MP1580 – 2A, 380KHz STEP-DOWN CONVERTER

MP1580 Rev. 3.0

www.MonolithicPower.com

4

12/5/2005

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2005 MPS. All Rights Reserved.

TM

OPERATION

The MP1580 is a current mode regulator; the

COMP pin voltage is proportional to the peak

inductor current. At the beginning of a cycle: the

upper transistor M1 is off; the lower transistor

M2 is on (refer to Figure 1); the COMP pin

voltage is higher than the current sense

amplifier output and the current comparator’s

output is low. The rising edge of the 380KHz

CLK signal sets the RS Flip-Flop. Its output

turns off M2 and turns on M1, 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 COMP pin

voltage, the RS Flip-Flop is reset and the

MP1580 reverts to its initial M1 off, M2 on,

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 1.222V bandgap reference. The polarity is

such that an FB pin voltage less than 1.222V

increases the COMP pin voltage. Since the

COMP pin voltage is proportional to the peak

inductor current, an increase in its voltage

increases the current delivered to the output.

The lower 10Ω switch ensures that the

bootstrap capacitor voltage is charged during

light load conditions. An external Schottky

Diode D1 carries the inductor current when M1

is off (see Figure 1).

MP1580_BD01

LOCKOUT

COMPARATOR

ERROR

AMPLIFIER

FREQUENCY

FOLDBACK

COMPARATOR

INTERNAL

REGULATORS

1.8V

SLOPE

COMP

CLK

CURRENT

COMPARATOR

CURRENT

SENSE

AMPLIFIER

SHUTDOWN

COMPARATOR

COMP

6

IN 2

EN 7

SYNC 8

GND

4

OSCILLATOR

40/380kHz

S

R

Q

SW

3

BS

1

5V

+

Q

0.7V

+

+

2.285V/

2.495V

+

1.222V

0.7V

+

+

FB

5

--

--

--

--

--

--

Figure 1—Functional Block Diagram