MAX1233_05 Datasheet, PDF (42/45 Pages) Maxim Integrated Products – ±15kV ESD-Protected Touch-Screen Controllers Include DAC and Keypad Controller

±15kV ESD-Protected Touch-Screen
Controllers Include DAC and Keypad Controller
CS
SCK
MISO
QSPI
V_DD
MOSI
SS
Figure 29. QSPI Interface
CS
DCLK
DOUT
MAX1233
MAX1234
DIN
BUSY
PENIRQ
KEYIRQ
+3V/+5V
SUPPLIES
GND
+3V/+5V
R* = 10Ω
AV_DD
GND
DV_DD V_DD DGND
MAX1233
MAX1234
DIGITAL
CIRCUITRY
*OPTIONAL
Figure 30. Power-Supply Grounding Connection
two 8-bit data streams write the command word into the
MAX1233/MAX1234. The next two 8-bit data streams
can contain either the input or output data.
QSPI Interface
Using the high-speed QSPI interface (Figure 29) with
CPOL = 0 and CPHA = 0, the MAX1233/MAX1234 sup-
port a maximum f_SCLK of 10MHz. DOUT data transi-
tions on the serial clock’s falling edge and is clocked
into the µP on the DCLK’s rising edge.
Layout, Grounding, and Bypassing
For best performance, use printed circuit boards with
good layouts; do not use wire-wrap boards even for
prototyping. Ensure that digital and analog signal lines
are separated from each other. Do not run analog and
digital (especially clock) lines parallel to one another, or
digital lines underneath the ADC package.
Figure 30 shows the recommended system ground
connections. Establish a single-point analog ground
(star ground point) at GND. Connect all analog grounds
to the star ground. Connect the digital system ground
to the star ground at this point only. For lowest noise oper-
ation, the ground return to the star ground’s power supply
should be low impedance and as short as possible.
High-frequency noise in the power supply may affect
the high-speed comparator in the ADC. Bypass the
supply to the star ground with a 0.1µF capacitor as
close to pins 1 and 2 of the MAX1233/MAX1234 as
possible. Minimize capacitor lead lengths for best sup-
ply-noise rejection. If the power supply is very noisy, a
10Ω resistor can be connected as a lowpass filter.
While using the MAX1233/MAX1234 with a resistive
touch screen, the interconnection between the convert-
er and the touch screen should be as short and robust
as possible. Since resistive touch screens have a low
resistance, longer or loose connections are a source of
error. Noise can also be a major source of error in
touch-screen applications (e.g., applications that
require a backlight LCD panel). This EMI noise can be
coupled through the LCD panel to the touch screen
and cause “flickering” of the converted data. Utilizing a
touch screen with a bottom-side metal layer connected
to ground couples the majority of noise to ground. In
addition, the filter capacitors from Y+, Y-, X+, and X-
inputs to ground also help reduce the noise further.
Caution should be observed for settling time of the
touch screen.
Definitions
Integral Nonlinearity
Integral nonlinearity (INL) is the deviation of the values
on an actual transfer function from a straight line. This
straight line can be either a best-straight-line fit or a line
drawn between the end points of the transfer function,
once offset and gain errors have been nullified. The
static linearity parameters for the MAX1233/MAX1234
are measured using the end-point method.
Differential Nonlinearity
Differential nonlinearity (DNL) is the difference between
an actual step width and the ideal value of 1LSB. A
DNL error specification of less than 1LSB guarantees
no missing codes and a monotonic transfer function.
Aperture Jitter
Aperture jitter (t_AJ) is the sample-to-sample variation in
the time between the samples.
Aperture Delay
Aperture delay (t_AD) is the time defined between the
falling edge of the sampling clock and the instant when
an actual sample is taken.
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