Data Sheet

LT8277

analog.com

Rev 0

17 of 31

Figure 29. Normalized Input Capacitor Ripple Current for a Boost Converter

Output Capacitor Selection

The output capacitor supplies transient current to the load. The X7R type ceramic chip capacitor is often the best

choice. Choose capacitors with a voltage rating around 60% higher than the target output voltage. For a boost or

SEPIC converter, the current flowing in the output capacitor can be large. Select the output capacitor based on

switching frequency, load current, number of phases (n), and acceptable ripple voltage. Note that increasing the

number of phases will decrease the voltage ripple for the same output capacitor and switching frequency. It is best

to use a capacitor with low equivalent series resistance and inductance (ESR and ESL) for this role. An additional

margin is recommended.

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Keep the current rating in mind when selecting an output capacitor. A plot of output capacitor RMS current over

switch duty appears in Figure 30. This plot is normalized to the DC load current.

Figure 30. Normalized Output Capacitor Ripple Current (RMS) for a Boost Converter

1-PHASE

2-PHASE

4-PHASE

8-PHASE

SWITCH DUTY

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0

91

182

272

363

454

545

635

726

817

908

1-PHASE

2-PHASE

4-PHASE

8-PHASE

BOTTOM SWITCH DUTY RATIO

0.05

0.15

0.25

0.35

0.45

0.55

0.65

0.75

0.85

0.95

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0