VIN

VIN

RIN

CIN

CBYPASS

LM3478

23

LM3478

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SNVS085X – JULY 2000 – REVISED DECEMBER 2017

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Typical Applications (continued)

Figure 31. Reducing IC Input Noise

8.2.1.2.9

Output Capacitor Selection

The output capacitor in a boost converter provides all the output current when the inductor is charging. As a

result it sees very large ripple currents. The output capacitor should be capable of handling the maximum RMS

current. Equation 32 shows the RMS current in the output capacitor.

(32)

Where

(33)

The ESR and ESL of the capacitor directly control the output ripple. Use capacitors with low ESR and ESL at the

output for high efficiency and low ripple voltage. Surface mount tantalums, surface mount polymer electrolytic,

polymer tantalum, or multi-layer ceramic capacitors are recommended at the output.

For applications that require very low output voltage ripple, a second stage LC filter often is a good solution. Most

of the time it is lower cost to use a small second Inductor in the power path and an additional final output

capacitor than to reduce the output voltage ripple by purely increasing the output capacitor without an additional

LC filter.

8.2.1.2.10

Compensation

For detailed explanation on how to select the right compensation components to attach to the compensation pin

for a boost topology, please see AN-1286 Compensation For The LM3748 Boost Controller SNVA067.

8.2.1.3 Application Curves

Figure 32. Efficiency vs Load Current (9-V In and 12-V Out)

Figure 33. Efficiency vs Load Current (3.3-V In and 5-V

Out)