ADT7476ARQZ-R7 datasheet(20/67 Pages) ONSEMI

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ADT7476

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Table 10. Programming Single−Channel ADC Mode

for Temperatures

Bits [7:5], Register 0x55

Channel Selected

101

Remote 1 Temperature

110

Local Temperature

111

Remote 2 Temperature

Configuration Register 2 (0x73)

[4] = 1, averaging off.

[6] = 1, single−channel convert mode.

TACH1 Minimum High Byte (0x55)

[7:5] selects ADC channel for single−channel convert mode.

Overtemperature Events

Overtemperature events on any of the temperature

channels can be detected and dealt with automatically in

automatic fan speed control mode. Register 0x6A to

temperature exceeds its THERM temperature limit, all

PWM outputs run at the maximum PWM duty cycle

(Register 0x38, Register 0x39, and Register 0x3A).

This effectively runs the fans at the fastest allowed speed.

The fans run at this speed until the temperature drops

below THERM minus hysteresis. This can be disabled by

setting Bit 2, the boost bit, in Configuration Register 3

(0x78). The hysteresis value for the THERM temperature

limit is the value programmed into the hysteresis registers

(0x6D and 0x6E). The default hysteresis value is 4

°C.

Figure 28. THERM Temperature Limit Operation

FANS

TEMPERATURE

100%

HYSTERESIS (°C)

THERM LIMIT

THERM can be disabled on specific temperature channels

using Bits [7:5] of Configuration Register 5 (0x7C).

THERM can also be disabled by:

• Writing −64°C to the appropriate THERM temperature

limit in Offset 64 mode.

• Writing −128°C to the appropriate THERM

temperature limit in twos complement mode.

Limits, Status Registers, and Interrupts

Limit Values

Associated with each measurement channel on the

ADT7476 are high and low limits. These can form the basis of

system status monitoring; a status bit can be set for any

out−of−limit condition and is detected by polling the device.

Alternatively, SMBALERT interrupts can be generated to flag

out−of−limit conditions to a processor or microcontroller.

8−Bit Limits

The following is a list of 8−bit limits on the ADT7476.

Voltage Limit Registers

Temperature Limit Registers

THERM Timer Limit Register

16−Bit Limits

The fan TACH measurements are 16−bit results. The fan

TACH limits are also 16 bits, consisting of a high byte and

low byte. Because fans running under speed or stalled are

normally the only conditions of interest, only high limits

exist for fan TACHs. Because the fan TACH period is

actually being measured, exceeding the limit indicates a

slow or stalled fan.

ADT7476ARQZ-R7 Datasheet(PDF) 20 Page - ON Semiconductor

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