ADT7476AARQZ-R datasheet(20/69 Pages) ONSEMI

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ADT7476A

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Single-channel ADC Conversions

Setting Bit 6 of Configuration Register 2 (0x73) places

the ADT7476A into single-channel ADC conversion mode.

In this mode, the ADT7476A can be made to read a single

temperature channel only. The appropriate ADC channel is

selected by writing to Bits [7:5] of the TACH1 minimum

high byte register (0x55).

Table 22. 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

Table 23. CONFIGURATION REGISTER 2 (REG. 0x73)

Bit

Description

[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,

0x39,

and

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

THERM LIMIT

TEMPERATURE

FANS

100%

HYSTERESIS (

°C)

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

ADT7476A 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 ADT7476A.

Table 24. VOLTAGE LIMIT REGISTERS

Description

Default

0x44

2.5 V Low Limit

0x00

0x45

2.5 V High Limit

0xFF

0x46

VCCP Low Limit

0x00

0x47

VCCP High Limit

0xFF

0x48

VCC Low Limit

0x00

0x49

VCC High Limit

0xFF

0x4A

5.0 V Low Limit

0x00

0x4B

5.0 V High Limit

0xFF

0x4C

12 V Low Limit

0x00

0x4D

12 V High Limit

0xFF

Table 25. TEMPERATURE LIMIT REGISTERS

Description

Default

0x4E

Remote 1 Temperature Low Limit

0x81

0x4F

Remote 1 Temperature High Limit

0x7F

0x6A

Remote 1 THERM Temp. Limit

0x64

0x50

Local Temperature Low Limit

0x81

0x51

Local Temperature High Limit

0x7F

0x6B

Local THERM Temperature Limit

0x64

0x52

Remote 2 Temperature Low Limit

0x81

0x53

Remote 2 Temperature High Limit

0x7F

0x6C

Remote 2 THERM Temp. Limit

0x64

Table 26. THERM TIMER LIMIT REGISTER

Description

Default

0x7A

THERM Timer Limit

0x00

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.

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