Diodes ZXSC310 - Manual (Page 6)

REFERENCE DESIGNS
Three typical LED driving applications are shown.
Firstly a typical LCD backlight circuit, then maximum
brightness LED driving solution and lastly an optimised
battery life LED driving solution.
This application shows the ZXSC310 in a typical LCD
backlight application for Digital Still Cameras and
PDA’s. The input voltage for these backlight circuits are
usually fixed from the main system power, typically
3.3V or 5V. The LED’s are connected serially so that the
light is distributed uniformly in each LED. The current
provided to the LED’s can either be pulsed or DC. The
DC current is programmable via a sense resistor,
R
SENSE , and is set to an optimum LED current of 20mA
for the reference designs. DC current is achieved by
adding a Schottky rectifying diode and an output
capacitor, as shown in the reference design below.
S E M I C O N D U C T O R S
ZXSC310
ISSUE 3 - SEPTEMBER 2007
6
V
IN
V
CC
V
= 3.3V / 5V
DRIVE
I
SENSE
Gnd
S
TDN
LCD backlight circuit
Ref Value Part Number Manufacture Comments
U1 N/A ZXSC310E5 Zetex Semiconductors Single cell converter, SOT23-5
Q1 N/A FMMT618 Zetex Semiconductors Low V
CE(sat)
NPN, SOT23
D1 N/A ZHCS1000 Zetex Semiconductors 1A Schottky diode, SOT23
C1 2.2 ␮F Generic Various 0805 Size
R1
(6)
150m ⍀ Generic Various 1206 Size
R1
(7)
250m ⍀ Generic Various 1206 Size
L1 (8) 68µH Surface mount inductor
Materials list
(6)
Used for 3.3V input, I LED set to 20mA Ϯ10%.
(7) Used for 5V input, I
LED
to 20mA Ϯ10%.
(8)
See Application section.
(Notes)