MIC23156 Datasheet, PDF (13/22 Pages) Micrel Semiconductor – 1.5A, 3MHz Synchronous Buck Regulator with HyperLight Load® and I2C Control for Dynamic Voltage Scaling

Micrel, Inc.
Application Information
The MIC23156 is a high-performance DC-to-DC step-
down regulator offering a small solution size and
supporting up to 1.5A in a 2.8mm × 2.5mm MLF and
1.81mm × 1.71mm WLCSP package. Using the
HyperLight Load switching scheme, the MIC23156 is able
to maintain high efficiency and exceptional voltage
accuracy throughout the entire load range while providing
ultra-fast load transient response. Another beneficial
feature is the ability to dynamically change the output
voltage in steps of 10mV. The following subsections
provide additional device application information.
Input Capacitor
A 2.2µF (or larger) ceramic capacitor should be placed as
close as possible to the PVIN and AVIN pins with short
trace for good noise performance. X5R or X7R type
ceramic capacitors are recommended for better tolerance
over temperature. The Y5V and Z5U type temperature
rating ceramic capacitors are not recommended due to
their large reduction in capacitance over temperature and
increased resistance at high frequencies. These reduce
their ability to filter out high-frequency noise. The rated
voltage of the input capacitor should be at least 20%
higher than the maximum operating input voltage over
the operating temperature range.
Output Capacitor
Output capacitor selection is also a trade-off between
performance, size, and cost. Increasing output capacitor
will lead to an improved transient response, however, the
size and cost also increase. The MIC23156 is designed
for use with a 2.2µF or greater ceramic output capacitor.
A low equivalent series resistance (ESR) ceramic output
capacitor is recommended based upon performance, size
and cost. Both the X7R or X5R temperature rating
capacitors are recommended. Refer to Table 1 for
additional information.
Inductor Selection
Inductor selection is a balance between efficiency,
stability, cost, size, and rated current. Since the
MIC23156 is compensated internally, the recommended
inductance of L is limited from 0.47µH to 2.2µH to ensure
system stability.
For faster transient response, a 0.47µH inductor will yield
the best result. For lower output ripple, a 2.2µH 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 30% loss
in inductance.
MIC23156
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 noted in Equation 1:
I_PEAK
=

^IOUT

+
V_OUT  ^1−

V_OUT / V_IN
2×f ×L


Eq. 1
As shown by Equation 1, 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 upon the requirements
of the application. Refer to the Typical Application 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 Efficiency
Considerations.
The transition between continuous-conduction mode
(CCM) to HyperLight Load mode is determined by the
inductor ripple current and the load current.
Figure 2 shows the signals for high-side switch drive
(HSD) for T_ON control, the Inductor current and the low
side switch drive (LSD) for T_OFF control.
Figure 2. HSD Signals for TON Control, Inductor Current,
and LSD for TOFF Control
April 22, 2013
13
Revision 1.0