ZXSC310 datasheet(5/14 Pages) ZETEX

5 / 14 page

DEVICE DESCRIPTION

The ZXSC310 is PFM, controller IC which, when

combined with a high performance external transistor,

enables the production of a high efficiency boost

converter for LED driving applications. A block

diagram is shown for the ZXSC310 below.

The on chip comparator forces the driver circuit and

therefore the external switching transistor off if the

voltage at ISENSE exceeds 19mV. An internal reference

circuit and divider set this threshold.

The voltage at ISENSE is taken from a current sense

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 1.7us. 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

exceeds the threshold of the ISENSE input. The on-pulse

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.

ZXSC310

PROVISIONAL ISSUE A - SEPTEMBER 2001

Drive

ISENSE

VRE

VDRIVE

GND

VCC

STDN

ZXSC310 Block Diagram

ZXSC310 Arkusz danych(PDF) 5 Page - Zetex Semiconductors