The BF6911AQ/BF6911AQ2/BF6911AT is a classic successive approximation register (SAR) analog-to
-digital converter (ADC). The architecture is based on capacitive redistribution, which inherently includes
a sample-and-hold function. The converter is fabricated on a 0.35μm CMOS process.
The basic operation of the BF6911AQ/BF6911AQ2/BF6911AT is shown in Figure 4. The device features
an internal 2.5V reference and uses an external clock. Operation is maintained from a single supply of
2.7V to 3.6V. The internal reference can be overdriven with an external, low-impedance source between
1V and +VCC. The value of the reference voltage directly sets the input range of the converter.
The analog input (X , Y , and Z-Position coordinates, auxiliary input, battery voltage, and chip
temperature) to the converter is provided via a multiplexer. A unique configuration of low on-resistance
touch panel driver switches allows an unselected ADC input channel to provide power and the
accompanying pin to provide ground for an external device, such as a touch screen. By maintaining a
differential input to the converter and differential reference architecture, it is possible to negate the error
from each touch panel driver switch's on-resistance (if this is a source of error for the particular
measurement).
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