8, 2015 13 Revision 2.1
Application Information
The MIC33263/4 is a high-performance DC/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
MIC3326 3/4 is a ble to maintain h igh ef f iciency throu gh out
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 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
capacita nce over temper ature, can also bec ome resist ive
at high frequencies. This reduces their ability to filter out
high-f r equency 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 lo w equiv alent se ries r esistanc e (ESR) cera m ic
output capacitor such as the TDK
C1608X5R1A226M080AC, size 0603, 22µF ceramic
capacitor is r ecom m ended based up on perfor m ance, 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 per f ormance.
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 hig h-side MO SFET switch is turne d on 100% for
one or more cycles. By decreasing the input voltage
further the high-side MOSFET switch turns on
complete ly. In this c ase t he sm all dif ferenc e betw een VIN
and VOUT is determined by RDSON and DCR of the
inductor. This is extremely useful in battery-powered
applications to accomplish longest operation time.
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power supplied, as
shown in Equati on 3:
100
IV IV
% Efficiency
ININ
OUTOUT
×
×
×
=
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 app licatio ns. Reduc ed c urrent dr aw from
a battery increases the device’s operating time and is
critical in hand held devices.
There ar e t wo t ypes of loss es in s w itchi ng c on vert er s ; DC
losses and switching losses. DC losses are simply the
power dissipation of I2R. Power is dissipated in the high
side switch dur i ng the o n cyc le. P o wer loss is equa l to the
high sid e MOSFET RDSON multiplied by the s witch 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.
Figure 2. Efficiency under Load
10
20
30
40
50
60
70
80
90
100
10 100 1000
EFFICIENCY (%)
OUTPUT CURRENT(mA)
Efficiency
vs. Output Current