CS8421

32

DS641PP1

9. APPLICATIONS

9.1

Reset, Power Down, and Start-up

When RST is low the CS8421 enters a low power mode, all internal states are reset, and the outputs are

disabled. After RST transitions from low to high the part senses the resistor value on the configuration

pins (MS_SEL, SAIF, and SAOF) and sets the appropriate mode of operation. After the mode has been

set (approximately 4

µs) the part is set to normal operation and all outputs are functional.

9.2

Power Supply, Grounding, and PCB layout

The CS8421 operates from a VD = +2.5 V and VL = +3.3 V or +5.0 V supply. These supplies may be set

independently. Follow normal supply decoupling practices, see Figure 5.

Extensive use of power and ground planes, ground plane fill in unused areas, and surface mount decou-

pling capacitors are recommended. Decoupling capacitors should be mounted on the same side of the

board as the CS8421 to minimize inductance effects and all decoupling capacitors should be as close to

the CS8421 as possible. The pin of the configuration resistors not connected to MS_SEL, SAIF, and

SAOF should be connected as close as possible to VL or GND.