Datasheet LM3722, LM3723, LM3724 (Texas Instruments) - 9

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LM3722 , LM3723, LM3724 www.ti.com
SNVS154E – MAY 2001 – REVISED MARCH 2013
NEGATIVE-GOING VCC TRANSIENTS
The LM3722/LM3723/LM3724 are relatively immune to short negative-going transients or glitches on VCC. Figure 14 shows the maximum pulse width a negative-going VCC transient can have without causing a reset pulse. In general, as the magnitude of the transient increases, going further below the threshold, the maximum allowable pulse width decreases. Typically, a VCC transient that goes 125 mV below the reset threshold and lasts 40 µs or less will not cause a reset pulse. A 0.1 µF bypass capacitor mounted as close as possible to the VCC pin will provide additional transient rejection. 600 500 400 (mV) ve ri 300 rd ve O 200 100 0 0 20 40 60 80 100 120 140 160 180 200 Max Transient Duration (Ps)
Figure 14. Maximum Transient Duration without Causing a Reset Pulse vs. Reset Comparator Overdrive INTERFACING TO µPS WITH BIDIRECTIONAL RESET PINS
Microprocessors with bidirectional reset pins, such as the Motorola 68HC11 series, can be connected to the LM3722 RESET output. To ensure a correct output on the LM3722 even when the microprocessor reset pin is in the opposite state, connect a 4.7kΩ resistor between the LM3722 RESET output and the µP reset pin, as shown in Figure 15. Buffer the LM3722 RESET output to other system components.
Typical Application Circuits Figure 15. Interfacing to Microprocessors with Bidirectional Reset I/O
Copyright © 2001–2013, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM3722 LM3723 LM3724 Document Outline FEATURES APPLICATIONS DESCRIPTION Typical Application Circuits Connection Diagram Absolute Maximum Ratings Electrical Characteristics Typical Performance Characteristics Timing Diagram Circuit Information RESET OUTPUT RESET THRESHOLD MANUAL RESET INPUT (MR) Applications Information BENEFITS OF PRECISION RESET THRESHOLDS ENSURING A VALID RESET OUTPUT DOWN TO VCC = 0V OPEN DRAIN OUTPUT (LM3724) NEGATIVE-GOING VCC TRANSIENTS INTERFACING TO µPS WITH BIDIRECTIONAL RESET PINS Typical Application Circuits Revision History