Analog Devices Inc./Maxim Integrated MAX6391KA31

Overview

MAX6391KA31 from Maxim Integrated is a dual-voltage microprocessor supervisory circuit with sequenced open-drain reset outputs, factory-set 3.08V VCC reset threshold, 625mV adjustable secondary reset input (RESET IN2), and guaranteed reset validity down to VCC = 1.0V. It monitors master and slave supplies in multivoltage systems and enforces strict power-up sequencing (RESET1 before RESET2) for reliable boot in industrial controllers and servers.

For engineers reviewing the MAX6391KA31 datasheet, MAX6391KA31 pinout, MAX6391KA31 application, or MAX6391KA31 equivalent, key selection criteria include its fixed 140ms min RESET1 timeout, capacitor-adjustable or fixed 140ms min RESET2 delay, internal 47kΩ pullup resistors on both reset outputs, and SOT23-8 package compatibility with space-constrained embedded designs.

Technical Context

The MAX6391KA31 implements two independent voltage monitoring paths: a primary comparator for VCC (with factory-trimmed 3.08V threshold) and a secondary high-impedance input (RESET IN2) referenced to an internal 625mV bandgap. RESET1 asserts only on VCC undervoltage and deasserts ≥140ms after VCC recovery; RESET2 asserts if either VCC or RESET IN2 falls below their thresholds and deasserts only after both recover and RESET1 has deasserted.

Timing control uses dual mechanisms: RESET1 timeout is fully internal and fixed; RESET2 timeout is selectable via CSRT pin-tied to VCC for 140ms min fixed delay or connected to external capacitor for user-adjustable delay (e.g., 3.1ms with 1500pF). The device guarantees functional reset assertion down to VCC = 1.0V and exhibits immunity to short negative VCC transients per published overdrive vs. pulse-width curves.

Key Specifications

Pinout & Package

MAX6391KA31 is housed in an 8-pin SOT23 package (JEDEC MO-178 compliant, 3.00mm × 1.75mm body, 0.65mm pitch). Pin 1 is marked with a dot; leads are lead-free compatible (suffix +T).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6392KA31, the MAX6391KA31 offers dedicated internal pullups (R1/R2) ideal for multi-VOH systems but lacks manual reset; versus TPS3808G33, it provides essential dual-monitoring and sequencing capability at the cost of higher design complexity and pin count.

Availability

MAX6391KA31 is available at Aetrix Electronics and suitable for industrial PLC controllers, telecom line cards, medical diagnostic equipment, and server/workstation power management requiring stable component supply, long-term lifecycle support, and guaranteed -40°C to +85°C operation.

Supply support for MAX6391KA31 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 applications.

The MAX6391/MAX6392 product line delivers dual-voltage microprocessor supervisory circuits with sequenced reset outputs, targeting multirail systems where deterministic power-up ordering and brownout resilience are critical.

FAQ

What is the factory-set VCC reset threshold voltage for MAX6391KA31?

The MAX6391KA31 has a factory-trimmed VCC reset threshold of 3.08V, with a tolerance of ±0.07V (min 3.00V, max 3.15V) across the full -40°C to +85°C temperature range. This value is laser-trimmed during production and is specified in the Electrical Characteristics table under "VCC Reset Threshold" for part suffix "UA31". The MAX6391KA31 uses this precise threshold to initiate reset assertion when the primary supply sags below 3.08V.

How does the MAX6391KA31 generate the RESET2 timeout period?

The MAX6391KA31 supports two RESET2 timeout modes: fixed or adjustable. When the CSRT pin is connected to VCC, RESET2 uses an internal fixed counter chain yielding ≥140ms delay. When CSRT is connected to an external capacitor to ground, a 600nA current source ramps voltage across the capacitor until it reaches 1.25V, triggering deassertion; delay = 2.08 × 10⁶ × CCSRT seconds. For example, 1500pF yields ~3.1ms. The MAX6391KA31's behavior is fully determined by this CSRT configuration.

Can the MAX6391KA31 monitor a 1.2V supply as the secondary voltage?

Yes - the MAX6391KA31 can monitor a 1.2V supply on RESET IN2 using an external resistor divider. With a fixed 625mV internal reference, a divider with R4 = 500kΩ and R3 = 460kΩ yields VRST ≈ 1.2V. The MAX6391KA31's high-impedance RESET IN2 input draws only 50nA, minimizing divider current and enabling accurate low-voltage monitoring without loading the source rail.

Does the MAX6391KA31 require external pullup resistors on RESET1 and RESET2?

No - the MAX6391KA31 integrates internal 47kΩ pullup resistors connected to RESET1 (via pin R1) and RESET2 (via pin R2). These allow direct connection to any desired VOH rail (e.g., 1.8V, 3.3V, 5V) without external components. While external pullups are optional, using R1/R2 simplifies layout and supports mixed-voltage reset signaling - a key advantage of the MAX6391KA31 over single-pullup alternatives.

What is the minimum VCC voltage at which the MAX6391KA31 guarantees valid reset operation?

The MAX6391KA31 guarantees functional reset assertion and deassertion down to VCC = 1.0V across the full operating temperature range (-40°C to +85°C). This is explicitly stated in the Electrical Characteristics table under "Guaranteed Reset Valid to VCC = 1V" and enables robust operation during deep brownout conditions where other supervisors may fail. The MAX6391KA31 maintains correct reset state integrity even as VCC collapses toward 1.0V.