MP1541 – 1.3MHZ BOOST CONVERTER

MP1541 Rev.1.3

www.MonolithicPower.com

4

3/20/2006

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© 2006 MPS. All Rights Reserved.

PIN FUNCTIONS

Pin #

Name Function

1

SW

Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power

inductor and output rectifier to SW. SW can swing between GND and 22V.

2

GND Ground.

3

FB

Feedback Input. FB voltage is 1.25V. Connect a resistor divider to FB.

4

EN

Regulator On/Off Control Input. A high input at EN turns on the converter, and a low input turns

it off. When not used, connect EN to the input source for automatic startup. The EN pin cannot

be left floating.

5

IN

Input Supply Pin. Must be locally bypassed.

OPERATION

The MP1541 uses a fixed frequency, peak current

mode boost regulator architecture to regulate

voltage at the feedback pin. The operation of the

MP1541 can be understood by referring to the

block diagram of Figure 1. At the start of each

oscillator cycle the MOSFET is turned on through

the control circuitry. To prevent sub-harmonic

oscillations at duty cycles greater than 50 percent,

a stabilizing ramp is added to the output of the

current sense amplifier and the result is fed into

the negative input of the PWM comparator. When

this voltage equals the output voltage of the error

amplifier the power MOSFET is turned off. The

voltage at the output of the error amplifier is an

amplified version of the difference between the

1.25V bandgap reference voltage and the

feedback voltage. In this way the peak current

level keeps the output in regulation. If the

feedback voltage starts to drop, the output of the

error amplifier increases. This results in more

current to flow through the power MOSFET, thus

increasing the power delivered to the output.

The MP1541 has internal soft start to limit the

amount of input current at startup and to also

limit the amount of overshoot on the output. The

current limit is increased by a fourth every 40

µs

giving a total soft start time of 120

µs.

PWM

COMPARATOR

ERROR

AMPLIFIER

CONTROL

LOGIC

CURRENT

SENSE

AMPLIFIER

SW

M1

GND

+

-

1

FB

3

2

1.3MHz

OSC

+

-

-

+

+

1.25V

MP1541-F01-BD01

Figure 1—Functional Block Diagram