WM8351 datasheet(322/330 Pages) WOLFSON

322 / 330 page

WM8351

Production Data

PD, April 2012, Rev 4.5

322

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

The DC-DC (Step-Up) Converter can operate as a Switch or as a Boost Converter. In Boost mode, it

operates in one of three different modes, set by the DC2_FBSRC register field. The following

subsections describe each of these modes in turn.

29.4.1

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

Constant voltage mode is selected by setting DC1_FBSRC[1:0] = 00, as described in Section 14.6.4.

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

Figure 89.

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

The DC-DC (Step-Up) Converter is 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:

R1 = R2 . (2VOUT –1)

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 varies depending on the required output voltage. For a

20V output, 0.47

F is recommended. For a 5V output, 10F is recommended.

WM8351 Datasheet(PDF) 322 Page - Wolfson Microelectronics plc