24

DS641F1

CS8421

4.5

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 (ap-

proximately 4

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

4.6

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 6.

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.

ILRCK

ISCLK

SDIN

OLRCK

OSCLK

SDOUT

TDM_IN

OLRCK

OSCLK

SDOUT

TDM_IN

ILRCK

ISCLK

SDIN

Output

Clock

Source

LRCK

SCLK

OLRCK

OSCLK

SDOUT

PCM Source 2

OLRCK

OSCLK

SDOUT

PCM Source 1

Slave

Slave

LRCK

SCLK

SDIN

DSP

Slave

OLRCK

OSCLK

SDOUT

TDM_IN

ILRCK

ISCLK

SDIN

Slave

OLRCK

OSCLK

SDOUT

TDM_IN

ILRCK

ISCLK

SDIN

Slave

OLRCK

OSCLK

SDOUT

PCM Source 3

OLRCK

OSCLK

SDOUT

PCM Source 4

Figure 13. TDM Mode Configuration (All CS8421 Outputs are Slave)

ILRCK

ISCLK

SDIN

OLRCK

OSCLK

SDOUT

TDM_IN

OLRCK

OSCLK

SDOUT

PCM Source 2

OLRCK

OSCLK

SDOUT

PCM Source 1

Master

LRCK

SCLK

SDIN

DSP

Slave

OLRCK

OSCLK

SDOUT

TDM_IN

ILRCK

ISCLK

SDIN

Slave

OLRCK

OSCLK

SDOUT

TDM_IN

ILRCK

ISCLK

SDIN

Slave

OLRCK

OSCLK

SDOUT

TDM_IN

ILRCK

ISCLK

SDIN

Slave

OLRCK

OSCLK

SDOUT

PCM Source 3

OLRCK

OSCLK

SDOUT

PCM Source 4

Figure 14. TDM Mode Configuration (First CS8421 Output is Master, All Others are Slave)