Datasheet

34
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TSC2200
SBAS191F
FIGURE 29. D/A Converter Circuit when Using V+ Higher
than V
SUPPLY
.
FIGURE 30. Keypad Scan Initiated by Keypress.
In the previous example, when the D/A converter current is
zero, the voltage on the A
OUT
pin will rise above the TSC2200
supply voltage. This is not a problem, however, since V+ was
within the absolute maximum ratings of the TSC2200, so no
special precautions are necessary. Many LCD displays re-
quire voltages much higher than the absolute maximum
ratings of the TSC2200. In this case, the addition of an NPN
transistor, as shown in Figure 29, will protect the A
OUT
pin
from damage.
OPERATION—KEYPAD INTERFACE
The TSC2200 contains a keypad interface that is suitable for
use with matrix keypads up to 4-by-4 keys. A control register,
the Keypad Control Register, is used to set the scan rate for
the keypad and de-bounce times. There is also a Keypad
Mask register which allows certain keys to be masked from
being read or causing the TSC2200 to detect a key press.
The results of keyboard scans are placed in the Keypad Data
register.
When a key press is detected, the TSC2200 automatically
scans the keypad and de-bounces the key press. It will then
drive the
KBIRQ LOW. All keys pressed at the time of the
scan will then be reflected in the Keypad Data Register. This
mode is shown in Figure 30.
D/A Converter
V+
V
SUPPLY
V
BIAS
A
OUT
ARNG
RRNG
R
2
R
1
8 Bits
Keypad Touch
Issue Interrupt KBIRQ
Reset KBIRQ
Keypad Scan
KBIRQ Initiated
Done
Start Clock
Read KPDATA
Register
Store Keypad Scan
Results in KPData Register
Scan and De-Bounce
Keys
Turn Off Clock