MP28368 – 1.8A, 24V, 1.4MHz STEP-DOWN CONVERTER

MP28368 Rev. 0.9

www.MonolithicPower.com

3

12/13/2007

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TM

PIN FUNCTIONS

Pin #

Name Description

1, 8

NC

No Connect.

2

SW

Switch Output.

3

IN

Supply Voltage. The MP28368 operates from a +4.5V to +24V unregulated input. C1 is needed

to prevent large voltage spikes from appearing at the input.

4

EN

On/Off Control Input. Pull above 1.2V to turn the device on.

5

FB

Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets the

output voltage. To prevent current limit run away during a short circuit fault condition the

frequency foldback comparator lowers the oscillator frequency when the FB voltage is below

250mV.

6

GND

Ground. This pin is the voltage reference for the regulated output voltage. For this reason care

must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to

prevent switching current spikes from inducing voltage noise into the part.

7

BST

Bootstrap. This capacitor is needed to drive the power switch’s gate above the supply voltage. It

is connected between SW and BST pins to form a floating supply across the power switch

driver.

TYPICAL PERFORMANCE CHARACTERISTICS

Efficiency vs

Load Currents

Current Limit vs

Duty Cycle

100

90

80

70

60

50

40

LOAD CURRENT (A)

100

90

80

70

60

50

40

0

1.0

0.5

1.5

2.0

2.5

LOAD CURRENT (A)

Efficiency vs

Load Current

0

1.0

0.5

1.5

2.0

2.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

DUTY CYCLE (%)

040

20

60

80

100