MAX6639FAEE+T [MAXIM]
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| 型号： | MAX6639FAEE+T |
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MAXIM INTEGRATED PRODUCTS |
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19-3682; Rev 0; 5/05
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
General Description
Features
The MAX6639 monitors its own temperature and one
external diode-connected transistor or the temperatures
of two external diode-connected transistors, typically
available in CPUs, FPGAs, or GPUs. The 2-wire serial
interface accepts standard System Management Bus
(SMBusTM) write byte, read byte, send byte, and
receive byte commands to read the temperature data
and program the alarm thresholds. Temperature data
can be read at any time over the SMBus, and three pro-
grammable alarm outputs can be used to generate
interrupts, throttle signals, or overtemperature shut-
down signals.
♦ 2 Thermal-Diode Inputs
♦ Up to 25kHz PWM Output Frequency
♦ 3 Selectable SMBus Addresses
♦ Local Temperature Sensor
♦ 1°C Remote Temperature Accuracy
♦ Two PWM Outputs for Fan Drive (Open Drain; Can
be Pulled Up to +13.5V)
♦ Programmable Fan-Control Characteristics
♦ Automatic Fan Spin-Up Ensures Fan Start
The temperature data is also used by the internal dual-
PWM fan-speed controller to adjust the speed of up to
two cooling fans, thereby minimizing noise when the
system is running cool, but providing maximum cooling
when power dissipation increases. Speed control is
accomplished by tachometer feedback from the fan, so
that the speed of the fan is controlled, not just the PWM
duty cycle. Accuracy of speed measurement is 4%.
♦ Controlled Rate-of-Change Ensures Unobtrusive
Fan-Speed Adjustments
♦
3ꢀ Fan-Speed Measurement Accuracy
♦ Temperature Monitoring Begins at POR for Fail-
Safe System Protection
♦ OT and THERM Outputs for Throttling or
The MAX6639 is available in 16-pin QSOP and 16-pin
TQFN 5mm x 5mm packages. It operates from 3.0V to
5.5V and consumes just 500µA of supply current.
Shutdown
♦ Measures Temperatures Up to +150°C
Applications
Ordering Information
Desktop Computers
Notebook Computers
Projectors
OPERATING MEASUREMENT PIN-
PART
RANGE
RANGE
PACKAGE
-40°C to
+125°C
MAX6639AEE
MAX6639ATE
0°C to +150°C
16 QSOP
Servers
Networking Equipment
SMBus is a trademark of Intel Corp.
16 TQFN
(5mm x
5mm)
-40°C to
+125°C
0°C to +150°C
Typical Application Circuit appears at end of data sheet.
Pin Configurations
TOP VIEW
12
11
10
9
PWM1
1
2
3
4
5
6
7
8
16 SCL
15 SDA
14 ALERT
13 ADD
12 DXP2
11 DXN
10 GND
DXP1
GND
SCL
SDA
8
7
6
5
13
14
15
16
TACH1
PWM2
TACH2
FANFAIL
THERM
OT
MAX6639
MAX6639
PWM1
TACH1
V
CC
*CONNECT EXPOSED
PADDLE TO GND
OT
1
2
3
4
V
CC
9
DXP1
QSOP
THIN QFN
5 mm x 5 mm
________________________________________________________________ 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.
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
ABSOLUTE MAXIMUM RATINGS
CC
V
to GND..............................................................-0.3V to +6V
ESD Protection (all pins, Human Body Model) ..................2000V
PWM1, PWM2, TACH1, and TACH2 to GND ......-0.3V to +13.5V
DXP1 and DXP2 to GND..........................-0.3V to +(V + 0.3V)
DXN to GND ..........................................................-0.3V to +0.8V
Continuous Power Dissipation (T = +70°C)
16-Pin QSOP (derated 8.3mW/°C above +70°C) ....... 667mW
16-Pin TQFN 5mm x 5mm
A
CC
SCL, SDA, THERM, OT, FANFAIL, ADD,
and ALERT to GND ..............................................-0.3V to +6V
SDA, OT, THERM, ALERT, FANFAIL,
PWM1, and PWM2 Current .............................-1mA to +50mA
DXN Current ....................................................................... 1mA
(derated at 33.3mW/°C above +70°C)................2666.7mW
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
= +3.0V to +5.5V, T = 0°C to +125°C, unless otherwise noted. Typical values are at V
= +3.3V, T = +85°C.) (Note 1)
CC A
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
+5.5
10
UNITS
V
Operating Supply Voltage Range
Standby Current
V
+3.0
CC
SMB static, sleep mode
Interface inactive, ADC active
= +3.3V, +60°C ≤ T ≤ +100°C and
3
µA
Operating Current
0.5
1
mA
V
CC
A
1
+60°C ≤ T ≤ +100°C
R
External Temperature Error
°C
V
= +3.3V, +40°C ≤ T ≤ +100°C and
A
CC
2.5
0°C ≤ T ≤ +145°C
R
V
V
V
= +3.3V, 0°C ≤ T ≤ +145°C
3.8
2
CC
CC
CC
R
= +3.3V, +25°C ≤ T ≤ +100°C
A
Internal Temperature Error
°C
= +3.3V, 0°C ≤ T ≤ +125°C
4
A
Supply Sensitivity of Temperature
Measurement
0.2
°C/V
+0.125
11
°C
Bits
ms
%
Temperature Resolution
Conversion Time
125
Conversion-Rate Timing Error
PWM Frequency Error
Tachometer Accuracy
-10
-10
+10
+10
3
%
V
= 3.0V to 3.63V, T = +60°C to +100°C
%
CC
A
High level
Low level
70
100
10
130
13.0
Remote-Diode Sourcing Current
DXN Source Voltage
µA
V
7.0
0.7
2
_______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
ELECTRICAL CHARACTERISTICS (continued)
(V
= +3.0V to +5.5V, T = 0°C to +125°C, unless otherwise noted. Typical values are at V
= +3.3V, T = +85°C.) (Note 1)
CC A
CC
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIGITAL INPUTS AND OUTPUTS
ALERT, FANFAIL, THERM, OT, SDA
Output Low Voltage (Sink
Current) (OT, ALERT, FANFAIL,
THERM, SDA, PWM1, and PWM2)
0.4
0.4
I
= 6mA
V
V
SINK
OL
PWM1, PWM2, I
= 4mA
SINK
Output High Leakage Current
(OT, ALERT, FANFAIL, THERM,
SDA, PWM1, and PWM2)
I
1
µA
OH
Logic-Low Input Voltage (SDA,
SCL, THERM, TACH1, TACH2)
V
0.8
V
V
IL
V
V
= 3.3V
= 5.5V
2.1
2.6
CC
CC
Logic-High Input Voltage (SDA,
SCL, THERM, TACH1, TACH2)
V
IH
Input Leakage Current (SDA,
SCL, THERM, TACH1, TACH2)
V
= V
or GND
CC
1
µA
pF
IN
Input Capacitance
C
5
IN
SMBus TIMING (Note 2)
Serial Clock Frequency
Clock Low Period
f
(Note 3)
10
4
100
kHz
µs
SCL
t
10% to 10%
90% to 90%
LOW
Clock High Period
t
4.7
µs
HIGH
Bus Free Time Between STOP
and START Conditions
SMBus START Condition Setup
Time
t
4.7
4.7
µs
µs
BUF
t
90% of SMBCLK to 90% of SMBDATA
SU:STA
START Condition Hold Time
t
10% of SDA to 10% of SCL
90% of SCL to 10% of SDA
10% of SDA to 10% of SCL
10% of SCL to 10% of SDA (Note 4)
4
µs
µs
ns
ns
ns
ns
ms
HD:STO
STOP Condition Setup Time
Data Setup Time
Data Hold Time
t
t
4
SU:STO
SU:DAT
HD:DAT
250
300
t
SMBus Fall Time
SMBus Rise Time
SMBus Timeout
t
300
1000
90
F
t
R
t
58
74
TIMEOUT
Note 1: All parameters tested at a single temperature. Specifications are guaranteed by design.
Note 2: Timing specifications guaranteed by design.
Note 3: The serial interface resets when SCL 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 SCL's falling edge.
_______________________________________________________________________________________
3
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Typical Operating Characteristics
(V
= 3.3V, T = +25°C.)
A
CC
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
OPERATING SUPPLY CURRENT
vs. SUPPLY VOLTAGE
REMOTE TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
10
800
700
600
500
400
300
200
2
1
9
8
7
6
5
4
3
2
1
0
0
-1
-2
FAIRCHILD 2N3906
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
0
25
50
75
100
125
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
LOCAL TEMPERATURE ERROR
vs. DIE TEMPERATURE
REMOTE TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
LOCAL TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
1.0
0.5
2.0
1.5
1.0
0.5
0
2.0
1.5
1.0
0.5
0
V
V
= 250mV SQUARE WAVE APPLIED TO
V
V
= 250mV SQUARE WAVE APPLIED TO
P-P
IN
P-P
IN
WITH NO BYPASS CAPACITOR
WITH NO BYPASS CAPACITOR
CC
CC
0
-0.5
-1.0
-1.5
-2.0
-0.5
-1.0
-1.5
-2.0
-0.5
-1.0
-1.5
-2.0
0
25
50
75
100
125
10
100
1k
10k
100k
1
10
100
1k
10k
100k
TEMPERATURE (°C)
FREQUENCY (Hz)
FREQUENCY (Hz)
REMOTE TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
REMOTE TEMPERATURE ERROR
vs. DIFFERENTIAL NOISE FREQUENCY
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
2.0
1.5
1.0
0.5
0
2.0
1.5
1.0
0.5
0
2.0
1.0
V
V
= AC-COUPLED TO DXP AND DXN
V
V
= AC-COUPLED TO DXP
IN
IN
IN
IN
= 100mV SQUARE WAVE
= 100mV SQUARE WAVE
P-P
P-P
0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
-0.5
-1.0
-1.5
-2.0
-0.5
-1.0
-1.5
-2.0
0.1
1
10
100
1k
10k 100k
10
100
1k
10k
100k
0.1
1
10
100
FREQUENCY (Hz)
FREQUENCY (Hz)
DXP-DXN CAPACITANCE (nF)
4
_______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Typical Operating Characteristics (continued)
(V
= 3.3V, T = +25°C.)
A
CC
PWMOUT FREQUENCY
vs. SUPPLY VOLTAGE
PWMOUT FREQUENCY
vs. DIE TEMPERATURE
35
34
33
32
31
30
35
34
33
32
31
30
-40
-15
10
35
60
85
110
3.0
3.5
4.0
4.5
5.0
5.5
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
Pin Description
PIN
TQFN QSOP
NAME
FUNCTION
Open-Drain Output to Power-Transistor Driving Fan. Connect to the gate of a MOSFET or base of a
bipolar transistor. PWM_ requires a pullup resistor. The pullup resistor can be connected to a supply
voltage as high as 13.5V, regardless of the MAX6639’s supply voltage.
PWM2,
PWM1
1, 15
2, 16
3, 1
4, 2
Tachometer Inputs. Connect to the tachometer output of the fan. TACH_ requires a pullup resistor. The
pullup resistor can be connected to a supply voltage as high as 13.5V, regardless of the MAX6639’s
supply voltage.
TACH2,
TACH1
3
4
5
6
FANFAIL Active-Low, Open-Drain, Fan-Failure Output. Open circuit when V = 0.
CC
Active-Low, Open-Drain Thermal Alarm Output. Typically used for clock throttling. Open circuit when
THERM
V
= 0.
CC
Active-Low, Open-Drain Overtemperature Output. Typically used for system shutdown or clock
throttling. Can be pulled up to 5.5V regardless of V . Open circuit when V = 0.
5
7
OT
CC
CC
6
7
8
V
Power-Supply Input. 3.3V nominal. Bypass V
to GND with a 0.1µF capacitor.
CC
CC
10
GND
Ground. Connect to a clean ground reference.
Combined Current Source and A/D Positive Input for Remote Diode. Connect to anode of remote-diode-
connected temperature-sensing transistor. Do not leave floating; connect to DXN if no remote diode is
used. Place a 2200pF capacitor between DXP_ and DXN for noise filtering.
DXP1,
DXP2
8, 10
9, 12
9
11
13
DXN
ADD
Connect Cathode of the Remote-Diode-Connected Transistor to DXN
Address Input. Sets device slave address. Connect to GND, V , or leave floating to give three unique
CC
addresses. See Table 1.
11
12
13
14
16
ALERT Active-Low, Open-Drain SMBus Alert Output
SCL
SMBus Serial-Clock Input. Can be pulled up to 5.5V regardless of V . Open circuit when V = 0.
CC CC
SMBus Serial-Data Input/Output, Open Drain. Can be pulled up to 5.5V regardless of V . Open
CC
14
15
SDA
circuit when V
= 0.
CC
_______________________________________________________________________________________
5
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Detailed Description
Block Diagram
The MAX6639 monitors its own temperature and a
remote-diode-connected transistor or the temperatures
of two external-diode-connected transistors, which typi-
cally reside on the die of a CPU or other integrated cir-
cuit. The 2-wire serial interface accepts standard
SMBus write byte, read byte, send byte, and receive
byte commands to read the temperature data and pro-
gram the alarm thresholds. Temperature data can be
read at any time over the SMBus, and a programmable
alarm output can be used to generate interrupts, throt-
tle signals, or overtemperature shutdown signals.
V
CC
MAX6639
DXP1
DXN
PWM1
PWM
GENERATOR
BLOCK
TEMPERATURE
PROCESSING
BLOCK
PWM2
DXP2
The temperature data is also used by the internal dual-
PWM fan-speed controller to adjust the speed of up to
two cooling fans, thereby minimizing noise when the
system is running cool, but providing maximum cooling
when power dissipation increases. RPM feedback
allows the MAX6639 to control the fan’s actual speed.
OT
THERM
FANFAIL
ALERT
ADD
LOGIC
SMBus
INTERFACE AND
REGISTERS
SDA
SCL
TACH1
TACH2
GND
Write Byte Format
S
ADDRESS
WR
ACK
COMMAND
ACK
DATA
ACK
P
7 bits
8 bits
8 bits
1
Slave Address: equiva-
lent 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)
Read Byte Format
S
ADDRESS
WR
ACK
COMMAND
ACK
S
ADDRESS
RD
ACK
DATA
///
P
7 bits
8 bits
7 bits
8 bits
Slave Address: equiva-
lent to chip-select line
Command Byte: selects
which register you are
reading from
Slave Address: repeated
due to change in data-
flow direction
Data Byte: reads from
the register set by the
command byte
Send Byte Format
Receive Byte Format
S
ADDRESS
RD
ACK DATA
///
P
S
ADDRESS WR ACK COMMAND ACK
P
7 bits
8 bits
7 bits
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
Command Byte: sends com-
mand with no data, usually
used for one-shot command
S = START CONDITION
P = STOP CONDITION
SHADED = SLAVE TRANSMISSION
/// = NOT ACKNOWLEDGED
Figure 1. SMBus Protocols
6
_______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SCL
SDA
t
t
BUF
SU:STO
t
t
t
SU:DAT
SU:STA HD:STA
A = START CONDITION
E = SLAVE PULLS SMBDATA LINE LOW
I = MASTER PULLS DATA LINE LOW
J = ACKNOWLEDGE CLOCKED INTO SLAVE
K = ACKNOWLEDGE CLOCK PULSE
L = STOP CONDITION
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER
G = MSB OF DATA CLOCKED INTO SLAVE
H = LSB OF DATA CLOCKED INTO SLAVE
M = NEW START CONDITION
Figure 2. SMBus Write Timing Diagram
A
B
C
D
E
F
G
H
I
J
K
L
M
t
t
HIGH
LOW
SCL
SDA
t
t
t
t
HD:DAT
HD:STA
SU:STA
SU:DAT
t
t
SU:STO
BUF
A = START CONDITION
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
B = MSB OF ADDRESS CLOCKED INTO SLAVE
C = LSB OF ADDRESS CLOCKED INTO SLAVE
D = R/W BIT CLOCKED INTO SLAVE
M = NEW START CONDITION
E = SLAVE PULLS SMBDATA LINE LOW
Figure 3. SMBus Read Timing Diagram
2
Table 1. I C Slave Address
SMBus Digital Interface
From a software perspective, the MAX6639 appears as
a set of byte-wide registers. This device uses a stan-
dard SMBus 2-wire/I2C*-compatible serial interface to
access the internal registers.
BINARY
EQUIVALENT
2
ADD INPUT STATE I C SLAVE ADDRESS
V
5Eh
5Ch
58h
0101 111
0101 110
0101 100
CC
Floating
GND
The MAX6639 features an address select input (ADD)
that allows the MAX6639 to have three unique addresses
(see Table 1).
ter systems, since a second master could overwrite the
command byte without informing the first master.
The MAX6639 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 instruc-
tion. Use caution with the shorter protocols in multimas-
Table 4 details the register addresses and functions,
whether they can be read or written to, and the power-
on reset (POR) state. See Tables 5–9 for all other regis-
ter functions and the Register Descriptions section.
Temperature Reading
Temperature data can be read from registers 00h and
01h. The temperature data format for these registers is
8 bits, with the LSB representing 1°C (Table 2) and the
MSB representing +128°C. The MSB is transmitted first.
*Purchase of I2C components from Maxim Integrated Products,
Inc., or one of its sublicensed Associated Companies, conveys
a license under the Philips I2C Patent Rights to use these com-
ponents in an I2C system, provided that the system conforms to
the I2C Standard Specification as defined by Philips.
_______________________________________________________________________________________
7
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
at least 5°C below the trip threshold or the trip thresh-
Table 2. Temperature Data Byte Format
old must be increased to at least 5°C above the current
TEMP (°C)
241
TEMP (°C)
+241
+240
+126
+25
DIGITAL OUTPUT
1111 0001
measured temperature. Asserting THERM internally or
externally forces both PWM outputs to 100% duty cycle
when bit 6 in address 13h (fan 1) or bit 6 in address
17h (fan 2) is set.
240
1111 0000
126
0111 1110
ALERT
The ALERT output asserts to indicate that a measured
temperature exceeds the ALERT trip threshold for that
temperature channel. The status bit and the ALERT out-
put clear by reading the ALERT status register. If the
ALERT status bit is cleared, but the temperature still
exceeds the ALERT temperature threshold, ALERT
reasserts on the next conversion, and the status bit sets
again. A successful alert response protocol clears
ALERT but does not affect the ALERT status bit.
25
0001 1001
1.50
0.00
1
0000 0001
0
0000 0000
Three additional temperature bits provide resolution
down to 0.125°C and are in the channel 1 extended
temperature (05h) and channel 2 extended tempera-
ture (06h) registers. All values below 0°C clip to 00h.
The MAX6639 employs a register lock mechanism to
avoid getting temperature results from the temperature
register and the extended temperature register sam-
pled at two different time points. Reading the extended
register stops the MAX6639 from updating the temper-
ature register for at least 0.25s, unless there is a tem-
perature register read before the scheduled update.
This allows enough time to read the main register
before it is updated, thereby preventing reading the
temperature register data from one conversion and the
extended temperature register data from a different
conversion.
TACH1 and TACH2 Inputs
To measure the fan speed, the MAX6639 has two
tachometers. Each tachometer has an accurate internal
clock to count the time elapsed in one revolution.
Therefore, it is counting the time between two tachome-
ter pulses for a fan with four poles. When the PWM sig-
nal is used to directly modulate the fan’s power supply,
the PWM frequency is normally in the 20Hz to 100Hz
range. In this case, the time required for one revolution
may be longer than the PWM on-time. For this reason,
the PWM pulses are periodically stretched to allow
tachometer measurement over a full revolution. Turn off
pulse stretching by setting bit 5 of register 13h or regis-
ter 17h when using a 4-wire fan.
The MAX6639 measures the temperature at a fixed rate
of 4Hz immediately after it is powered on. Setting bit 7
of the configuration register (04h) shuts down the tem-
perature measurement cycle.
The tachometer count is inversely proportional to the
fan’s RPM. The tachometer count data is stored in regis-
ter 20h (for TACH1) and register 21h (for TACH2).
Reading a value of 255 from the TACH count register
means the fan’s RPM is zero or too slow for the range.
Reading a value of zero in the TACH count register
means the fan’s RPM is higher than the range selected.
Table 2 shows the fan’s available RPM ranges. Use reg-
isters 10h or 14h to select the appropriate RPM range for
the fan being used.
OT Output
When a measured temperature exceeds the corre-
sponding OT temperature threshold and OT is not
masked, the associated OT status register bit sets and
the OT output asserts. If OT for the respective channel
is masked, the OT status register sets, but the OT out-
put does not assert. To deassert the OT output and the
associated status register bit, either the measured tem-
perature must fall at least 5°C below the trip threshold
or the trip threshold must be increased to at least 5°C
above the current measured temperature.
THERM
When a measured temperature exceeds the corre-
sponding THERM temperature threshold and THERM is
not masked, the associated THERM status register bit
is set and the THERM output asserts. If THERM for the
respective channel is masked, the THERM status regis-
ter is set, but the THERM output does not assert. To
deassert the THERM output and the associated status
register bit, either the measured temperature must fall
Table 3. Tachometer Setting
FAN RPM
RANGE
INTERNAL CLOCK
FREQUENCY (kHz)
2000
4000
1
2
4
8
8000
16,000
8
_______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
registers, the duty cycle changes to the new value at a
rate determined by the rate-of-change bits [6:4] in the
fan 1 or 2 configuration 1 register. The rate-of-change
of the duty cycle ranges from 000 (immediately
changes to the new programmed value) to 111
(changes by 1/120 every 4s). See Table 5 and the Fan
1 and 2 Configuration 1 (10h and 14h) section.
FANFAIL
The FANFAIL output asserts to indicate that one of the
fans has failed or is spinning slower than the required
speed. The MAX6639 detects fan fault depending on the
fan-control mode. In PWM mode, the MAX6639 pro-
duces a square wave with a duty cycle set by the value
written to the duty-cycle registers (26h and 27h). In this
mode, the MAX6639 signals a fan fault when the
tachometer count is greater than the maximum tachome-
ter count value stored in the appropriate register (22h
and 23h). After the MAX6639 asserts FANFAIL, the fan
with a tachometer fault goes to full speed for 2s in an
attempt to restart the fan and then returns to the original
duty-cycle settings. Reading the status register clears
the FANFAIL status bits and the output. The MAX6639
measures the fan speed again after 2s. The MAX6639
asserts FANFAIL if it detects the fan fault again.
Manual RPM Control Mode
Enter manual RPM control mode by setting bits 2, 3,
and 7 of the fan 1 or 2 configuration 1 register (10h and
14h) to zero. In the manual RPM control mode, the
MAX6639 adjusts the duty cycle and measures the fan
speed. Enter the target tachometer count in register
22h for fan 1 and register 23h for fan 2. The MAX6639
compares the target tachometer count with the mea-
sured tachometer count and adjusts the duty cycle so
that the fan speed gradually approaches the target
tachometer count.
In RPM mode (either automatic or manual), the
MAX6639 checks for fan failure only when the duty
cycle reaches 100%. It asserts FANFAIL when the
tachometer count is greater than twice the target
tachometer count. In manual RPM mode, registers 22h
and 23h store the target tachometer count value. In
automatic RPM mode, these registers store the maxi-
mum tachometer count.
The first time manual RPM control mode is entered, the
initial PWM duty cycle is determined by the target
tachometer count:
255 − targetTACH
Initial duty cycle =
2
Fan-Speed Control
The MAX6639 adjusts fan speed by controlling the duty
cycle of a PWM signal. This PWM signal then either
modulates the DC brushless fan’s power supply or dri-
ves a speed-control input on a fan that is equipped with
one. There are three speed-control modes: PWM, in
which the PWM duty cycle is directly programmed over
the SMBus; manual RPM, in which the desired
tachometer count is programmed into a register and
the MAX6639 adjusts its duty cycle to achieve the
desired tachometer count; and automatic RPM, in
which the tachometer count is adjusted based on a
programmed temperature profile.
where targetTACH is the value of the target tachometer
count in the target tach count register (22h or 23h).
If the initial duty-cycle value is over 120, the duty cycle
is 100%. If spin-up is enabled (bit 7 in registers 13h
and 17h) and the fan is not already spinning, the duty
cycle first goes to 100% and then goes to the initial
duty-cycle value. Every 2s, the MAX6639 counts the
fan’s period by counting the number of pulses stored in
registers 24h and 25h. If the count is different from the
target count, the duty cycle is adjusted.
If a nonzero rate-of-change is selected, the duty cycle
changes at the specified rate until the tachometer count
is within 5 of the target. Then the MAX6639 gets into a
locked state and updates the duty cycle every 2s.
The MAX6639 divides each PWM cycle into 120 time
slots. Registers 26h and 27h contain the current values
of the duty cycles for PWM1 and PWM2, expressed as
the effective time-slot length. For example, the PWM1
output duty cycle is 25% when register 26h reads 1Eh
(30/120).
Automatic RPM Control Mode
In the automatic RPM control mode, the MAX6639 mea-
sures temperature, sets a target tachometer count
based on the measured temperature, and then adjusts
the duty cycle so the fan spins at the desired speed.
Enter this mode by setting bit 7 of the fan 1 or 2 config-
uration 1 register (10h and 14h) to zero and selecting
the temperature channel that controls the fan speed
using bits 2 and 3 of the configuration register.
PWM Control Mode
Enter PWM mode by setting bit 7 of the fan 1 or 2 con-
figuration 1 register (10h and 14h) to 1. In PWM control
mode, the MAX6639 generates PWM signals whose
duty cycles are specified by writing the desired values
to fan duty-cycle registers 26h and 27h. When a new
duty-cycle value is written into one of the fan duty-cycle
In both RPM modes (automatic and manual), the
MAX6639 implements a low limit for the tachometer
_______________________________________________________________________________________
9
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
RPM
TACH
T
T
MIN
T
B
TEMPERATURE
RPM
MIN-5
MAX
0xFFh
TACH
B+1
TACH
MAX
TACH
A+1
TACH
A+1
RPM
MIN
TACH
B+1
TACH
MIN
TEMPERATURE
0
T
MIN
-5
T
MIN
T
B
Figure 4. Tachometer Target Calculation
Figure 5. RPM Target Calculation
counts. This limits the maximum speed of the fan by
ensuring that the fan’s tachometer count does not go
lower than the tachometer count specified by bits 5
through 0 of register 24h for fan 1 and register 25h for
fan 2. Typical values for the minimum tachometer count
are 30h to 60h. Set the value to correspond to the full-
rated RPM of the fan. See Figure 4.
Register Descriptions
Channel 1 and Channel 2 Temperature Registers
(00h and 01h)
These registers contain the results of temperature mea-
surements. The MSB has a weight of +128°C and the
LSB +1°C. Temperature data for remote diode 1 is in
the channel 1 temperature register. Temperature data
for remote diode 2 or the local sensor (selectable by bit
4 in the global configuration register) is in the channel 2
temperature register. Three additional temperature bits
provide resolution down to 0.125°C and are in the
channel 1 extended temperature (05h) and channel 2
extended temperature (06h) registers. The channel 1
and channel 2 temperature registers do not update
until at least 250ms after the access of the associated
extended temperature registers. All values below 0°C
return 00h.
Figure 5 shows how the MAX6639 calculates the target
tachometer value based on the measured temperature.
At T
, the fan spins at a minimum speed value corre-
MIN
sponding to the maximum tachometer count value
stored in register 22h or 23h. Bit 0 of register 11h (fan
1) and register 15h (fan 2) selects the behavior below
T
. If bit 0 is equal to zero, the fan is completely off
MIN
below T
. When the temperature is falling, it must
MIN
drop 5°C below T
set to 1, the fan does not turn off below T
before the fan turns off. If bit 0 is
MIN
, but
MIN
instead stays at the maximum tachometer count in reg-
ister 22h or 23h.
Status Register (02h)
A 1 indicates that an ALERT, THERM, OT, or fan fault has
occurred. Reading this register clears bits 7, 6, 1, and 0.
Reading the register also clears the ALERT and
FANFAIL outputs, but not the THERM and OT outputs. If
the fault is still present on the next temperature measure-
ment cycle, any cleared bits and outputs are set again.
A successful alert response clears the values on the out-
puts but does not clear the status register bits. The
ALERT bits assert when the measured temperature is
higher than the respective thresholds. The THERM and
OT outputs behave like comparators with 5°C hysteresis.
When the measured temperature is higher than T
,
MIN
the MAX6639 calculates the target tachometer count
value based on two linear equations. The target
tachometer count decreases by the tach step size
value stored in bits 7 through 4 of registers 11h and
15h each time the measured temperature increases by
the temperature step size value stored in bits 2 and 3 of
registers 11h and 15h. As the measured temperature
continues to increase, a second tachometer step size
goes into effect. Bits 3 through 0 of register 12h and
16h select the number temperature/PWM steps after
which the new step size takes effect. The new step size
is selected by bits 7 to 4 of registers 12h and 16h.
Mask Register (03h)
This register masks the ALERT, OT, THERM, and
FANFAIL outputs. A 1 prevents the corresponding fail-
ures from being asserted on these outputs. The mask
bits do not affect the status register.
10 ______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Table 4. Register Map
REGISTER
NO.
ADDRESS
READ/
WRITE
POR
STATE
FUNCTION
D7
D6
D5
D4
D3
D2
D1
D0
0000 Temperature
0000 channel 1
MSB
(+128°C)
LSB
(1°C)
R
R
00h
01h
02h
03h
—
—
—
—
—
—
—
—
—
—
—
0000 Temperature
MSB
(+128°C)
LSB
(1°C)
—
0000
channel 2
0000
0000
Channel 1 Channel 2 Channel 1 Channel 2 Channel 1 Channel 2
ALERT
Fan 2
fault
R
Status byte
Fan 1 fault
Fan 1 fault
ALERT
OT
OT
THERM
THERM
0000
0011
Channel 1 Channel 2 Channel 1 Channel 2 Channel 1 Channel 2
ALERT
Fan 2
fault
R/W
Output mask
ALERT
OT
OT
THERM
THERM
SMBus
Temp
PWM
output
timeout: channel 2
0 = source:
Run
0 = run,
1= stby
0011
Global
POR:
R/W
04h
Reserved Reserved Reserved
frequency
1 = reset enabled, 1 = local,
0000 configuration
1 =
disabled
0 = remote range
2
Channel 1
0000
MSB
(0.5°C)
LSB
(0.125°C)
Diode
fault
R
R
05h
06h
—
—
Reserved Reserved Reserved Reserved
Reserved Reserved Reserved Reserved
extended
0000
temperature
Channel 2
0000
MSB
(0.5°C)
LSB
(0.125°C)
Diode
fault
extended
0000
temperature
0101
0101
Channel 1
ALERT limit
LSB
(1°C)
R/W
R/W
R/W
R/W
R/W
R/W
08h
09h
0Ah
0Bh
0Ch
0Dh
MSB
MSB
MSB
MSB
MSB
MSB
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
0101
0101
Channel 2
ALERT limit
LSB
(1°C)
0110 Channel 1 OT
1110 limit
LSB
(1°C)
0110 Channel 2 OT
1110
LSB
(1°C)
limit
0101
Channel 1
LSB
(1°C)
0101 THERM limit
0101 Channel 2
0101 THERM limit
LSB
(1°C)
—
—
—
Fan 1
configuration
Rate of
change
(MSB)
Rate of
Fan 1
Fan 1
RPM
range
select
RPM
range
select
1000
0010
PWM
mode
Rate of
change
R/W
R/W
10h
11h
change channel 1 channel 2
(LSB)
1
control
control
Minimum
fan
speed:
Fan 1
0000
RPM step-
Configuration size A
RPM step- Temp
Temp
RPM step- RPM step-
size A size A
PWM
size A
(LSB)
step-size step-size
A (MSB) A (LSB)
0000
Polarity 0 = 0%,
1= value
2a
(MSB)
______________________________________________________________________________________ 11
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Table 4. Register Map (continued)
REGISTER
NO.
ADDRESS
READ/
WRITE
POR
STATE
FUNCTION
D7
D6
D5
D4
D3
D2
D1
D0
Fan 1
configuration size B
RPM step-
RPM
Start
Start
0000
0000
RPM step- RPM step-
Start step- Start step-
R/W
R/W
R/W
12h
13h
14h
step-size step-size step-size
B (LSB) B (MSB)
size B
size B
size B
size B (LSB)
2b
(MSB)
B
Fan 1
configuration
3
THERM to
full-speed stretching
enable
Pulse
Fan PWM Fan PWM
frequency frequency
0100
0001
Spin-up
disable
Reserved Reserved Reserved
disable
(MSB)
(LSB)
Fan 2
configuration
1
Step-size
delay
(MSB)
Step-size Fan 2
Fan 2
RPM
1000
0010
PWM
mode
Step-size
delay
RPM range
select
delay channel 1 channel 2 range
(LSB)
control
control
select
PWM
100%
duty
Minimum fan
speed:
0 = 0%, 1=
value in 22h
Fan 2
configuration size A
RPM step-
RPM
Temp
Temp
0000
0000
RPM step- RPM step-
step-size step-size step-size
A (LSB) A (MSB) A (LSB)
R/W
15h
size A
size A
2a
(MSB)
cycle
Fan 2
configuration size B
RPM step-
RPM
step-size step-size step-size
B (LSB) B (MSB)
Start
Start
0000
0000
RPM step- RPM step-
Start step- Start step-
size B size B (LSB)
R/W
R/W
R
16h
17h
20h
21h
size B
size B
2b
(MSB)
B
Fan 2
configuration
3
THERM to
Pulse
Fan PWM Fan PWM
0100
0001
Spin-up
disable
full-speed stretching Reserved Reserved Reserved frequency frequency
enable
disable
(MSB)
(LSB)
Fan 1
tachometer
count
1111
1111
MSB
MSB
—
—
—
—
—
—
—
—
—
LSB
Fan 2
tachometer
count
1111
1111
R
—
—
—
—
—
—
LSB
LSB
Fan 1 start
1111 tach count/
R/W
R/W
22h
23h
MSB
MSB
—
—
—
—
—
—
1111
target tach
count
Fan 2 max
tach count/
1111 target tach
count
1111
—
—
—
LSB
Pulses per
Pulse per Pulse per Fan 1 min Fan 1 min Fan 1 min Fan 1 min Fan 1 min Fan 1 min
revolution/
fan 1
minimum
0100
0000
R/W
24h
revolution revolution tach count
(MSB) (LSB) (MSB)
tach
count
tach
count
tach
count
tach
count
tach count
(LSB)
tach count
Pulses per
revolution/ Pulse per Pulse per Fan 2 min Fan 2 min Fan 2 min Fan 2 min Fan 2 min Fan 2 min
0100
0000
revolution revolution tach count
tach
tach
tach
tach
tach count
(LSB)
R/W
R
25h
26h
fan 2
minimum
tach count
(MSB)
(LSB)
(MSB)
count
count
count
count
0000 Fan 1 current
0000 duty cycle
MSB
—
—
—
—
—
—
LSB
12 ______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Table 4. Register Map (continued)
REGISTER
NO.
ADDRESS
READ/
WRITE
POR
STATE
FUNCTION
D7
D6
D5
D4
D3
D2
D1
D0
0011 Fan 1 target
1100 duty cycle
W
R
26h
27h
27h
MSB
MSB
MSB
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
LSB
LSB
LSB
0000 Fan 2 current
0000 duty cycle
0011 Fan 2 target
W
1100
duty cycle
Channel 1
minimum
fan-start
0100
000
R/W
R/W
28h
29h
MSB
MSB
—
—
—
—
—
—
—
—
—
—
—
—
LSB
LSB
temperature
Channel 2
minimum
fan-start
0100
0000
temperature
0101 Read device
R
R
R
3Dh
3Eh
3Fh
0
0
0
1
1
0
0
0
0
1
0
0
1
1
0
0
1
0
0
0
0
0
1
0
1000
ID
Read
manufacturer
ID
0100
1101
0000 Read device
0000 revision
Global Configuration Register (04h)
Extended Temperature Registers (05h and 06h)
The global configuration register controls the shutdown
mode, power-on reset, SMBus timeout, and tempera-
ture channel 2 source select:
These registers contain the extended temperature data
from channels 1 and 2. Bits D[7:5] contain the 3 LSBs
of the temperature data. The bit values are 0.5°C,
0.25°C, and 0.125°C. When bit 0 is set to 1, a diode
fault has been detected.
• D7: Run/Standby. Normal operation is run (0).
Setting this bit to 1 suspends conversions and puts
the MAX6639 into low-power sleep mode.
Channel 1 and Channel 2 ALERT, OT, and THERM
Limits (08h Through 0Dh)
• D6: Software POR. Writing a 1 resets all registers to
their default values.
These registers contain the temperatures above which
the ALERT, THERM, and OT status bits set and outputs
assert (for the temperature channels that are not
masked). The data format is the same as that of the
channel 1 and channel 2 temperature registers: the
LSB weight is +1°C and the MSB is +128°C.
• D5: SMBus Timeout Disable. Writing a zero
enables SMBus timeout for prevention of bus lockup.
When the timeout function is enabled, the SMBus
interface is reset if SDA or SCL remains low for more
than 74ms (typ).
• D4: Temperature Channel 2 Source. Selects either
local or remote 2 as the source for temperature
channel 2 register data. Writing a zero to this bit
selects remote 2 for temperature channel 2.
• D3: PWM Output Frequency Range. Selects either
the 20Hz to 100Hz range or the 5kHz to 25kHz range
for the PWM outputs (see Table 9).
______________________________________________________________________________________ 13
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Table 5. Fan Duty-Cycle Rate-of-Change
ACTUAL RATE OF CHANGE AT SPECIFIC PWM FREQUENCIES
REGISTER 10h NOMINAL RATE
OR 14h D[6:4] OF CHANGE (s)
NOMINAL TIME FROM
33ꢀ TO 100ꢀ (s)
100Hz (s)
50Hz (s)
33.3Hz (s)
0
20Hz (s)
000
001
010
011
100
101
110
111
0
0.0625
0.125
0.25
0.5
0
0.06
0.13
0.25
0.5
1
0
0.06
0.12
0.26
0.5
1
0
0.05
0.15
0.25
0.5
1
0
5
0.06
0.12
0.24
0.51
0.99
1.98
3.96
10
20
40
80
160
320
1
2
2
2
2
4
4
4
4
Fan 1 and 2 Configuration 1 (10h and 14h)
The following registers control the modes of operation
of the MAX6639:
changes can be traded for response time. Table 5
shows the effect of D[6:4] and, for reference, the
time required for the fan speed to change from 33%
to 100% duty cycle as a function of the rate-of-
change bits.
• D7: PWM Mode. D7 = 1 sets the fan into manual
PWM duty-cycle control mode. Write the target duty
cycle in the fan duty-cycle register. D7 = 0 puts the
fan into RPM control mode. To set RPM manually, set
both fan-control temperature channels (bits D2 and
D3) to zero and write the desired tachometer count
into the TACH count register.
• D[3:2]: Temperature Channel(s) for Fan Control.
Selects the temperature channel(s) that control the
PWM output when the MAX6639 is in automatic RPM
control mode (PWM mode bit is zero). If two chan-
nels are selected, the fan goes to the higher of the
two possible speeds. If neither channel is selected,
then the fan is in manual RPM mode and the speed
is forced to the value written to the target tach count
register 22h or 23h.
• D[6:4]: Fan Duty-Cycle Rate-of-Change. D[6:4]
sets the time between increments of the duty cycle.
Each increment is 1/120 of the duty cycle. By adjust-
ing the rate-of-change, audibility of fan-speed
• D[1:0]: RPM Range. Scales the tachometer counter
by setting the maximum (full-scale) value of the RPM
range to 2000, 4000, 8000, or 16,000. (Table 3
shows the internal clock frequency as a function of
the range.)
Table 6. Fan RPM Speed
REGISTER 10h OR 14h
FAN MAXIMUM RPM VALUE
00
01
10
11
2000
4000
8000
16,000
Table 7. RPM-to-Tachometer Count Relationship Examples
SELECTED NUMBER
OF PULSES PER
REVOLUTION
ACTUAL FAN PULSES TACHOMETER COUNT
MAXIMUM RPM VALUE
ACTUAL RPM
PER REVOLUTION
VALUE*
2000
4000
1000
1000
3000
3000
8000
8000
2
2
2
2
4
4
2
2
2
4
4
2
3Ch
78h
28h
14h
3Ch
78h
4000
4000
16,000
16,000
*Tachometer count value = ((internal clock frequency) x 60) / actual RPM) (selected number of pulses per revolution / actual fan pulses)
14 ______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Table 8. Temperature Step Size
Table 9. Fan PWM Frequency
REGISTER 11h
OR 15h
FAN CONTROL TEMPERATURE
LOW-FREQUENCY
(Hz) REGISTER
04h D3 = 0
HIGH-FREQUENCY
(kHz) REGISTER
04h D3 = 1
REGISTERS
13h AND 16h
STEP SIZE (°C)
00
01
10
11
1
2
4
8
20
33.33
50
5
00
01
10
11
8.33
12.5
25
100
Fan 1 and 2 Configuration 2a (11h and 15h)
The following registers apply to the automatic RPM
control mode:
• D7: Fan Spin-Up Disable. Set to zero to enable fan
spin-up. Whenever the fan starts up from zero drive,
it is driven with 100% duty cycle for 2s to ensure that
it starts. Set to 1 to disable the spin-up function.
• D[7:4]: Fan RPM (Tachometer) Step-Size A.
Selects the number of tachometer counts the target
value decreases for each temperature step increase
above the fan-start temperature. Value = n + 1 (1
through 16) where n is the value of D[7:4].
• D6: THERM to Full-Speed Enable. When this bit is
1, THERM going low (either by being pulled low
externally or by the measured temperature exceed-
ing the THERM limit) forces the fan to full speed. In
all modes, this happens at the rate determined by
the rate-of-change selection. When THERM is
deasserted (even if the fan has not reached full
speed), the speed falls at the selected rate-of-
change to the target speed.
• D[3:2]: Temperature Step Size. Selects the temper-
ature increment for fan control. For each temperature
step increase, the target tachometer count decreas-
es by the value selected by D[7:4] (Table 8).
• D1: PWM Output Polarity. PWM output is low at
100% duty cycle when this bit is set to zero. PWM
output is high at 100% duty cycle when this bit is set
to 1.
• D5: Disable Pulse Stretching. Pulse stretching is
enabled when this bit is set to zero. When modulat-
ing the fan’s power supply with the PWM signal, the
PWM pulses are periodically stretched to keep the
tachometer signal available for one full revolution.
Setting this bit to 1 disables pulse stretching. The
MAX6639 still measures the fan speed but does not
stretch the pulses for measurements, so the fan’s
power supply must not be pulse modulated.
• D0: Minimum Speed. Selects the value of the mini-
mum fan speed (when temperature is below the fan-
start temperature in the automatic RPM control
mode). Set to zero for 0% fan drive. Set to 1 to deter-
mine the minimum fan speed by the tachometer
count value in registers 22h and 23h (fan maximum
TACH).
• D[1:0]: PWM Output Frequency. These bits control
Fan 1 and 2 Configuration 2b (12h and 16h)
The following registers select the tachometer step sizes
and number of steps for step-size A to step-size B
slope changes (see Figure 1):
the PWM output frequency as shown in Table 9.
Fan Tach Count 1 and 2 (20h and 21h)
These registers have the latest tachometer measure-
ment of the corresponding channel. This is inversely
proportional to the fan’s speed. The fan RPM range
should be set so this count falls in the 30 to 160 range
for normal fan operation.
• D[7:4]: RPM (Tachometer) Step Size B. Selects
number of tachometer counts the target value
decreases for each temperature step increase after
the number of steps selected by D[3:0]. Value = n +
1 (1 through 16) where n is the value of D[7:4].
Fan Start Tach Count/Target Tach Count
(22h and 23h)
• D[3:0]: Selects the number of temperature/tachome-
ter steps above the fan-start temperature at which
step-size B begins.
D[7:0]: This sets the starting tachometer count for the
fan in automatic RPM mode. Depending on the setting
of the minimum duty-cycle bit, the tachometer count
has this value either at all temperatures below the fan-
start temperature or the count is zero below the fan-
start temperature and has this value when the fan-start
temperature is reached. These registers are the target
tach count when in manual RPM mode.
Fan 1 and Fan 2 Configuration 3 (13h and 17h)
The following registers control fan spin-up, PWM output
frequency, pulse stretching, and THERM to fan full-
speed enable:
______________________________________________________________________________________ 15
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Channel 1 and Channel 2 Fan-Start Temperature
Table 10. Tachometer Pulses per
Revolution
(28h and 29h)
These registers contain the temperatures at which fan
control begins (in automatic RPM mode).
REGISTERS 24h
OR 25h D[7:6]
TACHOMETER PULSES PER
REVOLUTION
Applications Information
00
01
10
11
1
2
3
4
Fan-Drive Circuits
A variety of fan-drive circuit configurations can be used
with the MAX6639 to control the fan’s speed. Four of
the most common are shown in Figures 6 through 10.
PWM Power-Supply Drive (High Side or Low Side)
The simplest way to control the speed of a 3-wire (sup-
ply, ground, and tachometer output) fan is to modulate
its power supply with a PWM signal. The PWM frequen-
cy is typically in the 20Hz to 40Hz range, with 33Hz
being a common value. If the frequency is too high, the
fan’s internal control circuitry does not have sufficient
time to turn on during a power-supply pulse. If the fre-
quency is too low, the power-supply modulation
becomes more easily audible.
Fan 1 and 2 Pulses and Min RPM (24h and 25h)
D[7:6]: This sets the number of tachometer pulses per
revolution for the fan. When set properly, a 2000RPM fan
with two pulses per revolution has the same tachometer
count as a 2000RPM fan with four pulses per revolution.
Table 10 lists tachometer pulses per revolution.
D[5:0]: This sets the minimum allowable fan tachometer
count (maximum speed). This limits the maximum
speed of the fan to reduce noise at high temperatures.
For reasonable speed resolution, the fan RPM range
should be set so this value is between approximately
30 and 60. If a maximum RPM limit is unnecessary, this
value can be set to the full-speed tachometer count.
The PWM can take place on the high side (Figure 6) or
the low side (Figure 7) of the fan’s power supply. In
either case, if the tachometer is used, it is usually nec-
essary to periodically stretch a PWM pulse so there is
enough time to count the tachometer pulse edges for
speed measurement. The MAX6639 allows this pulse
stretching to be enabled or disabled to match the
needs of the application.
Fan 1 and 2 Duty Cycle (26h and 27h)
These registers contain the present value of the PWM
duty cycle. In PWM fan-control mode, the desired (tar-
get) value of the PWM duty cycle can be written directly
into this register.
Pulse stretching can sometimes be audible if the fan
responds quickly to changes in the drive voltage. If the
acoustic effects of pulse stretching are too noticeable,
the circuit in Figure 8 can be used to eliminate pulse
V
CC
V
CC
V
V
FAN
FAN
(5V OR 12V)
(5V OR 12V)
3V TO 5.5V
4.7kΩ
4.7kΩ
TACH1
PWM1
PWM1
TACH1
TACH
OUTPUT
3V TO 5.5V
3V TO 5.5V
4.7kΩ
4.7kΩ
TACH
OUTPUT
Figure 6. High-Side PWM Drive Circuit
Figure 7. Low-Side Drive Circuit
16 ______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
V
CC
V
CC
V
FAN
(12V OR 5V)
3V TO 5.5V
4.7kΩ
4.7kΩ
PWM1
PWM1
3V TO 5.5V
(5V OR 12V)
3V TO 5.5V
V
FAN
5V
4.7kΩ
4.7kΩ
TACH1
TACH1
TACH
OUTPUT
TACH
OUTPUT
Figure 10. 4-Wire Fan with PWM Speed-Control Input
Figure 8. High-Side PWM Drive with “Keep-Alive” Supply
V
FAN
Linear Fan Supply Drive
(5V OR 12V)
While many fans are compatible with PWM power-supply
drive, some are excessively noisy with this approach.
When this is the case, a good alternative is to control the
fan’s power-supply voltage with a variable DC power-
supply circuit. The circuit in Figure 10 accepts the PWM
signal as an input, filters the PWM, and converts it to a
DC voltage that then drives the fan. To minimize the size
of the filter capacitor, use the highest available PWM fre-
quency. Pulse stretching is not necessary when using a
linear fan supply. Note that this approach is not as effi-
cient as PWM drive, as the fan’s power-supply current
flows through the MOSFET, which can have an apprecia-
ble voltage across it. The total power is still less than
that of a fan running at full speed. Table 11 is a summa-
ry of fan-drive options.
V
CC
100kΩ
3.3V
4.7kΩ
2N3904
100kΩ
PWM1
33kΩ
91kΩ
2.2µF
3V TO 5V
10µF
4.7kΩ
TACH1
4-Wire Fans
Some fans have an additional, fourth terminal that
accepts a logic-level PWM speed-control signal as
shown in Figure 10. These fans require no external
power circuitry and combine the low noise of linear
drive with the high efficiency of PWM power-supply
drive. Higher PWM frequencies are recommended
when using 4-wire fans.
TACH
OUTPUT
TACH OUTPUT
Figure 9. High-Side Linear Drive Circuit
stretching while still allowing accurate tachometer feed-
back. The diode connects the fan to a low-voltage
power supply, which keeps the fan’s internal circuitry
powered even when the PWM drive is zero. Therefore,
the tachometer signal is always available and pulse
stretching can be turned off. Note that this approach
prevents the fan from turning completely off, so even
when the duty cycle is 0%, the fan may still spin.
______________________________________________________________________________________ 17
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Table 11. Summary of Fan-Drive Options
FIGURE
DESCRIPTION
High-side PWM drive
PULSE STRETCHING
PWM FREQUENCY
PWM POLARITY
Negative
Positive
6
7
Yes
Yes
No
Low
Low
Low
High
High
Low-side PWM drive
8
High-side PWM drive with keep-alive supply
High-side linear supply
Negative
Positive
9
No
10
4-wire fan with PWM speed-control input
No
Positive
sense transistor with a different ideality factor is used,
the output data is different. Fortunately, the difference
is predictable.
Quick-Start Guide for 8000RPM 4-Pole
(2 Pulses per Revolution) Fan in Automatic
RPM Mode Using the Circuit of Figure 7
1) Write 02h to register 11h to set the PWM output to
drive the n-channel MOSFET.
Assume a remote-diode sensor designed for a nominal
ideality factor n
is used to measure the tem-
NOMINAL
perature of a diode with a different ideality factor, n .
1
2) Write 4Bh to register 22h to set the minimum RPM
to 3200.
The measured temperature T can be corrected using:
M
3) Write 5Eh to register 24h to set the pulses per revo-
lution to 2 and to set the maximum RPM speed to
8000RPM.
⎛
⎞
n
1
T
= T
ACTUAL
⎜
⎟
M
n
⎝
⎠
NOMINAL
4) Write 19h to register 28h to set the fan-start temper-
ature to +25°C.
where temperature is measured in Kelvin.
As mentioned above, the nominal ideality factor of the
MAX6639 is 1.008. As an example, assume the
MAX6639 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:
5) Write D2h to register 10h to start automatic
RPM mode.
Remote-Diode Considerations
Temperature accuracy depends upon having a good-
quality, diode-connected, small-signal transistor.
Accuracy has been experimentally verified for all the
devices listed in Table 12. The MAX6639 can also
directly measure the die temperature of CPUs and
other ICs with on-board temperature-sensing diodes.
⎛
⎞
⎛
⎞
n
1.008
1.002
NOMINAL
T
= T
= T
= T (1.00599)
M
⎜
⎟
ACTUAL
M
M ⎜
⎟
n
1
⎝
⎠
⎝
⎠
For a real temperature of +85°C (358.15K), the mea-
sured temperature is +82.91°C (356.02K), which is an
error of -2.13°C.
The transistor must be a small-signal type with a rela-
tively high forward voltage. This ensures that the input
voltage is within the A/D input voltage range. The for-
ward voltage must be greater than 0.25V at 10µA at the
highest expected temperature. The forward voltage
must be less than 0.95V at 100µA at the lowest expect-
ed temperature. The base resistance has to be less
than 100Ω. Tight specification of forward-current gain
(+50 to +150, for example) indicates that the manufac-
turer has good process control and that the devices
have consistent characteristics.
Table 12. Remote-Sensor Transistor
Manufacturers
MANUFACTURER
Central Semiconductor (USA)
Rohm Semiconductor (USA)
Samsung (Korea)
MODEL NO.
CMPT3906
SST3906
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 MAX6639 is optimized for n
KST3906-TF
SMBT3906
Siemens (Germany)
®
= 1.008, which is the typical value for the Intel
®
Pentium III and the AMD Athlon MP model 6. If a
Intel and Pentium are registered trademarks of Intel Corp.
18 ______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
places constraints on high-frequency noise rejection.
Lay out the PC board carefully with proper external
noise filtering for high-accuracy remote measurements
in electrically noisy environments.
Effect of Series Resistance
Series resistance in a sense diode contributes addition-
al errors. For nominal diode currents of 10µA and
100µA, change in the measured voltage is:
Filter high-frequency electromagnetic interference
(EMI) at DXP and DXN with an external 2200pF capaci-
tor connected between the two inputs. This capacitor
can be increased to approximately 3300pF (max),
including cable capacitance. A capacitance higher
than 3300pF introduces errors due to the rise time of
the switched-current source.
∆V = R (100µA - 10µA) = 90µA x R
S
Since 1°C corresponds to 198.6µV, series resistance
contributes a temperature offset of:
M
S
µV
90
°C
Ω
= 0.453
µV
Ω
198.6
°C
Twisted Pairs and Shielded Cables
For remote-sensor distances longer than 8in, or in par-
ticularly noisy environments, a twisted pair is recom-
mended. Its practical length is 6ft to 12ft (typ) before
noise becomes a problem, as tested in a noisy elec-
tronics laboratory. For longer distances, the best solu-
tion 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.
Connect the twisted pair to DXP and DXN and the
shield to ground, and leave the shield’s remote end
unterminated. Excess capacitance at DXN or DXP limits
practical remote-sensor distances (see the Typical
Operating Characteristics).
Assume that the diode being measured has a series
resistance of 3Ω. The series resistance contributes an
offset of:
°C
3Ω × 0.453
= 1.36°C
Ω
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 cal-
culated by adding error due to series resistance with
error due to ideality factor:
1.36°C - 2.13°C = -0.77°C
For very long cable runs, the cable’s parasitic capaci-
tance often provides noise filtering, so the recommend-
ed 2200pF capacitor can often be removed or reduced
in value. Cable resistance also affects remote-sensor
accuracy. A 1Ω series resistance introduces about
+1/2°C error.
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 12 lists examples of
discrete transistors that are appropriate for use with the
MAX6639.
PC Board Layout Checklist
1) Place the MAX6639 as close as practical to the
remote diode. In a noisy environment, such as a
computer motherboard, this distance can be 4in to
8in, or more, as long as the worst noise sources
(such as CRTs, clock generators, memory buses,
and ISA/PCI buses) are avoided.
The transistor must be a small-signal type with a rela-
tively high forward voltage; otherwise, the ADC 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 tempera-
ture, 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 < fl < 150,
for example) indicate that the manufacturer has good
process controls and that the devices have consistent
2) Do not route the DXP/DXN lines next to the deflection
coils of a CRT. Also, do not route the traces across a
fast memory bus, which can easily introduce +30°C
error, even with good filtering. Otherwise, most noise
sources are fairly benign.
3) Route the DXP and DXN traces parallel and close to
each other, away from any high-voltage traces such
as +12VDC. Avoid leakage currents from PC board
contamination. A 20MΩ leakage path from DXP
ground causes approximately +1°C error.
V
characteristics.
BE
ADC Noise Filtering
The integrating ADC has inherently good noise rejec-
tion, especially of low-frequency signals such as
60Hz/120Hz power-supply hum. Micropower operation
4) Connect guard traces to GND on either side of the
DXP/DXN traces. With guard traces, placing routing
______________________________________________________________________________________ 19
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Typical Operating Circuit
5V
V
FAN
(5V OR 12V)
3.3V TO 5.5V
5V
V
CPU
FAN
V
CC ADD TACH1
(5V OR 12V)
DXP1
DXN
PWM1
5V
DXP2
PWM2
3.3V TO 5.5V
3.3V TO 5.5V
3.3V TO 5.5V
MAX6639
SDA
SCL
TO SMBus
MASTER
GPU
TACH2
3.3V TO 5.5V
ALERT
TO SYSTEM SHUTDOWN
OT
3.3V TO 5.5V
TO CLOCK THROTTLE
THERM
FANFAIL
GND
near high-voltage traces is no longer an issue.
8) Placing an electrically clean copper ground plane
between the DXP/DXN traces and traces carrying
high-frequency noise signals helps reduce EMI.
5) Route as few vias and crossunders as possible to
minimize copper/solder thermocouple effects.
6) When introducing a thermocouple, make sure that
both the DXP and the DXN paths have matching
thermocouples. In general, PC board-induced ther-
mocouples are not a serious problem. A copper
solder thermocouple exhibits 3µV/°C, and it takes
approximately 200µV of voltage error at DXP/DXN
to cause a +1°C measurement error, so most para-
sitic thermocouple errors are swamped out.
Chip Information
TRANSISTOR COUNT: 39,283
PROCESS: BiCMOS
7) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10-mil widths
and spacings recommended are not absolutely nec-
essary (as they offer only a minor improvement in
leakage and noise), but use them where practical.
20 ______________________________________________________________________________________
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
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.)
D2
D
b
0.10 M
C A B
C
L
D2/2
D/2
k
L
MARKING
XXXXX
E/2
E2/2
C
(NE-1) X
e
L
E2
E
PIN # 1 I.D.
0.35x45°
DETAIL A
e/2
PIN # 1
I.D.
e
(ND-1) X
e
DETAIL B
e
L
C
C
L
L1
L
L
L
e
e
0.10
C
A
0.08
C
C
A3
A1
PACKAGE OUTLINE,
16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm
1
21-0140
H
-DRAWING NOT TO SCALE-
2
COMMON DIMENSIONS
20L 5x5 28L 5x5
EXPOSED PAD VARIATIONS
D2 E2
MIN. NOM. MAX. MIN. NOM. MAX. ±0.15
PKG.
SYMBOL MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX. MIN. NOM. MAX.
16L 5x5
32L 5x5
40L 5x5
DOWN
BONDS
ALLOWED
L
PKG.
CODES
A
0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80 0.70 0.75 0.80
T1655-1
T1655-2
3.00 3.10 3.20 3.00 3.10 3.20
3.00 3.10 3.20 3.00 3.10 3.20
NO
**
**
**
**
A1
A3
b
0
0.02 0.05
0.20 REF.
0
0.02 0.05
0.20 REF.
0
0.02 0.05
0.20 REF.
0
0.02 0.05
0.20 REF.
0
0.02 0.05
0.20 REF.
YES
NO
T1655N-1 3.00 3.10 3.20 3.00 3.10 3.20
0.25 0.30 0.35 0.25 0.30 0.35 0.20 0.25 0.30 0.20 0.25 0.30 0.15 0.20 0.25
4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10
4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10 4.90 5.00 5.10
T2055-2
T2055-3
T2055-4
T2055-5
3.00 3.10 3.20 3.00 3.10 3.20
3.00 3.10 3.20 3.00 3.10 3.20
3.00 3.10 3.20 3.00 3.10 3.20
NO
YES
NO
D
E
**
**
e
0.80 BSC.
0.25
0.65 BSC.
0.25
0.50 BSC.
0.25
0.50 BSC.
0.25
0.40 BSC.
YES
3.15 3.25 3.35 3.15 3.25 3.35 0.40
k
-
-
-
-
-
-
-
-
0.25 0.35 0.45
T2855-1
T2855-2
3.15 3.25 3.35 3.15 3.25 3.35
2.60 2.70 2.80 2.60 2.70 2.80
NO
NO
L
**
**
**
**
0.30 0.40 0.50 0.45 0.55 0.65 0.45 0.55 0.65 0.30 0.40 0.50 0.40 0.50 0.60
L1
-
-
-
-
-
-
-
-
-
-
-
-
0.30 0.40 0.50
40
T2855-3
T2855-4
3.15 3.25 3.35 3.15 3.25 3.35
2.60 2.70 2.80 2.60 2.70 2.80
2.60 2.70 2.80 2.60 2.70 2.80
3.15 3.25 3.35 3.15 3.25 3.35
YES
YES
NO
N
ND
NE
16
20
28
32
4
4
5
5
7
7
8
8
10
10
T2855-5
T2855-6
T2855-7
T2855-8
**
**
**
WHHB
WHHC
WHHD-1
WHHD-2
-----
JEDEC
NO
YES
2.80
3.35
3.35
3.20
2.60 2.70
3.15 3.25
2.60 2.70 2.80
3.15 3.25 3.35
3.15 3.25 3.35
3.00 3.10 3.20
0.40
YES
NO
NO
NOTES:
T2855N-1 3.15 3.25
**
**
**
1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.
2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.
3. N IS THE TOTAL NUMBER OF TERMINALS.
T3255-2
T3255-3
T3255-4
3.00 3.10
3.00 3.10 3.20 3.00 3.10 3.20
3.00 3.10 3.20 3.00 3.10 3.20
YES
NO
**
**
**
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL
CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE
OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1
IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE.
NO
T3255N-1 3.00 3.10 3.20 3.00 3.10 3.20
T4055-1 3.20 3.30 3.40 3.20 3.30 3.40
YES
**SEE COMMON DIMENSIONS TABLE
5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN
0.25 mm AND 0.30 mm FROM TERMINAL TIP.
6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.
7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.
8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
9. DRAWING CONFORMS TO JEDEC MO220, EXCEPT EXPOSED PAD DIMENSION FOR T2855-1,
T2855-3, AND T2855-6.
10. WARPAGE SHALL NOT EXCEED 0.10 mm.
11. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY.
12. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY.
13. LEAD CENTERLINES TO BE AT TRUE POSITION AS DEFINED BY BASIC DIMENSION "e", ±0.05.
PACKAGE OUTLINE,
16, 20, 28, 32, 40L THIN QFN, 5x5x0.8mm
2
-DRAWING NOT TO SCALE-
21-0140
H
2
______________________________________________________________________________________ 21
2-Channel Temperature Monitor with Dual,
Automatic, PWM Fan-Speed Controller
Package Information (continued)
(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 OUTLINE, QSOP .150", .025" LEAD PITCH
1
21-0055
E
1
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.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
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