ucb1400 NXP Semiconductors, ucb1400 Datasheet - Page 26

• Manufacturer Part Number: ucb1400
• Description: Audio Codec With Touch Screen Controller And Power Management Monitor
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 09611
Product data
Fig 18. Touch screen setup for X position measurement.
TSMY
TSMX
TOUCH
R
X1
R
Y1
10.2.1 Position measurement
10.2 Operational modes
R
R
t
X2
VBIAS
R
The UCB1400’s internal voltage reference (V
touch screen bias circuitry. This makes the touch screen biasing independent of
supply voltage and temperature variations. Four low pass filters, one on each touch
screen terminal, are built in to minimize the noise coupled from the LCD into the
touch screen signals. An LCD typically generates large noise glitches on the touch
screen, since they are closely coupled.
The setting of the touch screen bias circuitry and the ADC multiplexer is determined
by the setting of TM[1:0] in the touch screen control register according to
Table 8:
The UCB1400 supports three modes of touch screen measurements: position,
pressure, and plate resistances. Additionally, an interrupt mode is provided for
detection of touch events.
Two position (X, Y) measurements are needed to determine the location of the
pressed spot. The X plate is biased during the X position measurement and the
voltage on one or both Y terminals (TSPY, TSMY) is measured. The circuit can be
represented by a potentiometer, with the TSPY and/or TSMY electrode being the
‘wiper’. The measured voltage on the TSPY/TSMY terminal is proportional to the X
position of the pressed spot of the touch screen.
In the Y position mode, the X plate and Y plate terminals are interchanged, thus the Y
plate is biased and the voltage on the TSPX and/or TSMX terminal is measured.
TM[1:0]
00
01
10
11
Y2
TSPX
TSPY
TO ADC
Touch screen mode selection
Selected mode
Interrupt
Pressure
Position
Position
Rev. 02 — 21 June 2002
TSMY
Touch screen bias source
Resistor to AV
Touch screen bias circuit
Touch screen bias circuit
Touch screen bias circuit
TSMX
Audio codec with touch screen controller
DD
ref
) acts as the reference voltage for the
TSPX
and power management monitor
© Koninklijke Philips Electronics N.V. 2002. All rights reserved.
VBIAS
ADC multiplexer setting
Defined by AI[2:0]
Touch screen current monitor
Defined by AI[2:0]
Defined by AI[2:0]
TSPY
UCB1400
SN00247
TO ADC
Table
26 of 63
8.