19-2337; Rev 0; 1/02
Remote Temperature-Controlled Fan-Speed
Regulator with SPI-Compatible Interface
General Description
The MAX6661 is a remote temperature sensor and fan-
speed regulator that provides complete closed-loop fan
control. The remote temperature sensor is typically a
common-collector PNP, such as a substrate PNP of a
microprocessor, or a diode-connected transistor, typi-
cally a low-cost, easily mounted 2N3904 NPN type or
2N3906 PNP type.
The device also incorporates a closed-loop fan con-
troller that regulates fan speed with tachometer feed-
back. The MAX6661 compares temperature data to a
fan threshold temperature and gain setting, both pro-
grammed over the SPI™ bus by the user. The result is
automatic fan control that is proportional to the remote-
junction temperature. The temperature feedback loop
can be broken at any time for system control over the
speed of the fan.
Fan speed is voltage controlled as opposed to PWM
controlled, greatly reducing acoustic noise and maxi-
mizing fan reliability. An on-chip power device drives
fans rated up to 250mA.
Temperature data is updated every 500ms and is read-
able at any time over the SPI interface. The MAX6661 is
accurate to 1°C (max) when the remote junction is
between +60°C to +100°C. Data is formatted as a 10-
bit + sign word with 0.125°C resolution.
The MAX6661 is specified between -40°C to +125°C
and is available in a 16-pin QSOP package.
Features
o
Integrated Thermal Measurement and Fan
Regulation
o
Programmable Fan Threshold Temperature
o
Programmable Temperature Range for Full-Scale
Fan Speed
o
Accurate Closed-Loop Fan-Speed Regulation
o
On-Chip Power Device Drives Fans Rated
Up to 250mA
o
Programmable Under/Overtemperature Alarms
o
SPI-Compatible Serial Interface
o
±1°C (+60°C to +100°C) Thermal-Sensing
Accuracy
MAX6661
Ordering Information
PART
MAX6661AEE
TEMP RANGE
-40°C to +125°C
PIN-PACKAGE
16 QSOP
Typical Operating Circuit
12V
0.1µF
3V TO 5.5V
50Ω
10kΩ
EACH
Applications
Telecom Systems
Servers
Workstations
Electronic Instruments
1µF
5kΩ
V
FAN
V
CC
ALERT
INTERRUPT
TO
µP
TO SYSTEM
SHUTDOWN
FAN
TACH IN
OVERT
FAN
DXP
2200pF
MAX6661
SC
SDIN
DOUT
SPI CLOCK
SPI DATA IN
SPI DATA OUT
SPI CHIP SELECT
DXN
CS
Pin Configuration appears at end of data sheet.
SPI is a trademark of Motorola, Inc.
PENTIUM
AGND
PGND
________________________________________________________________
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.
Remote Temperature-Controlled Fan-Speed
Regulator with SPI-Compatible Interface
MAX6661
ABSOLUTE MAXIMUM RATINGS
V
CC
,
ALERT, OVERT
...............................................-0.3V to +6V
V
FAN
, TACH IN, FAN .............................................-0.3V to +16V
DXP,
CS,
SDOUT, GAIN, SCL, SDIN..........-0.3V to (V
CC
+ 0.3V)
DXN ..........................................................................-0.3V to +1V
SDOUT Current ...................................................-1mA to +50mA
DXN Current ......................................................................±1mA
FAN Out Current ..............................................................500mA
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
Operating Temperature Range ........................ -40°C to +125°C
Junction Temperature .....................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) ................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= 3V to 5.5V, V
FAN
= 12V, T
A
= -40°C to +125°C, unless otherwise specified. Typical values are at V
CC
= 3.3V and T
A
=
+25°C.) (Notes 1 and 2)
PARAMETER
ADC AND POWER SUPPLY
Temperature Resolution
(Note 3)
Remote-Junction Temperature
Measurement Error (Note 4)
Fan-Speed Measurement
Accuracy
V
CC
Supply Voltage Range
V
FAN
Supply Voltage Range
Conversion Time
Conversion Rate Timing Error
Undervoltage Lockout (UVLO)
Threshold
UVLO Threshold Hysteresis
POR Threshold (V
CC
)
POR Threshold Hysteresis
Standby Supply Current
Operating Supply Current
DXN Source Voltage
TACH Input Transition Level
TACH Input Hysteresis
TACH Input Resistance
Fan Output Current
Fan Output Current Limit
Fan Output On-Resistance
I
F
I
L
R
ONF
(Note 5)
250mA load
250
320
4
410
I
SHDN
I
CC
V
DXN
V
FAN
= 12V
V
FAN
= 12V
Shutdown, configuration bit 6 = 1
Fan off
V
UVLO
V
HYST
V
CC
rising
1.4
V
CC
falling
-25
2.50
2.80
90
2.0
90
3
450
0.7
10.5
190
250
20
700
2.5
V
CC
V
FAN
3.0
4.5
0.25
+25
2.95
T
E
T
A
= +85°C,
V
CC
= 3.3V
T
RJ
= +60°C to +100°C
T
RJ
= +25°C to +125°C
T
RJ
= -40°C to +125°C
0.125
11
-1
-3
-5
±25
5.5
13.5
+1
+3
+5
°C
Bits
°C
°C
°C
%
V
V
s
%
V
mV
V
mV
µA
µA
V
V
mV
kΩ
mA
mA
Ω
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
Remote Temperature-Controlled Fan-Speed
Regulator with SPI-Compatible Interface
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= 3V to 5.5V, V
FAN
= 12V, T
A
= -40°C to +125°C, unless otherwise specified. Typical values are at V
CC
= 3.3V and T
A
=
+25°C.) (Notes 1 and 2)
PARAMETER
Serial Bus Maximum Clock
Frequency (Note 5)
Logic Input High Voltage
Logic Input Low Voltage
Logic Output High-Voltage
DOUT
Logic Output Low-Voltage DOUT
Logic Output Low-Voltage
ALERT, OVERT
ALERT, OVERT
Output
High Leakage Current
Logic Input Current
SPI AC TIMING
(Figure 5)
CS
High to DOUT Three-State
CS
to SC Setup Time
SC Fall to DOUT Valid
DIN to SC Setup Time
DIN to SC Hold Time
SC Period
SC High Time
SC Low Time
CS High Pulse Width
Output Rise Time
Output Fall Time
SC Falling Edge to
CS
Rising
t
TR
t
CSS
t
DO
t
DS
t
DH
t
CP
t
CH
t
CL
t
CSW
t
R
t
F
t
SCS
(Note 5)
C
LOAD
= 100pF
C
LOAD
= 100pF
(Note 5)
200
(Note 5)
C
LOAD
= 100pF, R
GS
= 10kΩ (Note 5)
(Note 5)
C
LOAD
= 100pF
200
200
400
200
200
400
10
10
200
200
200
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX6661
INTERFACE PINS (SDIN, SC,
CS,
DOUT,
ALERT, OVERT)
SC
V
CC
= 3V
V
CC
= 5.5V
V
CC
= 3V to 5V
V
CC
= 3V, I
SOURCE
= 6mA (Note 5)
V
CC
= 3V, I
SINK
= 6mA (Note 5)
V
CC
= 3V, I
SINK
= 6mA (Note 5)
ALERT, OVERT
forced to 5.5V
Logic inputs forced to V
CC
or GND
-2
V
CC
-
0.4V
0.4
0.4
1
2
2.2
2.4
0.8
2.5
MHz
V
V
V
V
V
µA
µA
Note 1:
T
A
= T
J
. This implies zero dissipation in pass transistor (no load, or fan turned off).
Note 2:
All parameters are 100% production tested at a single temperature, unless otherwise indicated. Parameter values through
temperature are guaranteed by design.
Note 3:
The fan control section of the MAX6661 and temperature comparisons use only 9 bits of the 11-bit temperature measure-
ment with a 0.5°C LSB.
Note 4:
Wide-range accuracy is guaranteed by design, not production tested.
Note 5:
Guaranteed by design.
_______________________________________________________________________________________
3
Remote Temperature-Controlled Fan-Speed
Regulator with SPI-Compatible Interface
MAX6661
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
TEMPERATURE ERROR
vs. PC BOARD RESISTANCE
MAX6661 toc01
TEMPERATURE ERROR
vs. REMOTE-DIODE TEMPERATURE
MAX6661 toc02
TEMPERATURE ERROR
vs. POWER-SUPPLY NOISE FREQUENCY
15
TEMPERATURE ERROR (°C)
10
5
0
-5
-10
-15
-20
-25
-30
V
IN
= 100mV
P-P
V
IN
= 250mV
P-P
V
IN
= SQUARE WAVE APPLIED TO V
CC
WITH NO 0.1µF V
CC
CAPACITOR
MAX6661 toc03
20
15
TEMPERATURE ERROR (°C)
10
5
0
-5
-10
-15
-20
-25
-30
1
10
LEAKAGE RESISTANCE (MΩ)
PATH = DXP TO V
CC
(5V)
PATH = DXP TO GND
5
4
TEMPERATURE ERROR (°C)
3
2
1
0
-1
-2
-3
-4
-5
20
100
-50
0
50
TEMPERATURE (°C)
100
150
1
10
100 1k
10k 100k 1M 10M 100M
FREQUENCY (Hz)
TEMPERATURE ERROR
vs. COMMON-MODE NOISE FREQUENCY
MAX6661 toc04
TEMPERATURE ERROR
vs. DXP-DXN CAPACITANCE
0
TEMPERATURE ERROR (°C)
-1
-2
-3
-4
-5
-6
-7
-8
0
0 10 20 30 40 50 60 70 80 90 100
DXP-DXN CAPACITANCE (nF)
3.0
MAX6661 toc05
STANDBY SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6661 toc06
4.0
3.5
TEMPERATURE ERROR (°C)
3.0
2.5
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
1
10
100
1k
V
IN
= 25mV
P-P
V
IN
= 50mV
P-P
V
IN
= 100mV
P-P
V
IN
= SQUARE WAVE
AC-COUPLED TO DXN
1
5
STANDBY SUPPLY CURRENT (µA)
4
3
2
CONFIG BIT 6 = 1
1
10k 100k 1M 10M 100M
3.5
4.0
4.5
5.0
5.5
FREQUENCY (Hz)
SUPPLY VOLTAGE (V)
AVERAGE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX6661 toc07
AVERAGE SUPPLY CURRENT (µA)
450
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.1
5.4
SUPPLY VOLTAGE (V)
4
_______________________________________________________________________________________
Remote Temperature-Controlled Fan-Speed
Regulator with SPI-Compatible Interface
Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
NAME
V
FAN
V
CC
DXP
DXN
FAN
N.C.
PGND
AGND
OVERT
CS
ALERT
DOUT
GAIN
SCL
SDIN
TACH IN
Power Supply for Fan Drive: 4.5V to 13.5V
Power Supply: 3V to 5.5V. Bypass with a 0.1µF capacitor to GND.
Input: Remote-Junction Anode. Place a 2200pF capacitor between DXP and DXN for noise filtering.
Input: Remote-Junction Cathode. DXN is internally biased to a diode voltage above ground.
Output to Fan Low Side
No External Connection. Must be left floating.
Power Ground
Analog Ground
Output to System Shutdown. Active-low output, programmable for active high, if desired. Open drain.
SPI Chip Select. Active low.
Open-Drain Active-Low Output
SPI Data Output. High-Z when not being read.
Leave open if tachometer feedback is being used. Connect an external resistor to V
CC
to reduce the
gain of the current sense.
SPI Clock
SPI Data In
Fan Tachometer Input. 13.5V tolerant, pullup from V
CC
to 13.5V is allowed on this line.
FUNCTION
MAX6661
Detailed Description
The MAX6661 is a remote temperature sensor and fan
controller with an SPI interface. The MAX6661 converts
the temperature of a remote PN junction to a 10-bit +
sign digital word. The remote PN junction can be a
diode-connected transistor, such as a 2N3906, or the
type normally found on the substrate of many proces-
sors’ ICs. The temperature information is provided to the
fan-speed regulator and is read over the SPI interface.
The temperature data, through the SPI interface, can be
read as a 10-bit + sign two’s complement word with a
0.125°C resolution (LSB) and is updated every 0.5s.
The MAX6661 incorporates a closed-loop fan controller
that regulates the fan speed with tachometer feedback.
The temperature information is compared to a threshold
and range setting, which enables the MAX6661 to auto-
matically set fan speed proportional to temperature.
Full control of the fan is available by being able to open
either the thermal control loop or the fan control loop.
Figure 1 shows a simplified block diagram.
temperature is computed. The DXN pin is the cathode
of the remote diode and is biased at 0.7V above
ground by an internal diode to set up the ADC inputs
for a differential measurement. The worst-case DXP-
DXN differential input voltage range is 0.25V to 0.95V.
Excess resistance in series with the remote diode caus-
es about 1/2°C error per ohm. Likewise, 200mV of off-
set voltage forced on DXP-DXN causes approximately
1°C error.
A/D Conversion Sequence
A temperature-conversion sequence is initiated every
500ms in the free-running autoconvert mode (bit 6 = 0
in the configuration register) or immediately by writing a
one-shot command. The result of the new measurement
is available after the end of conversion. The results of
the previous conversion sequence are still available
when the ADC is converting.
Remote-Diode Selection
Temperature accuracy depends on having a good-
quality, diode-connected, small-signal transistor.
Accuracy has been experimentally verified for all
devices listed in Table 1. The MAX6661 can also direct-
ly measure the die temperature of CPUs and other ICs
that have on-board temperature-sensing diodes.
ADC
The ADC is an averaging type that integrates the signal
input over a 125ms period with excellent noise rejec-
tion. A bias current is steered through the remote
diode, where the forward voltage is measured, and the
_______________________________________________________________________________________
5
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