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General Description

The MAX6678 monitors its own temperature and the

temperatures of two external diode-connected transis-

tors, which typically reside on the die of a CPU or other

integrated circuit. The device reports temperature values

in digital form using a 2-wire serial interface. The

MAX6678 provides a programmable alarm output to gen-

erate interrupts, throttle signals, or overtemperature shut-

down signals.

The 2-wire serial interface accepts standard System

Management Bus (SMBus)

™

write byte, read byte, send

byte, and receive byte commands to read the tempera-

ture data and program the alarm thresholds. The tem-

perature 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 maxi-

mum cooling when power dissipation increases.

Five GPIO pins provide additional flexibility. The GPIO

power-up states are set by connecting the GPIO preset

inputs to ground or V

The MAX6678 is available in a 20-pin QSOP package

and a 5mm x 5mm thin QFN package. It operates from

3.0V to 5.5V and consumes just 500µA of supply current.

Applications

Desktop Computers

Notebook Computers

Workstations

Servers

Networking Equipment

Features

♦ Two Thermal-Diode Inputs

♦ Local Temperature Sensor

♦ Five GPIO Input/Outputs

♦ Two PWM Outputs for Fan Drive (Open Drain; May

Be Pulled Up to +5V)

♦ Programmable Fan-Control Characteristics

♦ Automatic Fan Spin-Up Ensures Fan Start

♦ Controlled Rate of Change Ensures Unobtrusive

Fan-Speed Adjustments

♦ 1°C Remote Temperature Accuracy (+60°C to

+145°C)

♦ Temperature Monitoring Begins at POR for Fail-

Safe System Protection

♦ OT Output for Throttling or Shutdown

♦ Four Versions Available, Each with a Different

Address

♦ 5mm x 5mm TQFN Package

MAX6678

2-Channel Temperature Monitor with Dual Automatic

PWM Fan-Speed Controller and Five GPIOs

________________________________________________________________ Maxim Integrated Products 1

20 19 18 17

PRESET3

PWMOUT2

PWMOUT1

GPIO0

GPIO3

GPIO2

GPIO1

PRESET0

PRESET4

GPIO4

SMBCLK

SMBDATA

5DXP1

6789

DXN

DXP2

GND

PRESET2

PRESET1

MAX6678

*CONNECT EXPOSED

PADDLE TO GND

TOP VIEW

5mm x 5mm THIN QFN

Pin Configurations

Ordering Information

19-3306; 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.

*EP = Exposed paddle.

PART TEMP RANGE

PIN-

PACKAGE

SMBus

ADDRESS

MAX6678AEP90 -40°C to +125°C 20 QSOP 1001000

MAX6678AEP92 -40°C to +125°C 20 QSOP 1001001

MAX6678AEP94 -40°C to +125°C 20 QSOP 1001010

MAX6678AEP96 -40°C to +125°C 20 QSOP 1001011

MAX6678ATP90 -40°C to +125°C

20 Thin

QFN-EP*

1001000

MAX6678ATP92 -40°C to +125°C

20 Thin

QFN-EP*

1001001

MAX6678ATP94 -40°C to +125°C

20 Thin

QFN-EP*

1001010

MAX6678ATP96 -40°C to +125°C

20 Thin

QFN-EP*

1001011

SMBus is a trademark of Intel Corp.

Pin Configurations continued at end of data sheet.

Typical Operating Circuit appears at end of data sheet.

Summary of content (19 pages)

PAGE 1
9-3306; Rev 0; 5/04 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs Features The MAX6678 monitors its own temperature and the temperatures of two external diode-connected transistors, which typically reside on the die of a CPU or other integrated circuit. The device reports temperature values in digital form using a 2-wire serial interface.
PAGE 2
MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs ABSOLUTE MAXIMUM RATINGS VCC to GND ..............................................................-0.3V to +6V OT, SMBDATA, SMBCLK, PWMOUT_, GPIO_ to GND ......................................................-0.3V to +6V DXP_ to GND ..........................................-0.3V to + (VCC + 0.3V) DXN to GND ..........................................................-0.3V to +0.8V PRESET_ to GND ...............
PAGE 3
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs (VCC = +3.0V to +5.5V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Clock Low Period tLOW 10% to 10% 4 µs Clock High Period tHIGH 90% to 90% 4.7 µs Bus Free Time Between Stop and Start Conditions tBUF 4.7 µs SMBus Start Condition Setup Time tSU:STA 90% of SMBCLK to 90% of SMBDATA 4.
PAGE 4
Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) 0 -1 -2 0.5 0 -0.5 50 75 100 125 -1.0 -1.5 0.1 1 10 100 1000 0.01 0.1 1 10 100 1000 TEMPERATURE (°C) FREQUENCY (kHz) FREQUENCY (kHz) REMOTE TEMPERATURE ERROR vs. COMMON-MODE NOISE FREQUENCY REMOTE TEMPERATURE ERROR vs. DIFFERENTIAL NOISE FREQUENCY TEMPERATURE ERROR vs. DXP-DXN CAPACITANCE 1.4 1.2 1.0 0.8 0.6 0.4 0.2 2 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 1 10 100 1000 -3 -4 0.01 0.
PAGE 5
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs PIN NAME DESCRIPTION THIN QFN QSOP 1 3 SMBDATA 2 4 SMBCLK 3, 12, 13, 14, 16 5, 14, 15, 16, 18 GPIO0–GPIO4 4, 9, 10, 11, 20 2, 6, 11, 12, 13 PRESET0–PRESET4 GPIO Preset Inputs. Connect to GND or VCC to set POR value of GPIO0–GPIO4. SMBus Serial-Data Input/Output, Open Drain. Can be pulled up to 5.5V, regardless of VCC. Open circuit when VCC = 0. SMBus Serial-Clock Input. Can be pulled up to 5.
PAGE 6
MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs Write Byte Format S ADDRESS WR ACK 7 bits — — — Slave address: equivalent to chip-select line of a 3-wire interface COMMAND ACK 8 bits — Command byte: selects which register you are writing to DATA ACK P 8 bits — 1 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 7 bits — —
PAGE 7
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs B tLOW C D E F G H tHIGH I J K L MAX6678 A M SMBCLK SMBDATA tSU:STA tHD:STA tSU:STO tSU:DAT 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 F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE tBUF I = MASTER PULLS DATA LINE LOW J
PAGE 8
MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs PWM Output 1) The PWMOUT_ signals are normally used in one of three ways to control the fan’s speed: 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_ driving an n-channel MOSFET. In this case, the PWM invert bit (D4 in register 02h) is set to 1.
PAGE 9
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs 1) Manual PWM control by setting the duty cycle of the fan directly through the fan target duty-cycle registers (0Bh and 0Ch). 2) Automatic PWM control by setting the duty cycle based on temperature. Manual PWM Duty-Cycle Control Clearing the bits that select the temperature channels for fan control (D5 and D4 for PWMOUT1 and D3 and D2 for PWMOUT2) in the fan-configuration register (11h) enables manual fan control.
PAGE 10
MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs 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.
PAGE 11
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs READ/ WRITE REGISTER NO.
PAGE 12
MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs Table 2. Register Map (continued) READ/ WRITE REGISTER NO.
PAGE 13
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs BIT NAME POR STATE FUNCTION 7 Reserved; set to 0 — — 6 Reserved; set to 0 — — 5 TIMEOUT 0 Set TIMEOUT to zero to enable SMBus timeout for prevention of bus lockup. Set to 1 to disable this function. 4 FAN1 PWM INVERT 0 Set FAN PWM INVERT to zero to force PWMOUT1 low when the duty cycle is 100%. Set to 1 to force PWMOUT1 high when the duty cycle is 100%.
PAGE 14
MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs Table 4. Setting the Time Between DutyCycle Increments Table 5. Setting the Duty-Cycle Change 000 0 0 001 0.0625 5 0000 0 TEMPERATURE RANGE FOR FAN CONTROL (1°C STEP, 33% TO 100%) 0 010 0.125 10 0001 2/240 80 011 0.25 20 0010 4/240 40 100 0.5 40 0011 6/240 27 101 1 80 0100 8/240 20 110 2 160 0101 10/240 16 111 4 320 … … ... 1000 16 10 ... ... ...
PAGE 15
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs Applications Information Remote-Diode Considerations Temperature accuracy depends upon having a goodquality, diode-connected, small-signal transistor. Accuracy has been experimentally verified for all the devices listed in Table 7. The MAX6678 can also directly measure the die temperature of CPUs and other ICs with on-board temperature-sensing diodes.
PAGE 16
MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs ADC Noise Filtering The integrating ADC has inherently good noise rejection, especially of low-frequency signals such as 60Hz/120Hz power-supply hum. Micropower operation 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.
PAGE 17
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs VFAN (5V OR 12V) 5.0V 3.0V TO 5.5V VCC CPU DXP1 VFAN (5V OR 12V) PWMOUT1 5V DXN REMOTE 1 DXP2 PWMOUT2 3.0V TO 5.5V MAX6678 TO CLOCK THROTTLE OR SYSTEM SHUTDOWN OT 3.0V TO 5.5V REMOTE 2 GPU SMBDATA 3.0V TO 5.5V TO SMBus MASTER 3.0V TO 5.5V SMBCLK GPIO0 3.0V TO 5.5V 3.0V TO 5.
PAGE 18
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.) QSOP.EPS MAX6678 2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs PACKAGE OUTLINE, QSOP .150", .
PAGE 19
2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller and Five GPIOs b CL 0.10 M C A B D2/2 D/2 PIN # 1 I.D. QFN THIN.EPS D2 0.15 C A D k 0.15 C B PIN # 1 I.D. 0.35x45∞ E/2 E2/2 CL (NE-1) X e E E2 k L DETAIL A e (ND-1) X e DETAIL B e L1 L CL CL L L e e 0.10 C A C A1 0.08 C A3 PACKAGE OUTLINE 16, 20, 28, 32, 40L, THIN QFN, 5x5x0.8mm E 21-0140 COMMON DIMENSIONS A1 A3 b D E k L 0 0.20 REF. 0.02 0.05 0 0.20 REF. 0.02 0.05 0.02 0.05 0 0.20 REF.