MP4572

– 60V, 2A, SYNCHRONOUS STEP-DOWN CONVERTER

MP4572 Rev. 1.0

www.MonolithicPower.com

21

3/9/2020

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© 2020 MPS. All Rights Reserved.

OPERATION

The MP4572 is a fully integrated, synchronous,

rectified, step-down, non-isolated switch-mode

converter. It offers a wide 4.5V to 60V input

supply range, and can achieve up to 2A of

continuous output current with excellent load and

line regulation across an ambient temperature

range of -40°C to +125°C. Figure 1 shows a

block diagram of the device.

PWM Control

At moderate to high output currents, the MP4572

operates in fixed-frequency, peak current control

mode to regulate the output voltage.

An internal clock initiates a PWM cycle. At the

rising edge of the clock, the high-side switch (HS-

FET) turns on, and the inductor current rises

linearly to provide energy to the load. The HS-

FET remains on until the current reaches the

value set by the COMP voltage (VCOMP), which is

the output of the internal error amplifier. VCOMP is

based on the difference between the output

feedback voltage and internal high-precision

reference. VCOMP determines how much energy

should be transferred to the load. A higher load

current creates a higher VCOMP. Once the HS-FET

is on, it remains on for at least 90ns.

When the HS-FET is off, the low-side switch (LS-

FET) turns on immediately, and stays on until the

next clock starts. During this time, the inductor

current flows through the LS-FET. Once the LS-

FET is on, it remains on for at least 100ns before

the next cycle starts. To avoid shoot-through, a

dead time is inserted to prevent the HS-FET and

LS-FET from turning on simultaneously.

If the current in the HS-FET does not reach the

COMP set current value within one PWM period,

the HS-FET remains on, saving a turn-off

operation.

Light-Load Operation

The

MP4572

features

configurable

forced

continuous conduction mode (FCCM) and light-

load

asynchronous

advanced

mode

(AAM),

which can be set by the CCM/SYNCO pin. FCCM

maintains a constant switching frequency and

smaller output ripple. However, FCCM has low

efficiency during light-load conditions, while AAM

achieves high efficiency (see Figure 2).

To force the device into FCCM, connect the

CCM/SYNCO pin to GND using a 10k

Ω to 300kΩ

resistor. In FCCM, the converter works with a

fixed frequency across a no-load to full-load

range. Float the CCM/SYNCO pin to force the

device into AAM under light-load conditions. The

device cannot change modes while it is operating,

so the mode must be selected before start-up.

AAM

Inductor

Current

t

t

t

Load

Decreased

FCCM

Inductor

Current

t

t

t

Load

Decreased

Figure 2: AAM and FCCM

When AAM is enabled, the switching frequency is

scaled down according to VCOMP during light-load

conditions.

The

MP4572

first

enters

nonsynchronous operation while the inductor

current approaches zero at light-load. If the load

further decreases or is at no-load, VCOMP drops

below the internally set AAM value (VAAM). The

MP4572 then enters sleep mode and consumes

a low quiescent current to improve light-load

efficiency.

In sleep mode, the internal clock is blocked, so

the MP4572 skips some pulses. VFB is below

VREF, so VCOMP ramps up until it exceeds VAAM.

Then the internal clock

is reset, and the

crossover time is used as the benchmark for the

next clock. This control scheme helps the device

achieve high efficiency by scaling down the

frequency to reduce switching and gate driver

losses.

As the output current increases from light load,

both VCOMP and the switching frequency rise. If

the output current exceeds the critical level set by

VCOMP,

the

MP4572

enters

discontinuous

conduction operation (DCM) or CCM, which has

a constant switching frequency.

Enable (EN) Control

The MP4572 can be enabled or disabled via a

remote EN signal that is referenced to ground. The

remote EN control operates with a positive logic