AS3642 datasheet(21/27 Pages) AMSCO

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AS3642

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

9 Application Information

The AS3642 can be directly connected to an (existing) I

2C bus (e.g. from the baseband or camera processor). All func-

tions are accessible by this interface. An strobe input can be done by adding a diode (with an optional resistor in

series) to the LED_OUT pin. Setting the register bit external_strobe=1 enable this input as a strobe input. The duration

of the flash is programmed by the I

2C interface, but the exact starting time is defined by this input- see External Strobe

Input on page 10.

External Components

Input Capacitor CVIN

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

capacitors are required for input decoupling and should be located as close to the device as is practical.

If a different input capacitor is chosen, ensure similar ESR value and at least 1.6

µF capacitance at the maximum input

supply voltage. Larger capacitor values (C) may be used without limitations.

Output Capacitor CVOUT

Low ESR capacitors should be used to minimize VOUT ripple. Multi-layer ceramic capacitors are recommended since

they have extremely low ESR and are available in small footprints. The capacitor should be located as close to the

device as is practical.

X5R dielectric material is recommended due to their ability to maintain capacitance over wide voltage and temperature

range.

If a different output capacitor is chosen, ensure similar ESR values and at least 1.0µF capacitance at maximum output

voltage.

Inductor LDCDC

The fast switching frequency (4MHz) of the AS3642 allows for the use of small SMDs for the external inductor. The

inductor should have low DC resistance (DCR) to reduce the I

2R power losses - high DCR values will reduce effi-

ciency.

Table 10. Recommended Input Capacitor

Part Number

TC Code

ESR

Rated

Voltage

Size

Manufacturer

CL05A395MQ5NQKL

4.7µF +/-10%

>1.6µF @ VVIN

X5R

<20m



6V3

0402

Samsung Electro-

Mechancs

www.sem.samsung.co.kr

Table 11. Recommended Output Capacitor

Part Number

TC Code

ESR

Rated

Voltage

Size

Manufacturer

ECJUNBPJ155K

2x1.5µF +/-15%

X5R

<10m



6V3

0405

2-array

Panasonic

www.panasonic.com

CL14A185MQ8SAKL

Samsung Electro-

Mechancs

www.sem.samsung.co.kr

Table 12. Recommended Inductor

Part Number

DCR

L @ 0.9A

Size

Manufacturer

LQM21PN1R0NGC

1.1µH

100m



>0.7µH

2x1.25x0.9mm

Murata

www.murata.com

ELGTEA1R0SN

1.0µH

>0.7µH

2x1.25x0.9mm

Panasonic

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