MP2225 –18V/5A SYNCHRONOUS STEP-DOWN CONVERTER

MP2225 Rev. 1.01

www.MonolithicPower.com

12

4/13/2016

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OPERATION

The MP2225 is a high-frequency, synchronous,

rectified, step-down, switch-mode converter

with built-in power MOSFETs. It offers a very

compact solution to achieve 5A output current

with excellent load and line regulation over a

wide input supply range.

The MP2225 operates in a fixed-frequency,

peak-current–control mode to regulate the

output voltage. An internal clock initiates a

PWM cycle. The integrated high-side power

MOSFET turns on and remains in on-state until

the 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

95% of one PWM period, the current in the

power MOSFET does not reach the value set

by the COMP value, the power MOSFET is

forced to turn off.

VCC Regulator

A 5V internal regulator powers most of the

than 5.0V, the output decreases, and the part

requires a 0.1µF ceramic capacitor to decouple

noise.

AAM Operation

The

MP2225

has

AAM

(Advanced

Asynchronous Modulation) which is Internal

Power-save Mode for light load operation. AAM

When the clock goes high, the high-side power

reaches the value set by the COMP voltage.

Under the light load condition, the value of

the internal clock is blocked, thus the MP2225

skips some pulses for PFM (Pulse Frequency

Modulation) mode and achieves the light load

power save.

Figure 2: Simplified AAM Control Logic

Under light load condition, the inductor peak

current is internally set to be fairly 800mA.

Error Amplifier

The error amplifier compares the FB pin voltage

against the internal 0.6V reference (REF) and

generates COMP voltage as output —COMP

controls the power MOSFET current. The

optimized

internal

compensation

network

minimizes the external component count and

simplifies the control loop design.

Enable/SYNC Control

EN/SYNC is a digital control pin that turns the

converter on and off. Drive EN/SYNC high to

turn on the converter; drive it low to turn it off.

An internal 1MΩ resistor from EN/SYNC to

GND allows EN/SYNC to be floated to shut

down the chip.

The EN/SYNC pin is clamped internally using a

5.6V series-Zener-diode as shown in Figure 3.

Connecting the EN/SYNC input pin through a

limits the EN/SYNC input current to less than

100µA.

For example, with 12V connected to Vin,

Connecting the EN/SYNC pin directly to a

voltage source without any pullup resistor

requires limiting the amplitude of the voltage

source to ≤5V to prevent damage to the Zener

diode.

5.6V-typ

Figure 3: 5.6V Zener Diode Connection