AD7877 datasheet(33/46 Pages) AD

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AD7877

Data Sheet

Rev. E | Page 32 of 45

GROUNDING AND LAYOUT

It is recommended that the ground pins, AGND and DGND, be

shorted together as close as possible to the device itself on the

user’s PCB.

For more information on grounding and layout considerations

for the AD7877, refer to the AN-577 Application Note, Layout

and Grounding Recommendations for Touch Screen Digitizers.

PCB DESIGN GUIDELINES FOR CHIP SCALE

PACKAGES

The lands on the chip scale package (CP-32) are rectangular.

The printed circuit board pad for these should be 0.1 mm

longer than the package land length and 0.05 mm wider than

the package land width. To ensure that the solder joint size is

maximized, center the land on the pad.

The bottom of the chip scale package has a central thermal pad.

The thermal pad on the printed circuit board should be at least

as large as this exposed pad. On the printed circuit board, provide a

clearance of at least 0.25 mm between the thermal pad and the

inner edges of the pad pattern to ensure that shorting is avoided.

Using thermal vias on the printed circuit board thermal pad

improves the thermal performance of the package. If vias are

used, incorporate them in the thermal pad at a 1.2 mm pitch

grid. Keep the via diameter between 0.3 mm and 0.33 mm. The

via barrel should be plated with 1 oz. copper to plug the via.

The user should connect the printed circuit board thermal pad

to AGND.

HOST

NC = NO CONNECT

AD7877

GPIO4

STOPACQ

DIN

PENIRQ

ALERT

DAV

BAT2

BAT1

AUX3/GPIO3

AUX2/GPIO2

AUX1/GPIO1

VCC

INT1

INT2

SCLK

MISO

MOSI

PENIRQ

GPIO

HSYNC SIGNAL

FROM LCD

VCC

RRNG

0.1

F

DC-DC

CONVERTER

VIN

OUT

TO LCD

BACKLIGHT

TOUCH

SCREEN

0.1

F

1.0

F–10F

(OPTIONAL)

VOLTAGE

REGULATOR

TEMPERATURE

MEASUREMENT

DIODE

MAIN

BATTERY

SECONDARY

BATTERY

FROM AUDIO

REMOTE CONTROL

FROM

HOTSYNC INPUTS

Figure 48. Typical Application Circuit

AD7877 Datasheet(PDF) 33 Page - Analog Devices

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