NSC LM3880EVAL Datasheet

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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