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Touch Screen Controller
Data Sheet
Rev. D
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FEATURES
4-wire touch screen interface
LCD noise reduction feature (STOPACQ pin)
Automatic conversion sequencer and timer
User-programmable conversion parameters
On-chip temperature sensor: 40°C to +85°C
On-chip 2.5 V reference
On-chip 8-bit DAC
3 auxiliary analog inputs
1 dedicated and 3 optional GPIOs
2 direct battery measurement channels (0.5 V to 5 V)
3 interrupt outputs
Touch-pressure measurement
Wake up on touch function
Specified throughput rate of 125 kSPS
Single supply, VCC of 2.7 V to 5.25 V
Separate VDRIVE level for serial interface
Shutdown mode: 1 A maximum
32-lead, LFCSP, 5 mm × 5 mm package
25-ball,WLCSP, 2.5 mm × 2.8 mm package
Qualified for automotive applications
APPLICATIONS
Personal digital assistants
Smart hand-held devices
Touch screen monitors
Point-of-sale terminals
Medical devices
Cell phones
Pagers
FUNCTIONAL BLOCK DIAGRAM
19
DIN
26
DCLK
27
DOUT
28
VDRIVE
18
CS
23
DAV
CONTROL LOGIC AND SERIAL PORT
DAC
REGISTER
CONTROL
REGISTERS
GPIO
REGISTERS
ALERT STATUS/
MASK REGISTER
LIMIT
REGISTERS
LIMIT
COMPARATOR
RESULTS
REGISTERS
SEQUENCER
8-BIT
DAC
29
ARNG
30
AOUT
4
AUX3/GPIO3
5
AUX2/GPIO2
6
AUX1/GPIO1
31
VREF
PEN INTERRUPT
AND WAKE-UP
ON TOUCH
17
PENIRQ
ALERT
LOGIC
22
ALERT
STOP
ACQ
LOGIC
20
STOPACQ
14
AGND
15
DGND
21
GPIO4
2.5V
REF
BUF
TO
GPIO1-3
ADC
D
A
T
A
12-BIT SUCCESSIVE
APPROXIMATION ADC
WITH TRACK-AND-HOLD
CLOCK
9 TO 1
INPUT
MUX
TEMPERATURE
SENSOR
2
BAT2
BATTERY
MONITOR
3
BAT1
BATTERY
MONITOR
11
Y–
13
Y+
10
X–
12
X+
7
VCC
REF–
IN
REF+
DUAL 3-1
MUX
X– Y– GND X+ Y+ VREF
AD7877
03796-
001
Figure 1.
GENERAL DESCRIPTION
The AD7877 is a 12-bit, successive approximation ADC with a
synchronous serial interface and low on resistance switches for
driving touch screens. The AD7877 operates from a single 2.7 V
to 5.25 V power supply (functional operation to 2.2 V), and
features throughput rates of 125 kSPS. The AD7877 features
direct battery measurement on two inputs, temperature and
touch-pressure measurement.
The AD7877 also has an on-board reference of 2.5 V. When not
in use, it can be shut down to conserve power. An external
reference can also be applied and varied from 1 V to +VCC, with
an analog input range of 0 V to VREF. The device includes a
shutdown mode that reduces its current consumption to less
than 1 A.
To reduce the effects of noise from LCDs, the acquisition phase
of the on-board ADC is controlled via the STOPACQ pin. User-
programmable conversion controls include variable acquisition
time and first conversion delay. Up to 16 averages can be taken
per conversion. There is also an on-board DAC for LCD back-
light or contrast control. The AD7877 runs in either slave or
master mode using a conversion sequencer and timer. It is ideal
for battery-powered systems such as personal digital assistants
with resistive touch screens and other portable equipment.
The part is available in a 32-lead lead frame chip scale package
(LFCSP), and a 25-ball wafer level chip scale package (WLCSP).