AW3643

Jan 2018 V1.4

www.awinic.com.cn

31

Copyright © 2016 SHANGHAI AWINIC TECHNOLOGY CO., LTD

APPLICATION INFORMATION

The AW3643 can drive two flash LEDs at currents up to 1.5 A per LED. The total allowed LED current

small value discrete external components. Below are some peripheral selection guidelines.

OUTPUT CAPACITOR SELECTION

The AW3643 is designed to operate with a 10µF ceramic output capacitor. When the boost converter is

running, the output capacitor supplies the load current during the boost converter on-time. When the NMOS

switch turns off, the inductor energy is discharged through the internal PMOS switch, supplying power to the

load and restoring charge to the output capacitor. This causes a sag in the output voltage during the on-time

and a rise in the output voltage during the off-time. The output capacitor is therefore chosen to limit the output

ripple to an acceptable level depending on load current and input/output voltage differentials and also to

ensure the converter remains stable.

Larger capacitors such as a 22µF or capacitors in parallel can be used if lower output voltage ripple is desired.

due

For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:

()

OUT

IN

LED

Q

OUT

OUT

V

V

I

V

V

f

C







The output voltage ripple due to the output capacitors ESR is found by:

2

OUT

LED

L

ESR

ESR

IN

VI

I

VR

V



















Where

()

IN

OUT

IN

L

OUT

V

V

V

I

V

f

L







In ceramic capacitors the ESR is very low so the assumption is that 80% of the output voltage ripple is due to

capacitor discharge and 20% from ESR. Table 1 lists different manufacturers for various output capacitors

and their case sizes suitable for use with the AW3643.

INPUT CAPACITOR SELECTION

Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the

switching of the AW3643 boost converter and reduce noise on the boost converter's input pin that can feed

through and disrupt internal analog signals. In the typical application circuit a 10-µF ceramic input capacitor

works well. It is important to place the input capacitor as close as possible to the AW3643 input (IN) pin. This

reduces the series resistance and inductance that can inject noise into the device due to the input switching

currents. Table 1 lists various input capacitors recommended for use with the AW3643.

Table 1

Recommended Input/ Output Capacitors (X5R/X7R Dielectric)

MANUFACTURER

PART NUMBER

VALUE

CASE

VOLTAGE RATING

TDK

C1608JB0J106M

10μF

0603

6.3V

TDK

C2012JB1A106M

10μF

0805

10V

Murata

GRM188R60J106M

10μF

0603

6.3V

Murata

GRM21BR61A106KE19

10μF

0805

10V