MP2355 – 3A, 23V, 380KHz STEP-DOWN CONVERTER

MP2355 Rev. 1.5

www.MonolithicPower.com

5

5/1/2006

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© 2006 MPS. All Rights Reserved.

TM

OPERATION

The MP2355 is a current-mode step-down

regulator. It regulates input voltages from 4.75V to

23V down to an output voltage as low as 1.222V,

and is able to supply up to 3A of load current.

The MP2355 uses current-mode control to

regulate the output voltage. The output voltage is

measured at FB through a resistive voltage

divider and amplified through the internal error

amplifier.

The

output

current

of

the

transconductance error amplifier is presented at

COMP where a network compensates the

regulation control system. The voltage at COMP

is compared to the switch current measured

internally to control the output voltage.

The converter uses an internal N-Channel

MOSFET switch to step-down the input voltage to

the regulated output voltage. Since the MOSFET

requires a gate voltage greater than the input

voltage, a boost capacitor connected between LX

and BST drives the gate. The capacitor is

internally charged while LX is low.

An internal 10Ω switch from LX to GND is used to

insure that LX is pulled to GND when LX is low to

fully charge the BST.capacitor.

MP2355_BD01

LOCKOUT

COMPARATOR

ERROR

AMPLIFIER

FREQUENCY

FOLDBACK

COMPARATOR

INTERNAL

REGULATORS

1.8V

SLOPE

COMP

CLK

CURRENT

COMPARATOR

CURRENT

SENSE

AMPLIFIER

SHUTDOWN

COMPARATOR

COMP

7

SS

1

VIN 3

RUN 8

GND

5

OSCILLATOR

42/380kHz

S

R

Q

LX

4

BST

2

5V

+

Q

0.7V

+

+

2.37V/

2.62V

+

1.222V

0.7V

+

+

FB

6

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Figure 1—Functional Block Diagram