MP5410—LOW START-UP VOLTAGE BOOST CONVERTER WITH FOUR SPDT SWITCHES

MP5410 Rev.1.01

www.MonolithicPower.com

8

3/28/2011

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© 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 0.65Ω 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

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

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.