MP5410—LOW START-UP VOLTAGE BOOST CONVERTER WITH FOUR SPDT SWITCHES
MP5410 Rev.1.01 www.MonolithicPower.com 10
3/28/2011 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
APPLICATION INFORMATION
Components referenced below apply to
Typical Application Circuit on page 11.
Setting the SW Current Limit
The resistor on ISET pin is used to set the SW
current limit. The relationship of the SW current
limit vs. the ISET resistor is showed as the curve
in page 5. For Constant-Peak-Current Operation,
when the power MOSFET is turned on the
inductor current increases until the current limit is
reached. Since the response delay, the actual
SW peak current value exceeds the setting
current limit a little. Under the higher input
voltage and with the lower inductor, the actual
SW peak current is higher due to the faster SW
current di/dt. Under same condition, a lower
current limit allows lower SW current and higher
switching frequency, while a higher current limit
allows higher SW current and lower switching
frequency.
Setting the Output Voltage
MP5410 features internal resistive voltage divider,
so floating the FB pin to achieve fixed about 10V
output. Connect to an external resistive voltage
divider from the output to FB to set the boost
converter output voltage. Set the output voltage
by selecting the resistive voltage divider ratio by
the equation:
OUT FB
R1 R2
VV
R2
+
=×
Where, V
OUT
is the output voltage, V
FB
= 1.23V.
For R1=178k and R2 = 24.9k, then V
OUT
=
10V.
Selecting the Inductor
A inductor with a DC current rating of at least
40% higher than the maximum input current is
recommended for most applications at wide input
range. For highest efficiency, the inductor’s DC
resistance should be as small as possible.
Selecting the Input Capacitor
The input capacitor reduces the surge current
drawn from the input supply and the switching
noise from the device. The input capacitor
impedance at the switching frequency should be
less than the input source impedance to prevent
high frequency switching current from passing
through the input. Ceramic capacitors with X5R
or X7R dielectrics are highly recommended
because of their low ESR and small temperature
coefficients. For most applications, a 4.7µF or
10µF capacitor is sufficient.
Selecting the Output Capacitor
The output capacitor keeps the output voltage
ripple small and ensures feedback loop stability.
The output capacitor impedance should be low at
the switching frequency. Ceramic capacitors with
X7R dielectrics are recommended for their low
ESR characteristics. For most applications, a
less than 10µF ceramic capacitor is sufficient.
Layout Considerations
Careful attention must be paid to the PCB board
layout and components placement. Proper layout
of the high frequency switching path is critical to
prevent noise and electromagnetic interference
problems. The loop of MP5410 SW to GND pin,
SW to OUT pin, and output capacitor is flowing
with high frequency pulse current. It must be as
short as possible. The IN pin is the power supply
input for the internal MOSFET switch gate driver
and the internal control circuitry. It must be locally
bypassed. See the MP5410 demo board layout
for reference.
