ASAHI KASEI
[AK4182A]
ON
YP
ON
YP
XP
VREF+
AIN+
touch
VREF+
AIN+
XP
touch
ADC
VREF-
AIN-
ADC
VREF-
AIN-
XN
XN
ON
YN
ON
YN
a)
Z1-Position Measurement Differential Mode
b)
Z2-Position Measurement Differential Mode
Figure 3 Pen Pressure Measurements
Voltage Reference
The AK4182A has an internal 2.5V voltage reference. This reference can be turned ON when PD1 = “1”, and OFF when PD1 =
“0”. This reference is used in the single-ended mode for the battery monitoring, temperature measurement, or for auxiliary input.
A 0.1µF or larger capacitor should be connected for stable operation of the VREF circuit. Settling time depends on this external
capacitance, but 500µs or longer time is required if the external capacitance is 0.1µF.
If an external voltage reference is used, PD1 bit should be set to “0”.
VCC should be more than 2.7V in order to be stable internal output reference when PD1 = “1” (internal voltage reference).
Battery Measurement
The AK4182A can directly measure the battery voltage up to 5V while the AK4182A operates at 2.2V to 3.6V. The VBAT input
voltage is divided internally by the resistance of R1 (7.5kΩ) and R2 (2.5kΩ) and applied to the input of AD converter (AIN+) as
shown in Figure 4. Minimum 5µs is required as tracking time.
.
VREF
PD1
Internal
VREF(2.5V)
VBAT
R0
R1=7.5K
AIN-
R2=2.5K
AIN+
ADC
VREF-
VREF+
Enable
Figure 4 Battery Monitoring
MS0482-E-00
9
2006/03
AKM [ ASAHI KASEI MICROSYSTEMS ]
