wm8351 Wolfson Microelectronics plc, wm8351 Datasheet - Page 321

• Manufacturer Part Number: wm8351
• Description: Wolfson Audioplus? Stereo Codec With Power Management
• Manufacturer: Wolfson Microelectronics plc

Production Data
29.3 DC-DC (STEP-UP) CONVERTER EXTERNAL COMPONENTS
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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.
29.3.1
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:
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, 0.47μF is recommended. For a 5V output, 10μF is recommended.
DC-DC (STEP-UP) CONVERTER - CONSTANT VOLTAGE MODE
PD, June 2009, Rev 4.1
WM8351
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