WM8352 datasheet(144/336 Pages) WOLFSON

144 / 336 page

WM8352

Production Data

PD, February 2011, Rev 4.4

144

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

BIT

LABEL

DEFAULT

DESCRIPTION

R13 (0Dh)

LS_ENA

Limit Switch enable

0 = disabled

1 = enabled

Note: internal conditions may prevent the

converter from actually switching on - see

DCDC/LDO Status register for actual

converter status.

R176 (B0h)

DC-DC / LDO

requested

Note: LS_ENA can be accessed through R13 or through R176. Reading from or writing to either

R199 (C7h)

Limit switch

control

13:10

LS_ENSLOT

[3:0]

0000

Time slot for Limit Switch start-up

0000 = Disabled (do not start up)

0001 = Start-up in time slot 1

… (total 14 slots available)

1110 = Start-up in time slot 14

1111 = Start-up on entering ACTIVE

9:6

LS_SDSLOT

[3:0]

0000

Time slot for Limit Switch shutdown.

0000 = Shut down on entering OFF

0001 = Shutdown in time slot 1

…. (total 14 slots available)

1110 = Shutdown in time slot 14

1111 = Shut down on entering OFF

LS_HIB_MO

Limit switch hibernate mode setting

0 = disabled

1 = leave setting as in Active mode

Table 91 Enabling and Disabling the Current Limit Switch

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