Analog Devices Inc./Maxim Integrated MAX6421US29+

Overview

MAX6421US29+ from Maxim Integrated is a low-power microprocessor supervisor IC that monitors 2.925V system supply voltage and asserts an active-low push-pull reset signal during brownout, power-up, or power-down events. It features capacitor-adjustable reset timeout (275µs base + 2.73s/F × CSRT), guaranteed reset validity down to VCC = 1V, and 1.6µA typical quiescent current. It is used in battery-powered controllers and portable medical instruments requiring precise, low-power voltage supervision.

For engineers reviewing the MAX6421US29+ datasheet, MAX6421US29+ pinout, MAX6421US29+ application, or MAX6421US29+ equivalent, key selection criteria include its 2.925V factory-trimmed reset threshold, SOT143-4 package, push-pull active-low RESET output, and immunity to sub-50µs VCC transients at 100mV overdrive - critical for reliable µP initialization in harsh or low-power environments.

Technical Context

The MAX6421US29+ implements a precision bandgap-based voltage detector with ±1.5% threshold accuracy at +25°C and ±2.5% over –40°C to +125°C. Its reset timeout is generated by a 240nA internal current source charging an external capacitor (CSRT) to a 0.65V ramp threshold, enabling programmable delays from 275µs to >100ms.

It uses BiCMOS process technology (295 transistors) and features hysteresis of 4×VTH (≈11.7mV), VCC-to-reset delay of 80µs (at 1mV/µs slew), and operates across full 1.0V–5.5V supply range while maintaining valid RESET output down to VCC = 1V.

Key Specifications

Pinout & Package

MAX6421US29+ is housed in a 4-pin SOT143-4 surface-mount package (2.1mm × 2.3mm × 0.95mm), optimized for space-constrained portable designs. 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 MAX6421XS29+, the MAX6421US29+ offers higher thermal robustness in SOT143 but larger footprint; compared with TLV803EB29DBZR, it trades lower IQ for field-programmable timeout and guaranteed VCC = 1V operation - essential for brownout resilience in mission-critical systems.

Availability

MAX6421US29+ is available at Aetrix Electronics and suitable for portable medical monitors, battery-powered industrial controllers, and automotive body control modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MAX6421US29+ 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, and computing applications.

The MAX6421 series belongs to Maxim's µP supervisor product line, designed specifically for low-power, precision voltage monitoring in space- and energy-constrained embedded systems where reliability across wide temperature and supply ranges is non-negotiable.

FAQ

What is the exact reset threshold voltage of the MAX6421US29+?

The MAX6421US29+ has a factory-trimmed 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 confirmed by the '29' suffix in the part number and verified in Table 1 of the official datasheet. The MAX6421US29+ uses laser-trimmed resistors to achieve this precision, ensuring consistent performance without external calibration.

Does the MAX6421US29+ require an external capacitor to function?

No, the MAX6421US29+ operates without an external capacitor: it provides a minimum reset timeout of 275µs even with CSRT = 0. However, adding a capacitor between SRT and GND extends the timeout per tRP = (2.73 × 10⁶ × CSRT) + 275µs. Ceramic capacitors with leakage <10nA are recommended. The MAX6421US29+ remains fully functional in voltage-detection mode with SRT floating, making it adaptable to both fixed- and adjustable-delay applications.

What package type does the MAX6421US29+ use, and what are its dimensions?

The MAX6421US29+ uses the SOT143-4 package: a 4-pin, surface-mount plastic package measuring 2.1mm × 2.3mm × 0.95mm with gull-wing leads. Pin 1 is SRT, Pin 2 is GND, Pin 3 is RESET, and Pin 4 is VCC. This package offers higher thermal dissipation (320mW at +70°C) than the SC70 variant and is compatible with standard reflow soldering processes. The MAX6421US29+ top mark is KADH, per the Standard Versions Table.

Can the MAX6421US29+ drive a reset input directly without a pullup resistor?

Yes, the MAX6421US29+ features an active-low push-pull RESET output, meaning it actively drives both low and high states. Unlike open-drain supervisors, it requires no external pullup resistor to assert logic-high when released. It can sink up to 3.2mA at VCC ≥ 4.5V and source sufficient current to meet CMOS input thresholds - enabling direct connection to most µP reset pins. This eliminates BOM cost and layout complexity associated with pullup networks.

Is the MAX6421US29+ suitable for automotive applications?

Yes, the MAX6421US29+ is rated for –40°C to +125°C operation and is widely used in automotive body control modules, infotainment power supplies, and telematics units. Its guaranteed reset validity down to VCC = 1V, immunity to 50µs VCC transients, and AEC-Q100-compatible packaging make it appropriate for under-hood and cabin applications. While not officially AEC-Q100 certified as a standalone part, its specifications and qualification data align with Grade 2 requirements, and it is referenced in automotive design guides by Maxim.