Analog Devices Inc./Maxim Integrated MAX6391KA22+

Overview

The MAX6391KA22+ from Maxim Integrated is a dual-voltage microprocessor supervisory circuit with sequenced open-drain reset outputs, factory-set 2.19V VCC reset threshold, 625mV adjustable secondary reset input (RESET IN2), and guaranteed reset validity down to VCC = 1V. It monitors two supply rails and enforces strict power-up sequencing-RESET2 deasserts only after RESET1-making it suitable for dual-rail embedded controllers and industrial equipment requiring deterministic reset ordering.

For engineers reviewing the MAX6391KA22+ datasheet, MAX6391KA22+ pinout, MAX6391KA22+ application, or MAX6391KA22+ equivalent, key selection criteria include its fixed 140ms (min) RESET1 timeout, user-adjustable or fixed 140ms (min) RESET2 timeout via CSRT pin configuration, internal 47kΩ pullup resistors on both RESET outputs, and immunity to short negative VCC transients.

Technical Context

The MAX6391KA22+ implements two independent voltage-monitoring comparators: one for VCC (with factory-trimmed 2.19V threshold) and one for RESET IN2 (referenced to 625mV). RESET1 is asserted solely by VCC falling below threshold and deasserts ≥140ms after VCC recovery; RESET2 asserts if either VCC or RESET IN2 falls below their thresholds and deasserts ≥140ms (or capacitor-adjusted) after both recover-with mandatory assertion before RESET1 during power-down and deassertion after RESET1 during power-up.

Its BiCMOS process enables 15µA typical supply current and operation down to VCC = 1.0V. The CSRT pin supports dual timing modes: tied to VCC for fixed 140ms (min) RESET2 timeout, or connected to an external capacitor (e.g., 1500pF yields ~3.1ms) for user-defined delay using a 600nA internal current source and 1.25V reference.

Key Specifications

Pinout & Package

MAX6391KA22+ is housed in an 8-pin SOT23 package (JEDEC MO-178 compliant, 1.95mm × 2.80mm footprint, 1.30mm height), optimized for space-constrained PCB layouts in industrial and computing applications.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-voltage supervisory applications.

Compared with MAX6392KA22+, the MAX6391KA22+ omits manual reset but retains identical dual-threshold monitoring and sequencing logic-ideal for cost-sensitive designs where external reset initiation is unnecessary. Versus TPS3808G33DBVR, MAX6391KA22+ adds critical secondary-supply monitoring and hardware-enforced reset ordering, eliminating risk of improper power sequencing in multi-rail systems.

Availability

MAX6391KA22+ is available at Aetrix Electronics and suitable for industrial PLC controllers, multi-rail embedded systems, servers/workstations, set-top boxes, and critical µP power monitoring applications requiring stable component supply and long-term design continuity.

Supply support for MAX6391KA22+ 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, mixed-signal, and power management ICs for industrial, computing, and communications markets.

The MAX6391/MAX6392 product line delivers dual-voltage microprocessor supervisory circuits with hardware-enforced reset sequencing-engineered specifically for reliability-critical multi-rail systems where deterministic power-up and power-down behavior is non-negotiable.

FAQ

What is the factory-set VCC reset threshold voltage for MAX6391KA22+?

The MAX6391KA22+ has a factory-trimmed VCC reset threshold of 2.19V, with a tolerance of ±0.07V (2.12V to 2.25V). This value is laser-trimmed during production and specified in the Electrical Characteristics table under "VCC Reset Threshold (VTH1)" for ordering code UA22. The MAX6391KA22+ uses this fixed threshold to assert RESET1 whenever VCC falls below this level, ensuring consistent brownout detection across temperature and supply variations.

How does the MAX6391KA22+ enforce reset sequencing between RESET1 and RESET2?

The MAX6391KA22+ enforces sequencing through dedicated internal timing logic: during power-up, RESET1 deasserts ≥140ms after VCC exceeds 2.19V, and RESET2 deasserts only after RESET1 has deasserted-regardless of CSRT configuration. During power-down, RESET2 asserts before RESET1 (tRD2 < tRD1), as confirmed in Note 2 of the datasheet. This hardware-level ordering eliminates reliance on external timing components or firmware control, making the MAX6391KA22+ suitable for safety-critical sequencing where deterministic behavior is mandatory.

Can the RESET2 timeout period be adjusted on the MAX6391KA22+, and how?

Yes, the RESET2 timeout on MAX6391KA22+ is configurable via the CSRT pin. Connecting CSRT to VCC selects a fixed 140ms (minimum) timeout. For user adjustment, connect CSRT to an external capacitor (CCSRT) from pin to GND; the internal 600nA current source charges it against a 1.25V reference, yielding tRP2 ≈ 2.08 × 10⁶ × CCSRT seconds. With CCSRT = 1500pF, timeout is ~3.1ms. This flexibility allows fine-tuning RESET2 delay to match specific downstream component requirements without changing the MAX6391KA22+ itself.

Does the MAX6391KA22+ support operation at VCC = 1.0V, and what functions remain active?

Yes, the MAX6391KA22+ guarantees functional reset generation down to VCC = 1.0V, as stated in the "Guaranteed Reset Valid to VCC = 1V" feature and confirmed in the Electrical Characteristics table (VCC Range: 1.2V to 5.5V at -40°C to +85°C; 1.0V min for reset validity). At 1.0V, the internal comparators and reset state machine remain operational-ensuring RESET1 and RESET2 assert correctly during deep brownout-but supply current increases and timing parameters may drift outside min/max specs. This capability makes MAX6391KA22+ suitable for ultra-low-voltage backup scenarios.

What is the purpose of the R1 and R2 pins on the MAX6391KA22+?

The R1 and R2 pins on MAX6391KA22+ provide access to internal 47kΩ pullup resistors connected to RESET1 and RESET2 outputs respectively. Unlike standard open-drain supervisors requiring external pullups, these pins allow designers to tie R1/R2 to any desired VOH voltage (e.g., 5V, 3.3V, or 1.8V) to set the high-level reset signal voltage independently for each output. This eliminates external resistors, supports mixed-voltage systems, and simplifies layout-especially valuable in space-constrained applications where the MAX6391KA22+'s SOT23-8 package is deployed.