General Description
The MAX6641 temperature sensor and fan controller
accurately measures the temperature of its own die and
the temperature of a remote pn junction. The device
reports temperature values 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)TMwrite byte, read byte,
send byte, and receive byte commands to read the
temperature data and program the alarm thresholds.
The temperature data controls a PWM output signal to
adjust the speed of a cooling fan, thereby minimizing
noise when the system is running cool, but providing
maximum cooling when power dissipation increases.
The device also features an over-temperature alarm
output to generate interrupts, throttle signals, or shut
down signals. The MAX6641 operates from supply voltages in the 3.0V to 5.5V range and typically consumes
500µA of supply current.
The MAX6641 is available in a slim 10-pin µMAX®package and is available over the automotive temperature
range (-40°C to +125°C).
Applications
Desktop Computers
Notebook Computers
Workstations
Servers
Networking Equipment
Industrial
Features
♦ Tiny 3mm x 5mm µMAX Package
♦ Thermal Diode Input
♦ Local Temperature Sensor
♦ Open-Drain PWM Output for Fan Drive
♦ Programmable Fan Control Characteristics
♦ Automatic Fan Spin-Up Ensures Fan Start
♦ ±1°C Remote Temperature Accuracy (+60°C to
+145°C)
♦ Controlled Rate of Change Ensures Unobtrusive
Fan-Speed Adjustments
♦ Temperature Monitoring Begins at Power-On for
Fail-Safe System Protection
♦ OT Output for Throttling or Shutdown
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-3304; Rev 0; 5/04
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-
SMBus
ADDRESS
MAX6641AUB90
-40°C to
+125°C
10 µMAX
1001 000x
MAX6641AUB92
-40°C to
+125°C
10 µMAX
1001 001x
MAX6641AUB94
-40°C to
+125°C
10 µMAX
1001 010x
MAX6641AUB96
-40°C to
+125°C
10 µMAX
1001 011x
1
2
3
4
5
10
9
8
7
6
PWMOUT
V
CC
SMBDATA
SMBCLKGND
DXP
DXN
I.C.
MAX6641
µMAX
TOP VIEW
I.C.OT
Pin Configuration
µMAX is a registered trademark of Maxim Integrated Products, Inc.
SMBus is a trademark of Intel Corp.
Typical Application Circuit appears at end of data sheet.
PACKAGE
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC= +3.0V to +5.5V, TA= 0°C to +125°C, unless otherwise noted. Typical values are at VCC= 3.3V, TA= +25°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.
All Voltages Referenced to GND
V
CC
, OT, SMBDATA, SMBCLK, PWMOUT...............-0.3V to +6V
DXP.........................................................…-0.3V to (V
CC
+ 0.3V)
DXN ......................................................................-0.3V to +0.8V
ESD Protection
(all pins, Human Body Model) ......…………………….±2000V
Continuous Power Dissipation (T
A
= +70°C)
10-Pin µMAX (derate 5.6mW/°C above +70°C) .......... 444mW
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
PARAMETER
CONDITIONS
UNITS
Operating Supply Voltage Range
V
CC
3.0 5.5 V
Operating Current SMBDATA, SMBCLK not switching 0.5 1 mA
+25°C ≤ TR ≤ +125°C,
T
A
= +60°C
±1
0°C ≤ TR ≤ +145°C,
+25°C ≤ T
A
= ≤ +100°C
±3
External Temperature Error
0°C ≤ TR ≤ +145°C,
0°C ≤ T
A
≤ +125°C
±4
°C
+25°C ≤ TA ≤ +100°C
Internal Temperature Error
0°C ≤ TA ≤ +125°C -4 +4
°C
1°C
Temperature Resolution
8 Bits
Conversion Time 200
300 ms
PWM Frequency Tolerance -20
%
High level 80
120
Remote-Diode Sourcing Current
Low level 8 10 12
µA
DXN Source Voltage 0.7 V
I/O
OT, SMBDATA, PWMOUT Output
Low Voltage
V
OL
I
OUT
= 6mA 0.4 V
OT, SMBDATA, PWMOUT
Output-High Leakage Current
I
OH
VCC = 5.5V 1 µA
SMBDATA, SMBCLK Logic-Low
Input Voltage
V
IL
VCC = 3V to 5.5V 0.8 V
SMBDATA, SMBCLK Logic-High
Input Voltage
V
IH
VCC = 3V to 5.5V 2.1 V
SMBDATA, SMBCLK Leakage
Current
1µA
SMBDATA, SMBCLK Input
Capacitance
C
IN
5pF
SYMBOL
VCC = 3.3V
VCC = 3.3V
MIN TYP MAX
-2.5 +2.5
250
100
+20
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
_______________________________________________________________________________________ 3
Note 1: Timing specifications guaranteed by design.
Note 2: The serial interface resets when SMBCLK is low for more than t
TIMEOUT
.
Note 3: A transition must internally provide at least a hold time to bridge the undefined region (300ns max) of SMBCLK’s falling edge.
ELECTRICAL CHARACTERISTICS (continued)
(VCC= +3.0V to +5.5V, TA= 0°C to +125°C, unless otherwise noted. Typical values are at VCC= 3.3V, TA= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SMBus-COMPATIBLE TIMING (Note 1) (See Figures 2, 3)
Serial Clock Frequency f
SCLK
(Note 2) 100 kHz
Clock Low Period t
LOW
10% to 10% 4 µs
Clock High Period t
HIGH
90% to 90% 4.7 µs
Bus Free Time Between Stop and
Start Condition
t
BUF
4.7 µs
Hold Time After (Repeated) Start
Condition
4µs
S M Bus S tar t C ond i ti on S etup Ti m e
t
SU:STA
90% of SMBCLK to 90% of SMBDATA 4.7 µs
Start Condition Hold Time
10% of SMBDATA to 10% of SMBCLK 4 µs
Stop Condition Setup Time
90% of SMBCLK to 10% of SMBDATA 4 µs
Data Setup Time
10% of SMBDATA to 10% of SMBCLK 250 ns
Data Hold Time
10% of SMBCLK to 10% of SMBDATA
(Note 3)
300 ns
SMBus Fall Time t
F
300 ns
SMBus Rise Time t
R
ns
SMBus Timeout
29 37 55 ms
Startup Time After POR t
POR
500 ms
Typical Operating Characteristics
(VCC= 3.3V, TA= +25°C, unless otherwise noted.)
OPERATING SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6641 toc01
SUPPLY VOLTAGE (V)
OPERATING SUPPLY CURRENT (µA)
5.04.54.03.5
350
400
450
500
550
600
300
3.0 5.5
NO SMBus ACTIVITY
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX6641 toc02
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
1007525 50
-1.5
-1.0
-0.5
0
0.5
1.0
1.5
2.0
-2.0
0125
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
MAX6641 toc03
TEMPERATURE (°C)
TEMPERATURE ERROR (°C)
100755025
-1
0
1
2
-2
0125
t
HD:STA
t
HD:STO
t
SU:STO
t
SU:DAT
t
HD:DAT
t
TIMEOUT
1000
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
4 _______________________________________________________________________________________
REMOTE TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6641 toc04
FREQUENCY (kHz)
TEMPERATURE ERROR (°C)
100101
-1.25
-1.00
-0.75
-0.50
-0.25
0
-1.50
0.1 1000
TA = +80°C, 250mV SQUARE WAVE APPLIED
AT V
CC
, NO BYPASS CAPACITOR
LOCAL TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
MAX6641 toc05
FREQUENCY (kHz)
TEMPERATURE ERROR (°C)
100101
-1.5
-1.0
-0.5
0
0.5
1.0
-2.0
0.1 1000
TA = +25°C, 250mV SQUARE WAVE APPLIED
AT V
CC
, NO BYPASS CAPACITOR
REMOTE TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
MAX6641 toc06
FREQUENCY (kHz)
TEMPERATURE ERROR (°C)
100101
-1.0
-0.5
0
0.5
1.0
-1.5
0.1 1000
TA = +80°C, VIN = 100mV
P-P
SQUARE WAVE APPLIED TO DXP
REMOTE TEMPERATURE ERROR
vs. DIFFERENTIAL-MODE NOISE FREQUENCY
MAX6641 toc07
FREQUENCY (kHz)
TEMPERATURE ERROR (°C)
100101
-0.5
0
0.5
1.0
1.5
-1.0
0.1 1000
TA = +80°C, VIN = 10mV
P-P
SQUARE WAVE APPLIED
TO DXP - DXN
REMOTE TEMPERATURE ERROR
vs. DXP - DXN CAPACITANCE
MAX6641 toc08
DXP - DXN CAPACITANCE (nF)
NORMALIZED TEMPERATURE ERROR (°C)
101
-4
-3
-2
-1
0
1
2
3
-5
0.1 100
TA = +80°C
PWM FREQUENCY ERROR
vs. DIE TEMPERATURE
MAX6641 toc09
TEMPERATURE (°C)
PWM FREQUENCY ERROR (Hz)
1007550250-25
-2
-1
0
1
2
-3
-50 125
PWM FREQUENCY ERROR
vs. SUPPLY VOLTAGE
MAX6641 toc10
SUPPLY VOLTAGE (V)
PWM FREQUENCY ERROR (Hz)
5.04.54.03.5
-0.5
0
0.5
1.0
1.5
2.0
-1.0
3.0 5.5
TA = +25°C
Typical Operating Characteristics (continued)
(VCC= 3.3V, TA= +25°C, unless otherwise noted.)
Detailed Description
The MAX6641 temperature sensor and fan controller
accurately measures the temperature of its own die and
the temperature of a remote pn junction. The device
reports temperature values in digital form using a 2wire serial interface. The remote pn junction is typically
the emitter-base junction of a common-collector pnp on
a CPU, FPGA, or ASIC. The MAX6641 operates from
supply voltages of 3.0V to 5.5V and consumes 500µA
of supply current. The temperature data controls a
PWM output signal to adjust the speed of a cooling fan.
The device also features an over-temperature alarm
output to generate interrupts, throttle signals, or shut
down signals.
SMBus Digital Interface
From a software perspective, the MAX6641 appears as
a set of byte-wide 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. These devices respond to the
same SMBus slave address for access to all functions.
The MAX6641 employs four standard SMBus protocols:
write byte, read byte, send byte, and receive byte
(Figures 1, 2, and 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 when using the shorter protocols in
multimaster systems, as a second master could overwrite the command byte without informing the first master. The MAX6641 has four different slave addresses
available; therefore, a maximum of four MAX6641
devices can share the same bus.
Temperature data within the 0°C to +255°C range can
be read from the read external temperature register
(00h). Temperature data within the 0°C to +125°C range
can be read from the read internal temperature register
(01h). The temperature data format for these registers is
8 bits, with the LSB representing +1°C (Table 1) and the
MSB representing +128°C. The MSB is transmitted first.
All values below 0°C are clipped to 00h.
Table 1 details the register address and function,
whether they can be read or written to, and the power-on
reset (POR) state. See Tables 1–5 for all other register
functions and the Register Descriptions section. Figure 4
is the MAX6641 block diagram.
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
_______________________________________________________________________________________ 5
PIN NAME FUNCTION
1, 6 I.C. Internally Connected. Must be connected to GND.
2DXN
Combined Remote-Diode Cathode Connection and A/D Negative Input. Connect the cathode of the
remote-diode-connected transistor to DXN.
3 DXP
Combined Remote-Diode Current Source and A/D Positive Input for Remote-Diode Channel. Connect
DXP to the anode of a remote-diode-connected temperature-sensing transistor. DO NOT LEAVE
DXP FLOATING; connect to DXN if no remote diode is used. Place a 2200pF capacitor between DXP
and DXN for noise filtering.
4 GND Ground
5 OT
Active-Low, Open-Drain, Over-Temperature Output. Use OT as an interrupt, a system shutdown
signal, or to control clock throttling. OT can be pulled up to 5.5V, regardless of the voltage on VCC.
OT is high impedance when V
CC
= 0.
7 SMBCLK
SMBus Serial Clock Input. SMBCLK can be pulled up to 5.5V, regardless of V
CC
. Open drain.
SMBCLK is high impedance when V
CC
= 0.
8
SMBus Serial Data Input/Output. SMBDATA can be pulled up to 5.5V, regardless of VCC. Open drain.
SMBDATA is high impedance when V
CC
= 0.
9VCCPositive Supply. Bypass with a 0.1µF capacitor to GND.
10
PWM Output to Fan Power Transistor. Connect PWMOUT to the gate of a MOSFET or the base of a
bipolar transistor to drive the fan’s power supply with a PWM waveform. Alternatively, the PWM output
can be connected to the PWM input of a fan with direct speed-control capability, or it can be
converted to a DC voltage for driving the fan’s power supply. PWMOUT requires a pullup resistor. The
pullup resistor can be connected to a voltage supply up to 5.5V, regardless of V
CC
.
Pin Description
SMBDATA
PWMOUT
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
6 _______________________________________________________________________________________
READ/
WRITE
REGISTER
POR
FUNCTION/
NAME
D7 D6 D5 D4 D3 D2 D1
D0
R 00h
Read remote
(external)
MSB
(+32°C)
LSB
(+1°C)
R 01h
Read local
(internal)
MSB
(+32°C)
LSB
(+1°C)
R/W
02h
Configuration
byte
Reserved
set to 0
Timeout: 0 =
Fan
PWM
Min duty
1 = fan-
Spin-up
XX
R/W
03h
Remote-diode
temperature
OT limit
MSB
(+32°C)
LSB
(+1°C)
R/W
04h
Local-diode
temperature
OT limit
MSB
(+32°C)
LSB
(+1°C)
R 05h
OT status
Remote 1
fault
XXXXXX
R/W
06h
OT mask
Remote 1
XXXXXX
R/W
07h
0110 000x
Fan-start duty
cycle
MSB
LSB
X
R/W
08h
1111 000x
(240 =
Fan maximum
MSB
(32/240)
LSB
X
R/W
09h
cycle
MSB
(32/240)
LSB
X
R 0Ah
Fan
instantaneous
MSB
(32/240)
LSB
X
R/W
0Bh
Remote-diode
fan-start
MSB
(+32°C)
LSB
(+1°C)
Table 1. Register Functions
ADDRESS
STATE
0000 0000
0000 0000
0000 00xx
0110 1110
0101 0000
00xx xxxx
00xx xxxx
(96 = 40%)
temperature
temperature
(+128°C)
(+128°C)
(+128°C)
(+128°C)
= fault
= masked
(128/240)
(+64°C)
(+64°C)
Reserved
set to 0
(+64°C)
(+64°C)
Local 1 =
Local 1 =
masked
(64/240) (32/240) ( 16/240) (8/240) (4/240)
enabled, 1 =
disabled
(+16°C) (+8°C) (+4°C) (+2°C)
(+16°C) (+8°C) (+4°C) (+2°C)
cycle:
0 = 0%,
invert
(+16°C) (+8°C) (+4°C) (+2°C)
(+16°C) (+8°C) (+4°C) (+2°C)
start duty
disable
cycle
(2/240)
100%)
0000 000x
0000 000x
0000 0000
duty cycle
Fan target duty
duty cycle
temperature
(128/240)
(128/240)
(128/240)
(+128°C)
(64/240)
(64/240)
(64/240)
(+64°C)
( 16/240) (8/240) (4/240)
( 16/240) (8/240) (4/240)
( 16/240) (8/240) (4/240)
(+16°C) (+8°C) (+4°C) (+2°C)
(2/240)
(2/240)
(2/240)
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
_______________________________________________________________________________________ 7
READ/
WRITE
REGISTER
POR
NAME
D7 D6 D5 D4 D3 D2 D1
R/W
0Ch
Local-diode
fan-start
MSB
(+32°C)
LSB
(+1°C)
R/W
0Dh
Fan
Temp
step: 0 =
1°C, 1 =
2°C
Fan
XXXX
R/W
0Eh
MSB — LSB XXXXX
R/W
0Fh
step size
MSB — —
XXXX
R/W
10h
PWM
frequency
select
XXXXX
R FDh
Read device
revision
00 0 00001
R FEh
Read
device ID
10 0 00111
R FFh
Read
manufacturer
ID
01 0 01101
Table 1. Register Functions (continued)
X = Don’t care. See register descriptions for further details.
ADDRESS
STATE
0000 0000
0000 xxxx
101x xxxx
0101 xxxx
010x xxxx
0000 0001
1000 0111
FUNCTION/
temperature
configuration
Duty-cycle
rate of change
Duty-cycle
(+128°C)
H yster esi s:
0 = 5°C ,
1 = 10°C
Select A Select B Select C
(+64°C)
Fan control:
1 = remote
D0
(+16°C) (+8°C) (+4°C) (+2°C)
control:
1 = local
LSB
0100 1101
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
8 _______________________________________________________________________________________
Write Byte Format
Read Byte Format
Send Byte Format
Receive Byte Format
Slave address: equivalent to chip-select line of
a 3-wire interface
Command byte: selects which
register you are writing to
Data byte: data goes into the register
set by the command byte (to set
thresholds, configuration masks, and
sampling rate)
Slave address: equivalent
to chip-select line
Command byte: selects
which register you are
reading from
Slave address: repeated
due to change in dataflow direction
Data byte: reads from
the register set by the
command byte
Command byte: sends command with no data, usually
used for one-shot command
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
S = Start condition Shaded = Slave transmission
P = Stop condition /// = Not acknowledged
Figure 1. SMBus Protocols
S ADDRESS RD ACK DATA /// P
7 bits 8 bits
WRS ACK COMMAND ACK P
8 bits
ADDRESS
7 bits
P
1
ACKDATA
8 bits
ACKCOMMAND
8 bits
ACKWRADDRESS
7 bits
S
S ADDRESS WR ACK COMMAND ACK S ADDRESS
7 bits8 bits7 bits
RD ACK DATA
8 bits
/// P
Figure 2. SMBus Write Timing Diagram
AB CDEFG
t
t
HIGH
LOW
SMBCLK
SMBDATA
t
SU:STAtHD:STA
A = START CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
t
SU:DAT
E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
HIJ
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
LMK
t
SU:STOtBUF
Register Descriptions
Temperature Registers (00h, 01h)
These registers contain the 8-bit results of the temperature measurements. Register 00h contains the temperature reading of the remote diode. Register 01h contains
the ambient temperature reading. The value of the MSB
is +128°C and the value of the LSB is +1°C. The MSB is
transmitted first. The POR state of the temperature registers is 00h.
Configuration Byte Register (02h)
The configuration byte register controls the timeout
conditions and various PWMOUT signals. The POR
state of the configuration byte register is 00h. See
Table 2 for configuration byte definitions.
Remote and Local OTLimits (03h, 04h)
Set the remote (03h) and local (04h) temperature thresholds with these two registers. Once the temperature is
above the threshold, the OT output is asserted low (for
the temperature channels that are not masked). The POR
state of the remote OT limit register is 6Eh and the POR
state of the LOCAL OT limit register is 50h.
OT
Status (05h)
Read the OT status register to determine which channel
recorded an over-temperature condition. Bit D7 is high if
the fault reading occurred from the remote diode. Bit D6
is high if the fault reading occurred in the local diode.
The OT status register is cleared only by reading its contents. Reading the contents of the register also makes
the OT output high impedance. If the fault is still present
on the next temperature measurement cycle, the corresponding bits and the OT output are set again. After
reading the OT status register, a temperature register
read must be done to correctly clear the appropriate status bit. The POR state of the OT status register is 00h.
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
_______________________________________________________________________________________ 9
SMBCLK
AB CDEFG HIJ
K
SMBDATA
t
SU:STA
t
HD:STA
t
LOWtHIGH
t
SU:DAT
t
HD:DAT
t
SU:STO
t
BUF
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
L
M
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
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
M = NEW START CONDITION
Figure 3. SMBus Read Timing Diagram
Figure 4. Block Diagram
GND
SMBus
INTERFACE AND
REGISTERS
LOGIC
PWM
GENERATOR
BLOCK
V
CC
TEMPERATURE
PROCESSING
BLOCK
SMBDATA
SMBCLK
DXP
DXN
PWMOUT
OT
MAX6641
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
10 ______________________________________________________________________________________
BIT NAME POR STATE FUNCTION
7— 0Reserved. Set to zero.
6— 0Reserved. Set to zero.
5 TIMEOUT 0
Set TIMEOUT to zero to enable SMBus timeout for
prevention of bus lockup. Set to 1 to disable this function.
4 FAN PWM INVERT 0
Set FAN PWM INVERT to zero to force PWMOUT low when
the duty cycle is 100%. Set to 1 to force PWMOUT high
when the duty cycle is 100%.
3 MIN DUTY CYCLE 0
Set MIN DUTY CYCLE to zero for a 0% duty cycle when
the measured temperature is below the fan-temperature
threshold in automatic mode. When the temperature
equals the fan-temperature threshold, the duty cycle is the
value in the fan-start duty-cycle register, which increases
with increasing temperature.
Set MIN DUTY CYCLE to 1 to force the PWM duty cycle to
the value in the fan-start duty-cycle register when the
measured temperature is below the fan-temperature
threshold. As the temperature increases above the
temperature threshold, the duty cycle increases as
programmed.
2 SPIN-UP DISABLE 0
Set SPIN-UP DISABLE to 1 to disable spin-up. Set to zero
for normal fan spin-up.
1— XDon’t care.
0— XDon’t care.
Table 2. Configuration Byte Definition (02h)
OT
Mask (06h)
Set bit D7 to 1 in the OT mask register to prevent the
OT output from asserting on faults in the remote-diode
temperature channel. Set bit D6 to 1 to prevent the OT
output from asserting on faults in the local-diode temperature channel. The POR state of the OT mask register is 00h.
Fan-Start Duty Cycle (07h)
The fan-start duty-cycle register determines the PWM
duty cycle where the fan starts spinning. Bit D3 in the
configuration byte register (MIN DUTY CYCLE) determines the starting duty cycle. If the MIN DUTY CYCLE
bit is 1, the duty cycle is the value written to the fanstart duty-cycle register at all temperatures below the
fan-start temperature. If the MIN DUTY CYCLE bit is
zero, the duty cycle is zero below the fan-start temperature and has this value when the fan-start temperature
is reached. A value of 240 represents 100% duty cycle.
Writing any value greater than 240 causes the fan
speed to be set to 100%. The POR state of the fan-start
duty-cycle register is 60h, 40%.
Fan Maximum Duty Cycle (08h)
The fan maximum duty-cycle register sets the maximum allowable PWMOUT duty cycle between 2/240
(0.83% duty cycle) and 240/240 (100% duty cycle).
Any values greater than 240 are recognized as 100%
maximum duty cycle. The POR state of the fan maximum duty-cycle register is F0h, 100%. In manual control mode, this register is ignored.
Fan-Target Duty Cycle (09h)
In automatic fan-control mode, this register contains the
present value of the target PWM duty cycle, as determined by the measured temperature and the dutycycle step size. The actual duty cycle needs a settling
time before it equals the target duty cycle if the dutycycle rate of change register is set to a value other than
zero. The actual duty cycle needs the time to settle as
defined by the value of the duty-cycle rate-of-change
register; therefore, the target duty cycle and the actual
duty cycle are often different. In manual fan-control
mode, write the desired value of the PWM duty cycle
directly into this register. The POR state of the fan-target duty-cycle register is 00h.
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
______________________________________________________________________________________ 11
Fan Instantaneous Duty Cycle (0Ah)
Read the fan instantaneous duty-cycle register to determine the duty cycle at PWMOUT at any time. The POR
state of the fan instantaneous duty-cycle register is 00h.
Remote- and Local-Diode
Fan-Start Temperature (0Bh, 0Ch)
These registers contain the temperature threshold values at which fan control begins in automatic mode. See
the Automatic PWM Duty-Cycle Control section for
details on setting the fan-start thresholds. The POR
state of the remote- and local-diode fan-start temperature registers is 00h.
Fan Configuration (0Dh)
The fan-configuration register controls the hysteresis
level, temperature step size, and whether the remote or
local diode controls the PWMOUT signal; see Table 1.
Set bit D7 of the fan-configuration register to zero to set
the hysteresis value to 5°C. Set bit D7 to 1 to set the
hysteresis value to 10°C. Set bit D6 to zero to set the
fan-control temperature step size to 1°C. Set bit D6 to 1
to set the fan-control temperature step size to 2°C. Set
bit D5 to 1 to control the fan with the remote-diode’s
temperature reading. Set bit D4 to 1 to control the fan
with the local-diode’s temperature reading. If both bits
D5 and D4 are high, the device uses the highest PWM
value. If both bits D5 and D4 are zero, the MAX6641
runs in manual fan-control mode where only the value
written to the fan-target duty-cycle register (09h) controls the PWMOUT duty cycle. In manual fan-control
mode, the value written to the fan-target duty-cycle register is not limited by the value in the maximum dutycycle register. It is, however, clipped to 240 if a value
above 240 is written. The POR state of the fan-configuration register is 00h.
Duty-Cycle Rate of Change (0Eh)
Bits D7, D6, and D5 of the duty-cycle rate-of-change
register set the time between increments of the duty
cycle. Each increment is 2/240 of the duty cycle; see
Table 3. This allows the time from 33% to 100% duty
cycle to be adjusted from 5s to 320s. The rate-ofchange control is always active in manual mode. To
make instant changes, set bits D7, D6, D5 = 000. The
POR state of the duty-cycle rate-of-change register is
A0h (1s time between increments).
Duty-Cycle Step Size (0Fh)
Bits D7–D4 of the duty-cycle step-size register change
the size of the duty-cycle change for each temperature
step. The POR state of the duty-cycle step-size register
is 50h; see Table 4.
PWM Frequency Select (10h)
Set bits D7, D6, and D5 (select A, select B, and select
C) in the PWM frequency-select register to control the
PWMOUT frequency; see Table 5. The POR state of the
PWM frequency select register is 40h, 33Hz. The lower
frequencies are usually used when driving the fan’s
power-supply pin as in the Typical Application Circuit,
with 33Hz being the most common choice. The 35kHz
D7, D6, D5
TIME BETWEEN
TIME FROM 33%
TO 100% (s)
000 0 0
001 0.0625 5
010 0.1250 10
011 0.2500 20
100 0.5000 40
101 1.0000 80
110 2.0000 160
111 4.0000 320
Table 3. Duty-Cycle Rate-of-Change
Register (0Eh)
D7–D4
CHANGE IN DUTY
CYCLE PER
TEMPERATURE RANGE
FOR FAN CONTROL
(1°C STEP, 33% TO 100%)
0000
0/240 N/A
0001
2/240 80.00
0010
4/240 40.00
0011
6/240 26.67
0100
8/240 20.00
0101
10/240 16.00
0110
12/240 13.33
0111
14/240 11.43
1000
16/240 10.00
1001
18/240 8.89
1010
20/240 8.00
1011
22/240 7.27
1100
24/240 6.67
1101
26/240 6.15
1110
28/240 5.71
1111
30/240 5.33
Table 4. Duty-Cycle Step-Size
Register (0Fh)
INCREMENTS (s)
TEMPERATURE STEP
frequency setting is used for controlling fans that have
logic-level PWM input pins for speed control. Dutycycle resolution is decreased from 2/240 to 4/240 at the
35kHz frequency setting.
PWM Output
The PWMOUT signal is normally used in one of three
ways to control the fan’s speed:
1) PWMOUT drives the gate of a MOSFET or the base
of a bipolar transistor in series with the fan’s power
supply. The Typical Application Circuit shows the
PWMOUT pin driving an n-channel MOSFET. In this
case, the PWM invert bit (D4 in register 02h) is set to
1. Figure 5 shows PWMOUT driving a p-channel
MOSFET and the PWM invert bit must be set to zero.
2) PWMOUT is converted (using an external circuit)
into a DC voltage that is proportional to duty cycle.
This duty-cycle-controlled voltage becomes the
power supply for the fan. This approach is less efficient than 1), but can result in quieter fan operation.
Figure 6 shows an example of a circuit that con-
verts the PWM signal to a DC voltage. Because this
circuit produces a full-scale output voltage when
PWMOUT = 0V, bit D4 in register 02h should be set
to zero.
3) PWMOUT directly drives the logic-level PWM
speed-control input on a fan that has this type of
input. This approach requires fewer external components and combines the efficiency of 1) with the
low noise of 2). An example of PWMOUT driving a
fan with a speed-control input is shown in Figure 7.
Bit D4 in register 02h should be set to 1 when this
configuration is used.
Whenever the fan has to start turning from a motionless
state, PWMOUT is forced high for 2s. After this spin-up
period, the PWMOUT duty cycle settles to the predetermined value. If spin-up is disabled (bit 2 in the configuration byte = 1), the duty cycle changes immediately
from zero to the nominal value, ignoring the duty-cycle
rate-of-change setting.
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
12 ______________________________________________________________________________________
PWM
FREQUENCY
(Hz)
SELECT A
SELECT B
SELECT C
20
00
0
33
01
0
50
10
0
100
11
0
35k
XX
1
Table 5. PWM Frequency Select (10h)
V
CC
PWMOUT
10kΩ
5V
P
Figure 5. Driving a P-Channel MOSFET for Top-Side PWM
Fan Drive
+3.3V
PWMOUT
18kΩ
27kΩ
10kΩ 120kΩ
P
+3.3V
+12V
500kΩ
V
OUT
TO FAN
1µF
1µF
0.01µF
Figure 6. Driving a Fan with a PWM-to-DC Circuit
V
CC
PWMOUT
4.7kΩ
5V
Figure 7. Controlling a PWM Input Fan with the MAX6641’s
PWM Output (Typically, the 35kHz PWM Frequency is Used)
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
______________________________________________________________________________________ 13
The frequency-select register controls the frequency of
the PWM signal. When the PWM signal modulates the
power supply of the fan, a low PWM frequency (usually
33Hz) should be used to ensure the circuitry of the
brushless DC motor has enough time to operate. When
driving a fan with a PWM-to-DC circuit, as in Figure 6,
the highest available frequency (35kHz) should be
used to minimize the size of the filter capacitors. When
using a fan with a PWM control input, the frequency
should normally be high as well, although some fans
have PWM inputs that accept low-frequency drive.
The duty cycle of the PWM can be controlled in two ways:
1) Manual PWM control by setting the duty cycle of
the fan directly through the fan-target duty-cycle
register (09h).
2) Automatic PWM control by setting the duty cycle
based on temperature.
Manual PWM Duty-Cycle Control
Setting bits D5 and D4 to zero in the fan-configuration
register (0Dh) enables manual PWMOUT control. In this
mode, the duty cycle written to the fan-target dutycycle register controls the PWMOUT duty cycle. The
value is clipped to a maximum of 240, which corresponds to a 100% duty cycle. Any value above that is
limited to the maximum duty cycle. In manual control
mode, the value of the maximum duty-cycle register is
ignored and does not affect the duty cycle.
Automatic PWM Duty-Cycle Control
In the automatic control mode, the duty cycle is controlled by the local or remote temperature, according to
the settings in the control registers. Below the value of
the fan-start temperature threshold (set by registers 03h
and 04h), the duty cycle is equal to the fan-start duty
cycle. Above the fan-start temperature, the duty cycle
increases by one duty-cycle step each time the temperature increases by one temperature step. Below the fanstart temperature, the duty cycle is either 0% or it is
equal to the fan-start duty cycle, depending on the value
of bit D3 in the configuration byte register. See Figure 8.
The target duty cycle is calculated based on the following formula:
For temperature > fan-start temperature:
where:
DC = DutyCycle
FSDC = FanStartDutyCycle
T = Temperature
FST = FanStartTemperature
DCSS = DutyCycleStepSize
TS = TempStep
Duty cycle is recalculated after each temperature conversion if temperature is increasing. If the temperature
begins to decrease, the duty cycle is not recalculated
until the temperature drops by 5°C from the last peak
temperature. The duty cycle remains the same until the
temperature drops 5°C from the last peak temperature
or the temperature rises above the last peak temperature. For example, if temperature goes up to +85°C and
starts decreasing, duty cycle is not recalculated until
the temperature reaches +80°C or the temperature
rises above +85°C. If temperature decreases further,
the duty cycle is not updated until it reaches +75°C.
For temperature < fan-start temperature and bit D3 of
the configuration byte register = 0:
DutyCycle = 0
For temperature < fan-start temperature and bit D3 of
the configuration byte register = 1:
Dutycycle = FanStartDutyCycle
Once the temperature crosses the fan-start temperature threshold, the temperature has to drop below the
fan-start temperature threshold minus the hysteresis
before the duty cycle returns to either 0% or fan-start
duty cycle. The value of the hysteresis is set by D7 of
the fan-configuration register.
DC FSDC T FST
DCSS
TS
=+ × ( ) -
FAN START
DUTY CYCLE
TEMPERATURE
DUTY CYCLE
REGISTER 02H,
BIT D3 = 1
DUTY CYCLE
STEP SIZE
FAN START
TEMPERATURE
TEMP
STEP
REGISTER 02H,
BIT D3 = 0
Figure 8. Automatic PWM Duty Control
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
14 ______________________________________________________________________________________
The duty cycle is limited to the value in the fan maximum duty-cycle register. If the duty-cycle value is larger than the maximum fan duty cycle, it can be set to the
maximum fan duty cycle as in the fan maximum dutycycle register. The temp step is bit D6 of the fan-configuration register (0Dh).
If duty cycle is an odd number, the MAX6641 automatically rounds down to the nearest even number.
Duty-Cycle Rate-of-Change Control
To reduce the audibility of changes in fan speed, the
rate of change of the duty cycle is limited by the values
set in the duty-cycle rate-of-change register. Whenever
the target duty cycle is different from the instantaneous
duty cycle, the duty cycle increases or decreases at
the rate determined by the duty-cycle rate-of-change
byte until it reaches the target duty cycle. By setting the
rate of change to the appropriate value, the thermal
requirements of the system can be balanced against
good acoustic performance. Slower rates of change
are less noticeable to the user, while faster rates of
change can help minimize temperature variations.
Remember that the fan controller is part of a complex
control system. Because several of the parameters are
generally not known, some experimentation may be
necessary to arrive at the best settings.
Power-Up Defaults
At power-up, the MAX6641 has the default settings
indicated in Table 1. Some of these settings are summarized below:
• Temperature conversions are active.
• Remote OT limit = +110°C.
• Local OT limit = +80°C.
• Manual fan mode.
• Fan duty cycle = 0.
• PWM Invert bit = 0.
• PWMOUT is high.
When using an nMOS or npn transistor, the fan starts at
full speed on power-up.
Applications Information
Remote-Diode Selection
The MAX6641 can directly measure the die temperature of CPUs and other ICs that have on-board temperature-sensing diodes (see the Typical Application
Circuit), or they can measure the temperature of a discrete diode-connected transistor.
Effect of Ideality Factor
The accuracy of the remote temperature measurements
depends on the ideality factor (n) of the remote diode
(actually a transistor). The MAX6641 is optimized for n =
1.008, which is the typical value for the Intel Pentium® III
and the AMD Athlon™ MP model 6. If a sense transistor
with a different ideality factor is used, the output data is
different. Fortunately, the difference is predictable.
Assume a remote-diode sensor designed for a nominal
ideality factor n
NOMINAL
is used to measure the temperature of a diode with a different ideality factor, n1.
The measured temperature TMcan be corrected using:
where temperature is measured in Kelvin.
As mentioned above, the nominal ideality factor of the
MAX6641 is 1.008. As an example, assume the MAX6641
is configured with a CPU that has an ideality factor of
1.002. If the diode has no series resistance, the measured data is related to the real temperature as follows:
For a real temperature of +85°C (358.15K), the measured temperature is +82.87°C (356.02K), which is an
error of -2.13°C.
Effect of Series Resistance
Series resistance in a sense diode contributes additional errors. For nominal diode currents of 10µA and
100µA, change in the measured voltage is:
∆VM= RS(100µA - 10µA) = 90µA x R
S
Since 1°C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
Assume that the diode being measured has a series
resistance of 3Ω. The series resistance contributes an
offset of:
:
30453 1 36Ω×
°
Ω
=+ °..
C
C
90
198 6
0 453
µ
Ω
µ
°
=
°
Ω
V
V
C
C
.
.
TT
n
n
TT
ACTUAL M M M
NOMINAL
=
==
()
1
1 008
1 002
1 00599
.
.
.
TT
n
n
M ACTUAL
NOMINAL
=
1
Pentium is a registered trademark of Intel Corp.
Athlon is a trademark of AMD.
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
______________________________________________________________________________________ 15
The effects of the ideality factor and series resistance
are additive. If the diode has an ideality factor of 1.002
and series resistance of 3Ω, the total offset can be calculated by adding error due to series resistance with
error due to ideality factor:
1.36°C - 2.13°C = -0.1477°C
for a diode temperature of +85°C.
In this example, the effect of the series resistance and
the ideality factor partially cancel each other.
For best accuracy, the discrete transistor should be a
small-signal device with its collector connected to GND
and base connected to DXN. Table 6 lists examples of
discrete transistors that are appropriate for use with
the MAX6641.
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, the 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.
ADC Noise Filtering
The integrating ADC used has good noise rejection for
low-frequency signals such as 60Hz/120Hz power-supply 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 larger values 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 MAX6641 as close as is practical to the
remote diode. In noisy environments, such as a
computer motherboard, this distance can be 4in to
8in typically. 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 9).
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 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 10-mil
widths and spacing recommended in Figure 9 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 VCCfor best
noise filtering (see the Typical Application Circuit).
8) Copper cannot be used as an EMI shield; only ferrous materials such as steel work well. Placing a
copper ground plane between the DXP-DXN traces
and traces carrying high-frequency noise signals
does not help reduce EMI.
MANUFACTURER MODEL NO.
Central Semiconductor (USA) CMPT3906
Rohm Semiconductor (USA) SST3906
Samsung (Korea) KST3906-TF
Siemens (Germany) SMBT3906
Table 6. Remote-Sensor Transistor
Manufacturers
Twisted-Pair and Shielded Cables
Use a twisted-pair cable to connect the remote sensor
for remote-sensor distance 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 0.5°C.
Thermal Mass and Self-Heating
When sensing local temperature, these devices are
intended to measure the temperature of the PC board
to which they are soldered. The leads provide 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 MAX6641,
the devices follow temperature changes on the PC
board with little or no perceivable delay. When measuring the temperature of a CPU or other IC with an onchip 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, such as µMAXes, yield the
best thermal response times. Take care to account for
thermal gradients between the heat source and the
sensor, and ensure 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.
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
16 ______________________________________________________________________________________
MINIMUM
10 mils
10 mils
10 mils
10 mils
GND
DXN
DXP
GND
Figure 9. Recommended DXP-DXN PC Traces
MAX6641
GND
V
CC
(3.0V TO 5.5V)
SMBDATA
SMBCLK
DXP
DXN
5V
V
FAN
(5V OR 12V)
TO CLOCK
THROTTLE OR
SYSTEM
SHUTDOWN
PWMOUT
µP
5V
2200pF
10kΩ
EACH
10kΩ
0.1µF
OT
Typical Application Circuit
Chip Information
TRANSISTOR COUNT: 18,769
PROCESS: BiCMOS
MAX6641
SMBus-Compatible Temperature Monitor with
Automatic PWM Fan-Speed Controller
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
© 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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
.)
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
.)
10LUMAX.EPS
PACKAGE OUTLINE, 10L uMAX/uSOP
1
1
21-0061
I
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
1
0.498 REF
0.0196 REF
S
6°
SIDE VIEW
α
BOTTOM VIEW
0° 0° 6°
0.037 REF
0.0078
MAX
0.006
0.043
0.118
0.120
0.199
0.0275
0.118
0.0106
0.120
0.0197 BSC
INCHES
1
10
L1
0.0035
0.007
e
c
b
0.187
0.0157
0.114
H
L
E2
DIM
0.116
0.114
0.116
0.002
D2
E1
A1
D1
MIN
-A
0.940 REF
0.500 BSC
0.090
0.177
4.75
2.89
0.40
0.200
0.270
5.05
0.70
3.00
MILLIMETERS
0.05
2.89
2.95
2.95
-
MIN
3.00
3.05
0.15
3.05
MAX
1.10
10
0.6±0.1
0.6±0.1
00.50±0.1
H
4X S
e
D2
D1
b
A2
A
E2
E1
L
L1
c
α
GAGE PLANE
A2 0.030 0.037 0.75 0.95
A1
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