Analog Devices Inc./Maxim Integrated MAX6391KA16+

Overview

MAX6391KA16+ from Maxim Integrated is a dual-voltage microprocessor supervisory circuit with sequenced active-low open-drain reset outputs, factory-set 1.58V VCC reset threshold, 625mV adjustable secondary reset input (RESET IN2), and guaranteed reset validity down to VCC = 1V. It monitors master and slave supplies in multivoltage systems to enforce power-up sequencing-RESET1 deasserts ≥140ms after VCC recovery, RESET2 follows only after RESET1 deassertion and its own timeout, enabling controlled boot order in industrial controllers and embedded servers.

For engineers reviewing the MAX6391KA16+ datasheet, MAX6391KA16+ pinout, MAX6391KA16+ application, or MAX6391KA16+ equivalent, key selection criteria include sequenced dual-reset timing control, internal 47kΩ pullup resistors for independent VOH level setting, immunity to short negative VCC transients (<100ns at 100mV overdrive), and operation across -40°C to +85°C in space-constrained SOT23-8 packages.

Technical Context

The MAX6391KA16+ implements two independent voltage monitoring paths: a fixed-threshold comparator for VCC (1.58V) driving RESET1, and a high-impedance 625mV reference comparator for RESET IN2 driving RESET2. RESET2 assertion depends on either VCC or RESET IN2 falling below their thresholds, but RESET2 deassertion requires both signals to exceed thresholds *and* RESET1 to be deasserted first-enforcing strict power-up sequence.

Timing is split between fixed and configurable domains: RESET1 timeout is internally fixed at ≥140ms; RESET2 timeout is either fixed (≥140ms, when CSRT tied to VCC) or user-adjustable via external capacitor (e.g., 3.1ms with 1500pF), using a 600nA current source charging CCSRT to 1.25V reference. Reset outputs remain valid down to VCC = 1V, supporting low-voltage brownout detection.

Key Specifications

Pinout & Package

MAX6391KA16+ is housed in an 8-pin SOT23 package (JEDEC MO-178 compliant, 1.95mm × 2.80mm footprint, 1.30mm height), optimized for high-density PCB layouts in space-constrained embedded systems.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6392KA16+, the MAX6391KA16+ provides dedicated open-drain RESET1 with internal R1 pullup-essential for mixed-voltage reset signaling-while TPS3808G15DBVR lacks secondary monitoring and sequencing logic entirely, making it a functional subset rather than drop-in replacement.

Availability

MAX6391KA16+ is available at Aetrix Electronics and suitable for industrial PLC controllers, embedded servers, multivoltage IoT gateways, medical diagnostic equipment, and critical µP power monitoring applications requiring stable component supply, long-term lifecycle support, and guaranteed -40°C to +85°C operation.

Supply support for MAX6391KA16+ 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 precision analog, mixed-signal, and high-reliability power management solutions for industrial, automotive, and communications markets.

The MAX6391/MAX6392 product line was designed specifically for multivoltage system supervision-delivering sequenced, glitch-immune reset outputs with minimal external components to reduce board area and improve system-level reliability in space- and power-constrained designs.

FAQ

What is the exact factory-set VCC reset threshold voltage for MAX6391KA16+?

The MAX6391KA16+ has a factory-trimmed VCC reset threshold of 1.58V, with guaranteed limits of 1.54V (minimum) and 1.61V (maximum) across the full -40°C to +85°C temperature range. This value is laser-trimmed during production and is specific to the KA16 suffix; other variants (e.g., KA22, KA44) have different thresholds. The 1.58V threshold makes MAX6391KA16+ ideal for monitoring 1.8V rails with sufficient margin against dropout.

How does the MAX6391KA16+ enforce power-up sequencing between RESET1 and RESET2?

The MAX6391KA16+ enforces sequencing by design: RESET2 remains asserted until *both* VCC and RESET IN2 exceed their thresholds *and* RESET1 has already deasserted. RESET1 deasserts ≥140ms after VCC recovery, so RESET2 cannot deassert earlier-even if RESET IN2 recovers first. This hardwired dependency ensures RESET1 always releases before RESET2, preventing race conditions in dual-rail systems. No external logic or timing components are needed to achieve this behavior in MAX6391KA16+.

Can the RESET2 timeout period of MAX6391KA16+ be adjusted, and how?

Yes, the RESET2 timeout period of MAX6391KA16+ is user-adjustable via an external capacitor connected from the CSRT pin to ground. A 600nA internal current source charges the capacitor to a 1.25V internal reference; timeout = 2.08 × 10⁶ × CCSRT (seconds). For example, a 1500pF capacitor yields ~3.1ms. Alternatively, tying CSRT to VCC selects a fixed ≥140ms timeout. The MAX6391KA16+ automatically detects the CSRT connection mode-no configuration bits or external resistors are required.

Does MAX6391KA16+ support independent pullup voltages for RESET1 and RESET2 outputs?

Yes, MAX6391KA16+ includes two internal 47kΩ pullup resistors-one connected to RESET1 (pin 7) and one to RESET2 (pin 5)-with dedicated terminals R1 (pin 8) and R2 (pin 6). Each can be tied to a different external voltage rail (e.g., R1 to 1.8V for RESET1, R2 to 3.3V for RESET2), enabling independent VOH levels without external resistors. This allows MAX6391KA16+ to drive reset signals into mixed-voltage logic families on the same board.

What is the minimum VCC voltage at which MAX6391KA16+ guarantees valid reset operation?

The MAX6391KA16+ guarantees valid reset assertion and deassertion down to VCC = 1.0V, as specified in the Absolute Maximum Ratings and Electrical Characteristics tables. This ensures reliable brownout detection even during severe undervoltage events where many supervisors cease functioning. Operation below 1.0V is not characterized; however, the 1.0V guarantee exceeds industry norms and supports robust low-voltage system design with MAX6391KA16+.