WM8351 datasheet(140/330 Pages) WOLFSON

140 / 330 page

WM8351

Production Data

PD, April 2012, Rev 4.5

140

14.8.2

DC-DC STEP DOWN CONVERTERS

DC-DC Converters 1, 3 and 4 are versatile step-down, pulse-width-modulated (PWM) DC-DC

converters designed to deliver high power efficiency across full load conditions. The converters offer

Active and Standby/Hysteretic operating modes in order to maximise efficiency for different loads. A

low-power LDO sleep mode is also available to further reduce quiescent current at very lightly loaded

conditions. The DC-DC Converters maintain output voltage regulation during the switch-over between

operating modes.

The step-down regulators are designed with fixed frequency current mode architecture. The current

feedback loop is through the PMOS current path and is amplified and summed with an internal slope

compensation network. The voltage feedback loop is through an internal feedback divider. The ON

time is determined by comparing the summed current feedback and the output of the switcher error

amplifier. The period is set by the internal RC oscillator, which provides a 2.0MHz clock.

A supply pin (PVDD) provides the core supply for DC-DC Converter 3. Another supply pin

(LINEDCDC) provides the core supply for DC-DC Converters 1 and 4. The input voltage connection to

DC-DC Converters 1, 3 and 4 is provided on PV1, PV3 and PV4 respectively. These input voltages

may be provided from the LINE voltage.

The connections to DC-DC Converter 1 are illustrated in Figure 69. The equivalent circuit applies to

DC-DC Converters 3 and 4 also.

Figure 69 Step-Down DC-DC Converter Connections

The external components at the converter output are required by the DC-DC Converter integral loop

compensation circuit. Note that the recommended output capacitor Cout varies according to the

required transient response on DC-DC1. A single recommended value is provided for Cout on DC-

DC3 and DC-DC4.

See Section 29.3 for details of the recommended external components.

WM8351 Datasheet(PDF) 140 Page - Wolfson Microelectronics plc