Analog Devices Inc./Maxim Integrated MAX821PUS

Overview

MAX821PUS from Maxim Integrated is an active-low microprocessor supervisory IC in SOT-143 package, designed to monitor +3V to +5V power supplies and assert a guaranteed logic-low RESET signal down to VCC = 1V. It provides pin-selectable reset timeout delays of 1ms (max), 20ms (min), or 100ms (min) and draws only 2.5µA supply current. Used in portable equipment and critical µP power monitoring where low quiescent current and robust brownout detection are required.

For engineers reviewing the MAX821PUS datasheet, MAX821PUS pinout, MAX821PUS application, or MAX821PUS equivalent, key selection considerations include its 4.00V nominal reset threshold, guaranteed RESET validity at VCC ≥ 1V, SRT pin-programmable timeout, -40°C to +125°C operation, and immunity to fast VCC transients.

Technical Context

The MAX821PUS implements a precision voltage comparator with 30ppm/°C tempco to detect VCC falling below its factory-trimmed 4.00V threshold. Its internal timer initiates on VCC rise above threshold and holds RESET low for the delay selected by SRT pin state (GND/VCC/unconnected).

Reset assertion is immune to transients ≤12µs when VCC dips 100mV below threshold; the device guarantees correct RESET state over full temperature range without external components, and operates with VCC as low as 1V while maintaining sink capability on RESET.

Key Specifications

Pinout & Package

SOT-143 (4-pin) surface-mount package with 1.3mm × 1.3mm footprint and 0.95mm height; lead-free option available (MAX821PUS+).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor supervisory applications.

Compared with MAX822PUS, the MAX821PUS provides identical supervision accuracy and temperature range but delivers active-low reset compatible with legacy µPs. Against TPS3808G01DBVR, it trades slightly higher ICC for field-programmable timeout-critical for systems needing configurable boot sequencing or brownout recovery timing.

Availability

MAX821PUS is available at Aetrix Electronics and suitable for portable equipment, industrial controllers, and critical µP power monitoring requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX821PUS includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) is a semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for industrial, automotive, communications, and computing markets.

The MAX821/MAX822 product line was engineered specifically for reliable, low-cost microprocessor supervision in space-constrained and battery-sensitive applications-emphasizing zero external components, guaranteed low-VCC reset behavior, and robust transient immunity.

FAQ

What is the exact reset threshold voltage for MAX821PUS and how is it trimmed?

The MAX821PUS has a nominal reset threshold of 4.00V, with guaranteed min/max values of 3.91V and 4.09V over temperature. This threshold is factory laser-trimmed during wafer test to achieve ±1.25% initial accuracy and 30ppm/°C temperature coefficient, ensuring stable operation without external calibration or adjustment across -40°C to +125°C.

How does the SRT pin configure the reset timeout delay on MAX821PUS?

The SRT pin on MAX821PUS selects one of three timeout modes: connect to GND for 1ms (maximum), connect to VCC for 20ms (minimum), or leave unconnected for 100ms (minimum). Capacitive loading on SRT must remain below 200pF when open to prevent unintended shorter timeouts due to parasitic charging.

Can MAX821PUS operate reliably when VCC drops below 2.0V?

Yes - the MAX821PUS guarantees correct RESET output state (low) for VCC down to 1.0V, and continues monitoring until VCC falls below that point. Below 1.0V, the RESET output becomes high-impedance, so a 100kΩ pull-down resistor is recommended if valid logic-low state is required all the way to 0V.

What is the maximum VCC transient duration the MAX821PUS can ignore without asserting reset?

At a 100mV comparator overdrive (i.e., VCC dipping 100mV below the 4.00V threshold), the MAX821PUS typically ignores transients ≤12µs. Immunity decreases as overdrive increases - for example, a 200mV dip allows only ~5µs. A 0.1µF bypass capacitor near VCC further enhances noise rejection.

Does MAX821PUS require external components to function in a typical application?

No - the MAX821PUS requires no external resistors, capacitors, or diodes to perform core supervision. Only a pull-up resistor on the open-drain RESET pin is needed for proper logic-level translation. All timing, threshold accuracy, and temperature compensation are integrated, enabling true "single-chip" reset solution in SOT-143.