Datasheet LM3880EVAL Datasheet (NSC)

LM3880 Power Sequencer
Demo Board

National Semiconductor
Application Note 1491
Chance Dunlap
November 2006

Introduction

The LM3880 evaluation board has been designed to permit
the designer to connect it directly to the power supplies of an
existing system to enable sequencing. Upon enabling the de­vice the three open drain output flags will rise in sequential
order, 1-2-3. Once the part is disabled, the shutdown se­quence will occur in reverse order 3-2-1. Therefore the last
power supply that started up, will be the first to shutdown. The
evaluation board contains the LM3880MF-1-AB device which

has been factory set, so that each time delay between flags
will be 30ms. Several different timing options are available as
standard off the shelf parts, but if a custom timing or shutdown
sequence is needed please contact National Semiconductor.
The LM3880 has an internal EPROM that can be factory pro­grammed to allow almost any sequencing combination to
occur. Please refer to the datasheet for programming possi­bilities.

Timing Sequence

The LM3880 demoboard timing sequence of the output flags
is shown below:

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LM3880 Power Sequencer Demo Board AN-1491

Schematic

The LM3880 demoboard has been designed with the pullup
resistors on board to permit connection to an enable pin of a

switcher. The demoboard can accommodate an input voltage
from +2.7V to +5.5V.

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Bill of Materials

Designator Description Part # Quantity Manufacturer

U1 LM3880, Sequence 1, 30ms timing LM3880MF-1-AB 1 NSC

R1 100K Resistor, 0603 CRCW0603100KFKEA 1 Vishay

R2 100K Resistor, 0603 CRCW0603100KFKEA 1 Vishay

R3 100K Resistor, 0603 CRCW0603100KFKEA 1 Vishay

Pin-Out

The pin-out and pin description of the LM3880 is shown be­low.

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Pin Descriptions

Pin # Name Function

1 VCC Input supply

2 GND Ground

3 EN Precision enable pin

4 FLAG3 Open drain output #3

5 FLAG2 Open drain output #2

6 FLAG1 Open drain output #1

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Layout

The demoboard layout is based on a small 0.8” x 1.0” FR4 demoboard with 2 layers of copper. The actual layout can be seen
below. When looking at the board, pin 1 on the LM3880 is the top left.

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LM3880 Top Layer

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LM3880 Bottom Layer

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Notes

AN-1491 LM3880 Power Sequencer Demo Board

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