AD7156_17 datasheet(15/29 Pages) AD

Part #	AD7156

Description	2-Channel Capacitance Converter

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Manufacturer	AD [Analog Devices]

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AD7156

Rev. 0 | Page 14 of 28

AUTO-DAC ADJUSTMENT

In adaptive threshold mode, the part can dynamically adjust the

CAPDAC to keep the CDC in an optimal operating capacitive

range. When the auto-DAC function is enabled, the CAPDAC

value is automatically incremented when the data average

exceeds ¾ of the CDC full range (average > 0xA800), and

the CAPDAC value is decremented when the data average

goes below ¼ of the CDC full range (average < 0x5800).

The auto-DAC increment or decrement step depends on

the selected CDC capacitive input range (see the Setup Registers

section).

When the CAPDAC value reaches 0, the ¼ threshold for further

decrementing is ignored. Similarly, when the CAPDAC value

reaches its full range, the ¾ threshold is ignored. The CDC and

the rest of the algorithm are continuously working, and they are

functional down to a capacitance input of 0 pF or as high as the

capacitance input of (CAPDAC full range + CDC full range),

respectively.

POWER-DOWN TIMER

In power sensitive applications, the AD7156 can be set to

automatically enter power-down mode after a programmed

period of time in which the outputs have not been activated.

The AD7156 can then be returned to a normal operational

mode either via the serial interface or by the power supply

off/on sequence.

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