ADP3191 datasheet(21/28 Pages) AD

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ADP3191

Rev. 0 | Page 21 of 28

Figure 11 and Figure 12 show the typical transient response

using these compensation values.

Figure 11. Typical Transient Response

for Design Example Load Step

Figure 12. Typical Transient Response

for Design Example Load Release

CIN SELECTION AND

INPUT CURRENT DI/DT REDUCTION

In continuous inductor current mode, the source current of the

high-side MOSFET is approximately a square wave with a duty

ratio equal to n × VOUT/VIN and an amplitude of one-nth the

maximum output current. To prevent large voltage transients,

a low ESR input capacitor, sized for the maximum rms current,

must be used. The maximum rms capacitor current is given by

14.7

0.108

108

−

CRMS

(34)

The capacitor manufacturer’s ripple current ratings are often

based on only 2000 hours of life. This makes it advisable to

further derate the capacitor or to choose a capacitor rated at a

higher temperature than required. Several capacitors can be

placed in parallel to meet size or height requirements in the

design. In this example, the input capacitor bank is formed by

two 2700 μF, 16 V aluminum electrolytic capacitors and eight

4.7 μF ceramic capacitors.

To reduce the input current di/dt to a level below the recom-

mended maximum of 0.1 A/μs, an additional small inductor

(L > 370 nH at 18 A) should be inserted between the converter

and the supply bus. This inductor also acts as a filter between

the converter and the primary power source.

OUTPUT CURRENT (A)

100

120

100

VOUT = 1.3V

TA = 25°C

Figure 13. Efficiency of the Circuit of Figure 10 vs. Output Current

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