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

MP1423 Rev. 1.1

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4

1/6/2006

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© 2006 MPS. All Rights Reserved.

TM

PIN FUNCTIONS (continued)

Pin #

Name

Description

6

COMP

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

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.

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. 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.

MP1423_BD01

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

40/385KHz

S

R

Q

SW

3

BS

1

5V

+

Q

0.7V

+

+

2.37V/

2.71V

+

1.222V

0.7V

+

+

FB

5

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Figure 1—Functional Block Diagram