LTC3525L-3

9

3525lf

OPERATIO

The maximum average load current that can be supported

is given by:

I

V

V

Amps

O MAX

IN

O

03

.•

•

η

Where is the efficiency (see Typical Performance Char-

acteristics).

The “burst” frequency (how often the LTC3525L-3 deliv-

ers a burst of current pulses to the load) is determined

by the internal hysteresis (output voltage ripple), the load

current and the amount of output capacitance. All Burst

Mode operation or hysteretic converters will enter the

audible frequency range when the load is light enough.

However, due to the low peak inductor current at light load,

circuits using the LTC3525L-3 do not typically generate

any audible noise.

Component Selection

Inductor values between 4.7µH and 15µH are recom-

mended. In most applications 10µH will yield the best

compromise between size and efficiency. The inductor

should be a low-loss ferrite design and must be rated for

peak currents of at least 400mA without saturating. Induc-

tors with lower DC resistance will improve efficiency. Note

that the inductor value does not have a significant effect

on ripple current, so while lower values will increase the

operating frequency, they do not reduce output voltage

ripple.

Some recommended inductor examples are Murata

LQH32C, Coilcraft LPO4812, LPO3310, DO3314, DS1608

and MSS4020, Sumida CDRH2D14 and Taiyo Yuden

NR3015T.

A ceramic input bypass capacitor should be located as

minimum value of 1µF is recommended. If the battery is

more than a few inches away, a bulk tantalum decoupling

The output capacitor should also be a ceramic, located close

recommended. Increasing the value of the output capacitor

to 22µF will result in lower output ripple. Higher capacitor

values will only offer a small reduction in output ripple,

while reducing light load efficiency by causing the peak

inductor current to increase above its minimum value of

150mA. The input and output capacitors should be X5R

or X7R types, not Y5V.