WM8352
Production Data
18 SYSTEM MONITORING AND UNDERVOLTAGE LOCKOUT (UVLO)
The WM8352 includes several mechanisms to prevent the system from starting up, or force it to shut
down, when power sources are critically low.
The under-voltage lockout (UVLO) is a non-programmable voltage limit. When the available supplies
are below this limit, the WM8352 enters the BACKUP state. The WM8352 can only proceed from
BACKUP to the OFF state if LINE is above the UVLO level. Whenever the WM8352 is in ACTIVE,
HIBERNATE or OFF state and LINE falls below the UVLO level, the WM8352 returns to the
BACKUP state.
The UVLO limit threshold is equal to VRTC + 50mV. The precise value of VRTC may vary between
devices, within the limits defined in the Electrical Characteristics (see Section 7.5).
The startup threshold is a programmable voltage limit. The WM8352 can only proceed from OFF to
the ACTIVE state if LINE is above the startup threshold. (Note that, in the case of USB-powered
operation, there are additional requirements; see Section 17.4). The startup threshold is determined
by the PCCMP_ON_THR register field.
The shutdown threshold is determined by the PCCMP_OFF_THR register field. When LINE falls
below this threshold, the WM8352 raises a SYS_HYST_COMP_FAIL_EINT interrupt. In addition, the
WM8352 takes the action set by PCCOMP_ERRACT. If this bit is set, then the WM8352 will shut
down in response to the LINE voltage falling below the shutdown threshold.
The startup and shutdown control register fields are described in Table 112. Note that the startup
threshold should always be set higher than the shutdown threshold in order to create a hysteresis,
making the system more stable.
The SYS_HYST_COMP_FAIL_EINT interrupt is one of the second-level interrupts which triggers a
first-level System Interrupt, SYS_INT (see Section 24). This can be masked by setting the mask bit
as described in Table 113.
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R179 (B3h)
14
PCCMP_ERRA
CT
0
Action to take when LINE falls
below PCCMP_OFF_THR level
(as well as generating an interrupt)
Power Check
Comparator
0 = ignore
1 = shut down system
6:4
PCCMP_OFF_T
HR [2:0]
010
Power check comparator system
shutdown threshold value
000 = 2.9V
001 = 3.0V
…
111 = 3.6V
Protected by security key.
2:0
PCCMP_ON_TH
R [2:0]
101
Power check comparator system
startup threshold value
000 = 2.9V
001 = 3.0V
…
111 = 3.6V
Protected by security key.
Table 112 Battery Monitoring and UVLO Control
PD, February 2011, Rev 4.4
168
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
