LTC3525L-3_15 Datasheet, PDF (8/12 Pages) Linear Technology – 400mA Micropower Synchronous Step-Up DC/DC Converter with Output Disconnect

LTC3525L-3
OPERATION
The maximum average load current that can be supported
is given by:
I_{O(MAX )}
=
0.3
• V_IN
V_O
•
η
Amps
where η 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
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.
Inductors 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 volt-
age 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
close as possible to the V_IN and GND pins of the IC. A
minimum value of 1µF is recommended. If the battery is
more than a few inches away, a bulk tantalum decoupling
cap of at least 10µF is recommended on V_IN.
The output capacitor should also be a ceramic, located close
to the V_OUT and GND pins. A minimum value of 10µF is
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.
3525lfa
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