Advanced Power

Electronics Corp.

APE1920

COMPENSATION TABLE

APPLICATION INFORMATION

Setting the Output Voltage

Soft Start Capacitor

Frequency Select Pin (FREQ)

6

Fre que ncy(Hz)

L1 (H)

VIN (V)

VOUT (V)

R6 (

Ω )C7 (F)

2.5~4.4

5

10K

1.2n

2.5~5.5

7

15K

470p

2.5~5.5

9

27K

270p

2.5~5.5

12

56K

150p

2.5~5.5

15

150K

120p

2.5~5.5

18

110K

100p

2.5~5.5

21

150K

82p

2.5~5.5

24

100K

47p

2.5~4.0

5

33K

1n

2.5~5.5

7

39K

390p

2.5~5.5

9

39K

220p

2.5~5.5

12

100K

100p

2.5~5.5

15

130K

68p

2.5~5.5

18

150K

56p

2.5~5.5

21

220K

47p

2.5~5.5

24

390K

39p

6.8u

4.7u

680K(FREQ=Low )

1.2M(FREQ=High)

Application circuit item shows the basic application circuit with APE1920 adjustable output version. The

external resistor sets the output voltage according to the following equation:

⎟

⎠

⎞

⎜

⎝

⎛

+

×

=

8

1

238

1

R

R

V

V

OUT

2

.

For most applications, R8 is a suggested a value by 10~30KΩ. Place the resistor-divider as close to the IC

as possible to reduce the noise sensitivity.

The soft-start function begins from SS pin Voltage=0V to VCC with a 7uA (typ.) constant current charging to

the soft-start capacitor, so the capacitor should be large enough to let the output voltage reach regulation inside

the soft-start cycle. Typical value of soft-start capacitor range is from 4.7nF to 100nF. After the cycle finished, the

load can start to draw maximum current as required.

The frequency select pin FREQ allows to set the switching frequency of the device to 680 KHz (FREQ = low)

or 1.2 MHz (FREQ = high). Higher switching frequency improves load transient response but reduces slightly the

efficiency. The other benefits of higher switching frequency are a lower output ripple voltage. Usually, it is

recommended to use 1.2 MHz switching frequency unless light load efficiency is a major concern.