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ADT7490

dBCool Remote Thermal Monitor and Fan Controller with PECI Interface

Analog Devices 

Extended Resolution Registers

Voltage measurements can be made with higher accuracy

using the extended resolution registers (0x1F, 0x76, and 0x77).

Whenever the extended resolution registers are read, the

corresponding data in the voltage measurement registers (0x1D,

0x1E, and 0x20 to 0x24) is locked until their data is read. That

is, if extended resolution is required, the extended resolution

register must be read first, immediately followed by the appropriate

voltage measurement register.

ADDITIONAL ADC FUNCTIONS FOR VOLTAGE

MEASUREMENTS

A number of other functions are available on the ADT7490

to offer the system designer increased flexibility. The functions

described in the following sections are enabled by setting the

appropriate bit in Configuration Register 2.

Configuration Register 2 (Register 0x73)

Bit 4 (AVG) = 1, averaging off.

Bit 5 (ATTN) = 1, bypass input attenuators.

Bit 6 (CONV) = 1, single-channel convert mode.

Turn-Off Averaging

For each voltage/temperature measurement read from a value

register, 16 readings have actually been made internally and

the results averaged before being placed into the value reg-

ister. When faster conversions are needed, setting Bit 4 (AVG)

of Configuration Register 2 (0x73) turns averaging off. This

effectively gives a reading that is 16 times faster, but the reading

can be noisier. The default round-robin cycle time takes 146.5 ms.

Table 8. Conversion Time with Averaging Disabled

Channel

Measurement Time (ms)

Voltage Channels

0.7

Remote Temperature 1

7

Remote Temperature 2

7

Local Temperature

1.3

When Bit 7 (ExtraSlow) of Configuration Register 6 (0x10) is

set, the default round-robin cycle time increases to 240 ms.

ADT7490

Bypass All Voltage Input Attenuators

Setting Bit 5 of Configuration Register 2 (Register 0x73)

removes the attenuation circuitry from the 2.5 VIN, VCCP,

VCC, 5 VIN, and 12 VIN inputs. This allows the user to directly

connect external sensors or rescale the analog voltage measure-

ment inputs for other applications. The input range of the ADC

without the attenuators is 0 V to 2.25 V.

Bypass Individual Voltage Input Attenuators

Bits [7:4] of Configuration Register 4 (0x7D) can be used

to bypass individual voltage channel attenuators.

Table 9. Bypassing Individual Voltage Input Attenuators

Configuration Register 4 (0x7D)

Bit No.

Channel Attenuated

4

Bypass +2.5VIN attenuator

5

Bypass VCCP attenuator

6

Bypass +5VIN attenuator

7

Bypass +12VIN attenuator

Single-Channel ADC Conversion

While single-channel mode is intended as a test mode that

can be used to increase sampling times for a specific channel,

therefore helping to analyze that channel’s performance in

greater detail, it can also have other applications.

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

ADT7490 into single-channel ADC conversion mode. In this

mode, the ADT7490 can read a single voltage channel only.

The selected voltage input is read every 0.7 ms. The appropriate

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

minimum high byte register (0x55).

Table 10. Programming Single-Channel ADC Mode

Bits [7:4] Register 0x55

Channel Selected1

0000

+2.5VIN

0001

VCCP

0010

VCC

0011

+5VIN

0100

+12VIN

0101

Remote 1 temperature

0110

Local temperature

0111

Remote 2 temperature

1000

VTT

1001

IMON

1 In the process of configuring single-channel ADC conversion mode, the

TACH1 minimum high byte is also changed, possibly trading off TACH1

minimum high byte functionality with single-channel mode functionality.

Rev. 0 | Page 17 of 76

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