19-3895; Rev 1; 1/06
Temperature Monitor with
Dual Serial Interface
General Description
The MAX6638 thermal-management sensor includes
internal (local) and external (remote) digital temperature
sensors and two independent SMBus™ serial ports. The
remote temperature accuracy is ±1.0°C, and the local
temperature accuracy is ±2°C. The MAX6638 also fea-
tures extended temperature resolution data available in
0.125°C increments.
The MAX6638 provides three system alarms: channel 1
alert (ALERT1), overtemperature (OVERT1), and chan-
nel 2 alert (ALERT2) that contain programmable thresh-
olds set independently by each of the SMBus serial
ports (SMBus1 and SMBus2). Each alert output asserts
when any of four temperature conditions is violated:
local overtemperature, remote overtemperature, local
undertemperature, or remote undertemperature. The
overtemperature signal asserts when the temperature
rises above the value in the overtemperature limit regis-
ter. Use the
OVERT1
output to activate a cooling fan or
trigger a system shutdown.
Each of the 2-wire serial-interface ports accepts stan-
dard System Management Bus (SMBus) write byte, read
byte, send byte, and receive byte commands indepen-
dently of one another with total collision avoidance han-
dled by the MAX6638. Each SMBus can operate its own
unique serial-data rate to access any register in the
MAX6638 for data reads or data writes. The MAX6638
manages all dual-port data register access functions
providing a seamless, conflict-free integration into a
multimaster architecture for thermal management.
The MAX6638 performs measurements autonomously,
at the programmed conversion rate, or in a single-con-
version mode. Each SMBus port can set the conversion
rate with the higher conversion and update rate domi-
nating the average power-supply current. Single-con-
version requests have a maximum delay of two
conversion cycles with channel-conversion manage-
ment and cycling regulated by the dual-port controller.
The MAX6638 operating temperature range is -40°C to
+125°C and measures temperatures between 0°C and
+145°C. The MAX6638 is available in a 16-pin, 4mm x
4mm TQFN with exposed paddle package.
♦
Two Independent
Interfaces with Collision Avoidance
Features
SMBus/I
2
C*-Compatible
♦
High Accuracy
±1.0°C from +85°C to +100°C (Remote)
♦
Remote and Local Temperature Measurements
♦
Three Programmable Output Alarms:
ALERT1,
OVERT1,
and
ALERT2
♦
Programmable Conversion Rates
♦
11-Bit Low-Noise Integrating ADC
♦
No Calibration Required
♦
Autoscan Conversions
MAX6638
Ordering Information
PART
MAX6638ATE+
TEMP
RANGE
-40°C to +125°C
PIN-
PACKAGE
16 TQFN-EP*
(4mm x 4mm)
PKG
CODE
T1644-4
*EP
= Exposed paddle.
+Denotes
lead-free package.
Pin Configuration
SCK1
N.C.
SDA1
10
TOP VIEW
12
11
ALERT1
9
N.C. 13
ALERT2 14
SDA2 15
SCK2 16
8
7
GND
N.C.
I.C.
N.C.
MAX6638
6
5
+
1
V
CC
2
DXP
3
DXN
4
OVERT1
Applications
Graphics Cards
Notebook Computers
Computer Motherboard Systems
Desktop Computers
Workstations
TQFN-EP
Typical Operating Circuit appears at end of data sheet.
SMBus is a trademark of Intel Corporation.
*Purchase
of I
2
C components from Maxim Integrated Products,
Inc., or one of its sublicensed Associated Companies, conveys
a license under the Philips I
2
C Patent Rights to use these com-
ponents in an I
2
C system, provided that the system conforms to
the I
2
C Standard Specification as defined by Philips.
1
________________________________________________________________
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.
Temperature Monitor with
Dual Serial Interface
MAX6638
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND, unless otherwise noted.)
V
CC ....................................................................................
-0.3V to +6.0V
DXP.............................................................-0.3V to (V
CC
+ 0.3V)
DXN .......................................................................-0.3V to +0.8V
SCK1, SDA1, SCK2, SDA2,
ALERT1,
OVERT1, ALERT2
.....................................................-0.3V to +6V
SDA1, SDA2,
ALERT1, OVERT1, ALERT2
..........-1mA to +50mA
DXN Current .......................................................................±1mA
Continuous Power Dissipation (T
A
= +70°C)
16-Pin TQFN (derate 16.9 mW/°C above +70°C) ....1349 mW
ESD Protection (all pins, Human Body Model) ................±2000V
Operating Temperature Range .........................-40°C to +125°C
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
(V
CC
= 3.0V to 5.5V, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at V
CC
= 3.3V and T
A
= +85°C.) (Note 1)
PARAMETER
Supply Voltage
Operating Current
Standby Supply Current
TEMPERATURE MEASUREMENT
Remote Diode-Source Current
I
RJ
High level
Low level
V
CC
= 3.3V, T
A
= +85°C to +100°C,
T
RJ
= +85°C to +145°C
Remote Temperature Error
V
CC
= 3.3V, T
A
= +25°C to +100°C,
T
RJ
= +25°C to +145°C
V
CC
= 3.3V, T
A
= +0°C to +125°C,
T
RJ
= 0°C to +145°C
Local Temperature Error
Supply Sensitivity of Temperature
Error
POWER-ON RESET
Power-On-Reset Threshold
POR Threshold Hysteresis
Undervoltage-Lockout Threshold
Undervoltage-Lockout Hysteresis
ANALOG-TO-DIGITAL CONVERTER
Conversion Time
ALERT1, OVERT1, ALERT2,
SDA1, SDA2
Output Low Voltage
Leakage Current
V
OL
I
LEAK
I
OL
= 6mA
V
OH
= 5.5V
0.6
±1
V
µA
Nonoverlapping single conversion from
stop bit to conversion complete
23
32
39
ms
V
CC
falling
2.30
V
CC
falling
1.9
90
2.60
90
2.95
V
mV
V
mV
V
CC
= 3.3V, T
A
= +25°C to +85°C
V
CC
= 3.3V, T
A
= 0°C to +125°C
80
8
-1.0
-2.0
-3.0
-2.0
-3.5
±0.2
100
10
120
12
+1.0
+2.0
+3.0
+2.0
+3.5
°C
°C/V
°C
µA
SYMBOL
V
CC
During conversion
ADC not converting
SMBus1 and SMBus2 static
3
CONDITIONS
MIN
3.0
600
TYP
MAX
5.5
950
80
10
UNITS
V
µA
µA
2
_______________________________________________________________________________________
Temperature Monitor with
Dual Serial Interface
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 3.0V to 5.5V, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at V
CC
= 3.3V and T
A
= +85°C.) (Note 1)
PARAMETER
Logic Input Low Voltage
Logic Input High Voltage
Input Leakage Current
Input Capacitance
Serial-Clock Frequency
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
Data Hold Time
SMBus Rise Time
SMBus Fall Time
SMBus Timeout
t
SU:STA
t
HD:STA
t
SU:STO
t
LOW
t
HIGH
t
SU:DAT
t
HD:DAT
t
R
t
F
t
TIMEOUT
SDA_ low period for interface reset
30
45
(Note 4)
90% of SCK_ to 90% of SDA_
10% of SDA_ to 90% of SCK_
90% of SCK_ to 90% of SDA_
10% to 10%
90% to 90%
SYMBOL
V
IL
V
IH
I
LEAK
C
IN
f
SCK
t
BUF
(Note 3)
4.7
4.7
50
4
4
4.7
4.0
250
300
1
300
60
V
IN
= GND or V
CC
5
100
2.1
±1
CONDITIONS
MIN
TYP
MAX
0.8
UNITS
V
V
µA
pF
kHz
µs
µs
ns
µs
µs
µs
µs
ns
ns
µs
ns
ms
SMBus INTERFACE (SCK1, SCK2, SDA1, SDA2)
MAX6638
SMBus-COMPATIBLE TIMING (Figure 5) (Note 2)
Note 1:
Note 2:
Note 3:
Note 4:
All parameters are tested at a single temperature. Specifications over temperature are guaranteed by design.
Timing specifications are guaranteed by design.
Each serial interface resets when its SCK_ is low for more than t
TIMEOUT
.
A transition must internally provide at least a hold time to bridge the unidentified region (300ns max) of SCK_’s falling edge.
_______________________________________________________________________________________
3
Temperature Monitor with
Dual Serial Interface
MAX6638
Typical Operating Characteristics
(V
CC
= 3.3V, T
A
= +25°C, unless otherwise noted.)
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6638 toc01
AVERAGE SUPPLY CURRENT
vs. CONVERSION RATE
MAX6638 toc02
OPERATING SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6638 toc03
7
6
SUPPLY CURRENT (µA)
5
4
3
2
1
0
3.0
3.5
4.0
4.5
5.0
T
A
= -40°C
T
A
= +25°C
T
A
= +85°C
600
500
SUPPLY CURRENT (µA)
400
300
200
100
0
700
650
SUPPLY CURRENT (µA)
600
550
500
T
A
= -40°C
450
400
T
A
= +25°C
T
A
= +85°C
5.5
0
5
10
15
20
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
CONVERSION RATE (Hz)
SUPPLY VOLTAGE (V)
REMOTE TEMPERATURE ERROR
vs. REMOTE DIODE TEMPERATURE
MAX6638 toc04
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
MAX6638 toc05
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6638 toc06
0.8
REMOTE TEMPERATURE ERROR (°C)
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
0
20
100 120
80
REMOTE DIODE TEMPERATURE (°C)
40
60
0
LOCAL TEMPERATURE ERROR (°C)
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
6
LOCAL
TEMPERATURE ERROR (°C)
4
2
0
REMOTE
140
0
20
40
60
80
100
120
140
-2
0.01
0.1
1
10
100
1,000 10,000
DIE TEMPERATURE (°C)
POWER-SUPPLY NOISE FREQUENCY (kHz)
LOCAL TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
MAX6638 toc07
REMOTE TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
MAX6638 toc08
0
LOCAL TEMPERATURE ERROR (°C)
-1
-2
-3
-4
-5
-6
0.01
2
REMOTE TEMPERATURE ERROR (°C)
0
-2
-4
-6
-8
0.1
1
10
100
1,000 10,000
0.01
0.1
1
10
100
COMMON-MODE NOISE FREQUENCY (kHz)
DXP-DXN CAPACITANCE (nF)
4
_______________________________________________________________________________________
Temperature Monitor with
Dual Serial Interface
Pin Description
PIN
1
2
3
4
5, 7, 12, 13
6
8
9
10
11
14
15
16
EP
NAME
V
CC
DXP
DXN
OVERT1
N.C.
I.C.
GND
ALERT1
SDA1
SCK1
ALERT2
SDA2
SCK2
GND
FUNCTION
Supply Voltage. Bypass V
CC
to GND with a 0.1µF capacitor. A 47Ω series resistor is recommended for
additional noise filtering, but not required.
Combined Current Source and ADC Positive Input for Remote Diode. If a remote-sensing junction is not
used, connect DXP to DXN.
Combined Current Sink and ADC Negative Input for Remote Diode. DXN is internally biased to a diode
voltage above ground.
Digital Open-Drain Output.
OVERT1
indicates an overtemperature condition on channel 1.
No Connection. Not connected internally.
Internally Connected.
I.C. must be connected to GND.
Power-Supply Ground
Digital Open-Drain Output.
ALERT1
indicates alert condition on channel 1.
SMBus Data Channel 1. Open-drain output.
SMBus Clock Channel 1
Digital Open-Drain Output.
ALERT2
indicates alert condition on channel 2.
SMBus Data Channel 2. Open-drain output.
SMBus Clock Channel 2
Ground. Connect to ground.
MAX6638
Detailed Description
The MAX6638 temperature monitor features dual-port
SMBus access for use in thermal management of
graphics processing unit (GPU) and CPU systems.
Each of the two SMBus serial ports can be accessed
independently by two thermal-monitoring systems with
all dual-port collision-avoidance logic controlled by the
MAX6638. Each SMBus thermal-monitoring channel
(channels 1 and 2) has a corresponding over/under-
temperature
ALERT_
open-drain output with indepen-
dently configurable limit registers. Channel 1 includes
an overtemperature indicator (OVERT1) with an initial
set-point limit that is always activated after a power-on
reset (POR). The initial
OVERT1
set point can be over-
written after POR by SMBus1 serial programming. The
overtemperature alarm
OVERT1
asserts if the set-point
limit is exceeded.
temperature conversion results of the two temperature
channels are in integer format. The MSBs of the tem-
perature data are in 8-bit registers (addresses 00h and
01h; see Table 1) that represent the data as 8 bits with
the full-scale reading to indicate a diode fault. The
remaining 3 bits of temperature data are available in
the extended data-registers format with the LSB equal
to +0.125°C (addresses 11h and 10h; see Table 2).
The converted readings are stored in SMBus reading
registers along with the limit-value registers and other
control functions.
Table 1. Temperature Data Format
(RLTS1, RRTS1, RLTS2, RRTS2)
TEMPERATURE
(°C)
+145
+130
+128
+25
0
<0
Diode fault
DIGITAL OUTPUT
(hex)
91
82
80
19
00
00
FF
DIGITAL OUTPUT
(bin)
1001 0001
1000 0010
1000 0000
0001 1001
0000 0000
0000 0000
1111 1111
ADC and Multiplexer
The MAX6638 converts temperatures to digital data
either at a programmed rate or in single conversions.
Either SMBus controller can set the programmed rate
with the higher rate setting taking precedence. The
MAX6638 begins conversions at the maximum rate
after POR to provide the
OVERT1
output signal asser-
tion for temperatures exceeding the set-point limit. The
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