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MP3221 Datasheet(PDF) 11 Page - Monolithic Power Systems

Part No. MP3221
Description  2.7A, 1.2MHz, High-Efficiency Step-Up Converter With Input Disconnect
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Maker  MPS [Monolithic Power Systems]
Homepage  http://www.monolithicpower.com
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MP3221 Datasheet(HTML) 11 Page - Monolithic Power Systems

 
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MP3221
–2.7A, 1.2MHZ, HIGH-EFFICIENCY STEP UP CONVERTER WITH INPUT DISCONNECT
MP3221 Rev. 1.0
www.MonolithicPower.com
11
9/23/2013
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
APPLICATION INFORMATION
COMPONENT SELECTION
Input Capacitor Selection
Low
ESR
input
capacitors
reduce
input
switching noise and reduce the peak current
drawn from the battery. Ceramic capacitors are
good choice for input decoupling and it should
be located as close as possible to the IN and
GND pin. Add a ceramic capacitor larger than
10μF close to the IC.
Selecting the Output Capacitor
The output capacitor requires a minimum
capacitance value of 22μF at the programmed
output voltage to ensure stability over the full
operating range. A higher capacitance value
may be required to lower the output ripple and
also
the
transient
response.
Low
ESR
capacitors, such as X5R- or X7R-type ceramic
capacitors, are recommended. Assuming that
the ESR is zero, estimate the minimum output
capacitance to support the ripple in the CCM
mode as:
O
OUT
F
IN(MIN)
O
S
OUT
F
I
(V
V
V
)
C
f
(V
V )
V
 
Where:
VOUT = output voltage
VIN(MIN) = Minimum Input voltage
VF= Diode Forward voltage
IO= Output current
fS = Switching frequency
ΔV= Acceptable output ripple
Selecting the Inductor
The inductor is required to force the higher
output voltage while being driven by the input
voltage. A larger value inductor results in less
ripple current that results in lower peak inductor
current, reducing stress on the internal N-
Channel.switch. However, the larger value
inductor has a larger physical size, higher
series
resistance,
and/or
lower
saturation
current.
A 2.2μH inductor is recommended for most
applications. However, a more exact inductance
value can be calculated. A good rule of thumb
is to allow the peak-to-peak ripple current to be
approximately 30-50% of the maximum input
current. Make sure that the peak inductor
current is below 75% of the current limit at the
operating
duty
cycle
to
prevent
loss
of
regulation due to the current limit. Also make
sure that the inductor does not saturate under
the worst-case load transient and startup
conditions. Calculate the required inductance
value by the equation:
IN
OUT
F
IN
OUT
F
SW
V
(V
V
V )
L
(V
V ) f
I
 
OUT
LOAD(MAX)
IN(MAX)
IN
VI
I
V

IN(MAX)
I
(30% 50%)I
 
Where ILOAD(MAX) is the maximum load current,
ΔI is the peak-to-peak inductor ripple current,
and η is efficiency.
Selecting the Diode
The output rectifier diode supplies current to the
inductor when the internal MOSFET is off. To
reduce power loss due to diode forward voltage
and recovery current, use a Schottky diode with
the MP3221. The diode should be rated for a
reverse voltage equal to or higher than the
output voltage. The average current rating must
be higher than the maximum load current, and
the peak current rating must be higher than the
peak inductor current.
Selecting the PMOS
The MP3221 is capable of driving P-Channel
power MOSFETS to disconnect input and
output. The critical parameter selection of a
MOSFET are:
1. Maximum drain to source voltage, VDS(MAX)
2. Maximum current ID(MAX)
3. On-resistance RDS(ON)
4. Total gate charge, QG.
Ideally,
the
off-state
voltage
across
the
MOSFET is equal to the input voltage. VDS(MAX)


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