ZXSC300

ISSUE 4 - SEPTEMBER 2007

5

DEVICE DESCRIPTION

The ZXSC300 is

PFM, controller IC which, when

combined with a high performance external transistor,

enables the production of a high efficiency boost

converter for use in single cell LED driving

applications. A block diagram is shown for the

ZXSC300 in Figure 1.

The on chip comparator forces the driver circuit and

therefore the external switching transistor off if the

by an internal reference circuit and divider.

resistor connected in series with the emitter of the

switching transistor. A monostable following the

output of the comparator forces the turn-off time of the

output stage to be typically 1.7µs. This ensures that

there is sufficient time to discharge the inductor coil

before the next on period.

With every on pulse the switching transistor is kept on

until the voltage across the current-sense resistor

length, and therefore the switching frequency, is

determined by the programmed peak current, the

input voltage and the input to output voltage

differential. See applications section for details.

The Driver circuit supplies the external switching

transistor with a fixed drive current. To maximise

efficiency the external transistor switched quickly,

typically being forced off within 30ns.

Figure 1 ZXSC300 Block Diagram

Pin Descriptions

Pin No.

Name

Description

Supply voltage, generally Alkaline, NiMH or NiCd single cell

2

Gnd

Ground

3

N/C

Not connected

Inductor current sense input. Internal threshold voltage set to 19mV.

Connect external sense resistor

Drive output for external switching transistor. Connect to base of external

switching transistor

Pinout Diagram