May 2011

Doc ID 5655 Rev 15

1/29

AN937

Application Note

Designing with L4971, 1.5 A high efficiency DC-DC converter

Introduction

The L4971 is a 1.5 A monolithic dc-dc converter, step- down, operating at fix frequency

continuous mode. It is designed in BCD60 II technology, and it is available in two plastic

packages, DIP8 and SO16L.

One direct fixed output voltage at 3.3 V ±1% is available, adjustable for higher output voltage

values, till 40 V, by an external voltage divider.

The operating input supply voltage ranges from 8 V to 55 V, while the absolute value, with no

load, is 60V. New internal design solutions and superior technology performance allow to

generate a device with improved efficiency in all the operating conditions and with reduced

EMI due to an innovative internal driving circuit, and reduced external component counts.

While internal limiting current and thermal shutdown are today considered standard

protection functions, mandatory for a safe load supply, oscillator with voltage feed forward

improves line regulation and overall control loop.

Soft-start avoids output over voltage at turn-on, while, shorting this pin to ground, the device

is completely disabled, going into zero consumption state.

Figure 1.

Demonstration board

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