MIC33030 Datasheet, PDF (11/18 Pages) Micrel Semiconductor – 8MHz 400mA Internal Inductor Buck Regulator with HyperLight Load

Micrel Inc.
Application Information
The MIC33030 is a high-performance DC/DC step down
regulator offering a small solution size. Supporting an
output current up to 400mA inside a tiny 2.5mm x 2.0mm
MLF^® package and requiring only two external
components, the MIC33030 meets today’s miniature
portable electronic device needs. Using the HyperLight
Load™ switching scheme, the MIC33030 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 VIN pin and PGND pin for bypassing. A TDK
C1608X5R0J475K, 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 MIC33030 was 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 increase solution size or
cost. A low equivalent series resistance (ESR) ceramic
output capacitor such as the TDK C1608X5R0J475K,
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.
Compensation
The MIC33030 is designed to be stable with a minimum
of 2.2µF ceramic (X5R) output capacitor.
Duty Cycle
The typical maximum duty cycle of the MIC33030 is
90%.
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
MIC33030
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 consumption of current for
battery powered applications. Reduced current draw
from a battery increases the devices operating time
which 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.
Device operating current also reduces efficiency. The
product of the quiescent (operating) current and the
supply voltage represents another DC loss. The current
required driving the gates on and off at a constant 8MHz
frequency and the switching transitions make up the
switching losses.
90.0%
Efficiency vs. Load
(VOUT = 2.5V)
80.0%
70.0%
VIN = 3.6V
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
1
10
100
1000
LOAD CURRENT (mA)
Figure 2. Efficiency under Load
Figure 2 shows an efficiency curve. From no load to
100mA, efficiency losses are dominated by quiescent
current losses, gate drive and transition losses. By using
the HyperLight Load™ mode, the MIC33030 is able to
maintain high efficiency at low output currents.
Over 100mA, efficiency loss is dominated by MOSFET
R_DSON and inductor losses. Higher input supply voltages
will increase the Gate-to-Source threshold on the
internal MOSFETs, thereby reducing the internal R_DSON.
This improves efficiency by reducing DC losses in the
device. All but the inductor losses are inherent to the
device. In which case, inductor selection becomes
increasingly critical in efficiency calculations. As the
inductors are reduced in size, the DC resistance (DCR)
can become quite significant.
February 2011
11
M9999-020311-C