ap1522wa Diodes, Inc., ap1522wa Datasheet - Page 5

• Manufacturer Part Number: ap1522wa
• Description: Step-up Dc/dc Converter
• Manufacturer: Diodes, Inc.

Step-Up DC/DC Converter
Inductor Selection
A 10
applications.
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
4.7
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 (C
represents the switching losses.
selection, both forward voltage drop and diode
capacitance need to be considered.
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.
200mA is sufficient for most AP1522 applications.
Anachip Corp.
www.anachip.com.tw
µ
F input capacitor and a 4.7
Typical Application Circuit (Continued)
Applications Information
µ
H inductor is recommended for most AP1522
A Schottky diode rated at 100mA to
Not Recommended for New Design
Although small size and high
2.5V to 5V
+20V Dual Output Converter with Output Disconnect
V
IN
µ
F output capacitor
4.7uF
C1
4
For diode
SHDN
Schottky
V
T
5
IN
or C
AP1522
10uH
GND
L1
D
1uF
C4
2
)
SW
5/8
FB
1
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).
than the maximum forward voltage of the V
The current rating of the zener should be larger
than 0.1mA.
1uF
V
C5
3
IN
D4
D1
D2
Figure 1. With Open-Circuit Protection
1uF
C
IN
150K
10K
SHDN
The zener voltage should be larger
D3
V
4.7pF
IN
22uH
AP1522
GND
L
C3
1uF
SW
10uF
C2
-20V
4mA
4mA
20V
FB
D
4.7pF
R2
1K
Rev. 1.0 May. 5, 2005
AP1522
14K
R3
200K
R1
C
2uF
OUT
OUT
.