MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER

MP1570 Rev. 1.5

www.MonolithicPower.com

4

1/31/2006

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© 2006 MPS. All Rights Reserved.

TM

PIN FUNCTIONS

Pin #

Name

Description

1

BS

High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET

switch. Connect a 0.01µF or greater capacitor from SW to BS to power the high side switch.

2

IN

Power Input. IN supplies the power to the IC, as well as the step-down converter switches.

Drive IN with a 4.75V to 23V power source. Bypass IN to GND with a suitably large capacitor

to eliminate noise on the input to the IC. See Input Capacitor.

3

SW

Power Switching Output. SW is the switching node that supplies power to the output. Connect

the output LC filter from SW to the output load. Note that a capacitor is required from SW to

BS to power the high-side switch.

4

GND

Ground (Connect Exposed Pad to Pin 4)

5

FB

Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a

resistive voltage divider from the output voltage. The feedback threshold is 1.230V. See

Setting the Output Voltage

.

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

Components.

7

EN

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

the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic startup.

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 20ms. To disable the

soft-start feature, leave SS unconnected.

BLOCK DIAGRAM

MP1570_BD01

LOCKOUT

COMPARATOR

INTERNAL

REGULATORS

IN

EN

+

ERROR

AMPLIFIER

1.2V

OVP

RAMP

CLK

1.23V

0.3V

CURRENT

COMPARATOR

CURRENT

SENSE

AMPLIFIER

1.5V

SHUTDOWN

COMPARATOR

7

COMP 6

SS 8

FB 5

GND

4

OSCILLATOR

100/340KHz

S

R

Q

SW

3

BS

1

IN

5V

2

OVP

IN < 4.05V

EN OK

+

Q

LATCH

+

+

1.5V

+

+

2.5V

+

+

Figure 1—Functional Block Diagram