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LC89210

High-speed fax modem data pump

SANYO -> Panasonic 

Printed Circuit Board Design Guidelines

LC89210

While the two most important factors influencing the performance of this fax modem are the performance of the

LC89210 itself and the appropriateness of the design of the printed circuit board, it is not the purpose of this section to

describe all aspects of modem printed circuit board design. Rather, this section presents the following few

recommendations.

1. 4-layer boards

The digital and analog system grounds should be separated and then connected at a single point (single-point

ground). Furthermore, the location of the single-point ground should be as close to the LC89210 as is possible.

AGNDR and AGNDT should be connected to the single-point ground location with an extremely low impedance.

2. 2-layer boards

Supply the ground grid to all empty spaces and the inner side of component spaces.

3. The 2.2 nF capacitors connected to the RXA1 and RXA2 pins should be located as close to the pins as possible.

4. The two 100 nF capacitors connected to the VREFP and VREFN pins should be located as close to the pins as possible.

5. To prevent latchup due to differences in power on timing between the analog and digital power supplies, insert two

diodes with reverse polarities in parallel between the VDD (digital) and AVDD (analog) power supplies.

Application Example

Note: The capacitors marked with asterisks (*) must be connected as close as possible to the LC89210 pins.

Signal names ending in “I” are active low signals.

If it is necessary to supply current to VCM, add the resistors R3, R4, R5, and R6.

No. 5382-9/10

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