Analog Devices Inc./Maxim Integrated MAX6721UTRVD3+

Overview

MAX6721UTRVD3+ 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 (VTH1) and 3.075V (VTH2), 210ms minimum reset timeout, watchdog input (WDI), manual reset (MR), and open-drain active-low RST output. It ensures reliable system reset during power-up, brownout, or software fault in battery-powered telecom and embedded controllers.

For engineers reviewing the MAX6721UTRVD3+ datasheet, MAX6721UTRVD3+ pinout, MAX6721UTRVD3+ application, or MAX6721UTRVD3+ equivalent, key selection criteria include dual-supply monitoring capability down to 0.8V VCC operation, guaranteed reset validity at ultra-low voltage, 14µA typical supply current, and integrated watchdog with 35s startup/1.12s normal timeout - critical for low-power, safety-critical embedded systems.

Technical Context

The MAX6721UTRVD3+ implements independent voltage comparators for VCC1 and VCC2, each with ±0.5% hysteresis and 20ppm/°C tempco, asserting reset when either supply falls below its threshold. Its watchdog timer features dual-mode timing: 35s minimum initial period after reset to accommodate boot sequences, then automatic transition to 1.12s normal timeout upon first WDI edge detection.

This device integrates MR with internal 50kΩ pullup to VCC1, supports noise-immune reset assertion via 200ns MR-to-RST delay, and guarantees valid reset logic state even when VCC1 or VCC2 drops to 0.8V - enabling robust operation in deep brownout conditions without external support circuitry.

Key Specifications

Pinout & Package

MAX6721UTRVD3+ is housed in a 6-pin SOT23-6 package (2.9mm × 1.6mm × 1.1mm), surface-mount, RoHS-compliant, with thermal pad option not included.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6721UTRVD3+, MAX6326UR29D3+ reduces functionality to single-rail supervision with no watchdog or manual reset, while TPS3808G33DBVR adds MR but omits VCC2 monitoring and WDI - making MAX6721UTRVD3+ uniquely suited for compact, dual-rail, watchdog-protected embedded systems requiring minimal BOM count.

Availability

MAX6721UTRVD3+ is available at Aetrix Electronics and suitable for telecom line cards, industrial PLCs, portable medical monitors, and set-top box SoC power sequencing requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant sourcing.

Supply support for MAX6721UTRVD3+ 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, communications, and computing markets.

The MAX6715–MAX6729 family was designed specifically for multivoltage embedded systems needing compact, ultra-low-power, dual- or triple-supply supervision with integrated watchdog and manual reset - targeting space-constrained, battery-sensitive, and reliability-critical applications.

FAQ

What is the exact reset timeout period for MAX6721UTRVD3+?

The MAX6721UTRVD3+ has a minimum reset timeout period of 210ms, as indicated by the "D3" suffix in its part number. This value is factory-trimmed and guaranteed over -40°C to +85°C. The actual timeout may vary slightly due to temperature and supply voltage but remains ≥210ms under all specified operating conditions. This timing ensures sufficient hold time for microprocessors and FPGAs to complete initialization before release from reset.

Does MAX6721UTRVD3+ support monitoring a third voltage rail?

No, MAX6721UTRVD3+ is a dual-voltage supervisor and does not include the RSTIN input required for third-rail monitoring. That function is reserved for variants like MAX6723–MAX6727. The MAX6721UTRVD3+ monitors only VCC1 and VCC2, with fixed thresholds of 4.625V and 3.075V respectively. For triple-voltage supervision, consider MAX6723UTRVD3+ or MAX6727KA33D3+, which add the RSTIN pin and internal 626mV reference.

What is the watchdog behavior of MAX6721UTRVD3+ during system boot?

The MAX6721UTRVD3+ implements a dual-mode watchdog: after any reset event (power-up, MR, or WDI timeout), it enters a 35s minimum startup period, allowing ample time for firmware boot. Upon detecting the first valid WDI edge (rising or falling), it transitions to the 1.12s minimum normal timeout mode. This prevents false resets during lengthy initialization while ensuring rapid fault detection during steady-state operation.

Can MAX6721UTRVD3+ operate with VCC1 = 1.8V and VCC2 = 1.2V?

Yes, MAX6721UTRVD3+ operates with VCC1 as low as 0.8V and VCC2 as low as 0.8V, but its factory-trimmed thresholds (4.625V/3.075V) are optimized for higher rails. At 1.8V/1.2V, the device remains functional and asserts reset if either supply drops below its respective threshold - however, those thresholds exceed the supply values, so reset would be continuously asserted. For low-voltage rails, select a variant with appropriate suffix (e.g., "W" for 1.665V VTH1).

Is the RST output of MAX6721UTRVD3+ push-pull or open-drain?

The MAX6721UTRVD3+ features an open-drain active-low RST output, as confirmed by the Selector Guide and Pin Description. It requires an external pullup resistor to VCC1 (or another logic rail) to generate a valid HIGH level. This configuration supports bidirectional µP reset pins and voltage-level translation, unlike push-pull variants (e.g., MAX6722UTRVD3+) which drive both logic states internally.