MP24943 –3A, 55V, 100kHz STEP-DOWN CONVERTER

MP24943 Rev. 0.83

www.MonolithicPower.com

8

12/11/2013

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OPERATION

Main Control Loop

The MP24943 is a current-mode buck regulator

where the error amplifier (EA) output voltage is

proportional to the peak inductor current.

At the beginning of the cycle, SW is off, the EA

output voltage is higher than the current sense

amplifier (CSA) output, and output of the

current limit comparator is low. The rising edge

of the 100kHz CLK signal sets the RS flip-flop:

this turns on the internal switch, which then

connects SW and the inductor to the input

supply.

The CSA detects the current flow through the

internal switch. If the sum of the CSA output

and the slope compensation output exceeds the

EA output voltage, the RS flip-flop resets, and

the MP24943 reverts to its initial SW off state—

otherwise, the falling edge of the CLK resets

the flip-flop.

The EA amplifies the voltage difference

is less than the 0.8V reference, the EA output is

proportional to the inductor current. An external

Schottky diode (D1) carries the inductor current

when SW is off.

Enable Control

The MP24943 has an enable-control pin (EN):

driving EN above 1.8V turns on MP24943, while

driving EN below 0.4V turns it off. Connect EN

Output Over-Voltage Protection

The

MP24943

has

output

over-voltage

through an external resistor divider, and a 0.9V

reference on the negative input of the OVP

comparator. If the voltage on VO pin is greater

than 0.9V, the high-side switch turns off after a

short delay, and the soft-start capacitor

discharges. If the voltage is less than 0.9V, the

part restarts automatically.