MP1423 データシートの表示（PDF） - Monolithic Power Systems

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MP1423

3A, 23V, 385KHz Step-Down Converter

Monolithic Power Systems 

TM

MP1423 – 3A, 23V, 385KHz STEP-DOWN CONVERTER

PIN FUNCTIONS (continued)

Pin # Name Description

Compensation Node. COMP is used to compensate the regulation control loop. Connect a

6 COMP series RC network from COMP to GND to compensate the regulation control loop. In some

cases, an additional capacitor from COMP to GND is required. See Compensation

7

EN

Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on the

regulator, low to turn it off. For automatic startup, leave EN unconnected.

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

8

SS to set the soft-start period. A 0.1µF capacitor sets the soft-start period to 10ms. To disable the

soft-start feature, leave SS unconnected.

OPERATION

The MP1423 is a current-mode step-down

regulator. It regulates input voltages from 6V to

23V down to an output voltage as low as

1.222V, and is able to supply up to 3A of load

current.

The MP1423 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 switch

current measured internally 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 while 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 to fully charge the BS.capacitor.

IN 2

EN 7

INTERNAL

REGULATORS

OSCILLATOR

SLOPE

COMP

40/385KHz

CLK

+

0.7V --

--

SHUTDOWN

COMPARATOR

LOCKOUT

COMPARATOR

2.37V/

2.71V

+

+

--

CURRENT

SENSE

AMPLIFIER

+

--

+

SQ

RQ

--

CURRENT

COMPARATOR

1.8V

FREQUENCY

FOLDBACK

COMPARATOR

-- 0.7V 1.222V + ERROR

AMPLIFIER

5 FB

6 COMP 8 SS

Figure 1—Functional Block Diagram

5V

1 BS

3 SW

4 GND

MP1423_BD01

MP1423 Rev. 1.1

www.MonolithicPower.com

4

1/6/2006

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2006 MPS. All Rights Reserved.

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