MIC33263 Datasheet, PDF (14/19 Pages) Micrel Semiconductor – Buck Regulator with Integrated Inductor

Micrel, Inc.
Application Information
The MIC33263/4 is a high-performance DC-to-DC step-
down regulator offering a small solution size of 4.6mm ×
7mm. Supporting an output current up to 2A inside a tiny
3mm × 2.5mm QFN package, the MIC33263/4 requires
very few external components while meeting today’s
miniature portable electronic device needs. Using the
HyperLight Load (HLL) switching scheme, the
MIC33263/4 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 PV_IN pin and PGND pin for bypassing. A TDK
C1608X5R0J475M, 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 MIC33263/4 is designed for use with a 22µF 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 TDK
C1608X5R1A226M080AC, size 0603, 22µF 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 MIC33263/4 is designed to be stable with a 22µF
ceramic (X5R) output capacitor. An external feedback
capacitor of 15pF to 68pF is required for optimum
regulation performance.
100% Duty Cycle Low Dropout Operation
The MIC33263/4 enters 100% duty cycle when the input
voltage gets close to the nominal output voltage, in this
case the high-side MOSFET switch is turned on 100% for
one or more cycles. By decreasing the input voltage
further the high-side MOSFET switch turns on
completely. In this case the small difference between VIN
and VOUT is determined by R_DSON and DCR of the
inductor. This is extremely useful in battery-powered
applications to accomplish longest operation time.
MIC33263/4
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power supplied, as
shown in Equation 3:
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 consumption of current 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. 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 4MHz frequency and
the switching transitions make up the switching losses.
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 HLL mode, the MIC33263/4 is able to maintain high
efficiency at low output currents.
100
90
80
70
60
50
40
30
20
10
10
Efficiency
vs. Output Current
V_OUT = 2.5V
V_OUT = 1.8V
V_OUT = 3.3V
V_OUT = 1.2V
V_IN = 5V
100
1000
OUTPUT CURRENT(mA)
Figure 2. Efficiency under Load
May 15, 2014
14
Revision 1.1