LM3533 Datasheet, PDF (49/53 Pages) Texas Instruments – Complete Lighting Power Solution for Smartphone Handsets

LM3533
FIGURE 19. Input RLC Network
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LAYOUT GUIDELINES (CHARGE PUMP)
The charge pump basically has three areas of concern regarding component placement:
1. The flying capacitor (CP)
2. The output capacitor (CPOUT)
3. The input capacitor
Flying Capacitor (CP)
The charge pump flying capacitor must quickly charge up to the input voltage and then supply the current to the output every
switching cycle. Since the charge pump switching frequency is 1MHz, the capacitor must be a low-inductance and low-resistive
ceramic. Additionally, there must be a low-inductive connection from CP to the LM3533’s flying capacitor terminals C+ and C−.
This is accomplished by placing CP as close as possible to the LM3533 and on the same layer to avoid vias.
Output Capacitor (CPOUT)
The charge pump output capacitor sees the switched charge from the flying capacitor every switching cycle (1MHz). This fast
switching action requires that a low inductive and low resistive capacitor (ceramic) be used and that CPOUT be connected to the
LM3533’s CPOUT terminal with a low inductive connection. This is done by placing CPOUT as close as possible to the CPOUT
and GND terminals of the LM3533 and on the same layer as the LM3533 to avoid vias.
Charge Pump Input Capacitor Placement
The input capacitor for the LM3533’s charge pump is the same one used for the LM3533’s inductive boost converter (see Boost
Input Capacitor Selection and Placement section).
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