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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.

Applications

Telecom Systems

Servers

Workstations

Electronic Instruments

Features

♦ Integrated Thermal Measurement and Fan

Regulation

♦ Programmable Fan Threshold Temperature

♦ Programmable Temperature Range for Full-Scale

Fan Speed

♦ Accurate Closed-Loop Fan-Speed Regulation

♦ On-Chip Power Device Drives Fans Rated

Up to 250mA

♦ Programmable Under/Overtemperature Alarms

♦ SPI-Compatible Serial Interface

♦ ±1°C (+60°C to +100°C) Thermal-Sensing

Accuracy

MAX6661

Remote Temperature-Controlled Fan-Speed

Regulator with SPI-Compatible Interface

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

1µF

5kΩ

FAN

12V

2200pF

PENTIUM

SDIN

ALERT

OVERT

SPI CLOCK

SPI DATA IN

DOUT

SPI DATA OUT

SPI CHIP SELECT

INTERRUPT

TO µP

TO SYSTEM

SHUTDOWN

FAN

PGND

0.1µF

3V TO 5.5V

50Ω

TACH IN

FAN

DXP

DXN

AGND

10kΩ

EACH

MAX6661

Typical Operating Circuit

19-2337; Rev 0; 1/02

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

PART TEMP RANGE PIN-PACKAGE

MAX6661AEE -40°C to +125°C 16 QSOP

Pin Configuration appears at end of data sheet.

SPI is a trademark of Motorola, Inc.

Summary of content (19 pages)

PAGE 1
9-2337; Rev 0; 1/02 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface Features ♦ Integrated Thermal Measurement and Fan Regulation ♦ Programmable Fan Threshold Temperature ♦ Programmable Temperature Range for Full-Scale Fan Speed ♦ Accurate Closed-Loop Fan-Speed Regulation ♦ On-Chip Power Device Drives Fans Rated Up to 250mA ♦ Programmable Under/Overtemperature Alarms ♦ SPI-Compatible Serial Interface ♦ ±1°C (+60°C to +100°C) Thermal-Sensing Accuracy Ordering Information PAR
PAGE 2
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface ABSOLUTE MAXIMUM RATINGS VCC, ALERT, OVERT ...............................................-0.3V to +6V VFAN, TACH IN, FAN .............................................-0.3V to +16V DXP, CS, SDOUT, GAIN, SCL, SDIN..........-0.3V to (VCC + 0.3V) DXN ..........................................................................-0.3V to +1V SDOUT Current ...................................................
PAGE 3
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface (VCC = 3V to 5.5V, VFAN = 12V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at VCC = 3.3V and TA = +25°C.) (Notes 1 and 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 2.5 MHz INTERFACE PINS (SDIN, SC, CS, DOUT, ALERT, OVERT) Serial Bus Maximum Clock Frequency (Note 5) SC Logic Input High Voltage Logic Input Low Voltage VCC = 3V 2.2 VCC = 5.5V 2.4 V VCC = 3V to 5V 0.8 VCC 0.
PAGE 4
Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) TEMPERATURE ERROR vs. REMOTE-DIODE TEMPERATURE 0 -5 -10 PATH = DXP TO VCC (5V) -15 3 2 1 0 -1 -2 -20 -3 -25 -4 -30 10 5 VIN = 250mVP-P 0 -5 -10 -15 VIN = 100mVP-P -20 -30 -50 100 10 -25 -5 1 VIN = SQUARE WAVE APPLIED TO VCC WITH NO 0.
PAGE 5
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface PIN NAME FUNCTION 1 VFAN Power Supply for Fan Drive: 4.5V to 13.5V 2 VCC Power Supply: 3V to 5.5V. Bypass with a 0.1µF capacitor to GND. 3 DXP Input: Remote-Junction Anode. Place a 2200pF capacitor between DXP and DXN for noise filtering. 4 DXN Input: Remote-Junction Cathode. DXN is internally biased to a diode voltage above ground. 5 FAN Output to Fan Low Side 6 N.C. No External Connection.
PAGE 6
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface VFAN TACH IN FAN-SPEED REGULATOR FAN FAN N REGISTERS TMAX DXP MUX ADC THYST COMPARAT0R OVERT DXN REMOTE TEMPERATURE DATA CONTROL LOGIC ALERT THIGH SC SDIN DOUT SPI INTERFACE TLOW CS CONFIGURATION FAN TACHOMETER DIVISOR (FTD) TFAN (FT) THERMAL OPEN/ CLOSE LOOP FAN OPEN/ CLOSE LOOP FAN CONTROL CIRCUIT FAN GAIN (FG) FULL SCALE (FS) FAN TACHOMETER PERIOD LIMIT (FTPL) MODE (M) FAN-CONVERSION RATE (FCR) FA
PAGE 7
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface MANUFACTURER MODEL NO. Central Semiconductor (USA) 2N3904, 2N3906 Fairchild Semiconductor (USA) 2N3904, 2N3906 Rohm Semiconductor (Japan) Samsung (Korea) SST3904 KST3904-TF Siemens (Germany) SMBT3904 Zetex (England) FMMT3904CT-ND Note: Transistors must be diode connected (base shorted to collector). The transistor must be a small-signal type with a relatively high forward voltage.
PAGE 8
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface 5) When introducing a thermocouple by inserting different metals in the connection path, make sure that both the DXP and the DXN paths have matching thermocouples, i.e., the connection paths are symmetrical. A copper-solder thermocouple exhibits 3µV/°C. Adding a few thermocouples causes a negligible error.
PAGE 9
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface REGISTERS COMMAND POR STATE RRL 81h 00000000 FUNCTION Read Remote Temperature Low Byte (3MSBs) RRH 83h 00000000 Read Remote Temperature High Byte (Sign Bit and First 7 Bits) RSL 85h 00000000 Read Status Byte RCL/WCL 87h/92h 00000000 Read/Write Configuration Byte RFCR/WFCR 89h/94h 00000010 Read/Write Fan-Conversion Rate Byte RTMAX/WTMAX A1h/A4h 01100100 (+100°C) RTHYST/WTHYST A3h/A6h 01011111 (+95°C)
PAGE 10
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface SC CS D15 DIN D8 D15 IS START BIT ALWAYS HIGH D8 IS READ/WRITE BIT HIGH FOR READ COMMAND BYTE D7–D0 DATA BYTE DOUT THREE-STATE D7 D6 THREE-STATE D0 Figure 3. Read Cycle SC CS D15 DIN D8 D15 IS START BIT ALWAYS HIGH DOUT D7 D8 IS READ/WRITE BIT LOW FOR WRITE D15–D8 COMMAND BYTE D0 D7–D0 DATA BYTE THREE-STATE THREE-STATE Figure 4.
PAGE 11
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface Overtemperature Output (OVERT) The MAX6661 has an overtemperature output (OVERT) that is set when the remote-diode temperature crosses the limits set in the TMAX register. It is always active if the remote-diode temperature exceeds T MAX . The OVERT line clears when the temperature drops below THYST. Bit 1 of the configuration register can be used to mask the OVERT output.
PAGE 12
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface Table 4. Configuration Register Bit Assignments BIT NAME POR STATE 7(MSB) ALERT Mask 0 DESCRIPTION When set to 1, ALERT is masked from internally generated errors. 6 Run/Stop 0 When set to 1, the MAX6661 enters low-power standby. 5 OVERT Polarity 0 0 provides active low, 1 provides active high. 0 When set to 1, Write Protect is in effect for the following applicable registers: 1.
PAGE 13
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface Manufacturer and Device ID Codes Two ROM registers provide manufacturer and device ID codes. Reading the manufacturer ID returns 4D, which is the ASCII code M (for Maxim). Reading the device ID returns 09h, indicating the MAX6661 device. POR and UVLO The MAX6661 has a volatile memory.
PAGE 14
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface Table 6. Fan Conversion Update Rate REMOTE SENSOR TEMPERATURE CONVERTER TEMP DATA UPDATE FAN CONVERSION RATE FCR 0.25s TO 16s FAN THRESHOLD TEMPERATURE (TFAN) FAN-SPEED CONTROL (FSC) Figure 6. MAX6661 Thermal Loop In thermal open-loop mode, the fan loop can operate in open or closed mode. In fan open loop, the FSC register programs fan voltage directly, accepting values from 0 to 64 (40h).
PAGE 15
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface MAX6661 Table 7. Fan Speed Control Register (RFSC/WFSC) REGISTER/ADDRESS FSC (ABH = READ, B4H = WRITE) COMMAND READ/WRITE FAN DAC REGISTER 7 Not Used Label POR State 0 6 Overflow Bit 5 (MSB) 4 Data 3 Data 2 Data 1 Data 0 Data 0 0 0 0 0 0 0 Table 8.
PAGE 16
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface using the FSC register. By selecting fan open-loop mode, the MAX6661 automatically invokes thermal open-loop mode. value in FTPL, a failure is indicated. In fan closed loop, a flag is activated when the fan is at full speed. Set the fan tachometer period limit byte to: Fan Conversion Rate Register fTACH = 8415 / [N ✕ f] where N = fan-fail ratio and fTACH = maximum frequency of the fan tachometer.
PAGE 17
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface MAX6661 TEMP DATA REF FREQ 8415Hz TACH IN FAN GAIN (FG) 8°C, 16°C, 32°C RANGE FAN TACHOMETER PERIOD (FTP) FAN TACHOMETER PERIOD LIMIT (FTPL) FAN-SPEED CONTROL 1 TO 63 COUNTER COMPARATOR FAN FULL SCALE (FS) 127 TO 255 FAN TACHOMETER DIVISOR (FTD) 1, 2, 4, 8 FAN OPEN/CLOSED LOOP FAN FAIL UP/DOWN VFAN TACH FAN DAC DRIVER N Figure 7. MAX6661 Fan Loop Functional Diagram Table 11.
PAGE 18
MAX6661 Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface The 83.4Hz value is out of the 33Hz to 66Hz decrement/increment range. Set bits in the FTD register to divide the signal down within the 33Hz to 66Hz range. Bits 1, 0 = 10 (divide by 2: P = 2). The result is 83.4Hz/2 = 41.7Hz.
PAGE 19
Remote Temperature-Controlled Fan-Speed Regulator with SPI-Compatible Interface TOP VIEW 16 TACH IN VFAN 1 VCC 2 15 SDIN DXP 3 14 SCL DXN 4 MAX6661 13 GAIN FAN 5 12 DOUT N.C. 6 11 ALERT PGND 7 10 CS AGND 8 9 OVERT QSOP QSOP.EPS Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.