MIC23303 Datasheet, PDF (12/21 Pages) Micrel Semiconductor – 4MHz PWM 3A Buck Regulator with HyperLight Load™ and Power Good

Micrel, Inc.
MIC23303
Application Information
The MIC23303 is a high-performance DC-to-DC step down
regulator offering a small solution size. Supporting an
output current up to 3A inside a tiny 3mm x 3mm DFN
package, the IC requires only six external components
while meeting today’s miniature portable electronic device
needs. Using the HyperLight Load switching scheme, the
MIC23303 is able to maintain high efficiency throughout
the entire load range while providing ultra-fast load
transient response. The following sections provide
additional device application information.
Input Capacitor
A 4.7µF ceramic capacitor or greater should be placed
close to the PVIN pin and PGND pin for bypassing. A
Murata GRM188R60J475ME19D, size 0603, 4.7µF
ceramic capacitor is recommended based upon
performance, size, and cost. A X5R or X7R temperature
rating is recommended for the input capacitor. Y5V
temperature rating capacitors, aside from losing most of
their capacitance over temperature, can also become
resistive at high frequencies. This reduces their ability to
filter out high frequency noise.
Output Capacitor
The MIC23303 is designed for use with a 10µF or greater
ceramic output capacitor. Increasing the output
capacitance will lower output ripple and improve load
transient response but could also increase solution size or
cost. A low equivalent series resistance (ESR) ceramic
output capacitor such as the Murata GRM21BR60J226ME39L,
size 0805, 22µF ceramic capacitor is recommended based
upon performance, size and cost. Two of these capacitors
in parallel will decrease ESR, resulting in decreased output
voltage ripple. Both the X7R or X5R temperature rating
capacitors are recommended. The Y5V and Z5U
temperature rating capacitors are not recommended due
to their wide variation in capacitance over temperature and
increased resistance at high frequencies.
Inductor Selection
When selecting an inductor, it is important to consider the
following factors (not necessarily in the order of
importance):
• Inductance
• Rated current value
• Size requirements
• DC resistance (DCR)
The MIC23303 is designed for use with a 0.33µH to 1.0µH
inductor. For faster transient response and greater
efficiency, a 0.33µH inductor will yield the best result. To
achieve lower output voltage ripple, a higher value inductor
such as a 1µH can be used. However, a greater value
inductor, when operating in low load mode will result in a
higher operating frequency. This effect with increased
DCR will result in a less efficient design.
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 that the inductor selected can handle
the maximum operating current. When saturation current is
specified, make sure that there are enough margins that
the peak current does not cause the inductor to saturate.
Peak current can be calculated as follows:
I_PEAK

= _I_OUT

+
V_OUT

1
− V_OUT /V_IN
2×f ×L

As shown by the calculation above, the peak inductor
current is inversely proportional to the switching frequency
and the inductance; the lower the switching frequency or
the inductance the higher the peak current. As input
voltage increases, the peak current is somewhat limited by
constant off time control.
The size of the inductor depends on the requirements of
the application. Refer to the Typical Application Schematic
and Bill of Materials for details.
DC resistance (DCR) is also important. While DCR is
inversely proportional to size, DCR can represent a
significant efficiency loss. Refer to the Efficiency
Considerations. The transition between high loads (CCM)
to HyperLight Load (HLL) mode is determined by the
inductor ripple current and the load current.
September 6, 2013
12
090613-2.0