MIC2206 Datasheet, PDF (10/12 Pages) Micrel Semiconductor – 2MHz PWM Synchronous Buck Regulator with LOWQ Mode and Voltage Scaling

Micrel
Applications Information
The MIC2206 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 scaled down
and regulated to 1.0V through the LDO output,
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 MIC2206 to enter
PWM mode. In this case, the LDO output makes a
"hand-off" to the PWM regulator. The LDO output
then turns off allowing up to 600mA of current to be
efficiently supplied through the PWM output to the
load.
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.
MIC2206
Output Capacitor
Even though the MIC2206 is optimized for a 2.2µF
output capacitor, output capacitance can be varied
from 1µF to 4.7µF. The MIC2206 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 2.2µF, 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.
Inductor Selection
The MIC2206 is designed for use with a 2.2µH
inductor. Proper selection should ensure the
inductor can handle the maximum average and peak
currents required by the load. Maximum current
ratings of the inductor are generally given in two
methods; permissible DC current and saturation
current. Permissible DC current can be rated either
for a 40°C temperature rise or a 10% to 20% loss in
inductance. Ensure the inductor selected can handle
the maximum operating current. When saturation
current is specified, make sure that there is enough
margin that the peak current will not saturate the
inductor. Peak inductor current can be calculated as
follows:
I_PK
= I_OUT
+
V_{OUT ⎜⎜⎝⎛}1−
V_OUT
V_IN
2×f ×L
⎟⎟⎠⎞
April 2005
10
M9999-041905
www.micrel.com