General Description
The MAX6646/MAX6647/MAX6649 are precise, two-
channel digital temperature sensors. The devices accu-
rately 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 junc-
tion 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 man-
agement 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 MAX6646/MAX6647/MAX6649
include an SMBus timeout. A fault queue prevents the
ALERT and OVERT outputs from setting until a fault has
been detected one, two, or three consecutive times
(programmable).
The MAX6646/MAX6647/MAX6649 provide two system
alarms: ALERT and OVERT. ALERT asserts when any of
four temperature conditions are violated: local overtem-
perature, remote overtemperature, local undertempera-
ture, or remote undertemperature. OVERT asserts when
the temperature rises above the value in either of the two
OVERT limit registers. The OVERT output can be used to
activate a cooling fan, or to trigger a system shutdown.
Measurements can be done autonomously, at the pro-
grammed conversion rate, or in a single-shot mode. The
adjustable conversion rate allows optimizing supply cur-
rent and temperature update rate to match system needs.
Remote accuracy is ±1°C maximum error between +60°C
and +145°C with no calibration needed. The
MAX6646/MAX6647/MAX6649 operate from -55°C to
+125°C, and measure temperatures between 0°C and
+145°C. The MAX6646/MAX6647/MAX6649 are available
in an 8-pin µMAX package.
Applications
Graphics Processors
Desktop Computers
Notebook Computers
Servers
Thin Clients
Workstations
Test and Measurement
Multichip Modules
Features
o Dual Channel: Measures Remote and Local
Temperature
o 0.125°C Resolution
o High Accuracy ±1°C (max) from +60°C to +145°C
(Remote), and ±2°C (max) from +60°C to +100°C
(Local)
o Measures High-Ideality Thermal Diodes Up to
+170°C (Apparent)
+145°C (Real)
o Two Alarm Outputs: ALERT and OVERT
o Programmable Under/Overtemperature Alarm
Temperature Thresholds
o Programmable Conversion Rate
o SMBus-Compatible Interface
o SMBus Timeout
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
________________________________________________________________ Maxim Integrated Products
1
Ordering Information
V
CC
DXP
DXN
10k
EACH
CLOCK
TO FAN DRIVER OR
SYSTEM SHUTDOWN
3.3V
DATA
INTERRUPT TO
µP
200
0.1
µF
SDA
SCLK
ALERT
GND
2200pF
µP
MAX6646
MAX6647
MAX6649
OVERT
Typical Operating Circuit
19-2540; Rev 1; 7/03
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.
PART
TEMP RANGE
PIN-
PACKAGE
MEASURED
TEMP RANGE
MAX6646MUA -55°C to +125°C 8 µMAX
0°C to +145°C
MAX6647MUA -55°C to +125°C 8 µMAX
0°C to +145°C
MAX6649MUA -55°C to +125°C 8 µMAX
0°C to +145°C
Selector Guide, Pin Configurations, and Functional Diagram
appear at end of data sheet.
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
All Voltages Referenced to GND
V
CC
...........................................................................-0.3V to +6V
DXP.............................................................-0.3V to (V
CC
+ 0.3V)
DXN .......................................................................-0.3V to +0.8V
SCLK, SDA, ALERT, OVERT.....................................-0.3V to +6V
SDA, ALERT, OVERT Current .............................-1mA to +50mA
DXN Current .......................................................................±1mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin µMAX (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
(V
CC
= 3.0V to 5.5V, T
A
= -55°C to +125°C, unless otherwise specified. Typical values are at V
CC
= 3.3V and T
A
= +100°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage
V
CC
3.0
5.5
V
0.125
°C
Temperature Resolution
11
Bits
V
CC
= 3.3V, T
A
= +100°C,
T
RJ
= +60°C to +145°C
-1.0
+1.0
V
CC
= 3.3V, T
A
= +60°C to +100°C,
T
RJ
= +25°C to +145°C
-1.6
+1.6
Remote Temperature Error
V
CC
= 3.3V, T
A
= +0°C to +100°C,
T
RJ
= +0°C to +145°C
-3.2
+3.2
°C
T
A
= +60°C to +100°C
-2.0
+2.0
Local Temperature Error
V
CC
= 3.3V
T
A
= 0°C to +125°C
-3.0
+3.0
°C
Supply Sensitivity of Temperature
Error
±0.2
°C/V
Undervoltage Lockout (UVLO)
Threshold
UVLO
Falling edge of V
CC
disables ADC
2.4
2.7
2.95
V
UVLO Hysteresis
90
mV
Power-On-Reset (POR) Threshold
V
CC
falling edge
2.0
V
POR Threshold Hysteresis
90
mV
Standby Supply Current
SMBus static
3
12
µA
Operating Current
During conversion
0.08
mA
0.25 conversions per second
40
80
Average Operating Current
2 conversions per second
250
400
µA
Conversion Time
t
CONV
From stop bit to conversion completion
95
125
156
ms
Conversion Time Error
-25
+25
%
DXP and DXN Leakage Current
Standby mode
100
nA
High level
80
100
120
Remote-Diode Source Current
I
RJ
Low level
8
10
12
µA
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 3.0V to 5.5V, T
A
= -55°C to +125°C, unless otherwise specified. Typical values are at V
CC
= 3.3V and T
A
= +100°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ALERT, OVERT
I
SINK
= 1mA
0.4
Output Low Voltage
I
SINK
= 4mA
0.6
V
Output High Leakage Current
V
OH
= 5.5V
1
µA
SMBus-COMPATIBLE INTERFACE (SCLK AND SDA)
Logic Input Low Voltage
V
IL
0.8
V
V
CC
= 3.0V
2.2
Logic Input High Voltage
V
IH
V
CC
= 5.5V
2.6
V
Input Leakage Current
I
LEAK
V
IN
= GND or V
CC
-1
+1
µA
Output Low-Sink Current
I
SINK
V
OL
= 0.6V
6
mA
Input Capacitance
C
IN
5
pF
SMBus-COMPATIBLE TIMING (Note 2)
Serial Clock Frequency
f
SCLK
(Note 3)
100
kHz
Bus Free Time Between STOP
and START Condition
t
BUF
4.7
µs
START Condition Setup Time
4.7
µs
Repeat START Condition Setup
Time
t
SU:STA
90% to 90%
50
ns
START Condition Hold Time
t
HD:STA
10% of SDA to 90% of SCLK
4
µs
STOP Condition Setup Time
t
SU:STO
90% of SCLK to 90% of SDA
4
µs
Clock Low Period
t
LOW
10% to 10%
4.7
µs
Clock High Period
t
HIGH
90% to 90%
4
µs
Data Setup Time
t
HD:DAT
(Note 4)
250
µs
Receive SCLK/SDA Rise Time
t
R
1
µs
Receive SCLK/SDA Fall Time
t
F
300
ns
Pulse Width of Spike Suppressed
t
SP
0
50
ns
SMBus Timeout
t
TIMEOUT
SDA low period for interface reset
25
37
45
ms
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 t
TIMEOUT
.
Note 4: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SCLK's falling edge.
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
4
_______________________________________________________________________________________
Typical Operating Characteristics
(V
CC
= 3.3V, T
A
= +25°C, unless otherwise noted.)
MAX6649 toc01
SUPPLY VOLTAGE (V)
STANDBY SUPPLY CURRENT (
µ
A)
5.0
4.5
4.0
3.5
3.0
3.5
4.0
4.5
5.0
2.5
3.0
5.5
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6649 toc02
CONVERSION RATE (Hz)
OPERATING SUPPLY CURRENT (
µ
A)
4.00
2.00
1.00
0.50
0.25
0.13
100
200
300
400
0
0.63
OPERATING SUPPLY CURRENT
vs. CONVERSION RATE
MAX6649 toc03
TEMPERATURE (
°C)
TEMPERATURE ERROR (
°
C)
125
100
75
50
25
-1.5
-0.5
0
0.5
1.0
1.5
2.0
-2.0
0
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
-1.0
T
A
= +85
°C
FAIRCHILD 2N3906
MAX6649 toc04
TEMPERATURE (
°C)
TEMPERATURE ERROR (
°
C)
100
75
50
25
-1.5
-1.0
-0.5
0
0.5
1.0
-2.0
0
125
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
MAX6649 toc05
FREQUENCY (Hz)
TEMPERATURE ERROR (
°
C)
10k
1k
100
10
1
-1
0
1
2
3
4
5
-2
0.1
100k
V
CC
= SQUARE WAVE APPLIED TO
V
CC
WITH NO BYPASS CAPACITOR
LOCAL ERROR
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
REMOTE ERROR
MAX6649 toc06
FREQUENCY (Hz)
TEMPERATURE ERROR (
°
C)
10k
1k
100
10
-1
0
1
2
3
4
5
6
7
8
9
-2
1
100k
LOCAL TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
LOCAL ERROR
REMOTE ERROR
V
IN
= AC-COUPLED TO DXN
V
IN
= 100mV
P-P
MAX6649 toc07
FREQUENCY (Hz)
TEMPERATURE ERROR (
°
C)
10k
1k
100
10
-0.5
0
0.5
1.0
1.5
2.0
-1.0
1
100k
TEMPERATURE ERROR
vs. DIFFERENTIAL-MODE NOISE FREQUENCY
MAX6649 toc08
DXP-DXN CAPACITANCE (nF)
TEMPERATURE ERROR (
°
C)
10.000
1.000
-4
-3
-2
-1
0
1
-5
0.100
100.000
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6646/MAX6647/MAX6649
+145°C Precision SMBus-Compatible Remote/
Local Sensors with Overtemperature Alarms
_______________________________________________________________________________________
5
Detailed Description
The MAX6646/MAX6647/MAX6649 are temperature sen-
sors designed to work in conjunction with a microproces-
sor or other intelligence in thermostatic, process-control,
or monitoring applications. Communication with the
MAX6646/MAX6647/MAX6649 occurs through the
SMBus-compatible serial interface and dedicated alert
and overtemperature outputs. ALERT asserts if the mea-
sured local or remote temperature is greater than the
software-programmed ALERT high limit or less than the
ALERT low limit in the MAX6649. ALERT also asserts, in
the MAX6649, if the remote-sensing diode pins are short-
ed or unconnected. The overtemperature alarm, OVERT,
asserts if the software-programmed OVERT limit is
exceeded. OVERT can be connected to fans, a system
shutdown, a clock throttle control, or other thermal-man-
agement circuitry.
The MAX6646/MAX6647/MAX6649 convert temperatures
to digital data either at a programmed rate or in single
conversions. Temperature data is represented as 11 bits,
with the LSB equal to 0.125°C. The "main" temperature
data registers (at addresses 00h and 01h) are 8-bit regis-
ters that represent the data as 8 bits with the full-scale
reading 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 Multiplexer
The 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 results of the unused channel can be ignored.
If the remote-diode channel is unused, connect DXP to
DXN rather than leaving the inputs open.
Pin Description
PIN
NAME
FUNCTION
1
V
CC
Supply Voltage Input, 3V to 5.5V. Bypass V
CC
to GND with a 0.1µF capacitor. A 200
series
resistor is recommended but not required for additional noise filtering.
2
DXP
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.
3
DXN
Combined Remote-Diode Current Sink and A/D Negative Input. DXN is internally connected to
ground.
4
OVERT
Overtemperature Alert/Interrupt Output, Open Drain.
OVERT is logic low when the temperature is
above the software-programmed threshold.
5
GND
Ground
6
ALERT
SMBus Alert (Interrupt) Output, Open Drain.
ALERT asserts when temperature exceeds limits
(high or low temperature).
ALERT stays asserted until acknowledged by either reading the status
register or by successfully responding to an alert response address, provided that the fault
condition no longer exists. See the
ALERT Interrupts section.
7
SDA
SMBus Serial-Data Input/Output, Open Drain
8
SCLK
SMBus Serial-Clock Input
TEMP (
°C)
DIGITAL OUTPUT
+145
1001 0001
+130
1000 0010
+128
1000 0000
+25
0001 1001
0
0000 0000
<0
0000 0000
Diode fault
(short or open)
1111 1111
Table 1. Main Temperature Data Register
Format (00h, 01h)
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