MP38900/MP38900-B–HIGHEFFICIENCY,FASTTRANSIENTSYNCHRONOUSSTEP-DOWNCONVERTER

MP38900/MP38900-B Rev. 1.1

www.MonolithicPower.com

6

6/25/2012

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© 2012 MPS. All Rights Reserved.

PIN FUNCTIONS

Pin #

Name

Description

1

AGND

Analog Ground.

2

FREQ

Frequency Set during CCM operation. The ON period is determined by the input

voltage and the frequency-set resistor connected to FREQ pin. Connect a resistor

to IN for line feed-forward. Decouple with a 1nF capacitor.

3

FB

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

pin, sets the output voltage.

4

SS

Soft Start. Connect an external SS capacitor to program the soft start time for the

switch mode regulator. When the EN pin becomes high, an internal current source

(8.5μA) charges up the SS capacitor and the SS voltage slowly ramps up from 0 to

source (8.5μA) discharges the SS capacitor and the SS voltage slowly ramps

down. For MP38900-B, SS will pull low as soon as EN goes low.

5

EN

EN=1 to enable the MP38900/MP38900-B. For automatic start-up, connect EN pin

to IN with a 100kΩ resistor. It includes an internal 1MΩ pull-down resistor.

6

PGOOD

Power Good Output. The output of this pin is an open drain and is high if the

output voltage is higher than 90% of the nominal voltage. There is delay from FB ≥

90% to PGOOD high, which is 50% of SS time plus 0.5ms. For MP38900-B, the

delay is fixed as 1.5ms.

7

BST

Bootstrap. A capacitor connected between SW and BS pins is required to form a

floating supply across the high-side switch driver.

8, 19

IN

Supply Voltage. The MP38900/MP38900-B operates from a +4.5V to +16V input

rail. C1 is needed to decouple the input rail. Use wide PCB traces and multiple vias

to make the connection.

9, 10, 17, 18

SW

Switch Output. Use wide PCB traces and multiple vias to make the connection.

11-16

PGND

System Ground. This pin is the reference ground of the regulated output voltage.

For this reason care must be taken in PCB layout.

20

VCC

MP38900: External 5V Supply. This 5V supply has to be applied in order to bias

the device. Decouple with a 1µF capacitor as close to this pin as possible.

MP38900-B: Internal 5V supply. Decouple with a 1μF capacitor as close to this pin

as possible.