AP1522 データシートの表示（PDF） - Anachip Corporation

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AP1522

Step-Up DC/DC Converter

Anachip Corporation 

Step-Up DC/DC Converter

„ Typical Application Circuit (Continued)

+20V Dual Output Converter with Output Disconnect

VIN

2.5V to 5V

D3

-20V

C4

1uF

L1

10uH

D2

C5

1uF D1

4mA

C3

1uF

20V

4mA

5

1

D4

C1

4.7uF

VIN

SW

AP1522 FB 3

4 SHDN

GND

2

150K 4.7pF

10K

C2

10uF

AP1522

„ Applications Information

Inductor Selection

A 10µH inductor is recommended for most AP1522

applications. Although small size and high

efficiency are major concerns, the inductor should

have low core losses at 1MHz and low DCR

(copper wire resistance).

Capacitor Selection

The small size of ceramic capacitors makes them

ideal for AP1522 applications. X5R and X7R types

are recommended because they retain their

capacitance over wider voltage and temperature

ranges than other types such as Y5V or Z5U. A

4.7µF input capacitor and a 4.7µF output capacitor

are sufficient for most AP1522 applications.

Diode Selection

Schottky diodes, with their low forward voltage drop

and fast reverse recovery, are the ideal choices for

AP1522 applications. The forward voltage drop of

a Schottky diode represents the conduction losses

in the diode, while the diode capacitance (CT or CD)

represents the switching losses. For diode

selection, both forward voltage drop and diode

capacitance need to be considered. Schottky

diodes with higher current ratings usually have

lower forward voltage drop and larger diode

capacitance, which can cause significant switching

losses at the 1MHz switching frequency of the

AP1522. A Schottky diode rated at 100mA to

200mA is sufficient for most AP1522 applications.

Open-Circuit Protection

In the cases of output open circuit, when the R1 are

disconnected from the circuit, the feedback voltage

will be zero. The AP1522 will then switch at a high

duty cycle resulting in a high output voltage, which

may cause the SW pin voltage to exceed its

maximum 36V rating. A zener diode can be used

at the output to limit the voltage on the SW pin

(Figure 1). The zener voltage should be larger

than the maximum forward voltage of the VOUT.

The current rating of the zener should be larger

than 0.1mA.

V IN

L

22uH

D

COUT

2uF

VIN

SW

CIN

1uF

AP1522

SHDN

FB

4.7pF

R2

1K

R1

200K

R3

GND

14K

Figure 1. With Open-Circuit Protection

Anachip Corp.

www.anachip.com.tw

Rev. 1.0 May. 5, 2005

5/8

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