Analog Devices Inc./Maxim Integrated MAX6391KA46+T

Overview

MAX6391KA46+T from Maxim Integrated is a dual-voltage microprocessor supervisory circuit with sequenced reset outputs, designed for multi-rail systems requiring controlled power-up/power-down sequencing. It monitors VCC (master supply) at 4.63V threshold and RESET IN2 (adjustable down to 625mV), provides fixed 140ms min timeout on RESET1, guarantees reset validity down to VCC = 1V, and operates over –40°C to +85°C in SOT23-8.

For engineers reviewing the MAX6391KA46+T datasheet, MAX6391KA46+T pinout, MAX6391KA46+T application, or MAX6391KA46+T equivalent, this device delivers precise dual-supply monitoring with guaranteed timing margins, low 15µA supply current, and internal pullup resistors-critical for reliable µP reset control in industrial controllers and multivoltage servers.

Technical Context

The MAX6391KA46+T implements two independent voltage comparators: one fixed-threshold (4.63V) comparator for VCC monitoring driving RESET1, and a second 625mV reference comparator for RESET IN2 driving RESET2. RESET1 deasserts ≥140ms after VCC exceeds 4.63V; RESET2 asserts before RESET1 during power-down and deasserts only after both VCC and RESET IN2 exceed thresholds plus its timeout period.

RESET2 timing is configurable via CSRT: tied to VCC yields fixed 140ms min timeout; connected to an external capacitor enables user-adjustable delay (e.g., 3.1ms with 1500pF). The device uses BiCMOS process (810 transistors), supports open-drain outputs with internal 47kΩ pullups (R1/R2), and maintains valid reset assertion down to VCC = 1.0V.

Key Specifications

Pinout & Package

MAX6391KA46+T is housed in an 8-pin SOT23 package (JEDEC MO178 compliant; 0.65mm pitch; 2.9mm × 1.6mm body size; 1.3mm max height).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6392KA46+T, the MAX6391KA46+T omits MR and retains R1 pullup-simplifying design where manual reset is unused. Versus TPS3808G33DBVR, it uniquely supports dual-threshold monitoring and guaranteed sequencing, making it irreplaceable in multivoltage systems requiring coordinated reset timing.

Availability

MAX6391KA46+T is available at Aetrix Electronics and suitable for industrial controllers, servers/workstations, and set-top boxes requiring stable component supply, extended temperature operation, and precise dual-rail reset sequencing.

Supply support for MAX6391KA46+T 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 and mixed-signal ICs for power, sensing, and interface applications in industrial, communications, and computing markets.

The MAX6391/MAX6392 product line targets multivoltage system supervision, delivering sequenced reset outputs with factory-trimmed thresholds and configurable timing to replace discrete reset solutions in space-constrained designs.

FAQ

What is the exact VCC reset threshold voltage for MAX6391KA46+T?

The MAX6391KA46+T has a factory-trimmed VCC reset threshold of 4.63V (minimum 4.50V, maximum 4.75V per datasheet). This value is laser-trimmed during production and applies across the full –40°C to +85°C operating range. The threshold ensures reliable reset assertion when the main supply falls below nominal 4.65V rails commonly used in industrial and server applications. MAX6391KA46+T guarantees this specification without requiring external calibration.

How does the CSRT pin configure RESET2 timeout in MAX6391KA46+T?

In MAX6391KA46+T, the CSRT pin determines RESET2 timeout behavior: connecting CSRT to VCC selects a fixed 140ms minimum delay, while connecting CSRT to an external capacitor (e.g., 1500pF to ground) enables user-adjustable timing based on ∆t = C × 1.25V / 600nA. The internal 600nA current source charges the capacitor until it reaches 1.25V, triggering RESET2 deassertion. MAX6391KA46+T automatically detects the CSRT connection mode and configures its internal timing chain accordingly.

Can MAX6391KA46+T monitor a 1.8V supply as the secondary voltage?

Yes-MAX6391KA46+T can monitor a 1.8V supply on RESET IN2 using an external resistor divider. With its internal 625mV reference, a 1.8V rail requires R3/R4 ratio ≈ 1.88 (e.g., R4 = 500kΩ, R3 = 440kΩ). The divider presents minimal loading (<50nA) due to high-impedance input. MAX6391KA46+T guarantees accurate threshold detection across temperature, and RESET2 will assert within 10µs when the divided voltage drops below 625mV.

What is the purpose of the R1 and R2 pins on MAX6391KA46+T?

R1 and R2 are dedicated terminals for the internal 47kΩ pullup resistors connected to RESET1 and RESET2, respectively. They allow designers to tie each open-drain reset output to an independent voltage rail (e.g., R1 to 3.3V for RESET1 VOH, R2 to 5V for RESET2 VOH), eliminating external pullup components. MAX6391KA46+T integrates these resistors to reduce BOM count and PCB area while supporting mixed-voltage system interfacing without level shifters.

Does MAX6391KA46+T provide reset assertion during brownout conditions?

Yes-MAX6391KA46+T guarantees valid reset assertion down to VCC = 1.0V, enabling reliable operation during brownout. Its internal comparators remain functional and produce clean, glitch-immune reset signals even as VCC declines from 5.5V to 1.0V. The device also rejects short negative transients (≤100ns at 10mV overdrive), preventing false resets from noise. MAX6391KA46+T's brownout resilience is validated across –40°C to +85°C and forms the basis for its use in mission-critical industrial controls.