Analog Devices Inc./Maxim Integrated MAX6391KA46

Overview

MAX6391KA46 from Maxim Integrated is a dual-voltage microprocessor supervisory circuit with sequenced reset outputs, designed for multi-rail systems requiring controlled power-up and power-down sequencing. It monitors VCC (master supply) at 4.63V threshold and RESET IN2 (adjustable secondary supply), provides open-drain RESET1 and RESET2 with fixed 140ms minimum timeout, and guarantees valid reset operation down to VCC = 1V. Used in servers, industrial controllers, and multivoltage embedded systems.

For engineers reviewing the MAX6391KA46 datasheet, MAX6391KA46 pinout, MAX6391KA46 application, or MAX6391KA46 equivalent, this page delivers verified technical context, exact pin functions, real-world timing behavior, and validated alternative options - all specific to the MAX6391KA46 variant with 4.63V VCC reset threshold and SOT23-8 package.

Technical Context

The MAX6391KA46 implements two independent voltage monitoring paths: a factory-trimmed VCC comparator (4.63V threshold) controlling RESET1, and a high-impedance RESET IN2 input referenced to a precise 625mV internal bandgap, enabling external resistor-divider configuration for secondary supply monitoring. RESET1 deasserts 140ms (min) after VCC exceeds 4.63V, while RESET2 deasserts either 140ms (min) after both VCC & RESET IN2 exceed thresholds (CSRT tied to VCC) or after a capacitor-adjustable delay (CSRT to ground).

RESET2 always deasserts after RESET1 during power-up and asserts before RESET1 during power-down, enforcing strict sequencing. Internal 47kΩ pullup resistors on RESET1 and RESET2 allow connection to external VOH voltages without discrete components, and the device operates reliably down to VCC = 1V with 15µA typical supply current.

Key Specifications

Pinout & Package

MAX6391KA46 is housed in an 8-pin SOT23-8 package (JEDEC MO-178 compliant), measuring 3.00mm × 1.75mm × 1.30mm, with gull-wing leads and lead-free option available (+T suffix). The package supports reflow soldering and high-density PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6391KA44, the MAX6391KA46 offers higher VCC threshold margin for 5V systems; compared with TPS3808G33, it delivers integrated dual-rail supervision and hardware-enforced sequencing - eliminating external logic and reducing design risk in multivoltage platforms.

Availability

MAX6391KA46 is available at Aetrix Electronics and suitable for servers/workstations, industrial PLCs, medical diagnostic equipment, and network switch ASIC power management requiring stable component supply, long-term lifecycle support, and guaranteed reset timing integrity.

Supply support for MAX6391KA46 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, communications, and automotive markets.

The MAX6391/MAX6392 family was designed specifically for multivoltage microprocessor systems needing deterministic, sequenced reset generation - addressing reliability gaps left by discrete supervisors or generic reset ICs.

FAQ

What is the exact VCC reset threshold voltage for MAX6391KA46?

The MAX6391KA46 has a factory-trimmed VCC reset threshold of 4.63V (nominal), with a specified range of 4.50V (min) to 4.75V (max) over temperature. This value is laser-trimmed during production and applies exclusively to the KA46 variant - other suffixes (e.g., KA44, KA31) correspond to different thresholds. The MAX6391KA46 uses this precise threshold to ensure reliable reset assertion in 5V systems operating near upper specification limits.

Does MAX6391KA46 support adjustable RESET2 timeout, and how is it configured?

Yes, MAX6391KA46 supports user-adjustable RESET2 timeout via the CSRT pin. Connecting CSRT to ground with an external capacitor (e.g., 1500pF) creates a voltage ramp using an internal 600nA current source; the time to reach the 1.25V internal reference determines the delay (tRP2 ≈ 2.08×10⁶ × CCSRT seconds). For fixed 140ms minimum timeout, tie CSRT directly to VCC. This flexibility allows fine-tuning of secondary reset timing without changing the MAX6391KA46 part number or layout.

Can MAX6391KA46 monitor a 1.2V supply as the secondary voltage, and what resistor values are needed?

Yes, MAX6391KA46 can monitor a 1.2V supply on RESET IN2 using an external resistive divider. With a fixed 625mV internal reference, use R4 = 500kΩ (to minimize current draw) and calculate R3 = R4 × (1.2V / 0.625V − 1) ≈ 460kΩ. This yields a practical divider that scales 1.2V down to 625mV at RESET IN2. The MAX6391KA46's high-impedance input (50nA max leakage) ensures minimal loading, preserving accuracy across temperature.

How does the sequencing behavior of MAX6391KA46 prevent race conditions during power-up?

MAX6391KA46 enforces strict sequencing: RESET2 remains asserted until RESET1 deasserts *and* the RESET2 timeout expires. During power-up, RESET1 deasserts first (after 140ms), then RESET2 follows only after its own delay - guaranteeing dependent subsystems initialize in order. During power-down, RESET2 asserts before RESET1 (tRD2 < tRD1), ensuring peripherals shut down before the CPU. This hardware-level timing coordination eliminates software or external logic dependencies, making the MAX6391KA46 inherently race-condition-free.

What is the purpose of the R1 and R2 pins on MAX6391KA46, and how should they be used?

R1 and R2 are dedicated terminals for the MAX6391KA46's internal 47kΩ pullup resistors connected to RESET1 and RESET2 outputs, respectively. To set RESET1 high level to 3.3V (not VCC), connect R1 to 3.3V; similarly, tie R2 to 5V to set RESET2 VOH = 5V. This allows independent voltage-domain interfacing without external resistors - critical when RESET1 drives a 3.3V FPGA and RESET2 controls a 5V peripheral. Leaving R1/R2 unconnected disables the internal pullups, requiring external components.