MAXIM MAX6680MEE

19-2305; Rev 0; 4/02
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
The MAX6680/MAX6681 include pin-programmable
default temperature thresholds for the OVERT output,
which provides fail-safe clock throttling or system shutdown. In addition, the devices are pin programmable to
select whether the OVERT output 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 function 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 temperature can be represented in extended mode as 10
bits + sign with a resolution of 0.125°C. When the conversion 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.
Features
♦ Two Alarm Outputs: ALERT and OVERT
♦ Pin-Programmable Threshold for OVERT Limit
♦ Programmable Under/Overtemperature ALERT
Limit
♦ Dual Channel: Measures Remote and Local
Temperature
♦ 11-Bit, 0.125°C Resolution for Remote Temperature
Measurements
♦ High Accuracy ±1°C (max) from +60°C to +100°C
(Remote)
♦ No Calibration Required
♦ SMBus/I2C™-Compatible Interface
♦ SMBus Timeout Prevents SMBus Lockup
Ordering Information
PART
TEMP RANGE
MAX6680MEE
-55°C to +125°C
16 QSOP
MAX6681MEE
-55°C to +125°C
16 QSOP
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.
PIN-PACKAGE
Typical Operating Circuit
0.1µF
200Ω
3.3V
Applications
Desktop Computers
10kΩ
EACH
Notebook
Computers
DXP
Servers
DXN
VCC STBY
SMBDATA
SMBCLK
DATA
CLOCK
2200pF
Thin Clients
MAX6680
MAX6681
Workstations
MICROPROCESSOR
Pin Configurations appear at end of data sheet.
ALERT
SENS_SEL
RESET
INT_SEL
OVERT
ADD0
ADD1 GND CRIT0
INTERRUPT
TO µP
TO SYSTEM
SHUTDOWN
CRIT1
SMBus is a trademark of Intel Corp.
I2C is a trademark of Philips Corp.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX6680/MAX6681
General Description
The MAX6680/MAX6681 are precise, two-channel digital thermometers. Each accurately measures the temperature 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 commoncollector PNP, such as a substrate PNP of a microprocessor.
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
ABSOLUTE MAXIMUM RATINGS
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
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
Temperature Resolution,
Legacy Mode
1
Temperature Resolution,
Extended Mode
0.125
TRJ = +60°C to +100°C, VCC = 3.3V
Remote Temperature Error (Note 1)
Local Temperature Error
Supply Voltage Range
Undervoltage Lockout Threshold
°C
11
Bits
°C
+1.0
TRJ = +50°C to +120°C, VCC = 3.3V
-2.0
+2.0
-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
+3.0
TA = -55°C to +125°C, VCC = 3.3V (Note 2)
-5.0
+5.0
2.60
Undervoltage Lockout Hysteresis
VCC, falling edge
1.5
POR Threshold Hysteresis
m°C/V
5.5
V
2.80
2.95
V
mV
2.5
V
2.0
90
Conversion Time
Legacy
62.5
Extended
125
mV
ms
Standby Supply Current
SMBus static
Operating Current
During conversion
Average Operating Current
(Note 3)
0.25 conversions/s
35
70
2 conversions/s
120
180
DXP and DXN Leakage Current
In standby mode
Remote-Diode Source Current
2
IRJ
°C
0.6
90
Power-On Reset (POR)
Threshold
°C
0.2
3.0
Falling edge of VCC disables ADC
UNITS
Bits
TRJ = -55°C to +125°C, VCC = 3.3V
VCC
UVLO
MAX
8
-1.0
3.0V ≤ VCC ≤ 5.5V
Line Regulation
TYP
3
10
µA
0.55
1.0
mA
2
High level
80
100
120
Low level
8
10
12
_______________________________________________________________________________________
µA
µA
µA
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
(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.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
0.8
V
+1
µA
CRIT0, CRIT1, ADD0, ADD1, RESET, INT_SEL, SENS_SEL
Logic Input Low Voltage
VIL
Logic Input High Voltage
VIH
2.4
ILEAK
-1
Input Leakage Current
V
(ALERT, OVERT)
Output Low Sink Current
VOL = 0.4V
1
mA
Output High Leakage Current
VOH = 5.5V
1
µA
0.8
V
SMBus INTERFACE (SMBCLK, SMBDATA, STBY)
Logic Input Low Voltage
Logic Input High Voltage
Input Leakage Current
VIL
VIH
ILEAK
Output Low Sink Current
IOL
Input Capacitance
CIN
VCC = 3.0V
2.2
VCC = 5.5V
2.4
V
VIN = GND or VCC
VOL = 0.6V
µA
6
mA
5
SMBus-COMPATIBLE TIMING (Note 5)
Serial Clock Frequency (Note 5)
fSCL
Bus Free Time Between STOP
and START Condition
±2
pF
100
tBUF
START Condition Setup Time
kHz
4.7
µs
4.7
µs
Repeat START Condition Setup
Time
tSU:STA
90% to 90%
50
ns
START Condition Hold Time
tHD:STA
10% of SMBDATA to 90% of SMBCLK
4
µs
STOP Condition Setup Time
tSU:STO
90% of SMDCLK to 90% of SMBDATA
4
Clock Low Period
tLOW
10% to 10%
Clock High Period
tHIGH
90% to 90%
Data Setup Time (Note 6)
tHD:DAT
µs
4.7
µs
4
µs
250
ns
Receive SCL/SDA Rise Time
tR
1
µs
Receive SCL/SDA Fall Time
tF
300
ns
Pulse Width of Spike Suppressed
SMBus Timeout (Note 5)
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
tSP
0
SMBDATA low period for interface reset
25
37
50
ns
45
ms
TA = +25°C to +85°C.
If both the local and the remote junction are below TA = -20°C, then VCC > 3.15V.
Conversions done in extended mode. For legacy mode, current is approximately half.
Timing specifications guaranteed by design.
The serial interface resets when SMBCLK or SMBDATA is low for more than tTIMEOUT.
A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling edge.
_______________________________________________________________________________________
3
MAX6680/MAX6681
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
7
6
5
4
3
2
8Hz IS 1°C
RESOLUTION
500
400
300
200
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
3
MAX6680/81 toc03
8
600
MAX6680/81 toc02
STANDBY SUPPLY CURRENT (µA)
9
OPERATING SUPPLY CURRENT (µA)
MAX6680/81 toc01
10
AVERAGE OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
2
TEMPERATURE ERROR (°C)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
1
0
-1
100
-2
0
-3
SUPPLY VOLTAGE (V)
8.0000
5.5
4.0000
5.0
2.0000
4.5
1.0000
4.0
0.5000
3.5
0.2500
3.0
0.0625
0
0.1250
1
-50
-25
0
25
50
75
100 125 150
TEMPERATURE (°C)
CONVERSION RATE (Hz)
1
0
-1
-2
0.8
0.6
LOCAL
DIODE
REMOTE
DIODE
0.4
0.2
0
-3
0
50
150
100
10
100
1k
10k 100k 1M 10M 100M
1
0
1
10
100
1k
1
VIN = 10mVP-P SQUARE WAVE
APPLIED TO DXP-DXN
MAX6680/81 toc08
1
0
TEMPERATURE ERROR (°C)
2
-1
-2
-3
-4
-1
-5
100
1k
10k
100k
1M
FREQUENCY (Hz)
10M
100M
10k 100k 1M 10M 100M
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6680/81 toc07
3
TEMPERATURE ERROR (°C)
2
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DIFFERENTIAL NOISE FREQUENCY
4
3
-2
1
TEMPERATURE (°C)
0
VIN = 100mVP-P SQUARE WAVE
AC-COUPLED TO DXN
4
-1
-0.2
-50
5
MAX6680/81 toc06
VIN = 100mV SQUARE WAVE
APPLIED TO VCC WITH NO
0.1µF VCC CAPACITOR
1.0
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
MAX6680/81 toc05
2
1.2
TEMPERATURE ERROR (°C)
MAX6680/81 toc04
3
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
TEMPERATURE ERROR (°C)
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
TEMPERATURE ERROR (°C)
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
0
10 20 30 40 50 60 70 80 90 100
DXP-DXN CAPACITANCE (nF)
_______________________________________________________________________________________
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
PIN
NAME
MAX6680
MAX6681
1
2
VCC
2, 5
1, 5
CRIT1,
CRIT0
FUNCTION
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.
Hardware-Programmable Default Alarm Threshold for OVERT Limits. Use Table
4 to set default temperatures.
3
3
DXP
Combined Remote-Diode Current Source and A/D Positive Input for RemoteDiode Channel. DO NOT LEAVE DXP FLOATING; connect DXP to DXN if no
remote diode is used. Place a 2200pF capacitor between DXP and DXN for
noise filtering.
4
4
DXN
Combined Remote-Diode Current Sink and A/D Negative Input. DXN is
internally biased to one diode drop above ground.
6
6
ADD1
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.
7
7
RESET
Reset Input. Drive RESET high to set all registers to their default values (POR
state). Drive RESET low or leave floating for normal operation.
8
8
GND
Ground
9
9
OVERT
10
10
ADD0
SMBus Slave Address Select Pin (see ADD1).
11
11
ALERT
SMBus Alert (Interrupt) Active-Low Output. Open drain.
12
12
SMBDATA
Overtemperature Active-Low Output. Open drain.
SMBus Serial-Data Input/Output, Open Drain
13
13
INT_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.
14
14
SMBCLK
SMBus Serial-Clock Input
15
15
STBY
16
16
SENS_SEL
Input. 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.
High = Local, Low = Remote, Open = Local and Remote
_______________________________________________________________________________________
5
MAX6680/MAX6681
Pin Description
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
VCC
RESET
RESET
CIRCUITRY
MAX6680
MAX6681
2
DXP
MUX
REMOTE
DXN
SENS_SEL
CONTROL
LOGIC
ADC
STBY
INT_SEL
LOCAL
DIODE
FAULT
SMBus
ALERT
S
Q
8
READ
SMBDATA
8
WRITE
SMBCLK
R
REGISTER BANK
7
COMMAND BYTE
ADD0
REMOTE TEMPERATURE
OVERT
S
LOCAL TEMPERATURE
R
ALERT THRESHOLD
Q
ADDRESS
DECODER
ADD1
ALERT RESPONSE ADDRESS
OVERT THRESHOLD (EXT)
OVERT THRESHOLD (INT)
CRIT0
CRIT1
Figure 1. MAX6680/MAX6681 Functional Diagram
Detailed Description
The 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 OVERT is asserted if
the software or hardware programmed temperature thresholds are exceeded. OVERT can be connected to a fan,
system shutdown, or other thermal management circuitry.
The MAX6680/MAX6681 convert temperatures at a programmed 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 repre6
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 measurement limit is 0 °C. The device temperature measurement can be placed in extended temperature range by
setting bit 3 of the Configuration register to 1. In extended temperature range, the remote and local temperature
measurement range is extended down to -64°C.
ADC and Multiplexer
The 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 Interface
A/D Conversion Sequence
A conversion sequence consists of a local temperature
measurement and a remote temperature measurement.
Each time a conversion begins, whether initiated automatically 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 conversion. 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 Selection
The 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 discrete 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-connected transistor, and if bit 5 is set to 1, the remote sensor 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 connected 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 relatively 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 temperature, 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 specifications for forward-current gain (50 < ß < 150, for
example) indicate that the manufacturer has good
process controls and that the devices have consistent
VBE characteristics.
Thermal Mass and Self-Heating
When sensing local temperature, these temperature
sensors are intended to measure the temperature of the
PC board to which they are soldered. The leads pro-
Table 1. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
Central Semiconductor (USA)
On Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
Siemens (Germany)
Zetex (England)
MODEL NO.
CMPT3904
2N3904, 2N3906
SST3904
KST3904-TF
SMBT3904
FMMT3904CT-ND
Note: Transistors must be diode connected (base shorted to
collector).
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-temperature measurements impractical. Because the thermal 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 virtually no effect; the measured temperature of the junction
tracks the actual temperature within a conversion cycle.
When measuring temperature with discrete remote sensors, smaller packages (e.g., a SOT23) yield the best
thermal response times. 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 autoconverting at the
fastest rate and simultaneously sinking maximum current at the ALERT output. For example, with V CC =
5.0V, an 8Hz conversion rate, and ALERT sinking 1mA,
the typical power dissipation is VCC ✕ 550µA + 0.4V ✕
1mA, which equals 2.75mW; θJ-A for the 16-pin QSOP
package is about +120°C/W, so assuming no copper
PC board heat sinking, the resulting temperature rise is:
∆T = 2.75mW × 120°C / W = 0.330°C
Even under these engineered circumstances, it is difficult to introduce significant self-heating errors.
ADC Noise Filtering
The integrating ADC used has good noise rejection for
low-frequency signals such as 60Hz/120Hz power-sup-
_______________________________________________________________________________________
7
MAX6680/MAX6681
age and computes the temperature based on this voltage. 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 converted whether or not they are used. The DXN input is
biased at one VBE above 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.
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
ply hum. In noisy environments, high-frequency noise
reduction is needed for high-accuracy remote measurements. 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 Layout
Follow these guidelines to reduce the measurement
error of the temperature sensors:
1) Place the MAX6680/MAX6681 as close as is practical 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.
2) Do not route the DXP-DXN lines next to the deflection coils of a CRT. Also, do not route the traces
across fast digital signals, which can easily introduce 30°C error, even with good filtering.
3) 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 carefully since a 20MΩ leakage 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).
4) Route through as few vias and crossunders as possible to minimize copper/solder thermocouple
effects.
5) 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 negligible error.
6) 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.
7) Add a 200Ω resistor in series with VCC for best noise
filtering (see the Typical Operating Circuit).
8
GND
10mils
10mils
DXP
10mils
DXN
MINIMUM
10mils
GND
Figure 2. Recommended DXP-DXN PC Traces
Twisted-Pair and Shielded Cables
Use 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 microphones. For example, Belden 8451 works well for distances 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 capacitance 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 1Ω of series resistance, the error is approximately 1/2°C error.
Low-Power Standby Mode
Standby mode reduces the supply current to less than
10µA by disabling the ADC. Enter hardware standby by
forcing the STBY pin low, or enter software standby by
setting the RUN/STOP bit to 1 in the Configuration Byte
register. Hardware and software standbys are very similar: all data is retained in memory, and the SMB interface 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 OneShot command is ignored. Activity on the SMBus causes the device to draw extra supply current (see the
Typical Operating Characteristics).
Driving the STBY pin low overrides any software conversion 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 Interface
MAX6680/MAX6681
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
7 bits
ACK
DATA
8 bits
Slave Address: equivalent to chip-select line of
a 3-wire interface
ACK
P
8 bits
Command Byte: selects which
register you are writing to
1
Data Byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Read Byte Format
ADDRESS
WR
ACK
7 bits
COMMAND
ACK
RD
ACK
7 bits
Command Byte: selects
which register you are
reading from
Send Byte Format
DATA
///
P
8 bits
Slave Address: repeated
due to change in dataflow direction
Data Byte: reads from
the register set by the
command byte
Receive Byte Format
WR
7 bits
ACK
COMMAND
ACK
P
8 bits
Command Byte: sends command with no data, usually
used for one-shot command
S = Start condition
P = Stop condition
ADDRESS
8 bits
Slave Address: equivalent to chip-select line
ADDRESS
S
Shaded = Slave transmission
/// = Not acknowledged
S
ADDRESS
7 bits
RD
ACK
DATA
///
P
8 bits
Data Byte: reads data from
the register commanded
by the last Read Byte or
Write Byte transmission;
also used for SMBus Alert
Response return address
Figure 3. SMBus Protocols
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 temperature 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 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
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 temperature 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 simultaneously. 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.
_______________________________________________________________________________________
9
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
To ensure valid extended data, read extended resolution temperature data using one of the following
approaches:
1) Put the MAX6680/MAX6681 into standby mode by
setting bit 6 of the Configuration register to 1. Initiate
a one-shot conversion using Send Byte command
0Fh. When this conversion is complete, read the
contents of the temperature data registers.
2) If the MAX6680/MAX6681 are in run mode, read the
Status register. If a conversion is in progress, the
BUSY bit is set to 1. Wait for the conversion to complete as indicated by the BUSY bit being set to zero,
then read the temperature data registers.
Diode Fault Alarm
There is a continuity fault detector at DXP that detects
an open circuit 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. Additionally, if the fault is an open circuit, bit 2
(OPEN) of the Status byte is set to 1 and the ALERT
condition is activated at the end of the conversion.
Immediately after power-on reset, the Status register
indicates that no fault is present until the end of the first
conversion.
Alarm Threshold Registers
Four registers store ALERT threshold values—one hightemperature (THIGH) and one low-temperature (TLOW)
register each for the local and remote channels. If
either measured temperature equals or exceeds the
corresponding ALERT threshold value, the ALERT output is asserted.
The POR state of both ALERT THIGH registers is 0111
1111 or +127°C and the POR state of TLOW registers is
1100 1001 or -55°C.
Two additional registers, RWOE and RWOI, store
remote and local alarm threshold data information corresponding to the OVERT output (see the OVERT
Overtemperature Alarm section).
ALERT
The ALERT output operates in two modes—the typical
interrupt mode and comparator mode. The INT_SEL
input determines the mode. When INT_SEL is connected to VCC high, using a weak pullup resistor, or left
floating, the ALERT functions in the interrupt mode.
ALERT Interrupt Mode
An ALERT interrupt occurs when the internal or external
temperature reading exceeds a high or low temperature limit (user programmed) or when the remote diode
is disconnected (for continuity fault detection). The
10
ALERT interrupt 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 even if the fault condition still exists, but is reasserted at the end of the next
conversion. The interrupt does not halt automatic conversions. The interrupt output pin is open drain so that
multiple devices can share a common interrupt line.
The interrupt rate never exceeds the conversion rate.
Comparator Mode
Connecting INT_SEL to ground operates the ALERT
output in comparator mode. In the comparator mode,
whenever the temperature of the remote or local temp
sensor goes outside the limits set by THIGH or TLOW,
the ALERT output becomes inactive after the tempera-
Table 2. Data Format (Two’s Complement)
TEMP (°C)
LEGACY MODE
DIGITAL OUTPUT
EXTENDED
RANGE
DIGITAL OUTPUT
127.00
0111 1111
0111 1111
25
0001 1001
0001 1001
1
0000 0001
0000 0001
0.00
0000 0000
0000 0000
-1
0000 0000
1111 1111
-25
0000 0000
1110 0111
-64
0000 0000
1000 0000
Diode Fault
(Short or
Open)
1000 0000
1000 0000
Table 3. Extended Resolution Register
FRACTIONAL
TEMPERATURE
CONTENTS OF
EXTENDED REGISTER
0.000
000X XXXX
0.125
001X XXXX
0.250
010X XXXX
0.375
011X XXXX
0.500
100X XXXX
0.625
101X XXXX
0.750
110X XXXX
0.875
111X XXXX
Note: Extended mode applies only for conversion rates of 4Hz
and slower.
______________________________________________________________________________________
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
tLOW
B
tHIGH
C
D
E
F
G
I
H
J
K
L
MAX6680/MAX6681
A
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
tHD:DAT
tSU:STO tBUF
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
I = MASTER PULLS DATA LINE LOW
Figure 4. SMBus Write Timing Diagram
A
tLOW
B
tHIGH
C
D
E
F
G
H
I
J
K
L
M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
tSU:DAT
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
E = SLAVE PULLS SMBDATA LINE LOW
tHD:DAT
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO MASTER
H = LSB OF DATA CLOCKED INTO MASTER
I = MASTER PULLS DATA LINE LOW
tSU:STO tBUF
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 5. SMBus Read Timing Diagram
ture returns within the limits. An open diode also sets
this output.
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 (see the Slave
Addresses section). Then, any slave device that generated an interrupt, attempts to identify itself by putting its
own address on the bus (Table 4).
The Alert Response can activate several different slave
devices simultaneously, similar to the I2C General Call.
If more than one slave attempts to respond, bus arbitration rules apply, and the device with the lower address
code wins. The losing device does not generate an
acknowledge and continues to hold the ALERT line low
until cleared. (The conditions for clearing an alert vary
______________________________________________________________________________________
11
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
depending on the type of slave device.) Successful
completion of the Alert Response protocol clears the
interrupt latch, provided the condition that caused the
alert no longer exists. If the condition still exists, the
device reasserts the ALERT interrupt at the end of the
next conversion.
OVERT Overtemperature Alarm
Two registers, RWOE and RWOI, store remote and local
alarm threshold data corresponding to the OVERT output. The values stored in these registers are high-temperature thresholds. If any one of the measured
temperatures equals or exceeds the corresponding
alarm threshold value, an OVERT output is asserted.
The overtemperature thresholds are both hardware and
software programmable. The overtemperature thresholds can be hardware programmed by pin strapping
CRIT0 and CRIT1. Use Table 4 to set the desired
remote and local threshold temperatures. Upon POR or
driving the RESET pin high, the Overtemperature register takes on the hardware-programmed values.
Afterward, any write to the Overtemperature registers
overwrites the hardware-programmable values.
OVERT always operates in comparator mode and is
asserted when the temperature rises to a value programmed in the appropriate threshold register. It is
deasserted when the temperature drops below this
threshold minus the programmed value in the Hysteresis
(HYST) register. An OVERT output can be used to activate a cooling fan, send a warning, initiate clock throttling, or trigger a system shutdown to prevent component
damage. The HYST byte sets the amount of hysteresis
to deassert the OVERT output. The data format for the
HYST byte is 7 bits + sign with 1°C resolution. Bit 7 of
the HYST register should always be zero.
Command Byte Functions
The 8-bit Command Byte register (Table 5) is the master index that points to the various other registers within
the MAX6680/MAX6681. This register’s POR state is
0000 0000, so a Receive Byte transmission (a protocol
that lacks the command byte) occurring immediately
after POR returns the current local temperature data.
One Shot
The One-Shot command immediately forces a new conversion cycle to begin. If the One-Shot command is
received when the MAX6680/MAX6681 is in software
standby mode (RUN/STOP bit = 1), 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 autoconvert mode (RUN/STOP
12
Table 4. OVERT Temperature Threshold
Programming
OVERT THRESHOLD (°C)
CRIT1
CRIT0
GND
VCC
GND
Open
+90
+75
GND
VCC
+95
+80
+85
REMOTE
LOCAL
+85
+70
Open
GND
+100
Open
Open
+105
+90
Open
VCC
+110
+95
VCC
GND
+115
+100
VCC
Open
+120
+105
VCC
VCC
+125
+110
bit = 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 Functions
The Configuration Byte register, Table 6, is a read-write
register with several functions. Bit 7 is used to mask
(disable) ALERT interrupts. Bit 6 puts the device into
software standby mode (STOP) or autonomous (RUN)
mode. Bit 5 selects the type of external junction (set to
0 for a substrate PNP on an IC or set to 1 for a discrete
diode-connected transistor) for optimized measurements. Bit 4 selects the extended temperature measurement for the remote sensor. If high, the temperature
data is available as 10 bits + sign with a 0.125°C resolution, otherwise, 7 bits + sign with 1°C resolution. Bit 4
extends the temperature range of the remote and local
temperature sensor to -64°C. Bit 2 disables the SMBus
timeout, as well as the Alert Response. Bit 1 provides a
software reset from the SMBus. Bit 0 is reserved and
returns a zero when read.
Status Byte Functions
The status byte (Table 7) indicates which (if any) temperature thresholds have been exceeded. This byte
also indicates whether the ADC is converting and if
there is an open-circuit fault detected with the external
sense junction. After POR, the normal state of the registers’ bits is zero, assuming no alert or overtemperature
conditions are present. When operating the
MAX6680/MAX6681 in ALERT interrupt mode, bits 2
through 6 of the Status register are cleared by any successful read of the Status register, unless the fault persists. The ALERT output follows the status flag bit. Both
are cleared when successfully read, but if the condition
______________________________________________________________________________________
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
MAX6680/MAX6681
Table 5. Command-Byte Register Bit Assignments
REGISTER
ADDRESS
POR STATE
FUNCTION
RLTS
00h
0000
at 0°C
Read Internal Temperature
RRTE
01h
0000
(0°C)
Read External Temperature
RSL
02h
0000 0000
Read Status Register
RCL/WCL
03h/09h
0010 0000
Read/Write Configuration Byte
RCRA/WCRA
04h/0A
0000 0010
Read/Write Conversion Rate Byte
RIH/WIH
05h/0Bh
0111 1111
(+127°C)
Read/Write Internal ALERT High Limit
RIL/WIL
06h/0Ch
1100 1001
( -55°C)
Read/Write Internal ALERT Low Limit
REH/WEH
07h/0Dh
0100 0110
(+127°C)
Read/Write External ALERT High Limit
REL/WEL
08h/0Eh
1100 1001
(-55°C)
Read/Write External ALERT Low Limit
OSHT
0Fh
0000
One Shot
REET
10h
0000 0000
RWOH
11h
0000 0000
Read External Extended Temperature
Read/Write External Offset High Byte
RWOL
12h
0000 0000
Read/Write External Offset Low Byte
RWOE
19h
See Table 4
Read/Write External OVERT Limit
RWOI
20h
See Table 4
Read/Write Internal OVERT Limit
HYST
21h
0000 0110
(+6°C)
RDID
FEh
0100 1101
Read Manufacturer ID
RDRV
Ff
0000 0001
Read Device Revision
OVERT Hysteresis
still exists, they are reasserted at the end of the next
conversion. If the MAX6680/MAX6681 are operating in
the comparator mode, bits 2–6 of the Status register
are cleared only after the local and/or remote temperatures return within the set limits.
The bits indicating OVTI and OVTE are cleared only
when the condition no longer exists. Reading the status
byte does not clear the OVERT output or fault bits. One
way to eliminate the fault condition is for the measured
temperature to drop below the temperature threshold
minus the hysteresis value. Another way to eliminate
the fault condition is by writing new values for the
RWOI, RWOE, or HYST registers so that a fault condition is no longer present.
The MAX6680/MAX6681 incorporate collision avoidance so that completely asynchronous operation is
allowed between SMBus operations and temperature
conversions.
When autoconverting, if the THIGH and TLOW limits 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. In
these circumstances, 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.
Hardware/Software Reset
The MAX6680/MAX6681 reset at power-on if pin 7 is
taken high, or by software reset through bit 1 of the
Configuration register. When reset occurs, all registers
go to default values, and the SMBus address pins are
sampled.
Conversion Rate Byte
The Conversion Rate register (Table 8) programs the
time interval between conversions in free-running
______________________________________________________________________________________
13
MAX6680/MAX6681
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
Table 6. Configuration-Byte Bit Assignment
BIT
NAME
POR STATE
FUNCTION
7 (MSB)
ALERT MASK
0
Mask ALERT active state when 1. When 1, ALERT does not respond to
any fault related to the four limit registers.
6
RUN/STOP
0
Standby mode control bit; if 1, immediately stops converting and enters
standby mode. If zero, it converts in either one-shot or timer mode.
5
SPNP
1
When 1, the remote sensor is a common-collector substrate PNP. When
zero, the remote sensor is a diode-connected transistor.
4
Extended Resolution
0
When zero, remote- and local-sensors’ temperature data are 7 bits +
sign with 1°C resolution. When 1, the remote-sensor temperature data is
10 bits + sign with 0.125°C resolution.
3
Extended Range
0
Extended temperature range. 0 = normal, 1 = extended to -64°C.
2
SMBus Timeout
0
When set to 1, it disables the SMBus timeout, as well as the alert
response.
1
Software Reset
0
Software reset from SMBus from customer.
0
RFU
0
Reserved
Table 7. Status Register Bit Assignments
BIT
NAME
POR
STATE
7 (MSB)
BUSY
0
When 1, the A/D is busy converting.
6
LHIGH
0
When 1, internal high-temperature alarm has tripped; cleared by POR or readout
of the Status register, if the fault condition no longer exists.
5
LLOW
0
When 1, internal low-temperature alarm has tripped; cleared by POR or readout of
the Status register, if the fault condition no longer exists.
4
RHIGH
0
When 1, external high-temperature alarm has tripped; cleared by POR or readout
of the Status register, if the fault condition no longer exists.
3
RLOW
0
When 1, external low-temperature alarm has tripped; cleared by POR or readout of
the Status register if the fault condition no longer exists.
2
OPEN
0
When 1 indicates an external diode open; cleared by POR or readout of the Status
register, if the fault condition no longer exists.
1
OVI
0
When 1, internal temperature exceeds the RWOI limit.
0
OVE
0
When 1, external temperature exceeds the RWOE limit.
FUNCTION
autonomous mode (RUN/STOP = 0). This variable rate
control can be used to reduce the supply current in
portable-equipment applications. The conversion rate
byte’s POR state is 02h (0.25Hz). The MAX6680/
MAX6681 use only the 3LSBs of this register. The
5MSBs are “don’t care” and should be set to zero when
possible. The conversion rate tolerance is ±25% at any
rate setting.
14
Valid A/D conversion results for both channels are available one total conversion time (125ms nominal, 156ms
maximum) after initiating a conversion, whether conversion is initiated through the RUN/STOP bit, hardware
STBY pin, One-Shot command, or initial power-up.
Slave Addresses
The MAX6680/MAX6681 device address can be initially
set to nine different values by pin strapping ADD0 and
ADD1 so that more than one MAX6680/MAX6681 can
______________________________________________________________________________________
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
POR and UVLO
The MAX6680/MAX6681 have a volatile memory. To
prevent unreliable 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 1.91V (typ, see Electrical
Characteristics). When power is first applied and VCC
rises above 2.0V (typ), the logic blocks begin operating,
although reads and writes at VCC levels below 3.0V are
not recommended. A second VCC comparator, the ADC
UVLO comparator, prevents the ADC from converting
until there is sufficient headroom (VCC = 2.8V typ).
Power-Up Defaults
• Interrupt latch is cleared.
• Address select pin is sampled.
• ADC begins autoconverting at a 1Hz rate (legacy
resolution).
• Command register is set to 00h to facilitate quick
internal Receive Byte queries.
• THIGH and TLOW registers are set to max and min
limits, respectively.
Table 8. Conversion-Rate Control Byte
DATA
CONVERSION RATE (Hz)
00h
0.0625
01h
0.125
02h
0.25
03h
0.5
04h
1
05h
2
06h
4
07h
8
Note: If extended resolution is selected using bit 4 of the
Configuration register, the extended conversion is limited to a
maximum of 4Hz.
Table 9. POR Slave Address Decoding
(ADD0 and ADD1)
ADD0
GND
GND
GND
HIGH-Z
HIGH-Z
HIGH-Z
VCC
VCC
VCC
• Hysteresis is set to 6°C.
• Transistor type is set to a substrate or common-collector PNP.
Temperature Offset
The MAX6680/MAX6681 are designed to provide ±1°C
accuracy for common microprocessors and discrete
transistors. To accommodate processes that differ significantly in their ideality factor, the user can
increase/decrease the Remote Temperature Sensor
Data register with an offset by writing to the External
Offset High and Low Byte registers (11h and 12h,
respectively). The offset temperature data is represented as a 10 bits + sign with a 0.125LSB resolution.
ADD1
GND
HIGH-Z
VCC
GND
HIGH-Z
VCC
GND
HIGH-Z
VCC
ADDRESS
0011 000
0011 001
0011 010
0101 001
0101 010
0101 011
1001 100
1001 101
1001 110
Chip Information
TRANSISTOR COUNT: 17,150
PROCESS: BiCMOS
______________________________________________________________________________________
15
MAX6680/MAX6681
reside on the same bus without address conflicts
(Table 9).
The address pin states are checked at POR and RESET
only, and the address data stays latched to reduce quiescent supply current due to the bias current needed
for high-Z state detection. The MAX6680/MAX6681 also
respond to the SMBus Alert Response slave address
(see the Alert Response Address section).
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
MAX6680/MAX6681
Pin Configurations
TOP VIEW
VCC 1
16 SENS_SEL
CRIT1 2
15 STBY
DXP 3
DXN 4
MAX6680
DXN 4
ADD1 6
RESET 7
15 STBY
14 SMBCLK
MAX6681
13 INT_SEL
CRIT0 5
12 SMBDATA
11 ALERT
ADD1 6
11 ALERT
10 ADDO
RESET 7
10 ADDO
9
QSOP
16
DXP 3
13 INT_SEL
12 SMBDATA
16 SENS_SEL
VCC 2
14 SMBCLK
CRIT0 5
GND 8
CRIT1 1
OVERT
GND 8
9
OVERT
QSOP
______________________________________________________________________________________
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
QSOP.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX6680/MAX6681
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)