MP2377 – 3A, 21V, 600KHz STEP-DOWN CONVERTER

MP2377 Rev. 0.92

www.MonolithicPower.com

6

4/19/2011

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OPERATION

IN

EN/SYNC

FB

GND

SW

BST

REGULATOR

OSCILLATOR

600KHz

DRIVER

CURRENT SENSE

AMPLIFIER

x40

ERROR

AMPLIFIER

CURRENT

LIMIT

COMPARATOR

PWM

COMPARATOR

D2

REGULATOR

REFERENCE

--

+

--

+

--

+

S

R

R

Q

VCC

PG

POWER

GOOD

Figure 1—Functional Block Diagram

The MP2377 is a fixed frequency, step-down

switching regulator with an integrated high-side

power MOSFET. It achieves 3A continuous

output current over a wide input supply range

with excellent load and line regulation. It

provides a single highly efficient solution with

current mode control for fast loop response and

easy compensation.

The MP2377 operates in a fixed frequency,

peak current control mode to regulate the

output voltage. A PWM cycle is initiated by the

internal clock. The integrated high-side power

MOSFET is turned on and remains on until its

current reaches the value set by the COMP

voltage. When the power switch is off, it

remains off until the next clock cycle starts. If, in

90% of one PWM period, the current in the

power MOSFET does not reach the COMP set

current value, the power MOSFET will be

forced to turn off.

Power Good Indicator

When the FB is below 0.74V, the PG pin will be

internally pulled low. When the FB is above

0.74V, the PG becomes an open-drain output.

Error Amplifier

The error amplifier compares the FB pin voltage

with the internal 0.808V reference (REF) and

outputs a current proportional to the difference

between the two. This output current is then

used to charge or discharge the internal

compensation network to form the COMP

voltage, which is used to control the power

MOSFET current. The optimized internal

compensation network minimizes the external

component counts and simplifies the control

loop design.

Internal Regulator

Most of the internal circuitries are powered from

the 5V internal regulator. This regulator takes

the VIN input and operates in the full VIN range.

When VIN is greater than 5.0V, the output of

the regulator is in full regulation. When VIN is

lower than 5.0V, the output decreases. Since

this internal regulator provides the bias current

for the bottom gate driver that requires

significant amount of current depending upon

the external MOSFET selection, a 1uF ceramic

capacitor for decoupling purpose is required.