LM3708/LM3709

Microprocessor Supervisory Circuits with Low Line

Output, Manual Reset and Watchdog Timer

General Description

The LM3708/LM3709 series of microprocessor supervisory

circuits provide the maximum flexibility for monitoring power

supplies and battery controlled functions in systems without

backup batteries. The LM3708/LM3709 series are available

in a 9-bump micro SMD package.

Built-in features include the following:

Reset: Reset is asserted during power-up, power-down, and

brownout conditions. RESET is guaranteed down to V

1.0V.

Manual Reset Input: An input that asserts reset when pulled

low.

Low Line Output: This early power failure warning indicator

goes low when the supply voltage drops to a value which is

2% higher than the reset threshold voltage.

Watchdog Timer: The WDI (Watchdog Input) monitors one of

the µP’s output lines for activity. If no output transition occurs

during the watchdog timeout period, reset is activated.

Features

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Standard Reset Threshold voltage: 3.08V

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Custom Reset Threshold voltages: For other voltages

between 2.2V and 5.0V in 10mV increments, contact

National Semiconductor Corp.

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No external components required

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Manual-Reset input

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RESET (LM3708) or RESET (LM3709) outputs

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Precision supply voltage monitor

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Factory programmable Reset and Watchdog Timeout

Delays

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Available in micro SMD package for minimum footprint

0.5% Reset threshold accuracy at room temperature

2% Reset threshold accuracy over temperature

extremes

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Reset assertion down to 1V V

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28 µA V

Applications

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Embedded Controllers and Processors

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Intelligent Instruments

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Automotive Systems

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Critical µP Power Monitoring

Typical Application

20011703

June 2002

© 2002 National Semiconductor Corporation

DS200117

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