AN3301 Hardware
Doc ID 18161 Rev 1 11/35
1.8 ADC controller
The STMPE812A is equipped with a 12-bit analog-to-digital converter (ADC). Besides the
use for ADC conversion during touchsceen controller operation, it is possible to be used as
general purpose ADC conversion for up to maximum two external auxiliary analog signals
feed through pins B2 and C2.
The touchscreen controller has the priority for the ADC conversion. Selection of conversion
of the two external auxiliary analog signals is programmed through Bit[0] of the ADC control
register (0x20).
Whenever the touchscreen data acquisition is initiated, the ADC conversion is triggered
automatically without needs to program the ADC control register. Writing ‘1’ to Bit[6] of ADC
Control register to initialize conversion for Touchscreen data is redundant and will result in
higher current consumption if ADC is in continuous capture mode.
The STMPE812A is integrated with an internal charge pump in order to ensure ADC
performance in low V
CC
condition. The internal charge pump should be turned on through
ADC control register in the device initialization phase whenever the V
CC
is less than 2.5 V.
Important: If V
CC
is higher than 2.5 V, it is important to ensure the charge pump is
disabled to prevent possible reliability issue or permanent damage of the device.
1.9 GPIO output configurations
The STMPE812A provides push-pull type of GPIO output. If open drain GPIO outputs are
required, it is configurable, with a tweak to the software programming routine. See Figure 5,
Figure 6 and Figure 7.
1.9.1 Push-pull
Set the GPIO to output state through PORT_FUNTION (0x04) register. Input path will be
disabled. Output path will be enabled in push-pull configuration.
Figure 5. GPIO push-pull configuration
AM004195V1
GPIOxGPIOx
STMPE812A
enabled
OUTPUT
INPUT
disabled
