WM8991 datasheet(36/174 Pages) WOLFSON

Part #	WM8991

Description	Mobile Multimedia CODEC with Dual-Mode Class AB/D Speaker Driver

PDF	174 Pages

Scroll/Zoom	100%

Manufacturer	WOLFSON [Wolfson Microelectronics plc]

Direct Link	http://www.wolfsonmicro.com

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36 / 174 page

WM8991

Pre-Production

PP, May 2008, Rev 3.1

INTERNAL POWER ON RESET CIRCUIT

Figure 13 Internal Power on Reset Circuit Schematic

The WM8991 includes an internal Power-On-Reset Circuit, as shown in Figure 13, which is used to

reset the digital logic into a default state after power up. The POR circuit is powered from AVDD and

monitors DCVDD. It asserts PORB low if AVDD or DCVDD is below a minimum threshold.

Figure 14 Typical Power up Sequence where AVDD is Powered before DCVDD

Figure 14 shows a typical power-up sequence where AVDD comes up first. When AVDD goes above

the minimum threshold, Vpora, there is enough voltage for the circuit to guarantee PORB is asserted

low and the chip is held in reset. In this condition, all writes to the control interface are ignored. Now

AVDD is at full supply level. Next DCVDD rises to Vpord_on and PORB is released high and all

registers are in their default state and writes to the control interface may take place.

On power down, where AVDD falls first, PORB is asserted low whenever AVDD drops below the

minimum threshold Vpora_off.

WM8991 Datasheet(PDF) 36 Page - Wolfson Microelectronics plc