MIC3385_15 Datasheet, PDF (12/15 Pages) Micrel Semiconductor – 8MHz Inductorless Buck Regulator with LDO Standby Mode

Micrel, Inc.
Application Information
The MIC3385 is a 600mA PWM power supply that
utilizes a LOWQ light load mode to maximize battery
efficiency in light load conditions. This is achieved with a
LOWQ control pin that when pulled low, shuts down all
the biasing and drive current for the PWM regulator,
drawing only 18µA of operating current. This allows the
output to be regulated through the LDO output. It is
capable of providing 60mA of output current. This
method has the advantage of producing a clean, low
current, ultra low noise output in LOWQ mode. During
LOWQ mode, the SW node becomes high impedance,
blocking current flow. Other methods of reducing
quiescent current, such as pulse frequency modulation
(PFM) or bursting techniques create large amplitude, low
frequency ripple voltages that can be detrimental to
system operation.
When more than 60mA is required, the LOWQ pin can
be forced high, causing the MIC3385 to enter PWM
mode. In this case, the LDO output makes a "hand-off"
to the PWM regulator with virtually no variation in output
voltage. The LDO output then turns off allowing up to
600mA of current to be efficiently supplied through the
PWM output to the load.
MIC3385
Input Capacitor
A minimum 1µF ceramic is recommended on the VIN pin
for bypassing. X5R or X7R dielectrics are recommended
for the input capacitor. Y5V dielectrics lose most of their
capacitance over temperature and are therefore, not
recommended.
A minimum 1µF is recommended close to the VIN and
PGND pins for high frequency filtering. Smaller case size
capacitors are recommended due to their lower ESR and
ESL. Please refer to layout recommendations for proper
layout of the input capacitor.
Output Capacitor
The MIC3385 is optimized for a 10µF output capacitor. A
larger value can be used to improve transient response
The MIC3385 utilizes type III internal compensation and
utilizes an internal high frequency zero to compensate
for the double pole roll off of the LC filter. For this
reason, larger output capacitors can create instabilities.
X5R or X7R dielectrics are recommended for the output
capacitor. Y5V dielectrics lose most of their capacitance
over temperature and are therefore, not recommended.
In addition to a 10µF, a small 10nF is recommended
close to the load for high frequency filtering. Smaller
case size capacitors are recommended due to there
lower ESR and ESL.
September 22, 2015
12
Revision 3.0