7

Rev.1.1

15 -

0 40 80 120 160 200 240 280 320 360 400

4.75

4.80

4.85

4.90

4.95

5.00

5.05

5.10

5.15

5.20

5.25

Vin=3.0V, Iout=100mA

Time (�s)

0 40 80 120 160 200 240 280 320 360 400

4.75

4.80

4.85

4.90

4.95

5.00

5.05

5.10

5.15

5.20

5.25

Vin=3.0V, Iout=100mA

Time (�s)

0 40 80 120 160 200 240 280 320 360 400

4.75

4.80

4.85

4.90

4.95

5.00

5.05

5.10

5.15

5.20

5.25

Vin=3.0V, Iout=100mA

Time (�s)

0 40 80 120 160 200 240 280 320 360 400

4.75

4.80

4.85

4.90

4.95

5.00

5.05

5.10

5.15

5.20

5.25

Vin=3.0V, Iout=100mA

Time (�s)

■External parts

To design DC/DC converter using ELM95 series, coil, diode, and capacitor are necessary.

(Refer to the standard circuit configuration.)

1) Coil

When choosing choke coil, please select that whose core is not magnetically saturated, DC resistance is low,

and which has sufficient margin for rated current. ELM recommends to use inductance around 220µH for

ELM995xxAxE, and ELM95xxBxE. For ELM95 series, ELM recommends following coil.

• SLF7045T (TDK corporation)

2) Diode

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

has sufficient margin for rated current.

For ELM95 series, ELM recommends schottky diodes.

3) Capacitor

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

comparatively large capacity, with small equivalent series resistance, and with large rated voltage.

For ELM95 series, ELM recommends ceramic capacitor, although Aluminum electrolytic and Tantalum ca-

pacitors also can be used. Under heavier load condition using small output capacitor, there might be cases that

few hundred hertz wave motion will happen in output voltage waveform. Under such cases, ELM recommends

to use capacitor with larger capacity. Examples are shown as follows. ELM recommends 47µF or larger for Cout

and 47µF for Cin. On the other hand, under light load use (Iout<20mA) only, it is possible to use smaller capacitors

such as Cin=Cout=22µF.

One of example of solution for large amplitude waveform with lower frequency are shown as follows:

ELM9550AxE Vout waveform

using Cout=22µF

ELM9550AxE Vout waveform

using Cout=47µF

4) Remedies for noise

The DC/DC converter may cause electromagnetic noise due to switching of coil under large current. Solution

is necessary especially when the IC is used in wireless devices. To reduce noise, this IC is designed in consider-

ation of coil switching characteristics. The following methods 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.