ZXSC100 datasheet(14/17 Pages) DIODES

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ZXSC100

SEMICO NDUC TORS

ISSUE 3 - JANUARY 2004

Designing with the ZXSC100

Introduction

This section refers to the ZXSC100, 3.3V/100mA

output reference design and demonstrates the

dynamic performance of the solution.

Figure 1.

ZXSC100 low power solution, 3.3V/100mA output.

Efficiency

Efficiency is often quoted as one of the key parameters

of a DC-DC converter. Not only does it give an

instantaneous idea of heat dissipation, but also an

idea as to the extent battery life can be extended.

Figure 2. Shows the efficiency of the ZXSC100 low

power solution. Efficiency v Output current is shown

for a 3.3V output at various input voltages.

Main switching waveforms

Steady state operation under constant load gives an

excellent indication of ZXSC100 performance.

Represented in Figure 3. is the main switching

waveform, measured at the collector of Q1, indicating

the transistor on-state and the diode energy transfer to

the output.

Figure 3.

Switching waveform

The peak switching current is derived from the

threshold of the ISENSE pin and the sense resistor value

(see Applications section for calculations). Figure 4.

shows the switching waveform associated with the

ISENSE pin

FMMT617

0.033R

22µH

ZHCS1000

110K

30K

220µF

3.3V/0.1A

BAS

ZXSC100

1NF

VBATT

VCC

GND

ISENSE

VDRIVE

FMMT617

0.033R

22µH

ZHCS1000

110K

30K

220µF

3.3V/0.1A

BAS

ZXSC100

1NF

VBATT

VCC

GND

ISENSE

VDRIVE

Figure 2.

ZXSC100 efficiency v output current

Figure 4.

ISENSE threshold

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