WM8581 datasheet(73/100 Pages) WOLFSON

73 / 100 page

Production Data

WM8581

PD Rev 4.0 April 2007

INTERNAL POWER ON RESET CIRCUIT

Figure 34 Internal Power On Reset Circuit Schematic

The WM8581 includes an internal Power-On Reset Circuit, which is used to reset the digital logic into

a default state after power up.

Figure 34 shows a schematic of the internal POR circuit. The POR circuit is powered from AVDD.

The circuit monitors DVDD and VMID and asserts PORB low if DVDD or VMID are below the

minimum threshold Vpor_off.

On power up, the POR circuit requires AVDD to be present to operate. PORB is asserted low until

AVDD, DVDD and VMID voltages have risen above their reset thresholds. When these three

conditions have been met, PORB is released high. When PORB is released high, all registers are in

their default state and writes to the digital interface may take place.

On power down, PORB is asserted low whenever DVDD or VMID drop below the minimum threshold

Vpor_off.

If AVDD is removed at any time, the internal Power On Reset circuit is powered down and the PORB

output will follow the AVDD voltage.

In most applications, the time required for the device to release PORB high will be determined by the

charge time of the VMID node.

WM8581 Datasheet(PDF) 73 Page - Wolfson Microelectronics plc