MP2494 –2A, 55V, 100kHz STEP-DOWN CONVERTER

MP2494 Rev. 1.0

www.MonolithicPower.com

7

4/25/2012

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OPERATION

Main Control Loop

The MP2494 is a current mode buck regulator.

That is, the EA output voltage is proportional to

the peak inductor current.

At the beginning of a cycle SW is off; the EA

output voltage is higher than the current sense

amplifier output; and the current comparator’s

output is low. The rising edge of the 100kHz

CLK signal sets the RS Flip-Flop. Its output

turns on SW thus connecting the SW pin and

inductor to the input supply.

The increasing inductor current is sensed and

amplified by the Current Sense Amplifier. Ramp

compensation is summed to Current Sense

Amplifier output and compared to the Error

Amplifier output by the Current Comparator.

When the Current Sense Amplifier plus Slope

Compensation signal exceeds the EA output

voltage, the RS Flip-Flop is reset and the

MP2494 reverts to its initial SW off state.

If the Current Sense Amplifier plus Slope

Compensation signal does not exceed the

COMP voltage, then the falling edge of the CLK

resets the Flip-Flop.

The output of the Error Amplifier integrates the

voltage difference between the feedback and

the 0.8V bandgap reference. The polarity is

such that an FB pin voltage lower than 0.8V

increases the EA output voltage. Since the EA

output voltage is proportional to the peak

inductor current, an increase in its voltage

increases current delivered to the output. An

external Schottky Diode (D1) carries the

inductor current when SW is off.

Enable Control

The MP2494 has an Enable control pin (EN).

Drive EN above 1.8V to turn on the MP2494.

Drive EN below 0.4V to turn it off. Tie EN to VIN

for automatic start up.