Analog Devices Inc./Maxim Integrated MAX6421XS23

Overview

MAX6421XS23 from Maxim Integrated is a low-power microprocessor reset supervisor IC in SC70-4 package, featuring active-low push-pull RESET output, 2.3V ±2.5% factory-trimmed reset threshold, capacitor-adjustable reset timeout (275µs to >100ms), and guaranteed operation down to VCC = 1V. It monitors system supply voltage during power-up, brownout, and power-down in portable battery-powered controllers.

For engineers reviewing the MAX6421XS23 datasheet, MAX6421XS23 pinout, MAX6421XS23 application, or MAX6421XS23 equivalent, key selection criteria include reset threshold accuracy over temperature, SRT capacitor-based timeout tuning, quiescent current at ultra-low VCC, immunity to sub-100µs VCC transients, and compatibility with 1.6V–5V system rails.

Technical Context

The MAX6421XS23 implements a precision bandgap-based voltage detector with 2.3V nominal reset threshold, ±2.5% tolerance over –40°C to +125°C, and 4mV hysteresis. Its internal 240nA current source charges an external capacitor on the SRT pin to generate a programmable reset timeout period.

Reset assertion occurs when VCC falls below the threshold; deassertion follows after the SRT capacitor ramps to 0.65V, ensuring deterministic delay independent of VCC slew rate. The push-pull output drives low with VOL ≤ 0.4V at 3.2mA sink and high with VOH ≥ 0.8×VCC at 800µA source, valid for VCC ≥ 1.0V.

Key Specifications

Pinout & Package

MAX6421XS23 is housed in a 4-pin SC70-4 package (outline 21-0098), footprint-compatible with SOT143-4. Pin 1 is SRT (Set Reset Timeout), Pin 2 is GND, Pin 3 is RESET (active-low push-pull), and Pin 4 is VCC.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6421US23-T, MAX6421XS23 offers identical functionality in a 30% smaller SC70 footprint with improved high-frequency layout stability; versus TPS3808G23DBVR, it trades fixed ultra-low ICC for field-programmable timeout and push-pull simplicity-critical for cost-sensitive, space-constrained embedded systems.

Availability

MAX6421XS23 is available at Aetrix Electronics and suitable for portable medical sensors, battery-powered industrial controllers, automotive body control modules, and smart energy meters requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX6421XS23 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) designs precision analog and mixed-signal ICs for power, sensing, and interface applications in industrial, automotive, and computing markets.

The MAX6421XS23 belongs to Maxim's low-power µP supervisor family, engineered specifically for reliable reset generation in battery-constrained and thermally demanding embedded systems where voltage margin is minimal.

FAQ

What is the exact reset threshold voltage of MAX6421XS23 and how tightly is it specified?

The MAX6421XS23 has a factory-trimmed nominal reset threshold of 2.3V, with guaranteed accuracy of ±2.5% over the full operating temperature range of –40°C to +125°C. This specification is confirmed in the Electrical Characteristics table of the official datasheet (Rev 5, Dec 2013), and applies directly to the MAX6421XS23 suffix. The threshold exhibits minimal drift with temperature, normalized to within ±0.5% of nominal across the range.

How do I calculate the external capacitor value needed for a specific reset timeout with MAX6421XS23?

Use the formula CSRT = (tRP − 275µs) / 2.73×10⁶, where tRP is the desired timeout in seconds and CSRT is the capacitor value in farads. For example, a 50ms timeout requires CSRT ≈ 18.3nF. The MAX6421XS23 datasheet specifies this relationship explicitly in the "Selecting a Reset Capacitor" section, and recommends low-leakage ceramic capacitors to ensure timing accuracy.

Does MAX6421XS23 support operation at VCC below 1.6V, and what happens to RESET output behavior?

Yes - the MAX6421XS23 is fully specified down to VCC = 1.0V, and its RESET output remains valid (VOL ≤ 0.4V, VOH ≥ 0.8×VCC) across that entire range. Below 1.0V, output drive capability degrades, but the device continues asserting RESET until VCC rises above the 2.3V threshold. This behavior is documented in the Absolute Maximum Ratings and Electrical Characteristics tables for MAX6421XS23.

Can MAX6421XS23 replace a MAX6421US23-T on the same PCB, and what layout changes are needed?

No direct replacement is possible without board modification: MAX6421XS23 uses SC70-4 (pin 1=SRT, 2=GND, 3=RESET, 4=VCC), while MAX6421US23-T uses SOT143-4 (pin 1=VCC, 2=GND, 3=RESET, 4=SRT). Pin order and package dimensions differ - SC70 is 1.25mm × 0.8mm vs. SOT143's 2.1mm × 1.3mm. Land pattern and routing must be redesigned to accommodate the MAX6421XS23.

Is the SRT pin of MAX6421XS23 sensitive to PCB leakage or noise, and how should it be routed?

Yes - the SRT pin connects to a precision 240nA current source, making it highly sensitive to stray capacitance and surface leakage. The MAX6421XS23 datasheet mandates short, isolated traces; avoidance of nearby high-speed signals or high-voltage nodes; and clean prototype boards during evaluation. Any added capacitance or leakage directly alters the reset timeout, violating the tRP = 2.73×10⁶×CSRT + 275µs equation.