ANALOG PRODUCTS DIVISION

561 E. Elliot Road #175 Chandler, AZ 85225 Tel: (480) 539-2900. Fax: (480) 632-1715

www.protekanalog.com

7

PA5910

Switching Type LED Driver.

95220 Rev.0. 04/09

NOT FOR USE IN LIFE SUPPORT SYSTEMS

Operation Frequency can be calculated by the following formula

OFF

T

D

T

F

−

=

=

1

1

Inductor Design.

Inductor selection criteria are to ensure that current flow through inductor is less than the maximum value

specified.

Referring to the typical application in Fig.5 the value can be calculated from the desired peak-to-peak LED ripple

current in the Inductor. Typically the ripple current is selected to be 30% of the nominal LED current. In this

For example, when the string consists of 12 High Brightness LED’s and each diode has a forward drop of 3.3V at

128

.

0

310

6

.

39

=

=

=

IN

LED

V

V

D

Given the switching frequency (20KHz) the required on time of the MOSFET can be calculated by:

µS

f

D

TON

OSC

4

.

6

=

=

The required value of the inductor is given by:

()

mH

I

T

V

V

L

LED

ON

LED

IN

16

3

.

0

=

×

×

−

=

BANDGAP

S Q

R

OFF

TIME

VDD

TOFF

EN

GND

DRV

CS

250mV

PA5910