LM3880EVAL - National Semiconductor

May 1, 2008

LM3880/LM3880Q

Power Sequencer

General Description

The LM3880 Power Sequencer offers the easiest method to

control power up and power down of multiple power supplies

(switchers or linear regulators). By staggering the startup se-

quence, it is possible to avoid latch conditions or large in-rush

currents that can affect the reliability of the system.

Available in a SOT23-6 package, the Power Sequencer con-

tains a precision enable pin and three open drain output flags.

Upon enabling the LM3880 the three output flags will sequen-

tially release, after individual time delays, permitting the con-

nected power supplies to startup. The output flags will follow

a reverse sequence during power down to avoid latch condi-

tions.

EPROM capability allows every delay and sequence to be

fully adjustable. Contact National Semiconductor if a non-

standard configuration is required.

Features

■Easiest method to sequence rails

■Power up and power down control

■Input voltage range of 2.7V to 5.5V

■Small footprint SOT23-6

■Low quiescent current of 25 µA

■Standard timing options available

■Customization of timing and sequence available through

factory programmability

■LM3880Q is AEC-Q100 Grade 1 qualified and is

manufactured on an Automotive Grade Flow

Applications

■Multiple supply sequencing

■Microprocessor / Microcontroller sequencing

■FPGA sequencing

■Automotive

Typical Application Circuit

20192601

LM3880/LM3880Q Power Sequencer

Connection Diagram

20192602

Top View

SOT23–6 Package

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

Nomenclature

20192603

Sequence Designator Table

Sequence Number Flag Order

Power Up Power Down

1 1 - 2 - 3 3 - 2 - 1

2 1 - 2 - 3 3 - 1 - 2

3 1 - 2 - 3 2 - 3 - 1

4 1 - 2 - 3 2 - 1 - 3

5 1 - 2 - 3 1 - 3 - 2

6 1 - 2 - 3 1 - 2 - 3

See timing diagrams for more information

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LM3880/LM3880Q

Timing Designator Table

Timing

Designator

td1 td2 td3 td4 td5 td6

AE 2ms 2ms 2ms 2ms 2ms 2ms

AA 10ms 10ms 10ms 10ms 10ms 10ms

AB 30ms 30ms 30ms 30ms 30ms 30ms

AC 60ms 60ms 60ms 60ms 60ms 60ms

AD 120ms 120ms 120ms 120ms 120ms 120ms

See timing diagrams for more information

LM3880 Ordering Information

Standard Parts for Order*

Order

Number

Timer settings Sequence

Order Supplied As Package

Type

NSC Package

Drawing

Package

Marking Feature

td1 to td6

LM3880MF-1AE 2ms 1 1k units T&R SOT23-6 MF06A F25A

LM3880MFX-1AE 2ms 1 3k units T&R SOT23-6 MF06A F25A

LM3880MFE-1AE 2ms 1 250 units T&R SOT23-6 MF06A F25A

LM3880MF-1AA 10ms 1 1k units T&R SOT23-6 MF06A F20A

LM3880MFX-1AA 10ms 1 3k units T&R SOT23-6 MF06A F20A

LM3880MFE-1AA 10ms 1 250 units T&R SOT23-6 MF06A F20A

LM3880MF-1AB 30ms 1 1k units T&R SOT23-6 MF06A F21A

LM3880MFX-1AB 30ms 1 3k units T&R SOT23-6 MF06A F21A

LM3880MFE-1AB 30ms 1 250 units T&R SOT23-6 MF06A F21A

LM3880MF-1AC 60ms 1 1k units T&R SOT23-6 MF06A F22A

LM3880MFX-1AC 60ms 1 3k units T&R SOT23-6 MF06A F22A

LM3880MFE-1AC 60ms 1 250 units T&R SOT23-6 MF06A F22A

LM3880MF-1AD 120ms 1 1k units T&R SOT23-6 MF06A F23A

LM3880MFX-1AD 120ms 1 3k units T&R SOT23-6 MF06A F23A

LM3880MFE-1AD 120ms 1 250 units T&R SOT23-6 MF06A F23A

LM3880QMFE-1AE 2ms 1 250 units T&R SOT23-6 MF06A F24A

AEC-Q100

Grade 1

qualified.

Automotive

Grade

Production

Flow**

LM3880QMF-1AE 2ms 1 1k units T&R SOT23-6 MF06A F24A

LM3880QMFX-1AE 2ms 1 3k units T&R SOT23-6 MF06A F24A

LM3880QMFE-1AA 10ms 1 250 units T&R SOT23-6 MF06A F27A

LM3880QMF-1AA 10ms 1 1k units T&R SOT23-6 MF06A F27A

LM3880QMFX-1AA 10ms 1 3k units T&R SOT23-6 MF06A F27A

LM3880QMFE-1AB 30ms 1 250 units T&R SOT23-6 MF06A F28A

LM3880QMF-1AB 30ms 1 1k units T&R SOT23-6 MF06A F28A

LM3880QMFX-1AB 30ms 1 3k units T&R SOT23-6 MF06A F28A

LM3880QMFE-1AC 60ms 1 250 units T&R SOT23-6 MF06A F29A

LM3880QMF-1AC 60ms 1 1k units T&R SOT23-6 MF06A F29A

LM3880QMFX-1AC 60ms 1 3k units T&R SOT23-6 MF06A F29A

LM3880QMFE-1AD 120ms 1 250 units T&R SOT23-6 MF06A F30A

LM3880QMF-1AD 120ms 1 1k units T&R SOT23-6 MF06A F30A

LM3880QMFX-1AD 120ms 1 3k units T&R SOT23-6 MF06A F30A

*Non-standard parts are available upon request. Please contact National Semiconductor for more information.

**Automotive Grade (Q) product incorporates enhanced manufacturing and support processes for the automotive market, including defect detection

methodologies. Reliability qualification is compliant with the requirements and temperature grades defined in the AEC-Q100 standard. Automotive grade products

are identified with the letter Q. For more information go to http://www.national.com/automotive.

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LM3880/LM3880Q

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

VCC −0.3V to +6.0V

EN, FLAG1, FLAG2, FLAG3 −0.3V to 6.0V

Max Flag 'ON' Current 50 mA

Storage Temperature Range −65°C to +150°C

Junction Temperature 150°C

Lead Temperature (Soldering, 5

sec.) 260°C

Minimum ESD Rating ±2 kV

Operating Ratings (Note 1)

VCC to GND 2.7V to 5.5V

EN, FLAG1, FLAG2, FLAG3 −0.3V to VCC + 0.3V

Junction Temperature −40°C to +125°C

Electrical Characteristics Specifications with standard typeface are for TJ = 25°C, and those in bold face type

apply over the full Operating Temperature Range (TJ = -40°C to +125°C). Minimum and Maximum limits are guaranteed through

test, design or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C and are provided for

reference purposes only. VCC = 3.3V, and limits apply to all timing options, unless otherwise specified.

Symbol Parameter Conditions Min

(Note 3)

Typ

(Note 4)

Max

(Note 3)

Unit

IQOperating Quiescent current 25 80 µA

Open Drain Flags

IFLAG FLAGx Leakage Current VFLAGx = 3.3V 1 20 nA

VOL FLAGx Output Voltage Low IFLAGx = 1.2mA 0.4 V

Power Up Sequence

td1 Timer delay 1 accuracy -15 15 %

2ms Timing Option -20 20

td2 Timer delay 2 accuracy -15 15 %

2ms Timing Option -20 20

td3 Timer delay 3 accuracy -15 15 %

2ms Timing Option -20 20

Power Down Sequence

td4 Timer delay 4 accuracy -15 15 %

2ms Timing Option -20 20

td5 Timer delay 5 accuracy -15 15 %

2ms Timing Option -20 20

td6 Timer delay 6 accuracy -15 15 %

2ms Timing Option -20 20

Timing Delay Error

(td(x) – 400 µs) / td(x+1) Ratio of timing delays For x = 1 or 4 95 105 %

For x = 1 or 4, 2ms option 90 110

td(x) / td(x+1) Ratio of timing delays For x = 2 or 5 95 105 %

For x = 2 or 5, 2ms option 90 110

ENABLE Pin

VEN EN pin threshold 1.0 1.25 1.4 V

IEN EN pin pull-up current VEN = 0V 7 µA

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

intended to be functional, but does not guarantee specific performance limits. For guaranteed specifications and conditions, see the Electrical Characteristics.

Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Note 3: Limits are 100% production tested at 25°. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control

(SQC) methods. The limits are used to calculate National's Average Outgoing Quality Level (AOQL).

Note 4: Typical numbers are at 25°C and represent the most likely parametric norm.

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LM3880/LM3880Q

Typical Performance Characteristics

Quiescent Current vs VCC

20192604

Quiescent Current vs Temperature (VCC = 3.3V)

20192605

Enable Threshold vs Temperature

20192606

Time Delay (30ms) vs VCC

20192607

Time Delay Ratio vs Temperature

20192608

Time Delay (30ms) vs Temperature

20192609

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LM3880/LM3880Q

FLAG VOL vs VCC

(RFLAG = 100 kΩ)

20192610

FLAG Voltage vs Current

20192611

Block Diagram

20192612

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LM3880/LM3880Q

Timing Diagrams (Sequence 1)

All standard options use this sequence for output flags rise and fall order.

20192613

Power Up Sequence

20192614

Power Down Sequence

Application Information

OVERVIEW

The LM3880 Power Sequencer provides an easy solution for

sequencing multiple rails in a controlled manner. Six inde-

pendent timers are integrated to control the timing sequence

(power up and power down) of three open drain output flags.

These flags permit connection to either a shutdown / enable

pin of linear regulators and switchers to control the power

supplies’ operation. This allows a complete power system to

be designed without worrying about large in-rush currents or

latch-up conditions that can occur.

The timing sequence of the LM3880 is controlled entirely by

the enable (EN) pin. Upon power up, all the flags are held low

until this precision enable is pulled high. After the EN pin is

asserted, the power up sequence will commence. An internal

counter will delay the first flag (FLAG1) from rising until a fixed

time period has expired. Upon the release of the first flag an-

other timer will begin to delay the release of the second flag

(FLAG2). This process repeats until all three flags have se-

quentially been released. The three timers that control the

delays are all independent of each other and can be individ-

ually programmed if needed. (See custom sequencer sec-

tion).

The power down sequence is the same as power-up, but in

reverse. When EN pin is de-asserted a timer will begin that

delays the third flag (FLAG3) from pulling low. The second

and first flag will then follow in a sequential manner after their

appropriate delays. The three timers that are used to control

the power down scheme can also be individually programmed

and are completely independent of the power up timers.

Additional sequence patterns are also available in addition to

customizable timers. For more information see the custom

sequencer section.

PART OPERATION

The timing sequence of the LM3880 is controlled by the as-

sertion of the enable signal. The enable pin is designed with

an internal comparator, referenced to a bandgap voltage

(1.25V), to provide a precision threshold. This allows a de-

layed timing to be externally set using a capacitor or to start

the sequencing based on a certain event, such as a line volt-

age reaching 90% of nominal. For an additional delayed

sequence from the rail powering VCC, simply attach a ca-

pacitor to the EN pin as shown below.

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LM3880/LM3880Q

20192615

Cap Timing

Using the internal pull-up current source to charge the exter-

nal capacitor (CEN) the enable pin delay can be calculated by

the equation below:

A resistor divider can also be used to enable the LM3880

based on a certain voltage threshold. Care needs to be taken

when sizing the resistor divider to include the effects of the

internal current source.

One of the features of the enable pin is that it provides glitch

free operation. The first timer will start counting at a rising

threshold, but will always reset if the enable pin is de-asserted

before the first output flag is released. This can be shown in

the timing diagram below:

20192617

EN Glitch

If the enable signal remains high for the entire power-up se-

quence, then the part will operate as shown in the standard

timing diagrams. However, if the enable signal is de-asserted

before the power-up sequence is completed the part will enter

a controlled shutdown. This allows the system to walk through

a controlled power cycling, preventing any latch conditions

from occuring. This state only occurs if the enable pin is de-

asserted after the completion of timer 1, but before the entire

power-up sequence is completed.

When this event occurs, the falling edge of enable pin resets

the current timer and will allow the remaining power-up cycle

to complete before beginning the power down sequence. The

power down sequence starts approximately 120ms after the

final power-up flag. This allows output voltages in the system

to stabilize before everything is shutdown. An example of this

operation can be seen below:

20192618

Incomplete Sequence

All the internal timers are generated by a master clock that

has an extremely low tempco. This allows for tight accuracy

across temperature and a consistent ratio between the indi-

vidual timers. There is a slight additional delay of approxi-

mately 400 µs to timers 1 and 4 which is a result of the

EPROM refresh. This refresh time is in addition to the pro-

grammed delay time and will be almost insignificant to all but

the shortest of timer delays.

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LM3880/LM3880Q

CUSTOM SEQUENCER

The LM3880 Power Sequencer is based on a CMOS process

utilizing an EPROM that has the capability to be custom pro-

grammed at the factory. Approximately 500,000,000 different

options are available allowing even the most complex system

to be simply sequenced. Because of the vast options that are

possible, customization is limited to orders of a certain quan-

tity. Please contact National Semiconductor for more infor-

mation.

The variables that can be programmed include the six delay

timers and the reverse sequence order. For the timers, each

can be individually selected from one of the timer selector

columns in the table shown below. However, all six time de-

lays must be from the same column.

Timer Options 1 Timer Options 2 Timer Options 3 Timer Options 4

0000

2468

4 8 12 16

6 12 18 24

8 16 24 32

10 20 30 40

12 24 36 48

14 28 42 56

16 32 48 64

18 36 54 72

20 40 60 80

22 44 66 88

24 48 72 96

26 52 78 104

28 56 84 112

30 60 90 120

All times listed are in milliseconds

The sequencing order for power up is always controlled by

layout. The flag number translates directly into the sequence

order during power up (ie FLAG1 will always be first). How-

ever, for some systems a different power down order could

be required. To allow flexibility for this aspect in a design, the

Power Sequencer incorporates six different options for con-

trolling the power down sequence. These options can be seen

in the timing diagrams on the next page. This ability can be

programmed in addition to the custom timers.

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LM3880/LM3880Q

20192619

Power Down Sequence Options

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LM3880/LM3880Q

Physical Dimensions inches (millimeters) unless otherwise noted

SOT23-6 Package

NS Package Number MF06A

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LM3880/LM3880Q

Notes

LM3880/LM3880Q Power Sequencer

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