ZXSC380

Issue 3 - September 2007

5

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© Zetex Semiconductors plc 2007

Device description

The ZXSC380 is non-synchronous PFM, DC-DC controller IC which, with a high performance

internal transistor, for a high efficiency boost converter for use in single cell applications. A block

diagram is shown in Figure 1.

Figure 1 ZXSC380 Block diagram

The on chip comparator forces the driver circuit and therefore the internal switching transistor to

emitter current of 80mA.

A monostable following the output of the comparator forces the turn-off time of the output stage

to be typically 2.2 s. This ensures that there is sufficient time to discharge a significant proportion

of the energy stored in 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

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 internal switching transistor with a fixed drive current. To maximize

efficiency the internal transistor is switched quickly, typically being switched off within 30ns.

R1

R2

R

SENSE

+

-

+

V

REF

GND

I

SENSE

R1

R2

R

SENSE

+

-

+

V

REF

GND

I

SENSE

V

CC

1

3

2

V

OUT