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MAX6648MUA-MAX6692MUA
Precision SMBus-Compatible Remote/Local Temperature Sensors with Overtemperature Alarms
General DescriptionThe MAX6648/MAX6692 are precise, two-channel digi-
tal temperature sensors. They accurately measure the
temperature of their own die and a remote PN junction,
and report the temperature in digital form using a 2-wire
serial interface. The remote PN junction is typically the
emitter-base junction of a common-collector PNP on a
CPU, FPGA, or ASIC.
The 2-wire serial interface accepts standard System
Management Bus (SMBus)™ write byte, read byte,
send byte, and receive byte commands to read the
temperature data and to program the alarm thresholds.
To enhance system reliability, the MAX6648/MAX6692
include an SMBus timeout. A fault queue prevents the
ALERTand OVERToutputs from setting until a fault has
been detected one, two, or three consecutive times
(programmable).
The MAX6648/MAX6692 provide two system alarms:
ALERTand OVERT. ALERTasserts when any of four tem-
perature conditions are violated: local overtemperature,
remote overtemperature, local undertemperature, or
remote undertemperature. OVERTasserts when the tem-
perature rises above the value in either of the two OVERT
limit registers. The OVERToutput can be used to activate
a cooling fan, or to trigger a system shutdown.
Measurements can be done autonomously, with the
conversion rate programmed by the user, or in a single-
shot mode. The adjustable conversion rate allows the
user to optimize supply current and temperature
update rate to match system needs.
Remote accuracy is ±0.8°C maximum error between
+25°C and +125°C with no calibration needed. The
MAX6648/MAX6692 operate from -55°C to +125°C, and
measure temperatures between 0°C and +125°C. The
MAX6648 is available in an 8-pin µMAX package, and the
MAX6692 is available in 8-pin µMAX and SO packages.
ApplicationsDesktop Computers
Notebook Computers
Servers
Thin Clients
Workstations
Test and Measurement
Multichip Modules
FeaturesDual Channel: Measures Remote and Local
Temperature0.125°C ResolutionHigh Accuracy: ±0.8°C (max) from +25°C to
+125°C (Remote), and ±2°C (max) from +60°C to
+100°C (Local)Two Alarm Outputs: ALERTand OVERTTwo Default OVERTThresholds Available
MAX6648: +110°C
MAX6692: +85°CProgrammable Conversion Rate SMBus-Compatible InterfaceSMBus TimeoutProgrammable Under/Overtemperature Alarm
Thresholds
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarms
Ordering Informationypical Operating Circuit19-2545; Rev 1; 10/02
SMBus is a trademark of Intel Corp.
Pin Configuration and Functional Diagram appear at end of
data sheet.
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarms
ABSOLUTE MAXIMUM RATINGSStresses 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.
All Voltages Referenced to GND
VCC...........................................................................-0.3V to +6V
DXP.............................................................-0.3V to (VCC+ 0.3V)
DXN.......................................................................-0.3V to +0.8V
SCLK, SDA, ALERT, OVERT.....................................-0.3V to +6V
SDA, ALERT, OVERTCurrent.............................-1mA to +50mA
DXN Current.......................................................................±1mA
Continuous Power Dissipation (TA= +70°C)
8-Pin µMAX (derate 5.9mW/°C above +70°C).............471mW
8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW
ESD Protection (all pins, Human Body Model)................±2000V
Junction Temperature......................................................+150°C
Operating Temperature Range.........................-55°C to +125°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s).................................+300°C
ELECTRICAL CHARACTERISTICS(VCC= 3.0V to 5.5V, TA= -55°C to +125°C, unless otherwise specified. Typical values are at VCC= 3.3V and TA= +85°C.) (Note 1)
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarms
ELECTRICAL CHARACTERISTICS (continued)(VCC= 3.0V to 5.5V, TA= -55°C to +125°C, unless otherwise specified. Typical values are at VCC= 3.3V and TA= +85°C.) (Note 1)
Note 1:All parameters tested at a single temperature. Specifications over temperature are guaranteed by design.
Note 2:Timing specifications guaranteed by design.
Note 3:The serial interface resets when SCLK is low for more than tTIMEOUT.
Note 4:A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK’s falling edge.
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarms
Typical Operating Characteristics(VCC= 3.3V, TA= +25°C, unless otherwise noted.)
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarms
Detailed DescriptionThe MAX6648/MAX6692 are temperature sensors
designed to work in conjunction with a microprocessor
or other intelligence in thermostatic, process-control, or
monitoring applications. Communication with the
MAX6648/MAX6692 occurs through the SMBus-com-
patible serial interface and dedicated alert pins. ALERT
asserts if the measured local or remote temperature is
greater than the software-programmed ALERThigh
limit or less than the ALERTlow limit. ALERTalso
asserts if the remote-sensing diode pins are shorted or
unconnected. The overtemperature alarm, OVERT,
asserts if the software-programmed OVERTlimit is
exceeded. OVERTcan be connected to fans, a system
shutdown, a clock throttle control, or other thermal-
management circuitry.
The MAX6648/MAX6692 convert temperatures to digital
data either at a programmed rate or in single conver-
sions. Temperature data is represented as 10 bits plus
sign, with the LSB equal to 0.125°C. The “main” tempera-
ture data registers (at addresses 00h and 01h) are 8-bit
registers that represent the data as 7 bits with the final
MSB indicating the diode fault status (Table 1). The
remaining 3 bits of temperature data are available in the
“extended” registers at addresses 11h and 10h (Table 2).
ADC and MultiplexerThe averaging ADC integrates over a 60ms period
(each channel, typically), with 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-
age and compute the temperature based on this volt-
age. Both channels are automatically converted once
the conversion process has started, either in free-run-
ning or single-shot mode. If one of the two channels is
not used, the device still performs both measurements,
and the user can ignore the results of the unused chan-
MAX6648/MAX6692nel. If the remote-diode channel is unused, connect
DXP to DXN rather than leaving the pins open.
The DXN input is biased to one VBEabove ground by
an internal diode to prepare the ADC inputs for a differ-
ential measurement. The worst-case DXP-DXN differen-
tial input voltage range is 0.25V to 0.95V. Excess
resistance in series with the remote diode causes
+0.5°C (typ) 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 autonomous mode (RUN= 0)
or by writing a one-shot command, both channels are
converted, and the results of both measurements are
available after the end of a conversion. A BUSY status bit
in the status byte indicates that the device is performing a
new conversion. The results of the previous conversion
are always available, even if the ADC is busy.
Low-Power Standby ModeStandby mode reduces the supply current to less than
10µA by disabling the ADC and timing circuitry. Enter
standby mode by setting the RUNbit to 1 in the configu-
ration byte register (Table 6). All data is retained in mem-
ory, and the SMBus interface is active and listening for
SMBus commands. Standby mode is not a shutdown
mode. With activity on the SMBus, the device draws more
supply current (see Typical Operating Characteristics). In
standby mode, the MAX6648/MAX6692 can be forced to
perform A/D conversions through the one-shot command,
regardless of the RUNbit status.
If a 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 a tempera-
ture register. The previous data is not changed and
remains available.
Supply-current drain during the 125ms conversion peri-
od is 500µA (typ). Slowing down the conversion rate
reduces the average supply current (see Typical
Operating Characteristics). Between conversions, the
conversion rate timer consumes about 25µA of supply
current. In standby mode, supply current drops to
about 3µA.
SMBus Digital Interface From a software perspective, the MAX6648/MAX6692
appear as a set of byte-wide 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. These devices respond to the
same SMBus slave address for access to all functions.
The MAX6648/MAX6692 employ four standard SMBus
protocols: write byte, read byte, send byte, and receive
byte (Figures 1, 2, and 3). The shorter receive byte proto-
col allows quicker transfers, provided that the correct
data register was previously selected by a read byte
instruction. Use caution when using the shorter protocols
in multimaster systems, as a second master could over-
write the command byte without informing the first master.
Temperature data can be read from the read internal
temperature (00h) and read external temperature (01h)
registers. The temperature data format for these regis-
ters is 7 bits plus 1 bit, indicating the diode fault status
for each channel, with the LSB representing 1°C (Table
1). The MSB is transmitted first.
An additional 3 bits can be read from the read external
extended temperature register (10h), which extends the
data to 10 bits plus sign and the resolution to 0.125°C
per LSB (Table 2). An additional 3 bits can be read
from the read internal extended temperature register
(11h), which extends the data to 10 bits (plus 1 bit indi-
cating the diode fault status) and the resolution to
0.125°C per LSB (Table 2).
When a conversion is complete, the main temperature
register and the extended temperature register are
updated simultaneously. Ensure that no conversions
are completed between reading the main register and
the extended register, so that both registers contain the
result of the same conversion.
To ensure valid extended data, read extended resolu-
tion temperature data using one of the following
approaches:Put the MAX6648/MAX6692 into standby mode by
setting bit 6 of the configuration register to 1. Initiate
a one-shot conversion using command byte 0Fh.
When this conversion is complete, read the contents
of the temperature data registers.
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarms
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature AlarmsIf the MAX6648/MAX6692 are in run mode, read the
status byte. If the BUSY bit indicates that a conversion
is in progress, wait until the conversion is complete
(BUSY bit set to zero) before reading the temperature
data. Following a conversion completion, immediately
read the contents of the temperature data registers. If
no conversion is in progress, the data can be read
within a few microseconds, which is a sufficiently short
period of time to ensure that a new conversion cannot
be completed until after the data has been read.
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarms
Alarm Threshold RegistersFour registers store ALERTthreshold values—one high-
temperature (THIGH) and one low-temperature (TLOW)
register each for the local and remote channels. If
either measured temperature equals or exceeds the
corresponding ALERTthreshold value, the ALERTinter-
rupt asserts.
The power-on-reset (POR) state of both ALERTTHIGH
registers is full scale (0101 0101, or +85°C). The POR
state of both TLOWregisters is 0000 0000, or 0°C.
Two additional registers store remote and local alarm
threshold data corresponding to the OVERToutput. The
values stored in these registers are high-temperature
thresholds. If either of the measured temperatures
equals or exceeds the corresponding alarm threshold
value, an OVERToutput asserts. The POR state of theOVERTthreshold is 0110 1110 or +110°C for the
MAX6648, and 0101 0101 or +85°C for the MAX6692.
Diode Fault AlarmA continuity fault detector at DXP detects an open cir-
cuit between DXP and DXN, or a DXP short to VCC,
GND, or DXN. If an open or short circuit exists, the
external temperature register is loaded with 1000 0000.
If the fault is an open-circuit fault bit 2 (OPEN) of the
status byte, it is set to 1 and the ALERTcondition is
activated at the end of the conversion. Immediately
after POR, the status register indicates that no fault is
present. If a fault is present upon power-up, the fault is
not indicated until the end of the first conversion.
ALERTInterruptsThe ALERTinterrupt occurs when the internal or exter-
nal temperature reading exceeds a high- or low-tem-
perature limit (user programmed) or when the remote
diode is disconnected (for continuity fault detection).
The ALERTinterrupt output signal is latched and can
be cleared only by either reading the status register or
by successfully responding to an alert response
address. In both cases, the alert is cleared only if the
fault condition no longer exists. Asserting ALERTdoes
not halt automatic conversion. The ALERToutput pin is
open drain, allowing multiple devices to share a com-
mon interrupt line.
The MAX6648/MAX6692 respond to the SMBus alert
response address, an interrupt pointer return-address
feature (see the Alert Response Address section). Prior
to taking corrective action, always check to ensure that
an interrupt is valid by reading the current temperature.
Fault Queue Register In some systems, it may be desirable to ignore a single
temperature measurement that falls outside the ALERT
limits. Bits 2 and 3 of the fault queue register (address
22h) determine the number of consecutive temperature
faults necessary to set ALERT(see Tables 3 and 4).
Alert Response AddressThe 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 ALERTinterrupt signal, the
host master can broadcast a receive byte transmission
to the alert response slave address (0001 100).
Following such a broadcast, any slave device that gen-
erated an interrupt attempts to identify itself by putting
its own address on the bus.
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
MAX6648/MAX6692
Precision SMBus-Compatible Remote/Localemperature Sensors with Overtemperature Alarmsrules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledge and continues to hold the ALERTline low
until cleared. (The conditions for clearing an ALERT
vary, depending on the type of slave device).
Successful completion of the read alert response proto-
col clears the interrupt latch, provided the condition
that caused the alert no longer exists.
OVERTOvertemperature Alarm/Warning
OutputsOVERTasserts when the temperature rises to a value
stored in one of the OVERTlimit registers (19h, 20h). It
deasserts when the temperature drops below the
stored limit, minus hysteresis. OVERTcan be used to
activate a cooling fan, send a warning, invoke clock
throttling, or trigger a system shutdown to prevent com-
ponent damage.
Command Byte FunctionsThe 8-bit command byte register (Table 5) is the master
index that points to the various other registers within the
MAX6648/MAX6692. The register’s POR state is 0000
0000, so a receive byte transmission (a protocol that
lacks the command byte) that occurs immediately after
POR, returns the current local temperature data.
The MAX6648/MAX6692 incorporate collision avoid-
ance so that completely asynchronous operation is
allowed between SMBus operations and temperature
conversions.
One-ShotThe one-shot command immediately forces a new con-
version cycle to begin. If the one-shot command is
received while the MAX6648/MAX6692 are in standby
mode (RUNbit = 1), a new conversion begins, after
which the device returns to standby mode. If a one-shot
conversion is in progress when a one-shot command is
received, the command is ignored. If a one-shot com-
mand is received in autonomous mode (RUNbit = 0)
between conversions, a new conversion begins, the
conversion rate timer is reset, and the next automatic
conversion takes place after a full delay elapses.
Configuration Byte FunctionsThe configuration byte register (Table 6) is a read-write
register with several functions. Bit 7 is used to mask (dis-
able) interrupts. Bit 6 puts the MAX6648/MAX6692 into
standby mode (STOP) or autonomous (RUN) mode.
Status Byte FunctionsThe status byte register (Table 7) indicates which (if
any) temperature thresholds have been exceeded. This
byte also indicates whether the ADC is converting and
whether there is an open-circuit fault detected in the
external sense junction. After POR, the normal state of
all flag bits is zero, assuming no alarm conditions are
present. The status byte is cleared by any successful
read of the status byte, after a conversion is complete
and the fault no longer exists. Note that the ALERT
interrupt latch is not automatically cleared when the
status flag bit indicating the ALERT is cleared. The fault
condition must be eliminated before the ALERToutput
can be cleared.
When autoconverting, if the THIGHand TLOWlimits are
close together, it is possible for both high-temp and
low-temp status bits to be set, depending on the
amount of time between status read operations (espe-
cially when converting at the fastest rate). In these cir-
cumstances, it is best not to rely on the status bits to
indicate reversals in long-term temperature changes.
Instead use a current temperature reading to establish
the trend direction.
Conversion Rate ByteThe conversion rate register (Table 8) programs the
time interval between conversions in free-running
autonomous mode (RUN= 0). This variable rate control
can be used to reduce the supply current in portable-
