MIC23450_13 Datasheet, PDF (13/22 Pages) Micrel Semiconductor – 3MHz, PWM, 2A Triple Buck Regulator with HyperLight Load® and Power Good

Micrel, Inc.
Application Information
The MIC23450 is a triple high performance DC-to-DC
step down regulator offering a small solution size.
Supporting 3 outputs with currents up to 2A inside a
5mm x 5mm QFN package, the IC requires only five
external components per channel while meeting today’s
miniature portable electronic device needs. Using the
HyperLight Load^® switching scheme, the MIC23450 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 2.2µF ceramic capacitor or greater should be placed
close to the PVIN pin for each channel and it’s
corresponding PGND pin for bypassing. For example,
Murata GRM188R60J475ME19D, size 0603, 4.7µF
ceramic capacitor is ideal, 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 MIC23450 is designed for use with a 2.2µF 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
GRM188R60J475ME84D, size 0603, 4.7µF 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 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)
MIC23450
The MIC23450 is designed for use with a 0.47µH to
2.2µH inductor. For faster transient response, a 0.47µH
inductor will yield the best result. On the other hand, a
2.2µH inductor will yield lower output voltage ripple. For
the best compromise of these, generally, a 1µH 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. Ensure 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 shown in
Equation 2:
I_PEAK
=

^IOUT

+
V_OUT

1
− V_OUT /V_IN
2×f ×L

Eq. 2
As shown in Equation 2, 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 Circuit
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 as illustrated in Figure 2.
November 5, 2013
Figure 2. Transition between CCM Mode and HLL Mode
13
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