Cirrus Logic AN150 - Manual (Page 12)

AN150
12 AN150REV2
an output latch pin. When the GB bit is set to ‘1’,
the instrumentation amplifier’s common-mode
voltage is output on the A0 pin.
The amplifier’s common-mode voltage is only out-
put on the A0 pin when the 2X-64X instrumenta-
tion amplifier is on, and the device is in the normal
operating mode. On power-up, the instrumentation
amplifier is off by default. To engage the amplifier,
a conversion or calibration must be started with the
part set up to use a gain from 2X to 64X. The am-
plifier will remain on until a conversion or calibra-
tion is performed in the 1X gain range. When the
part is in standby or sleep mode, the instrumenta-
tion amplifier is powered down.
It is important to note that the guard drive output
typically can only source about 10-20 uA of drive
current. If the guard signal is used in an application
which requires more drive current, an external
buffer should be used to provide the necessary cur-
rent. Also, the guard drive output should be protect-
ed against high voltage or current spikes, if they are
likely to occur. Voltage or current spikes into the
guard buffer can damage the ADC, and cause the
ADC to malfunction.