APL3218 datasheet(13/20 Pages) ANPEC

13 / 20 page

Rev. A.1 - Apr., 2012

APL3218

www.anpec.com.tw

Application Information

Capacitor Selection

The input capacitor is for decoupling and prevents the

input voltage from overshooting to dangerous levels. In

the AC adapter hot plug-in applications or load current

step-down transient, the input voltage has a transient

spike due to the parasitic inductance of the input cable. A

25V, X5R, dielectric ceramic capacitor with a value be-

tween 1

µF and 4.7µF placed close to the ACIN pin is

recommended.

The output capacitor of CHR_LDO is for CHR_LDO volt-

age decoupling. And also can be as the input capacitor of

the charging circuit. At least, a 1

µF, 10V, X5R capacitor is

recommended.

Layout Consideration

In some failure modes, a high voltage may be applied to

the device. Make sure the clearance constraint of the PCB

layout must satisfy the design rule for high voltage. The

exposed pad of the TDFN2x2-8 and DFN3x3-8 performs

the function of channeling heat away. It is recommended

that connect the exposed pad to a large copper ground

plane on the backside of the circuit board through sev-

eral thermal vias to improve heat dissipation. The input

and output capacitors should be placed close to the IC.

The high current traces like input trace and output trace

must be wide and short.

Recommended Minimum Footprint

TDFN2x2-8

Thermal Via diameter

12mil X 5

Ground plane for

Thermal PAD

0.241mm

0.508mm

0.222mm

0.8mm

0.572mm

Thermal Via diameter

12mil X 5

Ground plane for

Thermal PAD

0.305mm

0.66mm

0.305mm

0.61mm

DFN3X3-8

1.575mm

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