MXB7846EEE MAXIM [Maxim Integrated Products], MXB7846EEE Datasheet - Page 20

• Manufacturer Part Number: MXB7846EEE
• Description: 2.375V to 5.25V, 4-Wire Touch-Screen Controller with Internal Reference and Temperature Sensor
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 16. MXB7846-to-TMS320 Serial Interface Timing Diagram
2) The MXB7846’s CS pin is driven low by the TMS320’s
3) An 8-bit word (1XXXXXXX) should be written to the
4) The MXB7846’s BUSY output is monitored through
5) The TMS320 reads in 1 data bit on each of the next
6) Pull CS high to disable the MXB7846 until the next
For best performance, use printed circuit (PC) boards
with good layouts; wire-wrap boards are not recommend-
ed. Board layout should 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.
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 operation,
minimize the length of the ground return to the star
ground’s power supply.
2.375V to 5.25V, 4-Wire Touch-Screen Controller
with Internal Reference and Temperature Sensor
20
XF I/O port to enable data to be clocked into the
MXB7846’s DIN pin.
MXB7846 to initiate a conversion and place the
device into normal operating mode. See Table 3 to
select the proper XXXXXXX bit values for your spe-
cific applications.
the TMS320’s FSR input. A falling edge on the BUSY
output indicates that the conversion is in progress
and data is ready to be received from the device.
16 rising edges of DCLK. These bits represent the
12-bit conversion result followed by 4 trailing bits.
conversion is initiated.
______________________________________________________________________________________
CS
DCLK
DIN
BUSY
DOUT
Layout, Grounding, and Bypassing
START
A2
A1
A0
MODE
SER/DEF
PD1
PD0
Power-supply decoupling is also crucial for optimal
device performance. A good way to decouple analog
supplies is to place a 10µF tantalum capacitor in paral-
lel with a 0.1µF capacitor bypassed to GND. To maxi-
mize performance, place these capacitors as close as
possible to the supply pin of the device. Minimize
capacitor lead length for best supply-noise rejection. If
the supply is very noisy, a 10Ω resistor can be connect-
ed in series as a lowpass filter.
While using the MXB7846, the interconnection between
the converter and the touch screen should be as short
as possible. Since touch screens have low resistance,
longer or loose connections may introduce error. Noise
can also be a major source of error in touch-screen
applications (e.g., applications that require a backlight
LCD panel). EMI noise coupled through the LCD panel
to the touch screen may cause flickering of the convert-
ed data. Utilizing a touch screen with a bottom-side
metal layer connected to ground decouples the noise
to ground. In addition, the filter capacitors from Y+, Y-,
X+, and X- inputs to ground also help further reduce
the noise. Caution should be observed for settling time
of the touch screen, especially operating in the single-
ended measurement mode and at high data rates.
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 endpoints of the transfer function,
once offset and gain errors have been nullified. The
static linearity parameters for the MXB7846 are mea-
sured using the end-point method.
MSB
B10
B1
B0
Integral Nonlinearity
HIGH IMPEDANCE
HIGH IMPEDANCE
Definitions