MIC23603 Datasheet, PDF (12/19 Pages) Micrel Semiconductor – 4MHz PWM 6A Buck Regulator

Micrel Inc.
MIC23603
Application Information
The MIC23603 is a high-performance DC/DC step down
regulator offering a small solution size. Because it
supports an output current up to 6A inside a tiny 4mm x
5mm DFN package and requires only three external
components, the MIC23603 meets today’s miniature
portable electronic device needs. Using the HyperLight
Load switching scheme, the MIC23603 maintains high
efficiency throughout the entire load range while
providing ultra-fast load transient response. The
following sections provide additional device application
information.
Input Capacitor
Place a 10µF ceramic capacitor or greater close to the
VIN pin and PGND/GND pin for bypassing. Micrel
recommends the TDK C1608X5R0J106K, size 0603,
10µF ceramic capacitor based upon performance, size,
and cost. An 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 MIC23603 was designed for use with a 47µF or
greater ceramic output capacitor. Increasing the output
capacitance lowers output ripple and improves load
transient response, but could increase solution size or
cost. A low equivalent series resistance (ESR) ceramic
output capacitor such as the TDK C3216X6S1A476M,
size 1206, 47µF ceramic capacitor is recommended
based upon performance, size and cost. Both the X7R or
X5R temperature rating capacitors are recommended.
The Y5V and Z5U temperature rating capacitors are not
recommended because of their wide variation in
capacitance over temperature and increased resistance
at high frequencies.
Inductor Selection
When selecting an inductor, consider the following
factors (not necessarily in order of importance):
• Inductance
• Rated current value
• Size requirements
• DC resistance (DCR)
The MIC23603 was designed for use with a 0.33µH to
1µH inductor. For faster transient response, a 0.33µH
inductor yields the best result. For lower output ripple, a
1µH inductor is recommended.
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. Make sure that the inductor selected can
handle the maximum operating current. When saturation
current is specified, make sure that there is enough
margin so that the peak current does not cause the
inductor to saturate. Peak current can be calculated as
follows:
I_PEAK
=

^IOUT

+
V_OUT

1
− V_OUT /V_IN
2×f ×L

Eq. 2
As Equation 2 shows, 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 also increases.
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, it can represent a
significant efficiency loss. See Efficiency Considerations.
Compensation
The MIC23603 is designed to be stable with a 0.33µH to
1µH inductor with a minimum of 47µF ceramic (X5R)
output capacitor. A feedforward capacitor (C_FF) in the
range of 33pF to 68pF is recommended across the top
feedback resistor to reduce the effects of parasitic
capacitance and improve transient performance.
Duty Cycle
The typical maximum duty cycle of the MIC23603 is
80%.
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power supplied.
Efficiency
%
=

V_OUT
V_IN
× I_OUT
× I_IN

× 100
Eq. 3
Maintaining high efficiency serves two purposes. It
reduces power dissipation in the power supply, reducing
the need for heat sinks and thermal design
considerations, and it reduces current consumption for
battery powered applications. Reduced current draw
from a battery increases the device’s operating time and
is critical in hand-held devices.
There are two types of losses in switching converters:
DC losses and switching losses. DC losses are simply
the power dissipation of I²R. Power is dissipated in the
high side switch during the on cycle. Power loss is equal
to the high side MOSFET R_DSON multiplied by the Switch
Current squared. During the off cycle, the low side
N-channel MOSFET conducts, also dissipating power.
November 5, 2013
12
Revision 1.1