MP5410—LOW START-UP VOLTAGE BOOST CONVERTER WITH FOUR SPDT SWITCHES
MP5410 Rev.1.01 www.MonolithicPower.com 8
3/28/2011 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2011 MPS. All Rights Reserved.
OPERATION
The MP5410 is a step-up converter with four
single-pole/double-throw (SPDT) switches
designed for low-power bias supply application. It
operates from an input voltage as low as 1.8V.
The 0.65 internal N-Channel MOSFET power
switch and low dropout voltage schottky diode
are driven with a variable frequency, constant
peak-current architecture for improved regulation
and low operating current. Operation can be best
understood by referring to the Block Diagram.
Output Disconnection
The MP5410 integrates disconnect switch
between IN pin & L pin. The disconnect switch is
composed of a NMOS and a PMOS in parallel.
The MP5410 can disconnect all loads from input
DC power supply when EN pin is connected to
ground.
Under Voltage Lockout
An under voltage lockout function prevents
device startup if the supply voltage on VBat is
lower than approximately 1.5V. When in
operation and the battery is being discharged,
the device automatically enters the shutdown
mode if the voltage on V
IN
drops below 1.5V.
System Start-Up
When the MP5410 is enabled, the PMOS of
disconnect switch is turned on first, and then the
system starts boosting the step-up converter with
an internal soft-start and the output voltage rises
up. The NMOS of disconnect switch is driven by
Vout. It will be turned on once the output voltage
reaches the threshold level. The on-resistance of
NMOS is smaller than that of PMOS, so the
PMOS is shorted by NOMS at normal operation
to reduce the conduction loss.
It is recommended on the start up sequence that
the enable signal comes after input voltage
established.
Soft-start and inrush current limiting are provided
during start-up as well as normal mode
operation.
Soft-Start
The MP5410 provides soft-start by charging an
internal capacitor with a very weak current
source. The voltage on this capacitor, in turn,
slowly ramps the peak inductor current limit from
zero to the setting value. The MP5410 limits this
inrush current by increasing the current limit in
two steps, starting from I
LIM
/4 for 256 switching
cycles to I
LIM
/2 for the next 256 cycles, and then
full current limit. The soft-start time varies greatly
with load current; output voltage and input
voltage.
Variable Frequency
Constant-Peak-Current Operation
When the power MOSFET is turned on the
inductor current increases until the current limit is
reached. The Power MOSFET is then turned off
for a setting minimum off time. At the end of this
minimum of time transition if the feedback pin is
still lower than the 1.23V internal reference the
power MOSFET will again be turned on,
otherwise the MP5410 waits until the voltage
drops below the threshold before turning on the
MOSFET again. This process allows for optimal
use of the inductor, while minimizing the output
ripple and size of the output capacitor and
maintaining low operating current.
Integrated Schottky Diode
The high switching frequency demands a high-
speed rectification for optimum efficiency The
MP5410 integrates a low voltage-drop schottky
diode to reduce external parts to save critical
board space.
Four SPDT Switches
The MP5410 includes four SPDT analog
switches. S0~S1 control the switches
respectively. If the chip is enabled, a logic low
input switches the relative channel output to GND
and a logic high input switches it to OUT.
