AD7151 datasheet(13/28 Pages) AD

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AD7151

Rev. 0 | Page 13 of 28

AUTOCAPDAC ADJUSTMENT

In adaptive threshold mode, the part can dynamically adjust the

CAPDAC to keep the CDC in an optimal operating capacitive

range. When the AutoDAC function is enabled, the CAPDAC

value is automatically incremented when the data average

exceeds three-fourths of the CDC full range, and the CAPDAC

value is decremented when the data average goes below one-

fourth of the CDC full range. The AutoDAC increment or

decrement step depends on the selected CDC capacitive input

range. See the Setup Register section.

POWER-DOWN TIMER

In power sensitive applications, the AD7151 can be set to

automatically enter power-down mode after a programmed

period of time in which the output has not been activated. The

AD7151 can be then returned to a normal operational mode

either via the serial interface or by the power supply off/on

sequence.

POWER SUPPLY MONITOR

When the AD7151 VDD power supply voltage drops below a

defined level needed for correct CDC operation, the on-chip

power supply monitor stops the adaptive threshold logic and

holds it in reset. After the VDD reaches the required level, the

threshold logic is released, and the data average is reset to the

value of the first conversion finished at the correct power supply

voltage.

This feature prevents the adaptive threshold from being set

incorrectly after a very slow rise of the VDD voltage or from being

corrupted by accidental drops in the VDD voltage.

The other AD7151 functions continue working below the

power supply monitor threshold, down to approximately

1.0V..1.8V, the exact level depending on the manufacturing

process variation. In the region of the low VDD voltage, the part

is still accessible via the serial interface and continues conversion.

However, the conversion results may be incorrect and,

therefore, the data should not be considered valid if the part

operates below the power supply monitor threshold.

The status of the power supply monitor can be determined by

reading the PwrDown bit in the AD7151 status register.

AD7151 数据表(PDF) 13 Page - Analog Devices

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