APW7075 データシートの表示（PDF） - Anpec Electronics

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APW7075

Step-Up Converter and LDO Combo

Anpec Electronics 

APW7075

Function Description (Cont.)

LDO

The output voltage has two operation modes. When

VIN exceeds 3.9V, the output will become the LDO

regulator and the step-up converter will be disabled.

The LDO output is a P-channel low dropout regulator

with 1A current limit. When the VIN is below 3.8V, the

output will return to the step-up converter, and the LDO

mode will be disabled. Note that when LDO mode is

used, the output voltage should be under 3.8V

Low Battery Detection

The low battery detection is used to monitor the bat-

tery voltage and to generate a signal. This function

includes two pins, LBI is the inverting input of the com-

parator and LBO is an open drain output (see block

diagram). When the LBI voltage drops below the

threshold voltage 0.6V, the open drain device will turn

on and LBO becomes low. The Low battery threshold

voltage can be programmed with a resistive divider from

battery to LBI pin to ground. Since the LBO is an open

drain output, it usually requires an external pull-up

resistor.

Application Information

Output Voltage Selection

The output voltage of APW7075 can be adjusted by an

external resistor divider, or connect FB pin to OUT for

3.3V and to ground for 2.5V (see Application

Schematic). The internal reference voltage is 1.2V and

the allowed output voltage is from 2.5V to 5.5V. The

following equation can be used to calculate the output

voltage:

VOUT = 1 + R1  × 1.2V

 R2 

Programming Low Battery Threshold Voltage

The low battery threshold voltage can be programmed

with a resistive divider from battery to LBI pin to ground

(see Application Schematic). The internal reference

voltage is 0.6V, and the low battery threshold voltage

must be below the battery voltage. The following equa-

tion can be used to calculate the low battery thresh-

old voltage:

VBAT - TH = 1+ R3  × 0.6V

 R4 

Inductor Selection

The APW7075 works well with a 22uH inductor in most

applications. The inductance values determine the in-

ductor ripple current and affect the output current.

Higher inductance values reduce ripple and improve

efficiency. Lower inductance values have fast response

but increase the ripple and reduce the efficiency. The

maximum allowed LX current is 1A (the maximun.

output current shows in Typical Characteristics) and

so the peak inductor current cannot exceed it. The

following equations calculate the inductor current, and

output current.

IOUT = IL x (1-D)

( ) ∆IL = (VOUT− VIN)× 1−D

L×f

Where:

VOUT −VIN

D=

VOUT

Copyright © ANPEC Electronics Corp.

17

Rev. A.5 - Aug., 2005

www.anpec.com.tw

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