AD7889 Analog Devices, AD7889 Datasheet - Page 27

• Manufacturer Part Number: AD7889
• Description: Low Voltage Controller for Touch Screens
• Manufacturer: Analog Devices

Specifications of AD7889

• Resolution (bits): 12bit
• # Chan: 6
• Sample Rate: 105kSPS
• Interface: I²C/Ser 2-Wire,Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni Vdd
• Adc Architecture: SAR
• Pkg Type: CSP

ADC Channel (Control Register 1, Bits[14:12])
The ADC channel address is selected by Bits[14:12] of Control
Register 1 (CHNL ADD2 to CHNL ADD0). A complete list of
channel addresses is given in Table 21.
For single-channel conversion, the channel address is selected
by writing the appropriate code to the CHNL ADD2 to CHNL
ADD0 bits in Control Register 1.
For sequential channel conversion, the channels to be converted
are selected by setting the bits corresponding to the channel
number in Control Register 3 for slave and master mode
sequencing.
Table 21. Codes for Selecting Input Channel and Normal or Ratiometric Conversion
Channel
0
1
2
3
4
5
6
7
8
9
12
13
14
15
SER/DFR
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
CHNL ADD[2:0]
111
110
101
100
011
010
001
000
111
110
101
100
011
010
001
000
Analog Input
X+ (Y position)
Y+ (X position)
X+ (Z1 touch pressure)
Y− (Z2 touch pressure)
AUX
VBAT
TEMP
X+ (Y position)
Y+ (X position)
X+ (Z1 touch pressure)
Y− (Z2 touch pressure)
AUX
VBAT
TEMP
Rev. C | Page 27 of 40
For both single-channel and sequential conversion, a normal
conversion (single-ended) is selected by setting the SER/ DFR
bit in Control Register 2 (Bit 9). Ratiometric (differential)
conversion is selected by clearing the SER/ DFR bit.
PENIRQ Enable (Control Register 1, Bit 15)
The AD7879/AD7889 have a dual function output that performs
as PENIRQ or INT depending on the pen interrupt enable bit
(Bit 15 of Control Register 1). When this bit is set to 0, the pin
functions as a pen interrupt and goes low whenever the screen
is touched. When the pen interrupt enable bit is set to 1, the pen
interrupt request is disabled and the pin functions as an interrupt
when a measurement exceeds a preprogrammed limit ( INT ).
X Switches
Off
On
X+ off, X− on
X+ off, X− on
Off
Off
Off
Off
On
Off
Off
Off
Off
Off
Invalid address
Invalid address
Y Switches
On
Off
Y+ on, Y− off
Y+ on, Y− off
Off
Off
Off
On
Off
Off
Off
Off
Off
Off
AD7879/AD7889
REF+
Y+
X+
Y+
Y+
V
V
V
V
V
V
V
V
V
V
CC
CC
CC
CC
CC
CC
CC
CC
CC
CC
REF−
Y−
X−
X−
X−
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND