MIC23060 Datasheet, PDF (10/15 Pages) Micrel Semiconductor – Sequenced Power Management IC with HyperLight Load™ DC/DC and Dual Input LDO™

Micrel, Inc.
Application Information
The MIC23060 is a high performance DC/DC step down
regulator plus Dual input Low Dropout linear regulator
offering a small solution size. Supporting a
recommended maximum output current of 300mA and
300mA respectively inside a tiny 2.5mm x 2.5mm Thin
MLF^® package and requiring only four external
components, the MIC23060 meets today’s miniature
portable electronic device needs. Using the HyperLight
Load™ switching scheme, the MIC23060 DC/DC
converter 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 4.7μF ceramic capacitor should be placed close to the
DVIN pin and PGND pin for decoupling the high di/dt
pulses of the DC-DC section from the LDO section. 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 MIC23060 was designed for use with a 2.2μF or
greater ceramic output capacitor for the DC-DC section
and 1μF for the LDO. 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.
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)
MIC23060
The MIC23060 was designed for use with a 0.47μH to
2.2μH inductor. Typically, a 1μH inductor is
recommended for a balance of transient response,
efficiency and output ripple. For faster transient
response, a 0.47μH inductor will yield the best result. For
lower output ripple and improved regulation, 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 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 follows:
I_PEAK
=
⎡
⎢^IOUT
⎣
+ V_OUT
×
⎜⎜⎝⎛
1
− V_OUT /V_IN
2×f ×L
⎟⎟⎠⎞⎥⎦⎤
As shown by the calculation above, 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.
Compensation
The MIC23060 is designed to be stable with a 0.47μH to
2.2μH inductor with a minimum of 4.7μF ceramic (X5R)
output capacitor for the DC/DC output (SNS) and 1μF
ceramic (X5R) for the LDO (LDO). For 0.47μH inductors,
a 10µF capacitor is recommended to reduce ripple and
improve stability.
Enable Sequencing (S1/S2/S3)
The MIC23060 offers complete flexibility of start-up
sequencing of its two outputs. The sequence mode is set
in hardware (pin-strapping) which requires that only a
single GPIO be used for enable toggling. The Dual Input
LDO™ can turn-on prior to the DC/DC converter and
automatically switch to post regulation from the DC/DC
converter after it starts.
There are 3 modes available:
• S1=S2: Simultaneous (SIM)
• S3 = 0: First On/First Off (FOFO)
• S3 = 1: First On/Last Off (FOLO)
S3 is responsible for controlling the First-on/First-Off
April 2010
10
M9999-042210-B