MP2492 – 2A, 55V, 100kHz WITH PROGRAMMABLE OUTPUT CURRENT LIMIT

MP2492 Rev. 1.0

www.MonolithicPower.com

7

12/20/2010

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© 2010 MPS. All Rights Reserved.

OPERATION

The MP2492 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

MP2492 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 a 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.

The output current information is sensed via the

ISP and ISN pins. The sense voltage is set at

the power supply will be set by the FB pin. If

will pull down on SS and regulate the output at

a constant current.

EN

PWM

COMPARATOR

CURRENT

LIMIT

COMPARATOR

6pF

72.8pF

D

ISP

ISN

ENABLE

REGULATOR

4.0V

EN

SS

VIN

SS

FB

SW

OSCILLATOR

REFERENCE

X13.5

CURRENT SENSE

AMPLIFIER

-

BST

RAMP

GENERATOR

REGULATOR

POR

REGULATOR

100mV

DRIVER

RSEN

20mΩ

M1

6pF

2483kΩ

72.8pF

S

R

R

Q

ER

GND

100KHz

Figure 1—Function Block Diagram