WM8978 Wolfson Microelectronics Ltd., WM8978 Datasheet - Page 19

• Manufacturer Part Number: WM8978
• Description: The WM8978 is a low power, high quality stereo codec designed for portable applications such as Digital still camera or Digital Camcorde
• Manufacturer: Wolfson Microelectronics Ltd.

Preliminary Technical Data
INTERNAL POWER ON RESET CIRCUIT
Figure 7 Typical Power up Sequence where AVDD is Powered before DVDD
w
Figure 6 Internal Power on Reset Circuit Schematic
The WM8978 includes an internal Power-On-Reset Circuit (POR), as shown in Figure 6, 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.
the minimum threshold, V
low and the chip is held in reset. In this condition, all writes to the control interface are ignored.
AVDD will then ramp up to full supply level. Next DVDD rises to V
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 V
Figure 7 shows a typical power-up sequence where AVDD comes up first. When AVDD goes above
pora_off
pora
.
, there is enough voltage for the circuit to guarantee PORB is asserted
pord_on
PTD Rev 2.6 November 2005
and PORB is released high
WM8978
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