Product details


Number of supplies monitored 4 Threshold voltage 1 (Typ) (V) 1.8 Features Negative voltage monitoring, Undervoltage and overvoltage monitor, Wide input voltage Reset threshold accuracy (%) 1.5 Output driver type/reset output Active-low, Open-drain Time delay (ms) Programmable Rating Catalog Watchdog timer WDI (sec) None Operating temperature range (C) 0 to 70 open-in-new Find other Supervisor & reset ICs

Package | Pins | Size

SOIC (DW) 18 119 mm² 11.55 x 10.3 open-in-new Find other Supervisor & reset ICs


  • Inputs for Monitoring up to Four Separate Supply Voltage Levels
  • Internal Inverter for Sensing a Negative Supply Voltage
  • Line/Switch Sense Input for Early Power Source Failure Warning
  • Programmable Under- and Over-Voltage Fault Thresholds with Proportional Hysteresis
  • A Precision 2.5-V Reference
  • General Purpose Op-Amp for Auxiliary Use
  • Three High Current, >3 0mA, Open-Collector Outputs Indicate Over-Voltage, Under-Voltage and Power OK Conditions
  • 8-V to 40-V Supply Operation with 7-mA Stand-By Current

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The UC1903 family of quad supply and line monitor integrated circuits will respond to under- and over-voltage conditions on up to four continuously monitored voltage levels. An internal op-amp inverter allows at least one of these levels to be negative. A separate line/switcher sense input is available to provide early warning of line or other power source failures.

The fault window adjustment circuit on these devices provides easy programming of under- and over-voltage thresholds. The thresholds, centered around a precision 2.5-V reference, have an input hysteresis that scales with the window width for precise, glitch-free operation. A reference output pin allows the sense input fault windows to be scaled independently using simple resistive dividers.

The three open collector outputs on these devices sink in excess of 30 mA of load current when active. The under- and over-voltage outputs respond after separate, user defined, delays to respective fault conditions. The third output is active during any fault condition including under- and over-voltage, line/switcher faults, and input supply under-voltage. The off state of this output indicates a "power OK" situation.

An additional, uncommitted, general purpose op-amp is also included. This op-amp, capable of sourcing 20 mA of output current, can be used for a number of auxiliary functions including the sensing and amplification of a feedback error signal when the 2.5-V output is used as a system reference.

These parts operate over an 8-V to 40-V input supply range and require a typical stand-by current of only 7 mA.

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Technical documentation

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Type Title Date
* Data sheet Quad Supply and Line Monitor datasheet (Rev. A) Aug. 26, 2008
Application note Optimizing Resistor Dividers at a Comparator (Rev. B) Apr. 30, 2021
E-book Voltage Supervisor and Reset ICs: Tips, Tricks and Basics Jun. 28, 2019
Application note Choosing an Appropriate Pull-up/Pull-down Resistor for Open Drain Outputs Sep. 19, 2011
Application note DN-33 Optocoupler Feedback Drive Techniques Using the UC3901 and UC3903 Sep. 05, 1999

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