ADT7490ARQZ-R7 datasheet(22/75 Pages) ONSEMI

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ADT7490

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Table 13. Conversion Time with Averaging Disabled

Channel

Measurement Time (ms)

Voltage Channels

0.7

Remote Temperature 1

Remote Temperature 2

Local Temperature

1.3

When Bit 7 of Configuration Register 6 (0x10) is set, the

default round−robin cycle time increases to a maximum of

193 ms.

Table 14. Conversion Time with Averaging Enabled

Channel

Measurement Time (ms)

Voltage Channels

Remote Temperature

Local Temperature

Single−Channel ADC Conversions

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

places the ADT7490 into single−channel ADC conversion

mode. In this mode, the ADT7490 can be made to read a

single temperature channel only. The appropriate ADC

channel is selected by writing to Bits [7:4] of the TACH1

Minimum High Byte register (0x55).

Table 15. Programming Single−Channel ADC Mode

for Temperatures

Bits [7:4], Register 0x55

Channel Selected

Remote 1 Temperature

0101

Local Temperature

0110

Remote 2 Temperature

0111

Configuration Register 2 (Register 0x73)

Bit 4 (AVG) = 1, averaging off.

Bit 6 (CONV) = 1, 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

local and remote diode temperature channels. The

equivalent PECI limit is TCONTROL in Register 0x3D. When

a temperature exceeds its THERM temperature limit, all

PWM outputs run at 100% duty cycle (default). This can be

changed to maximum PWM duty cycle as programmed in

Bit 3 of Register 0x7D.

The fans run at this speed until the temperature drops

below THERM minus hysteresis. This can be disabled by

setting the BOOST bit in Configuration Register 3, Bit 2

(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 29. THERM Temperature Limit Operation

FANS

TEMPERATURE

100%

HYSTERESIS (5C)

THERM LIMIT

THERM can be disabled by setting Bit 2 of Configuration

• In Offset 64 mode, writing −64°C to the appropriate

THERM temperature limit.

• In twos complement mode, writing −128°C to the

appropriate THERM temperature limit.

Limits, Status Registers, and Interrupts

Limit Values

Associated with each measurement channel on the

ADT7490 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 micro−controller.

8−Bit Limits

The following is a list of 8−bit limits on the ADT7490:

Voltage Limit Registers

Temperature Limit Registers

default

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