WM8352
Production Data
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, 0.47μF is recommended. For a 5V output, 10μF is recommended.
PD, February 2011, Rev 4.4
328
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
