WM8351 datasheet(142/330 Pages) WOLFSON

142 / 330 page

WM8351

Production Data

PD, April 2012, Rev 4.5

142

14.9 LDO REGULATOR OPERATION

The WM8351 provides four identical LDO voltage regulators to generate accurate, low-noise supply

voltages for various system components. The LDOs can also operate as current-limited switches, with

no voltage regulation; this is useful for ‘Hot Swap’ outputs, i.e. supply rails for external devices that

are plugged in when the system is already powered up - the current-limiting function prevents the in-

rush current into the external device from disturbing other system power supplies.

The LDO regulators are dynamically programmable. Each regulator output is current-limited; the

output voltage is automatically throttled back if the load current exceeds the limit.

A single supply pin (LDOVDD) provides the core supply for all four LDOs. The input voltage

connection to LDO1 and LDO2 is provided on the VINA pin. The input voltage connection to LDO3

and LDO4 is provided on the VINB pin. These input voltages can be provided from one of the DC-DC

Converters or from the LINE voltage.

Note that separate voltage regulators are provided to generate the backup supply VRTC and the

microphone bias voltage MICBIAS.

The connections to LDO Regulator 1 are illustrated in Figure 71. The equivalent circuit applies to

LDO2, LDO3 and LDO4.

Figure 71 LDO Regulator Connections

An input and output capacitor are recommended for each LDO Regulator, as illustrated above. See

Section 29.5 for details of the recommended external components.

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