900844 datasheet(94/118 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

900844

FUNCTIONAL DEVICE OPERATION

ADC SUBSYSTEM

APPLICATION SUPPLY (IF USED)

Channel 22 can be used to read the application supply voltage at the VPWR pin. This can be enabled by setting the

VPWRCON bit in the FSLADCCNTL register high. The battery voltage is first scaled as VPWR/2 in order to fit the input range of

the ADC.

BACKUP VOLTAGE (IF USED)

Channel 25 can be used to read the voltage of the coin cell connected to the COINCELL. This is enabled by setting the LICON

bit in the FSLADCCNTL register to 1. Since the voltage range of the coin cell exceeds the input voltage range of the ADC, the

COINCELL voltage is first scaled as

VCOIN*2/3.

TOUCH SCREEN INTERFACE

The PMIC touch screen support consists of four analog input channels with built in bias control. The BIAS FET control bits are

part of the ADC round robin address register ADCADDRx. The touch screen X plate is connected to ADIN10 (X+) and ADIN11

(X-), while the Y plate is connected to ADIN12(Y+) and ADIN13(Y-). A local supply, TSREF, of 1.2 V will serve as a reference.

The system processor will handle the touch screen sequencing and any necessary conversion delays. The system processor

will direct the desired bias control for every reading though the ADCADDRx registers. If FET biasing is enabled though the

ADCADDRx registers, then touch screen readings will start according based on the channels chosen, and also by the

ADCADDRx registers. If the touch screen is not used, then the above inputs can be used as general purpose inputs. In this case,

the bias control will always be programmed to no bias.

Figure 50 is a touch screen representation.

Figure 50. Touch Screen Configuration Example

Table 64. Application Supply Voltage Reading Coding

Conversion Code

Voltage at ADC input

Voltage at VPWR

1 111 111 111

2.400 V

4.800 V

1 000 010 100

1.250 V

2.500 V

0 000 000 000

0.000 V

Table 65. Backup (Coin Cell) Voltage Reading Coding

Conversion Code Voltage at ADC input Voltage at COINCELL

1 111 111 111

2.400 V

3.600 V

1 000 000 000

1.200 V

1.800 V

0 000 000 000

0.000 V

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