MAX6639FATE+【PDF 18/22 页】IC 2CH TEMP MONITOR 16TQFN

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.

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癈.

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.

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礎 at the

highest expected temperature. The forward voltage

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

ed temperature. The base resistance has to be less

than 100? 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.

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

= 1.008, for Intel

?/DIV>

Pentium

?/DIV>

II and AMD Athlon

?/DIV>

MP

compatibility, and the MAX6639F is optimized for n =

1.021 for Penryn compatibiliy. If a sense transistor with

a different ideality factor is used, the output data is dif-

ferent. Fortunately, the difference is predictable.

Assume a remote-diode sensor designed for a nominal

ideality factor n

NOMINAL

is used to measure the tem-

perature of a diode with a different ideality factor, n

1

.

The measured temperature T

M

can be corrected using:

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:

For a real temperature of +85癈 (358.15K), the mea-

sured temperature is +82.91癈 (356.02K), which is an

error of -2.13癈.

T

n

T

ACTUAL

M

NOMINAL

M

=

?/DIV>

=

?/DIV>

=

1

1 008

1 002

1 00599

.

( .

)

T T

n

M

ACTUAL

NOMINAL

=

?/DIV>

1

2-Channel Temperature Monitor with Dual,

Automatic, PWM Fan-Speed Controller

18

Maxim Integrated

MAX6639/MAX6639F

FI RE

DESCRIPTION

PULSE STRETCHING PWM FREQUENCY PWM POLARITY

6

High-side PWM drive

Yes

Low

Negative

7

Low-side PWM drive

Yes

Low

Positive

8

High-side PWM drive with keep-alive supply

No

Low

Negative

9

High-side linear supply

No

High

Positive

10

4-wire fan with PWM speed-control input

No

High

Positive

Table 11. Summary of Fan-Drive Options

MANUFACTURER

MODEL NO.

Central Semiconductor (USA)

CMPT3906

Rohm Semiconductor (USA)

SST3906

Samsung (Korea)

KST3906-TF

Siemens (Germany)

SMBT3906

Table 12. Remote-Sensor Transistor

Manufacturers

Intel and Pentium are registered trademarks of Intel Corp.

AMD Athlon is a registered trademark of Advanced Micro

Devices, Inc.

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