WM8352
Production Data
15 CURRENT LIMIT SWITCH
15.1 GENERAL DESCRIPTION
The WM8352 includes an on-chip Current Limit Switch to control external devices and to support hot-
plugging of accessories and power supplies.
When the switch is enabled, it normally has a low resistance, allowing current to pass through (from
the IP pin to the OP pin). If the current limit threshold is reached, the WM8352 can raise an interrupt,
disable the switch and/or shut down the whole device.
15.2 CONFIGURING THE CURRENT LIMIT SWITCH
15.2.1 CURRENT LIMIT SWITCH ENABLE
The Current Limit Switch can be enabled in software using the register fields defined in Table 91.
In Active mode, the Current Limit Switch can be enabled in software using the LS_ENA bit. Setting
this bit whilst in the Pre-Active state (see Figure 65) will not immediately enable the Current Limit
Switch; this bit will only become effective once the WM8352 has reached the Active state.
The Current Limit Switch may be programmed to become enabled in a selected timeslot within the
start-up sequence. When this happens, the WM8352 will set the LS_ENA bit. Note that setting the
LS_ENSLOT field in software is only relevant to the Development Mode, as this field is assigned a
preset value in each of the Custom Modes.
The Current Limit Switch may be programmed to switch off in a selected timeslot within the shutdown
sequence. If the Limit Switch is not allocated to one of the 14 shutdown timeslots, it will be disabled
when the WM8352 enters the OFF state.
The Current Limit Switch behaviour in Hibernate mode is controlled by the LS_HIB_MODE bit.
ADDRESS
R13 (0Dh)
BIT
15
LABEL
LS_ENA
DEFAULT
DESCRIPTION
Limit Switch enable
0
0 = disabled
1 = enabled
R176 (B0h)
15
DC-DC / LDO
requested
Note: internal conditions may prevent the
converter from actually switching on - see
DCDC/LDO Status register for actual
converter status.
Note: LS_ENA can be accessed through R13 or through R176. Reading from or writing to either
register location has the same effect.
R199 (C7h)
13:10
9:6
4
LS_ENSLOT
[3:0]
0000
0000
0
Time slot for Limit Switch start-up
0000 = Disabled (do not start up)
0001 = Start-up in time slot 1
… (total 14 slots available)
Limit switch
control
1110 = Start-up in time slot 14
1111 = Start-up on entering ACTIVE
Time slot for Limit Switch shutdown.
0000 = Shut down on entering OFF
0001 = Shutdown in time slot 1
…. (total 14 slots available)
LS_SDSLOT
[3:0]
1110 = Shutdown in time slot 14
1111 = Shut down on entering OFF
Limit switch hibernate mode setting
0 = disabled
LS_HIB_MO
DE
1 = leave setting as in Active mode
Table 91 Enabling and Disabling the Current Limit Switch
PD, February 2011, Rev 4.4
144
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
