATA is low for more than tTIMEOUT.
Note 6:A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling edge.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
CRIT0, CRIT1, ADD0, ADD1, RESET, INT_SEL, SENS_SELLogic Input Low VoltageVIL0.8V
Logic Input High VoltageVIH2.4V
Input Leakage CurrentILEAK-1+1µA
(ALERT, OVERT)Output Low Sink CurrentVOL = 0.4V1mA
Output High Leakage CurrentVOH = 5.5V1µA
SMBus INTERFACE (SMBCLK, SMBDATA, STBY)Logic Input Low VoltageVIL0.8V
VCC = 3.0V2.2Logic Input High VoltageVIHVCC = 5.5V2.4V
Input Leakage CurrentILEAKVIN = GND or VCC±2µA
Output Low Sink CurrentIOLVOL = 0.6V6mA
Input CapacitanceCIN5pF
SMBus-COMPATIBLE TIMING (Note 5)Serial Clock Frequency (Note 5)fSCL100kHz
Bus Free Time Between STOP
and START ConditiontBUF4.7µs
START Condition Setup Time4.7µs
Repeat START Condition Setup
TimetSU:STA90% to 90%50ns
START Condition Hold TimetHD:STA10% of SMBDATA to 90% of SMBCLK4µs
STOP Condition Setup TimetSU:STO90% of SMDCLK to 90% of SMBDATA4µs
Clock Low PeriodtLOW10% to 10%4.7µs
Clock High PeriodtHIGH90% to 90%4µs
Data Setup Time (Note 6)tHD:DAT250ns
Receive SCL/SDA Rise TimetR1µs
Receive SCL/SDA Fall TimetF300ns
Pulse Width of Spike SuppressedtSP050ns
SMBus Timeout (Note 5)SMBDATA low period for interface reset253745ms
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
MAX6680/81 toc01
SUPPLY VOLTAGE (V)
STANDBY SUPPLY CURRENT (
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6680/81 toc02
CONVERSION RATE (Hz)
OPERATING SUPPLY CURRENT (
AVERAGE OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
8Hz IS 1°C
RESOLUTION
MAX6680/81 toc03
TEMPERATURE (°C)
TEMPERATURE ERROR (
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX6680/81 toc04
TEMPERATURE (°C)
TEMPERATURE ERROR (
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
MAX6680/81 toc05
FREQUENCY (Hz)
TEMPERATURE ERROR (10k100
110M100k1k10100M
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCYVIN = 100mV SQUARE WAVE
APPLIED TO VCC WITH NO
0.1µF VCC CAPACITOR
LOCAL
DIODEREMOTE
DIODE
MAX6680/81 toc06
FREQUENCY (Hz)
TEMPERATURE ERROR (
10M1M100k10k1k10010100M
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCYVIN = 100mVP-P SQUARE WAVE
AC-COUPLED TO DXN
MAX6680/81 toc07
FREQUENCY (Hz)
TEMPERATURE ERROR (
10M1M100k10k1k
100100M
TEMPERATURE ERROR
vs. DIFFERENTIAL NOISE FREQUENCYVIN = 10mVP-P SQUARE WAVE
APPLIED TO DXP-DXN
MAX6680/81 toc08
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (8070605040302010
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
Pin Description
PIN
MAX6680MAX6681NAMEFUNCTIONVCC
Supply Voltage Input, 3V to 5.5V. Bypass VCC to GND with a 0.1µF capacitor.
A 200Ω series resistor is recommended, but not required for additional noise
filtering. See the Typical Operating Circuit.
2, 51, 5CRIT1,
CRIT0
Hardware-Programmable Default Alarm Threshold for OVERT Limits. Use Table
4 to set default temperatures.3DXP
Combined Remote-Diode 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.DXNCombined Remote-Diode Current Sink and A/D Negative Input. DXN is
internally biased to one diode drop above ground.6ADD1
SMBus Address Select Pin (Table 9). ADD0 and ADD1 are sampled upon
power-up. Excess capacitance (>50pF) at the address pins when floating may
cause address-recognition problems.7RESETReset Input. Drive RESET high to set all registers to their default values (POR
state). Drive RESET low or leave floating for normal operation.8GNDGroundOVERTOvertemperature Active-Low Output. Open drain.10ADD0SMBus Slave Address Select Pin (see ADD1).11ALERTSMBus Alert (Interrupt) Active-Low Output. Open drain.12SMBDATASMBus Serial-Data Input/Output, Open Drain13INT_SEL
Input. Connect high or leave floating to conform to the standard SMBus ALERT
protocol. See the ALERT Interrupts section. Connect to GND to invoke
comparator mode, where ALERT is asserted whenever any of the temperature
conditions is violated by the remote sensor. In this mode, ALERT can only be
deasserted by the condition returning within the temperature limits by enabling
the mask bit in the Configuration register.14SMBCLKSMBus Serial-Clock Input15STBYInput. Hardware Standby. Connect to ground to place in device in standby.
Supply current drops below 10µA and all registers’ data are maintained.
Input. Selects which temperature sensor (local, remote, or both) activates
OVERT.1616SENS_SEL
High = Remote, Low = Local, Open = Local and Remote
MAX6680/MAX6681
Detailed DescriptionThe MAX6680/MAX6681 are temperature sensors designed
to work in conjunction with a microprocessor or other
intelligence in thermostatic, process-control, or monitoring
applications. Communication with the MAX6680/MAX6681
occurs through the SMBus serial interface and dedicated
alert pin. The overtemperature alarm OVERTis asserted if
the software or hardware programmed temperature thresh-
olds are exceeded. OVERTcan be connected to a fan,
system shutdown, or other thermal management circuitry.
The MAX6680/MAX6681 convert temperatures at a pro-
grammed rate or a single conversion. Legacy mode
conversions have a 1°C resolution. Legacy resolution
represents temperature as 7 bits + sign bit and allows
for faster autonomous conversion rates at 8Hz. The
remote diode temperature can also be represented in
extended-resolution mode. Extended resolution repre-
sents temperature as 10 bits + sign bit and is available
for autonomous conversions that are 4Hz or slower and
single-shot conversions.
The MAX6680/MAX66681 default low-temperature mea-
surement limit is 0 °C. The device temperature measure-
ment can be placed in extended temperature range by
setting bit 3 of the Configuration register to 1. In extend-
ed temperature range, the remote and local temperature
measurement range is extended down to -64°C.
ADC and MultiplexerThe averaging ADC integrates over a 60ms period
(each channel, typically, in the 7-bit + sign “legacy”
mode). Using an averaging ADC attains excellent noise
rejection.
The multiplexer automatically steers bias currents
through the remote and local diodes. The ADC and
associated circuitry measure each diode’s forward volt-
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus InterfaceRESET
CIRCUITRY
MUX
REMOTE
LOCAL
ADC
CONTROL
LOGIC
SMBus
READ
WRITE
ADDRESS
DECODERQ
DIODE
FAULT
DXP
DXN
ADD0
SMBCLK
SMBDATA
ADD1
REGISTER BANK
COMMAND BYTE
REMOTE TEMPERATURE
LOCAL TEMPERATURE
ALERT THRESHOLD
ALERT RESPONSE ADDRESS
OVERT THRESHOLD (EXT)
OVERT THRESHOLD (INT)CRIT0
CRIT1
INT_SEL
STBY
RESETVCCQ
OVERT
ALERT
SENS_SEL
MAX6680
MAX6681
Figure 1. MAX6680/MAX6681 Functional Diagram
age and computes the temperature based on this volt-
age. If the remote channel is not used, connect DXP to
DXN.
Do not leave DXP and DXN unconnected.When a conversion is initiated, both channels are con-
verted whether or not they are used. The DXN input is
biased at one VBEabove ground by an internal diode
to set up the ADC inputs for a differential measurement.
Resistance in series with the remote diode causes
about 1/2°C error per ohm.
A/D Conversion SequenceA conversion sequence consists of a local temperature
measurement and a remote temperature measurement.
Each time a conversion begins, whether initiated auto-
matically in the free-running autoconvert mode
(RUN/STOP = 0) or by writing a One-Shot command,
both channels are converted, and the results of both
measurements are available after the end of conver-
sion. A BUSY status bit in the Status register shows that
the device is actually performing a new conversion. The
results of the previous conversion sequence are still
available when the ADC is busy.
Remote-Diode SelectionThe MAX6680/MAX6681 can directly measure the die
temperature of CPUs and other ICs that have on-board
temperature-sensing diodes (see the Typical Operating
Circuit) or they can measure the temperature of a dis-
crete diode-connected transistor. The type of remote
diode used is set by bit 5 of the Configuration Byte. If
bit 5 is set to zero, the remote sensor is a diode-con-
nected transistor, and if bit 5 is set to 1, the remote sen-
sor is a substrate or common-collector PNP transistor.
For best accuracy, the discrete transistor should be a
small-signal device with its collector and base connect-
ed together. Accuracy has been experimentally verified
for all of the devices listed in Table 1.
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 at
the highest expected temperature must be greater than
0.25V at 10µA, and at the lowest expected tempera-
ture, forward voltage must be less than 0.95V at 100µA.
Large power transistors must not be used. Also, ensure
that the base resistance is less than 100Ω. Tight speci-
fications for forward-current gain (50 < ß < 150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
VBEcharacteristics.
Thermal Mass and Self-HeatingWhen sensing local temperature, these temperature
sensors are intended to measure the temperature of the
PC board to which they are soldered. The leads pro-
vide a good thermal path between the PC board traces
and the die. Thermal conductivity between the die and
the ambient air is poor by comparison, making air-tem-
perature measurements impractical. Because the ther-
mal mass of the PC board is far greater than that of the
MAX6680/MAX6681, the device follows temperature
changes on the PC board with little or no perceivable
delay.
When measuring the temperature of a CPU or other IC
with an on-chip sense junction, thermal mass has virtu-
ally no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sen-
sors, smaller packages (e.g., a SOT23) yield the best
thermal response times. Take care to account for ther-
mal 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 autoconverting at the
fastest rate and simultaneously sinking maximum cur-
rent at the ALERToutput. For example, with VCC=
5.0V, an 8Hz conversion rate, and ALERTsinking 1mA,
the typical power dissipation is VCC✕550µA + 0.4V ✕
1mA, which equals 2.75mW; θJ-Afor the 16-pin QSOP
package is about +120°C/W, so assuming no copper
PC board heat sinking, the resulting temperature rise is:
Even under these engineered circumstances, it is diffi-
cult to introduce significant self-heating errors.
ADC Noise FilteringThe integrating ADC used has good noise rejection for
low-frequency signals such as 60Hz/120Hz power-sup-
∆TmWCWC=×°=°2751200330./.
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
MANUFACTURERMODEL NO.Central Semiconductor (USA)CMPT3904
On Semiconductor (USA)2N3904, 2N3906
Rohm Semiconductor (USA)SST3904
Samsung (Korea)KST3904-TF
Siemens (Germany)SMBT3904
Zetex (England)FMMT3904CT-ND
Table 1. Remote-Sensor Transistor
Manufacturers
Note:Transistors must be diode connected (base shorted to
collector).
MAX6680/MAX6681ply hum. In noisy environments, high-frequency noise
reduction is needed for high-accuracy remote mea-
surements. The noise can be reduced with careful PC
board layout and proper external noise filtering.
High-frequency EMI is best filtered at DXP and DXN
with an external 2200pF capacitor. Larger capacitor
values can be used for added filtering, but do not
exceed 3300pF because it can introduce errors due to
the rise time of the switched current source.
PC Board LayoutFollow these guidelines to reduce the measurement
error of the temperature sensors:Place the MAX6680/MAX6681 as close as is practi-
cal to the remote diode. In noisy environments, such
as a computer motherboard, this distance can be
4in to 8in (typ). This length can be increased if the
worst noise sources are avoided. Noise sources
include CRTs, clock generators, memory buses, and
ISA/PCI buses.Do not route the DXP-DXN lines next to the deflec-
tion coils of a CRT. Also, do not route the traces
across fast digital signals, which can easily intro-
duce 30°C error, even with good filtering.Route the DXP and DXN traces in parallel and in
close proximity to each other, away from any higher
voltage traces, such as 12VDC. Leakage currents
from PC board contamination must be dealt with care-
fully since a 20MΩleakage path from DXP to ground
causes about 1°C error. If high-voltage traces are
unavoidable, connect guard traces to GND on either
side of the DXP-DXN traces (Figure 2).Route through as few vias and crossunders as pos-
sible to minimize copper/solder thermocouple
effects.When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. 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. Adding a few thermocouples causes a negligi-
ble error.Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10mil widths
and spacings that are recommended in Figure 2 are
not absolutely necessary, as they offer only a minor
improvement in leakage and noise over narrow
traces. Use wider traces when practical.Add a 200Ωresistor in series with VCCfor best noise
filtering (see the Typical Operating Circuit).
Twisted-Pair and Shielded CablesUse a twisted-pair cable to connect the remote sensor
for remote-sensor distances longer than 8in or in very
noisy environments. Twisted-pair cable lengths can be
between 6ft and 12ft before noise introduces excessive
errors. For longer distances, the best solution is a
shielded twisted pair like that used for audio micro-
phones. For example, Belden 8451 works well for dis-
tances up to 100ft in a noisy environment. At the
device, connect the twisted pair to DXP and DXN and
the shield to GND. Leave the shield unconnected at the
remote sensor.
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.
For every 1Ωof series resistance, the error is approxi-
mately 1/2°C error.
Low-Power Standby ModeStandby mode reduces the supply current to less than
10µA by disabling the ADC. Enter hardware standby by
forcing the STBYpin low, or enter software standby by
setting the RUN/STOP bit to 1 in the Configuration Byte
register. Hardware and software standbys are very sim-
ilar: all data is retained in memory, and the SMB inter-
face is alive and listening for SMBus commands, but
the SMBus timeout is disabled. The only difference is
that in software standby mode, the One-Shot command
initiates a conversion. With hardware standby, the One-
Shot command is ignored. Activity on the SMBus caus-
es the device to draw extra supply current (see the
Typical Operating Characteristics).
Driving the STBYpin low overrides any software con-
version command. If a hardware or software standby
command is received while a conversion is in progress,
the conversion cycle is interrupted, and the tempera-
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus InterfaceMINIMUM
10mils
10mils
10mils
10mils
GND
DXN
DXP
GND
Figure 2. Recommended DXP-DXN PC Traces
ture registers are not updated. The previous data is not
changed and remains available.
SMBus Digital Interface From a software perspective, the MAX6680/MAX6681
appear as a series of 8-bit registers that contain tem-
perature data, alarm threshold values, and control bits.
A standard SMBus-compatible 2-wire serial interface is
used to read temperature data and write control bits
and alarm threshold data. The device responds to the
same SMBus slave address for access to all functions.
The MAX6680/MAX6681 employ four standard SMBus
protocols: Write Byte, Read Byte, Send Byte, and
Receive Byte (Figure 3). The shorter Receive Byte pro-
tocol allows quicker transfers, provided that the correct
data register was previously selected by a Read Byte
instruction. Use caution with the shorter protocols in
multimaster systems, since a second master could
overwrite the command byte without informing the first
master.
When the conversion rate is 8Hz, temperature data can
be read from the Read Internal Temperature (00h) and
Read External Temperature (01h) registers. The tem-
perature data format in these registers is 7 bits + sign
in two’s-complement form for each channel, with the
LSB representing 1°C (Table 2). The MSB is transmitted
first. Extended range extends the temperature data
range of the local and remote sensor to -64°C. Extended
range is activated by setting bit 3 of the Configuration
register to 1.
When the conversion rate is 4Hz or less, temperature
data can be read from the Read Internal Temperature
(00h) and Read External Temperature (01h) registers,
the same as for faster conversion rates. An additional 3
bits can be read from the Read External Extended
Temperature (10h), which extends the remote tempera-
ture data to 10 bits + sign and the resolution to 0.125°C
per LSB (Table 3).
When a conversion is complete, the Main register and
the Extended register are updated almost simultane-
ously. Ensure that no conversions are completed
between reading the Main and Extended registers so
that when data that is read by both registers contain
the result of the same conversion.
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
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
///PCOMMANDSlave 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
COMMANDACKPACK7 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
