9

2) Diode

3) Capacitor

When choosing diode, please select that whose forward voltage is small, switching speed is high and which

has sufficient margin for rated current.

ELM recommends diode which is around 1A class.

* Cout

When choosing capacitor, please select that which is generally used for smoothing power supply circuit,

with comparatively large capacity and whose rated voltage is at least three times larger than rated output

voltage of used ELM92 series. ELM recommends capacitor which is 47μF to 220μF. When Vin is high

(Vin>Vout×0.7), it is possible that large ripple of Iout may happen because of intermittent operation; ELM

recommends to use larger capacitor under such circumstance.

* Cin

Using Cin in the circuit can lower feedback noise to Input; this method is also effective in improving

efficiency because input voltage drop during switching can be eased. To gain this effect, please connect

tantalum capacitor of 47μF to 220μF to coil as close as possible.

0.1

1

10

100

1000

0

10

20

30

40

50

60

70

80

90

100

Iout (mA)

EFFICIENCY - Iout

Vin=0.9V

1.1V

1.8V

1.5V

2.4V

0.1

1

10

100

1000

0

10

20

30

40

50

60

70

80

90

100

Iout (mA)

EFFICIENCY - Iout

Vin=1.8V

3.0V

2.4V

3.6V

ELM9230xx

ELM9250xx

* CR43/CD43/CR54/CD54 : Sumida Electric Co., Ltd are recommended.

This DC/DC converter may cause electromagnetic noise due to switching of coil under large current. Solu-

tion is necessary especially when the IC is used in wireless devices.

To reduce noise, this IC is designed in consideration of coil switching characteristics. The following meth-

ods are also effective to reduce noise.

• Use shield-type, or magnetic shield coil.

• Locate coil and diode to the LX terminal of IC as close as possible.

• Select ground wire as thick and short as possible.

• Connect ground wire of circuit to one point.

4) Remedies for noise

15 -