Pre-Production
WM8940
Table 59 shows the estimated 3.3V AVDD current drawn by various circuits, by register bit.
REGISTER BIT
MONOEN
PLLEN
AVDD CURRENT (MILLIAMPS)
0.2mA
1.4mA (with clocks applied)
MICBEN
0.5mA
BIASEN
0.3mA
BUFIOEN
VMIDSEL
BOOSTEN
INPPGAEN
ADCEN
0.1mA
10K=>0.3mA, less than 0.1mA for 100k/500k
0.2mA
0.2mA
2.6mA
MONOEN
SPKPEN
0.2mA
1mA from SPKVDD
1mA from SPKVDD
0.2mA
SPKNEN
MONOMIXEN
SPKMIXEN
DACEN
0.2mA
1.8mA
Table 59 AVDD Supply Current
POP MINIMISATION
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
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
Power on Bias Control
R7
6
POB_CTRL
0
Additional
Control
0=normal (current bias based on VMID)
1=Startup (current bias not based on
VMID)
5
4
SOFT_START
TOGGLE
0
0
VMID Soft Start
0=disabled
1=enabled
Fast VMID Discharge
0=normal
1=enable (used during power-down)
Table 60 POP Minimisation Control
Pre-Production, Rev 3.0, February 2007
65
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
