MP2305 – 2A, 23V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER

MP2305 Rev. 1.7

www.MonolithicPower.com

5

4/17/2006

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TM

OPERATION

FUNCTIONAL DESCRIPTION

The MP2305 is a synchronous rectified,

current-mode, step-down regulator. It regulates

input voltages from 4.75V to 23V down to an

output voltage as low as 0.923V, and supplies

up to 2A of load current.

The MP2305 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

transconductance error amplifier. The voltage at

the COMP pin is compared to the switch current

measured internally to control the output

voltage.

The

converter

uses

internal

N-Channel

MOSFET switches to step-down the input

voltage to the regulated output voltage. Since

the high side MOSFET requires a gate voltage

greater than the input voltage, a boost capacitor

connected between SW and BS is needed to

drive the high side gate. The boost capacitor is

charged from the internal 5V rail when SW is low.

When the MP2305 FB pin exceeds 20% of the

nominal regulation voltage of 0.923V, the over

voltage comparator is tripped and the COMP

pin and the SS pin are discharged to GND,

forcing the high-side switch off.

MP2305_F01_BD01

INTERNAL

REGULATORS

IN

EN

+

ERROR

AMPLIFIER

1.2V

EN OK

OVP

RAMP

CLK

0.923V

0.3V

CURRENT

COMPARATOR

CURRENT

SENSE

AMPLIFIER

1.1V

SHUTDOWN

COMPARATOR

LOCKOUT

COMPARATOR

7

COMP 6

SS 8

FB 5

GND

4

OSCILLATOR

100/340KHz

S

R

Q

SW

3

BS

1

IN

5V

2

OVP

IN < 4.10V

5V

+

Q

+

+

1.5V

2.5V

+

+

+

+

EN

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Figure 1—Functional Block Diagram