WM8352 datasheet(328/336 Pages) WOLFSON

328 / 336 page

WM8352

Production Data

PD, February 2011, Rev 4.4

328

29.4 DC-DC (STEP-UP) CONVERTER EXTERNAL COMPONENTS

The DC-DC (Step-Up) Converters can operate as Switches or as Boost Converters. In Boost mode,

they operate in one of three different modes, set by the DC2_FBSRC and DC5_FBSRC register

fields. The following subsections describe each of these modes in turn.

29.4.1

DC-DC (STEP-UP) CONVERTERS - CONSTANT VOLTAGE MODE

Constant voltage mode is selected by setting DCn_FBSRC[1:0] = 00, as described in Section 14.6.4.

The recommended connections to the DC-DC (Step-Up) Converters in this mode are illustrated in

Figure 89.

Figure 89 DC-DC (Step-Up) Converters External Components - Constant Voltage Mode

The DC-DC (Step-Up) Converters are capable of generating output voltages of up to 30V. The output

voltage is determined by the two external resistors R1 and R2, which form a resistive divider between

load connection and the voltage feedback pin FB2 or FB5. The output voltage is set as described in

the following equation:

Setting R2 to 47kΩ is recommended for most applications; R1 can be calculated using the following

equation, given the required output voltage:

When selecting suitable capacitors, is it imperative that the effective capacitance is within the

required limits at the applicable input/output voltage of the converter. Ceramic X7R or X5R types are

recommended.

The choice of output capacitor for DC-DC2 and DC-DC varies depending on the required output

voltage. For a 20V output, 0.47

μF is recommended. For a 5V output, 10μF is recommended.

WM8352 Datasheet(PDF) 328 Page - Wolfson Microelectronics plc