AK4650 Datasheet, PDF (45/86 Pages) Asahi Kasei Microsystems – 16Bit ΔΣ CODEC with MIC/HP/SPK-AMP & TSC

[AK4650]
■ A/D Converter for Touch Screen
The AK4650 incorporates a 12-bit successive approximation resistor A/D converter for position measurement, and
battery voltage. The architecture is based on capacitive redistribution algorithm, and an internal capacitor array functions
as the sample/hold circuit.
The A/D converter output is a straight binary format as shown in Table 40:
Input Voltage
(ΔVREF−1.5LSB) ~ ΔVREF
(ΔVREF−2.5LSB) ~ (ΔVREF−1.5LSB)
:
0.5LSB ~ 1.5LSB
0 ~ 0.5LSB
ΔVREF: (VREF+) – (VREF−)
Table 40. Output Code
Output Code
FFFH
FFEH
:
001H
000H
The A/D converter’s full scale measurements depend on the input mode.
■ Analog Inputs
Analog input is selected via the A2-0 and SER bits in the control register. If the analog inputs are the X or Y-axis and the
SER bit is set to “0”(differential mode), the full scale (ΔVREF) is the differential voltage between the non-inverting
terminal and the inverting terminal of the measured axis (e.g. (XP) – (XN)). Analog non-inverting input to A/D converter
(ΔAIN) is the non-inverting terminal of the non-measured axis while the inverting input is the inverting terminal of the
measured axis. If the SER bit is set to “1” (single-ended mode), the full scale of A/D converter (ΔVREF) is the internal
reference voltage, or external reference voltage. Note that the SER bit should be set to “0” if the IN2 pin is selected as
analog input; nevertheless, the IN2 pin is actually measured by single-ended mode.
SER bit
0
1
Analog Input Type
ΔVREF
ΔAIN
Differential
X-axis measurement: XP − XN
Y-axis measurement: YP − YN
X-axis measurement: YP − XN
Y-axis measurement: XP − YN
Single-ended
VREF − TSVSS
AIN − TSVSS
Table 41. Analog Input Type, ΔVREF and ΔAIN
MS0502-E-01
- 45 -
2007/04