Datasheet

X-Plate
Y-Plate
TSX1 TSX2
TSY1
TSY2
RX1 RX2
RY1
RY2
Rcontact
TPS65070, TPS65072, TPS65073
TPS650731, TPS650732, TPS650701, TPS650702, TPS650721
www.ti.com SLVS950G –JULY 2009–REVISED MAY 2013
Figure 34. Touch Screen
The touch screen interface consists of a digital state machine, a voltage reference, and an analog switch matrix
which is connected to the four wire resistive touch screen inputs (TSX1, TSX2, TSY1, TSY2) and an internal 10-
Bit ADC. The state machine controls the sequencing of the switch matrix to cycle through the three types of
measurement modes (position, pressure, plate resistance) and the low power standby mode. The separate
internal voltage reference (TSREF) is disabled in standby and off modes. The voltage is generated by an internal
LDO. Its voltage is bypassed by a capacitor connected to pin INT_LDO. The state of the touch screen is
controlled by the TSC_M[2,0] Bits of the TSCMODE register (08h) as shown in Table 2. The touch screen
controller uses transfer gates to the internal ADC on input channels AD_IN14 and AD_IN15.
Table 2. TSC Modes
CONTROL MULTIPLEXER CONNECTIONS
MODE MEASUREMENT
TSC_M2 TSC_M1 TSC_M0 TSX1 TSX2 TSY1 TSY2
0 0 0 TSREF GND ADC_IN3 ADC_IN4 X-Position Voltage TSY1
PMOS NMOS TGATE TGATE
0 0 1 ADC_IN1 ADC_IN2 TSREF GND Y-Position Voltage TSX1
TGATE TGATE PMOS NMOS
0 1 0 TSREF TSREF GND GND Pressure Current TSX1 and TSX2
NMOS NMOS
0 1 1 TSREF GND HiZ HiZ Plate X Current TSX1
PMOS NMOS Reading on ADC_IN14
1 0 0 HiZ HiZ TSREF GND Plate Y Current TSY1
PMOS NMOS Reading on ADC_IN14
1 0 1 TSREF TSREF GND GND TSC standby Voltage TSX1 and TSX2
TGATE TGATE NMOS NMOS
1 1 0 A/D A/D A/D A/D A/D ADC used as stand alone
TGATE TGATE TGATE TGATE ADC using its analog inputs
1 1 1 OPEN OPEN OPEN OPEN Disabled (no interrupt) None
If the Touch screen multiplexer is set to disabled mode [111], touch to the screen will not be detected. Standby
mode is entered by setting TSC_M[2:0] to 101. When there is a touch, the controller will detect a change in
voltage at the TSX1 point and after a 8ms deglitch the INT pin will be asserted if the interrupt is unmasked in
register INT. Once the host detects the interrupt signal, will enable the ADC converter and set the TSC_M<2:0>
via the I
2
C bus to select any of five measurements (position, pressure, plate) as shown in Table 3.
Table 3. TSC Equations
MEASUREMENT CHANNEL EQUATION
X Plate resistance AD_IN14 Rx = VTSREF/ [(V
ADC
/ 22k) × 150]
Y plate resistance AD_IN14 Ry = VTSREF / [(V
ADC
/ 22k) × 150]
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