Analog Devices Inc./Maxim Integrated MAX6391KA23

Overview

MAX6391KA23 from Maxim Integrated is a dual-voltage microprocessor supervisory circuit with sequenced active-low reset outputs for multi-rail systems. It monitors VCC (master supply) at 2.32V threshold and RESET IN2 (adjustable secondary supply), provides fixed 140ms min timeout on RESET1, guarantees reset validity down to VCC = 1V, and operates in -40°C to +85°C industrial temperature range - used in servers and multivoltage power sequencing.

For engineers reviewing the MAX6391KA23 datasheet, MAX6391KA23 pinout, MAX6391KA23 application, or MAX6391KA23 equivalent, key selection criteria include its factory-set 2.32V VCC reset threshold, open-drain RESET1/RESET2 outputs with internal 47kΩ pullups, CSRT-configurable RESET2 timeout, immunity to short negative VCC transients, and guaranteed operation at VCC ≥ 1V.

Technical Context

The MAX6391KA23 implements two independent voltage monitoring paths: one dedicated to VCC (with fixed 2.32V threshold) driving RESET1, and another monitoring both VCC and RESET IN2 (625mV reference) to control RESET2. RESET1 deasserts 140ms (min) after VCC exceeds 2.32V; RESET2 deasserts either 140ms (min) after both supplies exceed thresholds (CSRT tied to VCC) or after a capacitor-adjustable delay (CSRT to external cap).

During power-up, RESET2 always deasserts after RESET1; during power-down, RESET2 asserts before RESET1. The device uses BiCMOS process (810 transistors), features 15µA typical supply current, and maintains valid reset assertion even as VCC falls to 1.0V - enabling reliable brownout detection in low-voltage systems.

Key Specifications

Pinout & Package

Package: 8-pin SOT23 (3.00mm × 1.75mm × 1.30mm body, 0.65mm pitch), lead-free compatible, rated for -40°C to +85°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6391KA22, the MAX6391KA23 offers higher VCC threshold (2.32V vs. 2.19V) for tighter tolerance on 2.5V systems; compared with TPS3808G33, it uniquely provides dual-supply monitoring and guaranteed reset sequencing - making it irreplaceable in true multivoltage sequencing designs.

Availability

MAX6391KA23 is available at Aetrix Electronics and suitable for servers, industrial controllers, set-top boxes, and multivoltage embedded systems requiring stable component supply, long-term lifecycle support, and guaranteed reset timing integrity.

Supply support for MAX6391KA23 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, computing, and communications applications.

The MAX6391/MAX6392 product line delivers dual-voltage microprocessor supervisory circuits with sequenced reset outputs - designed specifically for reliable power sequencing in multirail systems where timing-critical, independent reset control of master and slave supplies is required.

FAQ

What is the factory-set VCC reset threshold voltage for MAX6391KA23?

The MAX6391KA23 has a factory-set VCC reset threshold of 2.32V (typical), with a guaranteed range of 2.25V to 2.38V across temperature and process variation. This value is laser-trimmed during manufacturing and is specific to the KA23 suffix. The MAX6391KA23 uses this fixed threshold to assert RESET1 whenever VCC falls below this level, ensuring consistent power-on reset behavior in 2.5V-based systems.

Does MAX6391KA23 support adjustable timeout for RESET2, and how is it configured?

Yes, the MAX6391KA23 supports user-adjustable timeout for RESET2 via the CSRT pin. Connecting CSRT to an external capacitor (to ground) enables adjustable delay calculated as tRP2 ≈ 2.08 × 10⁶ × CCSRT seconds; for example, 1500pF yields ~3.1ms. Alternatively, tying CSRT to VCC selects a fixed 140ms (minimum) timeout. The MAX6391KA23 internally detects the CSRT connection mode and configures the timing path accordingly - no external logic is needed.

What is the purpose of pins R1 and R2 on MAX6391KA23, and how are they used?

Pins R1 (pin 8) and R2 (pin 6) are internal 47kΩ pullup resistors connected to RESET1 and RESET2, respectively. They allow each open-drain reset output to be pulled to an external voltage (e.g., 3.3V for RESET1, 5V for RESET2) without adding discrete resistors. This enables independent VOH levels per output - essential in mixed-voltage systems. The MAX6391KA23 leverages these internal resistors to reduce component count and simplify layout, especially in space-constrained applications.

Can MAX6391KA23 operate reliably when VCC drops below 1.5V, and what is the lower limit?

Yes, the MAX6391KA23 guarantees valid reset assertion down to VCC = 1.0V, as explicitly specified in the Electrical Characteristics table. This means RESET1 and RESET2 remain logically asserted (low) and electrically functional even as VCC collapses to 1.0V - a key feature for brownout detection in low-voltage or battery-depleted scenarios. Operation below 1.0V is not guaranteed; the MAX6391KA23 is not functional at VCC < 1.2V per absolute minimum rating, but reset validity is assured down to 1.0V.

How does MAX6391KA23 ensure correct reset sequencing between RESET1 and RESET2 during power-up and power-down?

The MAX6391KA23 enforces strict sequencing: during power-up, RESET2 deasserts only after RESET1 has deasserted (140ms min delay), and during power-down, RESET2 asserts before RESET1 (tRD2 < tRD1, typically by >10µs). This behavior is hardwired in the internal timing architecture and verified across -40°C to +85°C. The MAX6391KA23 achieves this using separate delay chains and comparator hysteresis - eliminating need for external timing components while guaranteeing race-free system initialization and shutdown.