WM8976CGEFLSLASHV datasheet(18/114 Pages) WOLFSON

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WM8976

Production Data

PD, Rev 4.5, November 2011

INTERNAL POWER ON RESET CIRCUIT

Figure 7 Internal Power on Reset Circuit Schematic

The WM8980 includes an internal Power-On-Reset Circuit, as shown in Figure 7, which is used reset

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

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

Figure 8 Typical Power up Sequence where AVDD is Powered before DVDD

Figure 8 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 DVDD 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.

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