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AS1337

Datasheet - A p p l i c a t i o n I n f o r m a t i o n

Component Selection

Only three power components are required to complete the design of the buck-boost converter, except the additional

allow the use of low value, low profile inductors and tiny external ceramic capacitors.

Inductor Selection

The inductor should have low ESR to reduce the I²R power losses, and must be able to handle the peak inductor

current without saturating. High-frequency ferrite core inductor materials reduce frequency dependent power losses

compared to less expensive powdered iron types, which result in improved converter efficiency.

A 4.7µH to 15µH inductor value with a >850mA current rating and low DCR is recommended. For applications where

radiated noise is a concern, a toroidal or shielded inductor can be used.

Capacitor Selection

X5R and X7R ceramic capacitors are recommend as they retain capacitance over wide ranges of voltages and temper-

atures.

Output Capacitor Selection

they have extremely low ESR and are available in small footprints. A 1 to 10µF output capacitor is sufficient for most

applications. Larger values up to 22µF may be used to obtain extremely low output voltage ripple and improve tran-

sient response.

An additional phase lead capacitor may be required with output capacitors larger than 10µF to maintain acceptable

phase margin. X5R and X7R dielectric materials are recommended due to their ability to maintain capacitance over

wide voltage and temperature ranges.

Input Capacitor Selection

Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. Ceramic

capacitors are recommended for input decoupling and should be located as close to the device as is practical. A 4.7µF

input capacitor is sufficient for most applications. Larger values may be used without limitations.

PCB Layout Guidelines

The high-speed operation of the AS1337 requires proper layout for optimum performance.

!

A large ground pin copper area will help to lower the device temperature.

!

A multi-layer board with a separate ground plane is recommended.

!

Traces carrying large currents should be direct.

!

Trace area at pin FB should be as small as is practical.

!

The lead-length to the battery should be as short as is practical.

Table 4. Recommended External Components

Name

Part Number

Value

Rating

Type

Size

Manufacturer

GRM219R60J106KE19

10µF

6.3V

X5R

0805

Murata

www.murata.com

GRM21BR60J226ME39

22µF

6.3V

X5R

0805

L1

MOS6020-472ML

4.7µH

1.82A

50m

Ω

6.8x6.0x2.4mm

Coilcraft

www.coilcraft.com