MP4558

– 1A, 2MHz, 55V STEP-DOWN CONVERTER

MP4558 Rev. 1.01

www.MonolithicPower.com

9

10/28/2013

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© 2013 MPS. All Rights Reserved.

BLOCK DIAGRAM

Figure 1: Functional Block Diagram

OPERATION

The

MP4558

is

a

programmable-frequency,

non-synchronous, step-down, switching regulator

with an integrated high-side, high-voltage power

MOSFET. It provides a single, highly efficient

solution with current-mode control for fast loop

response and easy compensation. It features a

wide input voltage range, internal soft-start

control, and precision current limiting. Its very low

operational quiescent current makes it suitable

for battery-powered applications.

PWM Control Mode

At moderate-to-high output current, the MP4558

operates in a fixed-frequency, peak-current

–

control mode to regulate the output voltage. The

internal clock initiates a PWM cycle. The power

MOSFET turns on and remains on until its

current reaches the value set by the COMP

voltage. When the power MOSFET is off, it

remains off for at least 100ns before the next

cycle starts. If, in one PWM period, the power

MOSFET current does not reach the COMP set

current value, the power MOSFET remains on to

saves on a turn-off operation.

Pulse-Skipping Mode

Under

light-load

condition,

the

switching

frequency drops to zero to reduce switching and

driving losses.

Error Amplifier

The error amplifier compares the FB pin voltage

with the internal reference (REF) and outputs a

current proportional to the difference between the

two. This output current then charges the

external compensation network to form the

COMP

voltage,

which

controls

the

power

MOSFET current.

While in operation, the minimum COMP voltage

is clamped to 0.9V and its maximum is clamped

to 2.0V. COMP is internally pulled down to GND

in shutdown mode. Avoid pulling COMP up

beyond 2.6V.