Pop Minimisation - Cirrus Logic WM8940 Manual

POP MINIMISATION

Rev 4.4
Power-On-Bias Control (POB_CTRL) selects the bias current source for the output stages of the
WM8940. 0 selects the VMID derived bias source (normal operation), 1 selects a non-VMID derived
source which allows the output amplifiers to be enabled before VMID at start-up. This feature can be
used to minimise pops. Once VMID is enabled and has stabilised, POBCTRL should be set to 0.
Register SOFT_START is the enable bit for the VMID soft-start function. Setting the bit to 1 causes
charging of the VMID decoupling cap to follow a soft-start profile which minimises pops. This soft-start
profile has minimal impact on VMID charge time.
Fast VMID discharge is enabled using TOGGLE. Setting to 1 opens a low impedance discharge path
from VMID to GND. This function can be used during power down to reduce the discharge time of the
VMID decoupling cap. Must be set to 0 for normal operation.
REGISTER BIT LABEL
ADDRESS
R7 6 POB_CTRL
Additional
Control
5 SOFT_START
4 TOGGLE
Table 60 POP Minimisation Control
DEFAULT DESCRIPTION
0 Power on Bias Control
0=normal (current bias based on VMID)
1=Startup (current bias not based on
VMID)
0 VMID Soft Start
0=disabled
1=enabled
0 Fast VMID Discharge
0=normal
1=enable (used during power-down)
WM8940
67