MP38875 – 15A, 16V, 800kHz STEP-DOWN WITH SYNCHRONOUS GATE DRIVER

MP38875 Rev. 0.9

www.MonolithicPower.com

7

11/20/2009

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FUNCTION BLOCK DIAGRAM

IN

EN

FB

SW

VCC

BG

GND

PG

BST

REGULATOR

OSCILLATOR

800KHz

DRIVER

CURRENT SENSE

AMPLIFIER

ERROR

AMPLIFIER

CURRENT

LIMIT

COMPARATOR

PWM

COMPARATOR

D

REGULATOR

REFERENCE

--

+

--

+

--

+

S

R

R

Q

Q

COMP

Power

Good

SS/TRK

SYNCOUT

SYNCIN

DRIVER

Figure 2—Functional Block Diagram

OPERATION

The MP38875 is a fixed frequency, synchronous,

step-down switching regulator with an integrated

high-side power MOSFET and a gate driver for a

low-side external MOSFET. It achieves 15A

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 MP38875 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.

Error Amplifier

The error amplifier compares the FB pin voltage

with the internal 0.8V reference (REF) and

outputs a current proportional to the difference

between the two. This output current is then used

to

charge

or

discharge

the

external

compensation network to form the COMP

voltage, which is used to control the power

MOSFET

current.

The

optimized

external

compensation network minimizes the external

component counts and simplifies the control loop

design.

See

Application

Information

for

compensation network design.