MAX6640AEE Datasheet_PDF文件下载_芯片资料查询

2-Channel Temperature Monitor with Dual

Automatic PWM Fan-Speed Controller

MAX6640

V

CC

V

FAN

(12V OR 5V)

3V TO 5.5V

V

CC

4.7k鈩?/div>

PWM1

3V TO 5.5V

5V

4.7k鈩?/div>

TACH1

TACH

OUTPUT

TACH1

PWM1

4.7k鈩?/div>

3V TO 5.5V

V

FAN

(5V OR 12V)

4.7k鈩?/div>

TACH

OUTPUT

Figure 8. High-Side PWM Drive with 鈥淜eep-Alive鈥?Supply

V

FAN

(5V OR 12V)

V

CC

100k鈩?/div>

3.3V

Figure 10. 4-Wire Fan with PWM Speed-Control Input

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.

2) Write 4Bh to register 22h to set the minimum RPM

to 3200.

4.7k鈩?/div>

100k鈩?/div>

PWM1

2N3904

3) Write 5Eh to register 24h to set the pulses per revo-

lution to 2 and to set the maximum RPM speed to

8000RPM.

4) Write 19h to register 28h to set the fan-start temper-

ature to +25掳C.

10碌F

33k鈩?/div>

3V TO 5V

2.2碌F

91k鈩?/div>

4.7k鈩?/div>

5) Write D2h to register 10h to start automatic

RPM mode.

TACH1

TACH OUTPUT

Remote-Diode Considerations

TACH

OUTPUT

Figure 9. High-Side Linear Drive Circuit

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.

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 11. The MAX6640 can also

directly measure the die temperature of CPUs and

other ICs with on-board temperature-sensing diodes.

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 10碌A at the

highest expected temperature. The forward voltage

must be less than 0.95V at 100碌A at the lowest expect-

ed temperature. The base resistance has to be less

than 100鈩? 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.

17

______________________________________________________________________________________

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