Analog Devices Inc./Maxim Integrated MAX6421XS31

Overview

MAX6421XS31 from Maxim Integrated is a low-power microprocessor reset supervisor IC in SC70-4 package, monitoring VCC from 1.6V to 5V with factory-trimmed 3.075V reset threshold (suffix '31'), active-low push-pull RESET output, and capacitor-adjustable reset timeout (275µs minimum). It asserts reset during brownout and holds it for user-defined delay after VCC recovery, used in battery-powered controllers and portable medical instruments.

For engineers reviewing the MAX6421XS31 datasheet, MAX6421XS31 pinout, MAX6421XS31 application, or MAX6421XS31 equivalent, key selection criteria include its 1.6µA quiescent current, guaranteed RESET validity down to VCC = 1V, immunity to sub-50µs VCC transients at 100mV overdrive, and compatibility with 4-pin SC70 layout constraints.

Technical Context

The MAX6421XS31 implements a precision voltage comparator with ±1.5% threshold accuracy at +25°C and ±2.5% over –40°C to +125°C, paired with a 240nA internal ramp current source that charges an external SRT capacitor to generate the reset timeout period per t_RP = 2.73×10⁶ × C_SRT + 275µs.

Its push-pull RESET output drives low to ≤0.4V at 3.2mA sink (VCC ≥ 4.5V) and high to ≥0.8×VCC at 800µA source, eliminating need for external pullup resistors, while the SRT pin requires low-leakage ceramic capacitors (<10nA) and careful PCB routing to avoid timing errors from stray capacitance or leakage.

Key Specifications

Pinout & Package

MAX6421XS31 is housed in a 4-pin SC70-4 package (outline 21-0098), measuring 2.0mm × 2.1mm × 0.95mm, with gull-wing leads and RoHS-compliant finish. Pin 1 is marked by a dot or beveled edge.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6421XS31, MAX6421US31-T provides identical functionality in a marginally larger package better suited for manual assembly, while TLV803EC30DBZR trades timeout adjustability for ultra-low current and fixed delay - making MAX6421XS31 the optimal choice for designs needing both precision threshold control and programmable reset duration in minimal area.

Availability

MAX6421XS31 is available at Aetrix Electronics and suitable for portable medical monitors, battery-powered industrial controllers, and automotive cabin sensors requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX6421XS31 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 MAX6421 series belongs to Maxim's microprocessor supervisory product line, engineered specifically for ultra-low-power, capacitor-programmable reset supervision in space-constrained, battery-operated systems.

FAQ

What is the exact reset threshold voltage for MAX6421XS31?

The MAX6421XS31 has a factory-trimmed nominal reset threshold of 3.075V, with tolerance of ±1.5% at +25°C and ±2.5% over the full –40°C to +125°C operating range. This value is confirmed by the '31' suffix in the part number and verified in Table 1 of the datasheet. The MAX6421XS31 uses laser-trimmed resistors to achieve this precision, ensuring consistent brownout detection across production lots.

Can MAX6421XS31 operate with a 1.8V supply?

Yes, MAX6421XS31 operates fully across 1.0V to 5.5V supply range. At 1.8V, its supply current remains 1.6µA typical, RESET output low voltage is ≤0.3V at 500µA sink, and reset threshold accuracy holds within ±2.5%. The device guarantees valid RESET assertion down to VCC = 1V, making MAX6421XS31 suitable for single-cell Li-ion or NiMH systems where supply drops below 2.0V during discharge.

How do I calculate the capacitor value for a 100ms reset timeout with MAX6421XS31?

Use the formula CSRT = (tRP – 275µs) / 2.73×10⁶, where tRP = 0.1s. Substituting gives CSRT = (0.1 – 0.000275) / 2,730,000 ≈ 36.5nF. A standard 33nF or 39nF X7R ceramic capacitor meets this requirement. The MAX6421XS31 datasheet specifies low-leakage (<10nA) ceramics; avoid electrolytics or high-leakage dielectrics to prevent timeout drift.

Is MAX6421XS31 pin-compatible with other devices in the MAX6421 family?

Yes, MAX6421XS31 shares identical 4-pin SC70-4 pinout with all MAX6421x variants (e.g., MAX6421XS16, MAX6421XS26), including SRT, GND, RESET, and VCC assignments. It is not pin-compatible with MAX6422 (active-high RESET) or MAX6423 (open-drain), nor with 5-pin SOT23 versions like MAX6424. The MAX6421XS31 pin mapping is validated in the "Pin Configurations" section of the datasheet.

Does MAX6421XS31 require an external pullup resistor on the RESET pin?

No, MAX6421XS31 does not require an external pullup resistor because it features an active-low push-pull RESET output. The output actively drives high to ≥0.8×VCC and low to ≤0.4V (at rated loads), eliminating reliance on external components for logic-level translation. This distinguishes MAX6421XS31 from open-drain variants like MAX6423 and simplifies schematic design.