ZXSC310
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.
LCD backlight circuit
V
IN
= 3.3V / 5V
V
CC
V
DRIVE
S
TDN
I
SENSE
Gnd
(Notes)
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.
Materials list
Ref
U1
Q1
D1
C1
R1
6
R1
7
Value
N/A
N/A
N/A
2.2 F
150m
250m
68µH
Part Number
ZXSC310E5
FMMT618
ZHCS1000
Generic
Generic
Generic
Manufacture
Zetex Plc
Zetex Plc
Zetex Plc
Various
Various
Various
Comments
Single cell converter, SOT23-5
Low V
CE(sat
) NPN, SOT23
1A Schottky diode, SOT23
0805 Size
1206 Size
1206 Size
Surface mount inductor
L1
8
6
7
Used for 3.3V input, I
LED
set to 20mA 10%.
Used for 5V input, I
LED
to 20mA 10%.
8
See Application section.
PROVISIONAL ISSUE A - SEPTEMBER 2001
6
ZETEX [ ZETEX SEMICONDUCTORS ]
