4-Pin, µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay

4-Pin SOT Reset ICs with Selectable Reset Timeout Delay

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The MAX821/MAX822 microprocessor (µP) supervisory circuits monitor power supplies in µP and digital systems. They provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 5V-powered or 3V-powered circuits. The MAX821/MAX822 also provide a power-on reset timeout delay that is pin selectable to 1ms (max), 20ms (min), or 100ms (min).

These devices perform a single function: they assert a reset signal whenever the VCC supply voltage falls below a preset threshold, and they keep reset asserted for the pin-selected reset timeout delay after VCC has risen above the reset threshold. The only difference between the two devices is that the MAX821 has an active-low RESET output (which is guaranteed to be in the correct state for VCC down to 1V), while the MAX822 has an active-high RESET output. The reset comparator is designed to ignore fast transients on VCC. Reset thresholds suitable for operation with a variety of supply voltages are available.

Low supply current makes the MAX821/MAX822 ideal for use in portable equipment. These devices come in a 4-pin SOT143 package.
MAX821, MAX821L, MAX821M, MAX821P, MAX821R, MAX821S, MAX821T, MAX821U, MAX822, MAX822L, MAX822M, MAX822R, MAX822S, MAX822T: Typical Operating Circuit MAX821, MAX821L, MAX821M, MAX821P, MAX821R, MAX821S, MAX821T, MAX821U, MAX822, MAX822L, MAX822M, MAX822R, MAX822S, MAX822T: Typical Operating Circuit Enlarge+

Key Features

  • Pin-Selectable, Precision Power-On Reset Delay: 1ms (max), 20ms (min), or 100ms (min)
  • Precision Monitoring of +3V to +5V Power-Supply Voltages
  • 2.5µA Supply Current
  • Guaranteed Over Temperature (-40°C to +125°C)
  • Guaranteed Active-Low RESET Valid to VCC = 1V (MAX821)
  • Power-Supply Transient Immunity
  • No External Components
  • SOT143 Package


  • Bar-Code Scanners
  • Computers: Desktop, Workstation, Server
  • Controllers
  • Critical µP and µC Power Monitoring
  • Intelligent Instruments
  • Portable Battery-Powered Equipment

See parametric specs for Supervisors (1 Monitored Voltage) (252)

Part NumberReset Thresh.
Reset OuttRESETWatchdog FeatureReset Thresh. Accur.
min@ +25°CmaxSee Notes
2.5 to 3.3
3.3 to 5.5
Active Low
15ms to 85ms
85ms to 300ms
No Watchdog1.57
$1.38 @1k
Active High
$1.43 @1k

Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.
Request Reliability Report for: MAX822 
Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C   Material Composition  

Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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