MAX6640ATE 查看數據表（PDF） - Maxim Integrated

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MAX6640ATE

2-Channel Temperature Monitor with Dual Automatic PWM Fan-Speed Controller

Maxim Integrated 

2-Channel Temperature Monitor with Dual

Automatic PWM Fan-Speed Controller

Table 1. Temperature Data Byte Format

TEMP (°C)

241

240

126

25

1.50

0.00

TEMP (°C)

+241

+240

+126

+25

1

0

DIGITAL OUTPUT

1111 0001

1111 0000

0111 1110

0001 1001

0000 0001

0000 0000

updated, thereby preventing reading the temperature

register data from one conversion and the extended

temperature register data from a different conversion.

The MAX6640 measures the temperature at a fixed rate

of 4Hz immediately after it is powered on. Setting bit 7

of the configuration register (04h) shuts down the tem-

perature measurement cycle.

OT Output

When a measured temperature exceeds the corre-

sponding OT temperature threshold and OT is not

masked, the associated OT status register bit sets and

the OT output asserts. If OT for the respective channel

is masked, the OT status register sets, but the OT out-

put does not assert. To deassert the OT output and the

associated status register bit, either the measured tem-

perature must fall at least 5°C below the trip threshold

or the trip threshold must be increased to at least 5°C

above the current measured temperature.

THERM

When a measured temperature exceeds the corre-

sponding THERM temperature threshold and THERM is

not masked, the associated THERM status register bit

is set and the THERM output asserts. If THERM for the

respective channel is masked, the THERM status regis-

ter is set, but the THERM output does not assert. To

deassert the THERM output and the associated status

register bit, either the measured temperature must fall

at least 5°C below the trip threshold or the trip threshold

must be increased to at least 5°C above the current

measured temperature. Asserting THERM internally or

externally forces both PWM outputs to 100% duty cycle

when bit 6 in address 13h (fan 1) or bit 6 in address

17h (fan 2) is set.

ALERT

The ALERT output asserts to indicate that a measured

temperature exceeds the ALERT trip threshold for that

temperature channel. The status bit and the ALERT out-

put clear by reading the ALERT status register. If the

ALERT status bit is cleared, but the temperature still

exceeds the ALERT temperature threshold, ALERT

reasserts on the next conversion, and the status bit sets

again. A successful alert response protocol clears

ALERT, but does not affect the ALERT status bit.

TACH1 and TACH2 Inputs

To measure the fan speed, the MAX6640 has two

tachometers. Each tachometer has an accurate internal

clock to count the time elapsed in one revolution.

Therefore, it is counting the time between two tachome-

ter pulses for a fan with four poles. When the PWM sig-

nal is used to directly modulate the fan’s power supply,

the PWM frequency is normally in the 20Hz to 100Hz

range. In this case, the time required for one revolution

may be longer than the PWM on-time. For this reason,

the PWM pulses are periodically stretched to allow

tachometer measurement over a full revolution. Turn off

pulse stretching by setting bit 5 of register 13h or regis-

ter 17h when using a 4-wire fan.

The tachometer count is inversely proportional to the

fan’s RPM. The tachometer count data is stored in regis-

ter 20h (for TACH1) and register 21h (for TACH2).

Reading a value of 255 from the TACH count register

means the fan’s RPM is zero or too slow for the range.

Reading a value of zero in the TACH count register

means the fan’s RPM is higher than the range selected.

Table 2 shows the fan’s available RPM ranges. Use reg-

isters 10h or 14h to select the appropriate RPM range for

the fan being used.

FANFAIL

The FANFAIL output asserts to indicate that one of the

fans has failed or is spinning slower than the required

speed. The MAX6640 detects fan fault depending on

the fan control mode. In PWM mode, the MAX6640 pro-

duces a square wave with a duty cycle set by the value

written to the duty-cycle registers (26h and 27h). In this

mode, the MAX6640 signals a fan fault when the

tachometer count is greater than the maximum

tachometer count value stored in the appropriate regis-

ter (22h and 23h). After the MAX6640 asserts FAN FAIL,

the fan with a tachometer fault goes to full speed for 2s in

an attempt to restart the fan and then returns to the origi-

nal duty-cycle settings. Reading the status register clears

Table 2. Tachometer Setting

FAN RPM

RANGE

2000

4000

8000

16,000

INTERNAL CLOCK

FREQUENCY (kHz)

1

2

4

8

8 _______________________________________________________________________________________

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