WM8770
Production Data
INTERNAL POWER ON RESET CIRCUIT
Figure 9 Internal Power On Reset Circuit Schematic
The WM8770 includes an internal Power On Reset Circuit which is used to reset the digital logic into
a default state after power up.
Figure 9 shows a schematic of the internal POR circuit. The POR circuit is powered from AVDD. The
circuit monitors DVDD and VMIDADC and asserts PORB low if DVDD or VMIDADC 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 VMIDADC are established. When AVDD, DVDD, and VMIDADC have been
established, 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 VMIDADC drop below the minimum
threshold Vpor_off.
If AVDD is removed at any time, the internal Power On Reset circuit is powered down and PORB will
follow AVDD.
In most applications the time required for the device to release PORB high will be determined by the
charge time of the VMIDADC node.
PD Rev 4.1 June 2005
14
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
