ELM91xxxxA CMOS PFM Step-up DC/DC converter and controller
■External parts
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)
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.
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)
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 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}
Vout-Iout
EFFICIENCY-Iout
RIPPLE VOLTAGE-Iout
100
90
80
70
60
50
40
600
500
400
300
200
100
0
3.5
3
330�F(Ta)
100�F(Ta)
1000�F(AL)
100�F(Ta)
2.5
2
1000�F(AL)
100�F(Ta)
330�F(Ta)
330�F(Ta)
1.5
1
1000�F(AL)
0
100 200 300 400 500 600 700 800
Iout (mA)
200
400
600
800
1000
0
100 200 300 400 500 600 700 800
Iout (mA)
Iout (mA)
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ELM-TECH [ ELM Technology Corporation ]
