Datasheet

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.