APW7071 データシートの表示（PDF） - Anpec Electronics

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APW7071

White LED DC/DC Step-Up Converter

Anpec Electronics 

APW7071

Function Descriptions

OPERATION

Over Voltage Protection (OVP)

The APW7071 operates in a pulse frequency modu-

lation (PFM) scheme with constant peak current

control.The operation can be understood by referring

to the block diagram of Figure 1. The converter moni-

tors the output voltage, and if the feedback voltage

falls below the reference voltage (typical 0.25V), the

internal switch turns on and the inductor current ramps

up. The switch turns off if the inductor current reaches

the internally set peak current (typical 400mA) or

maximum on-time detected. As the switch is turned

off, the inductor current ramps down to zero and

charge output capacitor through external Schottky

diode. The switch remains off for a minimum of 400

ns (typical), or until the feedback voltage drops be-

low the reference voltage again. The operation fre-

quency is up to 1MHz and is determined by the out-

put current, current limit, inductor value, input volt-

age and output voltage. This regulation scheme is

inherently stable, allowing a wider selection range

for the inductor and output capacitor.

OVP is integrated to prevent the output voltage

increase over the maximum switching voltage rating.

In some cases an LED may fail, this will result in

the feedback voltage always being zero. The device

will boost the output voltage higher and higher.

When the output voltage exceeds the OVP thresh-

old voltage (typical 17V), the switch turns off. The

converter switch remains off until the output voltage

falls below the OVP threshold voltage.

Thermal Shutdown

A thermal shutdown function is integrated to shut-

down device when junction temperature exceed

160°C. If thermal shutdown detected, converter

switch turn off until junction temperature falls bellow

120°C.

Enable

Force SHDN pin greater than 1.3 V to enable the

device works in normal operation. Pulling SHDN pin

less than 0.4V to shut down reducing the shutdown

current to 0.1 µA (typical). The SHDN pin should

not be left floating.

Soft Start

The APW7071 limits this inrush current by increas-

ing the current limit at start-up.

Under Voltage Lockout

Transients during powering on or instantaneous

glitches in the supply voltage can cause system

damage or failure. The undervoltage lockout circuit

turned the main switch off to prevent malfunction at

low input voltage.

Copyright © ANPEC Electronics Corp.

8

Rev. A.1 - Feb., 2006

www.anpec.com.tw

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