MP1593 – 3A, 28V, 385KHz STEP-DOWN CONVERTER

MP1593 Rev. 1.9

www.MonolithicPower.com

5

9/14/2006

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2006 MPS. All Rights Reserved.

OPERATION

LOCKOUT

COMPARATOR

ERROR

AMPLIFIER

FREQUENCY

FOLDBACK

COMPARATOR

INTERNAL

REGULATORS

1.8V

SLOPE

COMP

CLK

CURRENT

COMPARATOR

CURRENT

SENSE

AMPLIFIER

SHUTDOWN

COMPARATOR

SS

8

COMP

6

IN 2

EN 7

GND

4

OSCILLATOR

45/385KHz

S

R

Q

SW

3

BS

M1

M2

1

5V

+

Q

1.2V

+

+

2.60V/

2.39V

+

1.22V

0.7V

+

+

FB

5

--

--

--

--

--

--

Figure 1—Functional Block Diagram

The MP1593 is a current-mode step-down

regulator. It regulates input voltages from 4.75V to

28V down to an output voltage as low as 1.22V,

and is able to supply up to 3A of continuous load

current.

The MP1593 uses current-mode control to

regulate the output voltage. The output voltage

is measured at FB through a resistive voltage

divider and amplified through the internal error

amplifier.

The

output

current

of

the

transconductance error amplifier is presented at

COMP where a network compensates the

regulation control system. The voltage at COMP

is compared to the internally measured switch

current to control the output voltage.

The converter uses an internal N-Channel

MOSFET switch to step-down the input voltage

to the regulated output voltage. Since the

MOSFET requires a gate voltage greater than

the input voltage, a boost capacitor connected

between SW and BS drives the gate. The

capacitor is internally charged when SW is low.

An internal 10Ω switch from SW to GND is used

to insure that SW is pulled to GND when it is

low to fully charge the BS capacitor.