Analog Devices Inc./Maxim Integrated MAX6421XS22+

Overview

MAX6421XS22+ from Analog Devices is a low-power microprocessor supervisor IC that monitors VCC supply voltage and asserts an active-low push-pull reset signal when voltage falls below 2.188 V (typical), with capacitor-adjustable timeout (3.0–5.75 ms at CSRT = 1500 pF), guaranteed operation down to VCC = 1 V, and 1.6 µA typical quiescent current - used in battery-powered controllers and portable equipment for reliable power-up/brownout protection.

For engineers reviewing the MAX6421XS22+ datasheet, MAX6421XS22+ pinout, MAX6421XS22+ application, or MAX6421XS22+ equivalent, key selection considerations include its 2.188 V reset threshold accuracy (±1.5% at +25°C), SC70-4 package footprint, push-pull RESET output drive capability (VOL ≤ 0.3 V at ISINK = 500 µA), and immunity to sub-50 µs VCC transients ≥100 mV below threshold.

Technical Context

The MAX6421XS22+ implements a precision voltage detector with laser-trimmed internal resistive divider setting the 2.188 V nominal reset threshold, paired with a 240 nA SRT pin ramp current source that charges an external capacitor to generate the reset timeout delay. Its comparator-based architecture ensures monotonic reset assertion/deassertion without false triggering during VCC ramping.

It operates across –40°C to +125°C, supports VCC from 1.0 V to 5.5 V, and guarantees valid RESET output down to VCC = 1 V - enabling robust supervision in ultra-low-voltage embedded systems where supply rails may dip near brownout limits before full system shutdown.

Key Specifications

Pinout & Package

MAX6421XS22+ is housed in a 4-pin SC70-4 package (package code X4+1, outline 21-0098), measuring 1.25 mm × 0.85 mm × 0.55 mm, with gull-wing leads and RoHS-compliant lead-free finish ("+" suffix).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6421XS22+, MAX6421US22+T offers identical functionality in a larger package for easier hand-soldering or thermal margin, while TLV803EB22DBZR trades ultra-low power and adjustable timing for lower cost and simpler BOM - making MAX6421XS22+ optimal for compact, long-life battery-powered designs requiring precise timing control.

Availability

MAX6421XS22+ is available at Aetrix Electronics and suitable for portable medical sensors, battery-powered industrial controllers, and automotive body control modules requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for MAX6421XS22+ 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

Analog Devices, Inc. is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies for precision measurement and control.

The MAX6421XS22+ belongs to the MAX6340/MAX6421–MAX6426 family of low-power µP supervisors, designed specifically for reliable power-monitoring in space-constrained, battery-operated, and automotive-grade embedded systems.

FAQ

What is the exact reset threshold voltage of MAX6421XS22+ and how is it trimmed?

The MAX6421XS22+ has a nominal reset threshold of 2.188 V, with ±1.5% accuracy at +25°C and ±2.5% over –40°C to +125°C. This value is set by factory laser-trimming of internal resistive divider elements during wafer test, ensuring high initial accuracy without external calibration. The "22" suffix in the part number directly references Table 1 in the datasheet, confirming the 2.188 V typ specification.

Can MAX6421XS22+ operate with VCC below 1.6 V, and what happens to RESET output below that level?

Yes, MAX6421XS22+ is fully specified down to VCC = 1.0 V and guarantees valid RESET output behavior (VOL ≤ 0.3 V, VOH ≥ 0.8×VCC) across that entire range. Below 1.0 V, RESET output drive degrades rapidly; however, the device continues asserting RESET until VCC rises above threshold, ensuring µP remains held in reset during deep brownout conditions common in battery discharge profiles.

How do I calculate the external capacitor value for a 4.0 ms reset timeout with MAX6421XS22+?

Use the formula CSRT = (tRP − 275 µs) / 2.735 × 10⁶, where tRP = 4.0 ms = 0.004 s. Substituting gives CSRT ≈ (0.004 − 0.000275) / 2,735,000 ≈ 1362 pF. A standard 1500 pF X7R ceramic capacitor yields ~4.375 ms (within datasheet spec), and is recommended due to its low leakage (<10 nA) and stability over temperature.

Is MAX6421XS22+ pin-compatible with any industry-standard reset ICs like the MAX809 or TPS3808?

No - MAX6421XS22+ uses a 4-pin SC70 configuration (GND, RESET, VCC, SRT) with dedicated SRT pin for timeout programming, whereas MAX809 (SOT23-3) lacks timeout adjustment and TPS3808 (SOT23-6) integrates enable and watchdog functions. Its pinout is unique to the MAX6340/MAX6421–MAX6426 family; direct replacement requires PCB redesign unless migrating to another member of the same family (e.g., MAX6421US22+T).

Does MAX6421XS22+ require external components beyond the SRT capacitor for basic operation?

No - MAX6421XS22+ operates autonomously with only the SRT-to-GND capacitor. Unlike open-drain supervisors, its push-pull RESET output needs no pullup resistor. No bypass capacitor is mandatory, though a 0.1 µF ceramic cap near VCC/GND is recommended for noise immunity. The device draws only 1.6 µA, eliminating need for enable/disable logic or power sequencing aids.