MP1471 – SYNCHRONOUS, STEP-DOWN CONVERTER WITH INTERNAL MOSFETS

MP1471 Rev. 1.01

www.MonolithicPower.com

10

8/27/2013

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© 2013 MPS. All Rights Reserved.

OPERATION

The MP1471 is a high-frequency, synchronous,

rectified, step-down, switch-mode converter

with internal power MOSFETs. It offers a very

compact solution to achieve a 3A peak output

current over a wide input supply range, with

excellent load and line regulation.

The MP1471 operates in a fixed-frequency,

peak-current–control mode to regulate the

output voltage. An internal clock initiates the

PWM cycle to turn on the integrated high-side

power MOSFET. This MOSFET 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

the current in the power MOSFET does not

reach the COMP set current value within 90%

of one PWM period, the power MOSFET is

forced to turn off.

Internal Regulator

The 5V internal regulator powers most of the

exceeds 5.0V, the regulator output is in full

output decreases.

Error Amplifier

The error amplifier compares the FB voltage

against the internal 0.8V reference (REF) and

outputs a current proportional to the difference

between the two. This output current charges or

discharges 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.

AAM Operation

The

MP1471

has

AAM

(Advanced

Asynchronous Modulation) power-save mode

for light load. The AAM voltage is set at 0.5V

internally. Under the heavy load condition, the

high, the high-side power MOSFET turns on

set by the COMP voltage. The internal clock

During this time, the internal clock is blocked,

thus the MP1471 skips some pulses for PFM

(Pulse Frequency Modulation) mode and

achieves the light load power save.

Clock

R1

1.2pF

47pF 500k

20k

R2

HS_driver

+

-

QS

R

+

-

Figure 2: Simplified AAM Control Circuit

When the load current is light, the inductor peak

current is set internally to about 340mA for

shows the inductor peak current vs. inductor

value curve.

1.2

Figure 3: Inductor Peak Current vs. Inductor

Value

Enable

EN is a digital control pin that turns the

regulator on and off: Drive EN HIGH to turn on

the regulator, drive it LOW to turn it off. An

internal 1MΩ resistor from EN to GND allows

EN to float to shut down the chip.

The EN pin is clamped internally using a 6.5V

series-Zener-diode as shown in Figure 4.

Connecting the EN input pin through a pullup