ZXSC100 Zetex Semiconductors plc., ZXSC100 Datasheet - Page 9

• Manufacturer Part Number: ZXSC100
• Description: Single Cell Dc-dc Converter Solution
• Manufacturer: Zetex Semiconductors plc.

ISSUE 3 - JANUARY 2004
OTHER APPLICATIONS
Driving white LED’s in a flashlight application
The ZXSC100 solution is ideal for LED lamp driving
applications operating from a single cell. In principal
conversion from 1.2V to the 3.6V, typically required by
white LEDs, is necessary. Load currents in the region of
20mA to 50mA being required for a single LED element.
To minimise size, weight and cost, single cell operation
is an advantage. The ZXSC is well matched to single cell
NiCd and NiMH characteristics. The circuit will turn on at
1.06V, to maximise the life the battery can offer, the
converter does not turn off until the battery voltage falls
to 0.93V.
V
BATT
U1
ZXSC100
V
EM
BAS
RE
CC
L1
100µH
V
I
SENSE
DRIVE
G
FB
ND
Q1
FMMT617
R2
0.22R
D1
WHITE LED
9
The circuit itself is very simple, a minimum number
of components are used and they are all small size.
The ZXSC uses the very small MSOP8 package, the
pass transistor is SOT23. No capacitors are required
as the circuit is stable under all conditions. The
inductor recommended is a low cost miniature
component.
No compromise is made on efficiency however. In a
standard configuration efficiency well over 80% can
be achieved. With careful inductor selection
efficiency over 90% is possible.
The inherent flexibility of the ZXSC circuit means
that parallel or series LEDs can be driven depending
on application needs. A simple modification to the
application circuit means that the maximum pulse
current can be programmed to match the
characteristics of the chosen LED load, pulse current
in the range 10mA to 3A and beyond can be easily
achieved.
An application note (AN33) is available describing
various circuits for driving white LEDs. This
application note includes details of circuits that
optimise battery life, maximise brightness and can
be constructed for minimal cost. Contact your local
Zetex office for further details.
S E M I C O N D U C T O R S
ZXSC100