ADT7476AARQZ-R datasheet(21/69 Pages) ONSEMI

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ADT7476A

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Table 27. FAN LIMIT REGISTERS

Description

Default

0x54

TACH1 Minimum Low Byte

0xFF

0x55

TACH1 Minimum High Byte

0xFF

0x56

TACH2 Minimum Low Byte

0xFF

0x57

TACH2 Minimum High Byte

0xFF

0x58

TACH3 Minimum Low Byte

0xFF

0x59

TACH3 Minimum High Byte

0xFF

0x5A

TACH4 Minimum Low Byte

0xFF

0x5B

TACH4 Minimum High Byte

0xFF

Out-of-Limit Comparisons

Once all limits have been programmed, the ADT7476A

can be enabled for monitoring. The ADT7476A measures

all voltage and temperature measurements in round robin

format and sets the appropriate status bit for out-of-limit

conditions. TACH measurements are not part of this round

robin cycle. Comparisons are done differently depending on

whether the measured value is being compared to a high or

low limit.

High Limit: > Comparison Performed

Low Limit:

≤ Comparison Performed

Voltage and temperature channels use a window

comparator for error detecting and, therefore, have high and

low limits. Fan speed measurements use only a low limit.

This fan limit is needed only in manual fan control mode.

Analog Monitoring Cycle Time

The analog monitoring cycle begins when a 1 is written to

the start bit (Bit 0) of Configuration Register 1 (0x40). The

ADC measures each analog input in turn, and, as each

measurement is completed, the result is automatically stored

in the appropriate value register. This round robin

monitoring cycle continues unless disabled by writing a 0 to

Bit 0 of Configuration Register 1.

As the ADC is normally left to free-run in this manner, the

time taken to monitor all the analog inputs is normally not

of interest, because the most recently measured value of any

input can be read out at any time.

For applications where the monitoring cycle time is

important, it can easily be calculated.

The total number of channels measured is:

• Four Dedicated Supply Voltage Inputs

• Supply Voltage (VCC Pin)

• Local Temperature

• Two Remote Temperatures

As mentioned previously, the ADC performs round robin

conversions and takes 11 ms for each voltage measurement,

12 ms for a local temperature reading, and 39 ms for each

remote temperature reading. The total monitoring cycle time

for averaged voltage and temperature monitoring is,

therefore, nominally:

11)

) 12 ) (2

39)

+ 145 ms

(eq. 3)

ADT7476AARQZ-R Datasheet(PDF) 21 Page - ON Semiconductor

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