MP1583 – 3A, 23V, 385KHz STEP-DOWN CONVERTER

MP1583 Rev. 3.1

www.MonolithicPower.com

5

6/20/2011

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2011 MPS. All Rights Reserved.

Pin #

Name Description

7

EN

Enable/UVLO. A voltage greater than 2.71V enables operation. For complete low

current shutdown the EN pin voltage needs to be at less than 900mV. When the

voltage on EN exceeds 1.2V, the internal regulator will be enabled and the soft-start

capacitor will begin to charge. The MP1583 will start switching after the EN pin

voltage reaches 2.71V. There is 7V zener connected between EN and GND. If EN is

driven by external signal, the voltage should never exceed 7V.

8

SS

Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to

set the soft-start period. To disable the soft-start feature, leave SS unconnected.

OPERATION

The MP1583 is a current-mode step-down

regulator. It regulates input voltages from 4.75V to

23V down to an output voltage as low as 1.222V,

and is able to supply up to 3A of load current.

The MP1583 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 RC 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 SW is

low in order to fully charge the BS capacitor.

LOCKOUT

COMPARATOR

ERROR

AMPLIFIER

FREQUENCY

FOLDBACK

COMPARATOR

GM = 800

μ A/V

INTERNAL

REGULATORS

1

μ A

7V

1.8V

SLOPE

COMP

CLK

CURRENT

COMPARATOR

CURRENT

SENSE

AMPLIFIER

SHUTDOWN

COMPARATOR

SS

8

COMP

6

IN 2

EN 7

GND

4

OSCILLATOR

40/385KHz

S

R

Q

SW

3

BS

1

5V

+

Σ

Q

1.2V

+

+

2.54V

+

1.222V

0.7V

+

+

FB

5

--

--

--

--

--

--

Figure 1—Functional Block Diagram