Z-World eDisplay OP7200, Руководство пользователя

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eDisplay (OP7200)
B.1.1 Power for Analog Circuits
Power to the analog circuits is provided by way of a single-stage low-pass filter, which
isolates the analog section from digital noise generated by the other components. The ana-
log power vV powers the A/D converter chip, the touchscreen controller, and the
reference circuit. The maximum current draw on +V is less than 10 mA. +V is not acces-
sible to the user.
B.1.2 Grounds
There are three grounds, one digital ground on screw-terminal headers J3 (pin 12) and J10
(pin 12), and an analog ground on screw-terminal header J2 (pin 12). The digital and ana-
log grounds share a single split ground plane on the printed-circuit board. Keeping the
grounds separate isolates the noise of the digital section from the analog circuits, provid-
ing for improved performance of the A/D converter chip and the touchscreen controller.
The analog ground is connected at a single point to the digital ground by a single copper
bridge to eliminate the possibility of ground loops. Analog ground should be used as the
return path for inputs connected to the A/D converter chip via pins 4–11 of screw-terminal
header J2.