6

■External parts

1) Coil

2) Diode

To design DC/DC converters using ELM91xx1xA series, coil, diode, and capacitor are necessary. Except these

external parts, switching transistor is also needed when using ELM91xx3xA. Please locate external parts to IC

as close as possible, and lower the impedance of ground line. (Please refer to standard circuit)

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.

The typical characteristics graphics of ELM91xx1xA series is done by following coil : SLF7045(TDK)

The typical characteristics graphics of ELM91xx3xA series is done by following coil : SLF10145(TDK)

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

has sufficient margin for rated current.

For ELM91 series, ELM recommends schottoky diodes.

3) Capacitor

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 ELM91 series.

For ELM91 series, ELM recommends Aluminum electrolytic or Tantalum capacitor.

Under different conditions, such as different input voltage, load current, etc. larger output voltage ripple

may happen and thus result in intermittent switching. To prevent output voltage ripple from becoming

larger, please use capacitor with comparatively larger capacity or small ESR.

The output voltage of ELM91xx3xA may lower when the load current is large. To prevent this, please use

output capacitor with comparatively large capacity or small ESR.

Following characteristics graphics are made with ELM91303xA, when Vin=1.5V.{Cin=100μF(Ta),

L=33μH}

0 100 200 300 400 500 600 700 800

1

1.5

2

2.5

3

3.5

100�F(Ta)

330�F(Ta)

Vout-Iout

Iout (mA)

1000�F(AL)

200

400

600

800

1000

0

100

200

300

400

500

600

100�F(Ta)

1000�F(AL)

RIPPLE VOLTAGE-Iout

Iout (mA)

330�F(Ta)

0 100 200 300 400 500 600 700 800

40

50

60

70

80

90

100

100�F(Ta)

1000�F(AL)

EFFICIENCY-Iout

Iout (mA)

330�F(Ta)

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