Analog Devices Inc./Maxim Integrated MAX6721UTRGD3

Overview

MAX6721UTRGD3 from Maxim Integrated is a dual-voltage microprocessor supervisory circuit in 6-pin SOT23 package, monitoring VCC1 (primary supply) and VCC2 (secondary supply) with factory-trimmed reset thresholds of 4.625V and 3.075V respectively, 210ms minimum reset timeout, and integrated watchdog timer with 35s startup/1.12s normal mode. It ensures reliable system reset during power-up, brownout, or software fault in multivoltage embedded systems.

For engineers reviewing the MAX6721UTRGD3 datasheet, MAX6721UTRGD3 pinout, MAX6721UTRGD3 application, or MAX6721UTRGD3 equivalent, key selection criteria include dual-supply monitoring capability, guaranteed reset validity down to VCC = 0.8V, watchdog input with dual-mode timing, manual reset support, and open-drain active-low RST output compatible with bidirectional µP reset pins.

Technical Context

The MAX6721UTRGD3 implements a dual-threshold voltage monitor with independent VCC1 and VCC2 inputs, each feeding dedicated comparators referenced to factory-trimmed internal references (4.625V ±125mV and 3.075V ±75mV). Reset assertion occurs when either supply falls below its threshold, and reset remains asserted for ≥210ms after both supplies recover.

It integrates a dual-mode watchdog timer: a 35s minimum initial timeout after any reset event enables full system boot, followed by a 1.12s minimum normal timeout requiring periodic WDI transitions. The device uses BiCMOS process (1072 transistors), draws 14µA typical supply current at 3.6V, and guarantees correct reset logic state with VCC1 or VCC2 ≥ 0.8V.

Key Specifications

Pinout & Package

MAX6721UTRGD3 is housed in a 6-pin SOT23-6 package (2.9mm × 1.6mm × 1.1mm), surface-mount, RoHS-compliant, with gull-wing leads and thermal pad option per Maxim's lead-free packaging standard.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6722UTRGD3, MAX6721UTRGD3 offers safer interface to bidirectional µP reset pins via open-drain output, while TPS3808G33DBVR trades dual-supply capability and watchdog functionality for lower 2.5µA supply current - making MAX6721UTRGD3 optimal for systems requiring robust multivoltage supervision with fault detection.

Availability

MAX6721UTRGD3 is available at Aetrix Electronics and suitable for telecom power sequencing, industrial PLC controllers, portable medical monitors, network switch ASIC power-up, and battery-operated embedded systems requiring stable component supply across extended temperature ranges.

Supply support for MAX6721UTRGD3 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, automotive, communications, and computing markets.

The MAX6715–MAX6729 family delivers ultra-low-voltage dual/triple supervisory circuits targeting multivoltage embedded systems where reliability, small size, and guaranteed reset behavior under brownout are critical design requirements.

FAQ

What is the exact reset threshold voltage for VCC1 on the MAX6721UTRGD3?

The MAX6721UTRGD3 has a factory-trimmed VCC1 reset threshold of 4.625V (minimum 4.500V, maximum 4.750V) as defined by the "T" suffix in its part number. This threshold is guaranteed over -40°C to +85°C and exhibits 20ppm/°C tempco. The device asserts RST low when VCC1 falls below this level and holds reset for ≥210ms after VCC1 recovers above 4.625V.

Does the MAX6721UTRGD3 support monitoring a third voltage rail?

No, the MAX6721UTRGD3 is a dual-voltage supervisor and does not include the RSTIN input required for triple-voltage monitoring. That function is implemented in MAX6723–MAX6727 variants. The MAX6721UTRGD3 monitors only VCC1 and VCC2, with fixed thresholds of 4.625V and 3.075V respectively, and provides no auxiliary voltage input pin.

What is the watchdog timeout behavior of the MAX6721UTRGD3 after power-on reset?

The MAX6721UTRGD3 features a dual-mode watchdog: after any reset event (including power-on), it enters a 35s minimum startup timeout period, allowing full system initialization. Once the first valid WDI transition occurs, it switches to 1.12s minimum normal timeout mode. If WDI remains static beyond either timeout, RST asserts for 210ms. This behavior is inherent to the MAX6721UTRGD3 silicon design.

Can the MAX6721UTRGD3 operate with VCC1 = 2.8V and still guarantee reset validity?

Yes, the MAX6721UTRGD3 guarantees correct reset output logic state as long as either VCC1 or VCC2 remains greater than 0.8V. At VCC1 = 2.8V, the device fully operates: VCC1 threshold comparison remains valid, RST output drives correctly (VOL ≤ 0.3V at 500µA sink), and watchdog timing functions normally. This specification is explicitly guaranteed in the Absolute Maximum Ratings and Electrical Characteristics tables for MAX6721UTRGD3.

What package type and pin count does the MAX6721UTRGD3 use?

The MAX6721UTRGD3 uses a 6-pin SOT23-6 package (2.9mm × 1.6mm × 1.1mm body size) with gull-wing leads. Pinout is standardized across the MAX6721–MAX6722 series: Pin 1 = RST (open-drain), Pin 2 = GND, Pin 3 = MR, Pin 4 = VCC2, Pin 5 = VCC1, Pin 6 = WDI. This package is RoHS-compliant and available in both leaded and lead-free versions.