AP65352

Document number: DS38482 Rev. 2 - 3

12 of 15

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December 2017

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AP65352

Application Information (cont.)

Output Capacitor

The output capacitor keeps the output voltage ripple small, ensures feedback loop stability and reduces the overshoot of the output voltage. The

output capacitor is a basic component for the fast response of the power supply. In fact, during load transient, for the first few microseconds it

supplies the current to the load. The converter recognizes the load transient and sets the duty cycle to maximum, but the current slope is limited

by the inductor value.

Maximum capacitance required can be calculated from the following equation:

ESR of the output capacitor dominates the output voltage ripple. The amount of ripple can be calculated from the equation below:

ESR

*

ΔI

Vout

inductor

capacitor 

An output capacitor with ample capacitance and low ESR is the best option. For most applications, a 22µF to 68µF ceramic capacitor will be

sufficient.

2

out

2

out

2

inductor

out

o

V

)

V

V

(

Δ

)

2

ΔI

L(I

C









Where

ΔV is the maximum output voltage overshoot.

Bootstrap Capacitor

To ensure the proper operation, a ceramic capacitor must be connected between the VBSTT and SW pin. A 0.1µF ceramic capacitor is sufficient.

VREG5 Capacitor

To ensure the proper operation, a ceramic capacitor must be connected between the VREG5 and PGND pin. A 1µF ceramic capacitor is sufficient.

PC Board Layout

1.

The AP65352 works at 3A load current, heat dissipation is a major concern in layout of the PCB. A 2oz Copper in both top and bottom

layer is recommended.

2.

Provide sufficient vias in the thermal exposed pad for heat dissipate to the bottom layer.

3.

Provide sufficient vias in the Output capacitor PGND side to dissipate heat to the bottom layer.

4.

Make the bottom layer under the device as PGND layer for heat dissipation. The PGND layer should be as large as possible to provide

better thermal effect.

5.

Make the Vin capacitors as close to the device as possible.

6.

Make the VREG5 capacitor as close to the device as possible.

7.

The thermal pad of the device should be soldered directly to the PCB exposed copper plane to work as a heatsink. The thermal vias in

the exposed copper plane increase the heat transfer to the bottom layer.

Figure 6 PC Board Layout