19-2305; Rev 1; 1/05
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
General Description
The 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
OVERT
output,
which provides fail-safe clock throttling or system shut-
down. 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 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.
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/I
2
C™-Compatible Interface
♦
SMBus Timeout Prevents SMBus Lockup
MAX6680/MAX6681
Ordering Information
PART
MAX6680MEE
MAX6681MEE
TEMP RANGE
-55°C to +125°C
-55°C to +125°C
PIN-PACKAGE
16 QSOP
16 QSOP
Typical Operating Circuit
3.3V
0.1µF
200Ω
Applications
Desktop Computers
Notebook
Computers
Servers
Thin Clients
Workstations
MICROPROCESSOR
INT_SEL
ADD0
ADD1 GND CRIT0
CRIT1
2200pF
DXP
DXN
V
CC
STBY
SMBDATA
SMBCLK
DATA
CLOCK
INTERRUPT
TO
µP
10kΩ
EACH
MAX6680
MAX6681
SENS_SEL
ALERT
RESET
OVERT
Pin Configurations appear at end of data sheet.
TO SYSTEM
SHUTDOWN
SMBus is a trademark of Intel Corp.
I
2
C is a trademark of Philips Corp.
________________________________________________________________
Maxim Integrated Products
1
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°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
MAX6680/MAX6681
ABSOLUTE MAXIMUM RATINGS
V
CC
...........................................................................-0.3V to +6V
DXP.............................................................-0.3V to (V
CC
+ 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 (T
A
= +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, V
CC
= 3.0V to 5.5V, T
A
= -25°C to +125°C, unless otherwise specified. Typical values are at V
CC
= 3.3V and T
A
= +25°C.)
PARAMETER
Temperature Resolution,
Legacy Mode
Temperature Resolution,
Extended Mode
T
RJ
= +60°C to +100°C, V
CC
= 3.3V
Remote Temperature Error (Note 1)
T
RJ
= +50°C to +120°C, V
CC
= 3.3V
T
RJ
= -55°C to +125°C, V
CC
= 3.3V
T
A
= +60°C to +100°C, V
CC
= 3.3V
Local Temperature Error
Line Regulation
Supply Voltage Range
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
Power-On Reset (POR)
Threshold
POR Threshold Hysteresis
Conversion Time
Standby Supply Current
Operating Current
Average Operating Current
(Note 3)
DXP and DXN Leakage Current
Remote-Diode Source Current
I
RJ
Legacy
Extended
SMBus static
During conversion
0.25 conversions/s
2 conversions/s
In standby mode
High level
Low level
80
8
100
10
V
CC
, falling edge
1.5
V
CC
UVLO
Falling edge of V
CC
disables ADC
T
A
= 0°C to +125°C, V
CC
= 3.3V
T
A
= -55°C to +125°C, V
CC
= 3.3V (Note 2)
3.0V
≤
V
CC
≤
5.5V
3.0
2.60
2.80
90
2.0
90
62.5
125
3
0.55
35
120
10
1.0
70
180
2
120
12
2.5
SYMBOL
CONDITIONS
MIN
1
8
0.125
11
-1.0
-2.0
-3.0
-1.5
-3.0
-5.0
0.2
+1.0
+2.0
+3.0
+1.5
+3.0
+5.0
0.6
5.5
2.95
m°C/V
V
V
mV
V
mV
ms
µA
mA
µA
µA
µA
°C
°C
TYP
MAX
UNITS
°C
Bits
°C
Bits
2
_______________________________________________________________________________________
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Typical Operating Circuit, V
CC
= 3.0V to 5.5V, T
A
= -25°C to +125°C, unless otherwise specified. Typical values are at V
CC
= 3.3V and T
A
= +25°C.)
PARAMETER
Logic Input Low Voltage
Logic Input High Voltage
Input Leakage Current
(ALERT,
OVERT)
Output Low Sink Current
Output High Leakage Current
Logic Input Low Voltage
Logic Input High Voltage
Input Leakage Current
Output Low Sink Current
Input Capacitance
V
IL
V
IH
I
LEAK
I
OL
C
IN
V
CC
= 3.0V
V
CC
= 5.5V
V
IN
= GND or V
CC
V
OL
= 0.6V
5
100
4.7
4.7
t
SU:STA
t
HD:STA
t
SU:STO
t
LOW
t
HIGH
t
HD:DAT
t
R
t
F
t
SP
SMBDATA low period for interface reset
0
25
37
90% to 90%
10% of SMBDATA to 90% of SMBCLK
90% of SMDCLK to 90% of SMBDATA
10% to 10%
90% to 90%
4
250
1
300
50
45
50
4
4
4.7
2.2
2.4
±2
6
V
OL
= 0.4V
V
OH
= 5.5V
1
1
0.8
mA
µA
V
V
µA
mA
pF
kHz
µs
µs
ns
µs
µs
µs
µs
ns
µs
ns
ns
ms
SYMBOL
V
IL
V
IH
I
LEAK
2.4
-1
+1
CONDITIONS
MIN
TYP
MAX
0.8
UNITS
V
V
µA
MAX6680/MAX6681
CRIT0, CRIT1, ADD0, ADD1, RESET, INT_SEL, SENS_SEL
SMBus INTERFACE (SMBCLK, SMBDATA,
STBY)
SMBus-COMPATIBLE TIMING
(Note 5)
Serial Clock Frequency (Note 5)
f
SCL
Bus Free Time Between STOP
and START Condition
START Condition Setup Time
Repeat START Condition Setup
Time
START Condition Hold Time
STOP Condition Setup Time
Clock Low Period
Clock High Period
Data Setup Time (Note 6)
Receive SCL/SDA Rise Time
Receive SCL/SDA Fall Time
Pulse Width of Spike Suppressed
SMBus Timeout (Note 5)
t
BUF
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
T
A
= +25°C to +85°C.
If both the local and the remote junction are below T
A
= -20°C, then V
CC
> 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 t
TIMEOUT
.
A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling edge.
_______________________________________________________________________________________
3
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
MAX6680/MAX6681
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6680/81 toc01
AVERAGE OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
MAX6680/81 toc02
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX6680/81 toc03
10
9
STANDBY SUPPLY CURRENT (µA)
8
7
6
5
4
3
2
1
0
3.0
3.5
4.0
4.5
5.0
600
OPERATING SUPPLY CURRENT (µA)
500
400
300
200
100
0
0.0625
0.1250
0.2500
0.5000
1.0000
2.0000
8Hz IS 1°C
RESOLUTION
3
2
TEMPERATURE ERROR (°C)
1
0
-1
-2
-3
5.5
4.0000
8.0000
-50
-25
0
25
50
75
100 125 150
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
CONVERSION RATE (Hz)
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
MAX6680/81 toc04
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6680/81 toc05
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
V
IN
= 100mV
P-P
SQUARE WAVE
AC-COUPLED TO DXN
MAX6680/81 toc06
3
2
TEMPERATURE ERROR (°C)
1
0
-1
-2
-3
-50
0
50
TEMPERATURE (°C)
100
1.2
1.0
TEMPERATURE ERROR (°C)
0.8
0.6
0.4
0.2
0
-0.2
LOCAL
DIODE
V
IN
= 100mV SQUARE WAVE
APPLIED TO V
CC
WITH NO
0.1µF V
CC
CAPACITOR
5
4
TEMPERATURE ERROR (°C)
3
2
1
0
-1
-2
REMOTE
DIODE
150
1
10
100
1k
10k 100k 1M 10M 100M
1
10
100
1k
10k 100k 1M 10M 100M
FREQUENCY (Hz)
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. DIFFERENTIAL NOISE FREQUENCY
MAX6680/81 toc07
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6680/81 toc08
3
1
0
TEMPERATURE ERROR (°C)
-1
-2
-3
-4
-5
TEMPERATURE ERROR (°C)
2
1
0
V
IN
= 10mV
P-P
SQUARE WAVE
APPLIED TO DXP-DXN
-1
100
1k
10k
100k
1M
10M
100M
FREQUENCY (Hz)
0
10 20 30 40 50 60 70 80 90 100
DXP-DXN CAPACITANCE (nF)
4
_______________________________________________________________________________________
±1°C Fail-Safe Remote/Local Temperature
Sensors with SMBus Interface
Pin Description
PIN
MAX6680
1
MAX6681
2
NAME
FUNCTION
Supply Voltage Input, 3V to 5.5V. Bypass V
CC
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.
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.
Combined Remote-Diode Current Sink and A/D Negative Input. DXN is
internally biased to one diode drop above ground.
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.
Reset Input. Drive RESET high to set all registers to their default values (POR
state). Drive RESET low or leave floating for normal operation.
Ground
Overtemperature Active-Low Output. Open drain.
SMBus Slave Address Select Pin (see ADD1).
SMBus Alert (Interrupt) Active-Low Output. Open drain.
SMBus Serial-Data Input/Output, Open Drain
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.
SMBus Serial-Clock Input
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 = Remote, Low = Local, Open = Local and Remote
MAX6680/MAX6681
V
CC
CRIT1,
CRIT0
2, 5
1, 5
3
3
DXP
4
4
DXN
6
6
ADD1
7
8
9
10
11
12
7
8
9
10
11
12
RESET
GND
OVERT
ADD0
ALERT
SMBDATA
13
13
INT_SEL
14
15
14
15
SMBCLK
STBY
16
16
SENS_SEL
_______________________________________________________________________________________
5
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