Analog Devices Inc./Maxim Integrated MAX6421XS29+T

Overview

MAX6421XS29+T 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 2.925V (typical), with capacitor-adjustable timeout (3.0–5.75ms at CSRT = 1500pF), guaranteed valid down to VCC = 1V, and quiescent current of 1.6µA (typ) - used in battery-powered controllers and portable equipment for reliable power-on reset and brownout protection.

For engineers reviewing the MAX6421XS29+T datasheet, MAX6421XS29+T pinout, MAX6421XS29+T application, or MAX6421XS29+T equivalent, key selection criteria include reset threshold accuracy (±1.5% at +25°C), SRT pin ramp current (240nA), RESET output low voltage (0.3V at 500µA sink), operating temperature range (−40°C to +125°C), and SC70-4 package compatibility with space-constrained embedded designs.

Technical Context

The MAX6421XS29+T implements a precision voltage-detection architecture using laser-trimmed resistors to set its 2.925V nominal reset threshold, with ±2.5% tolerance over −40°C to +125°C. Its internal 240nA current source charges an external capacitor on the SRT pin to generate a programmable reset timeout period via a 0.65V reference comparator.

It features push-pull RESET output logic with guaranteed validity down to VCC = 1V, immunity to short VCC transients (e.g., ≤50µs at 100mV overdrive), and operation across 1.0V–5.5V supply range - enabling robust µP reset assertion during power-up, power-down, and brownout events without external pullup components.

Key Specifications

Pinout & Package

MAX6421XS29+T is housed in a 4-pin SC70-4 package (package code X4+1, outline 21-0098), measuring 1.25mm × 0.85mm × 0.55mm, with wettable flank leads for automated optical inspection. Pin 1 is marked by a dot; pin numbering follows standard SC70 top-view orientation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6421XS29+T, MAX6421US29+T offers identical functionality in a thermally robust SOT143 package, while TLV803EB29DBZR trades timeout programmability and push-pull drive for lower quiescent current and simpler BOM - making MAX6421XS29+T optimal for designs needing precise, adjustable reset hold time and direct µP interface.

Availability

MAX6421XS29+T is available at Aetrix Electronics and suitable for battery-powered portable controllers, automotive body electronics, and medical infusion pump controllers requiring stable component supply, long-term lifecycle support, and RoHS-compliant lead-free packaging.

Supply support for MAX6421XS29+T 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 systems.

The MAX6421XS29+T belongs to the MAX6340/MAX6421–MAX6426 family of low-power µP supervisors, designed specifically for reliable reset generation in space-constrained, battery-sensitive, and automotive-grade applications where voltage monitoring accuracy and timing flexibility are critical.

FAQ

What is the exact reset threshold voltage of the MAX6421XS29+T?

The MAX6421XS29+T has a nominal reset threshold of 2.925V, with ±1.5% accuracy at +25°C and ±2.5% over the full −40°C to +125°C operating range. This value is laser-trimmed at wafer test and confirmed per Table 1 in the datasheet, where suffix "29" corresponds to 2.925V typical. The threshold remains stable across supply voltage (1.0V–5.5V) and temperature, ensuring consistent brownout detection in 3.3V systems.

Does the MAX6421XS29+T require an external pullup resistor on the RESET pin?

No, the MAX6421XS29+T does not require an external pullup resistor because it features an active-low push-pull RESET output. Unlike open-drain variants (e.g., MAX6423XS29+T), this configuration actively drives both high and low states - delivering VOH ≥ 0.8×VCC and VOL ≤ 0.3V - enabling direct connection to µP reset inputs without additional components. This simplifies layout and improves noise immunity in dense PCB environments.

How is the reset timeout period set on the MAX6421XS29+T?

The reset timeout period on the MAX6421XS29+T is set by connecting an external capacitor (CSRT) between the SRT pin and GND. The relationship is tRP = 2.73 × 10⁶ × CSRT + 275µs, where tRP is in seconds and CSRT in farads. For example, a 1500pF capacitor yields 3.00–5.75ms timeout. Ceramic capacitors with leakage <10nA are recommended; trace routing to SRT must minimize parasitic capacitance and leakage to maintain timing accuracy.

Is the MAX6421XS29+T qualified for automotive applications?

The MAX6421XS29+T is rated for −40°C to +125°C operation and meets AEC-Q100 stress testing requirements *as part of the broader MAX6340/MAX6421–MAX6426 family*, though specific AEC-Q100 certification is documented for MAX6340UK31/V+T. Its wide temperature range, supply voltage immunity (1.0V–5.5V), and transient rejection make it suitable for non-safety-critical automotive modules such as infotainment power sequencing and body control units - pending customer qualification per application requirements.

Can the MAX6421XS29+T operate reliably when VCC drops below 1.0V?

The MAX6421XS29+T guarantees RESET output validity only down to VCC = 1.0V; below this, RESET current-sinking capability declines sharply and logic state becomes indeterminate. While the device continues to function electrically, it cannot ensure correct reset assertion during deep undervoltage. For applications requiring valid RESET down to 0V, a 100kΩ pulldown resistor on the RESET line is recommended - but note that MAX6421XS29+T's push-pull architecture makes this less critical than for open-drain variants.