Analog Devices Inc./Maxim Integrated MAX6721UTLTD3-T

Overview

MAX6721UTLTD3-T from Maxim Integrated is a dual-voltage microprocessor supervisory circuit in SOT23-6 package, monitoring VCC1 (4.625V threshold) and VCC2 (3.075V threshold) with 210ms reset timeout, watchdog timer, manual reset input, and power-fail input functionality. It asserts active-low open-drain reset when either supply drops below its threshold and maintains reset for ≥210ms after recovery - used in telecom power management and industrial embedded controllers requiring reliable brownout detection.

For engineers reviewing the MAX6721UTLTD3-T datasheet, MAX6721UTLTD3-T pinout, MAX6721UTLTD3-T application, or MAX6721UTLTD3-T equivalent, key selection criteria include dual-supply monitoring range (1.8V–5.0V / 0.9V–3.3V), guaranteed reset validity down to VCC = 0.8V, 14µA typical supply current at 3.6V, and integrated watchdog with 35s startup + 1.12s normal timeout.

Technical Context

The MAX6721UTLTD3-T implements two independent voltage comparators with factory-trimmed thresholds (VTH1 = 4.625V, VTH2 = 3.075V), each referenced to internal bandgap references with 20ppm/°C tempco and 0.5% hysteresis. Its reset logic combines ORed fault conditions - VCC1 undervoltage, VCC2 undervoltage, MR assertion, or WDI timeout - driving a single open-drain RST output.

It integrates a dual-mode watchdog timer: 35s minimum initial timeout after any reset event (enabling full system boot), followed by 1.12s minimum normal timeout triggered by first WDI edge; WDI accepts CMOS/TTL levels with 0.3×VCC1/0.7×VCC1 thresholds and 100ns glitch rejection. Power-fail input (PFI) uses same 626.5mV reference as RSTIN but feeds a dedicated comparator driving PFO without reset timeout.

Key Specifications

Pinout & Package

MAX6721UTLTD3-T 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 not present.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6722UTLTD3-T, the MAX6721UTLTD3-T offers open-drain flexibility for multi-source reset arbitration, while TPS3808G33DBVR reduces BOM count in basic 3.3V applications but sacrifices dual-supply supervision and system-level fault coverage.

Availability

MAX6721UTLTD3-T is available at Aetrix Electronics and suitable for telecom infrastructure, industrial PLCs, and portable medical devices requiring stable component supply, long-lifecycle support, and guaranteed -40°C to +85°C operation.

Supply support for MAX6721UTLTD3-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 connectivity applications, with emphasis on high-reliability industrial and communications markets.

The MAX6715–MAX6729 family delivers ultra-low-voltage dual/triple supervisory circuits targeting multivoltage embedded systems where space, power, and fault coverage are critical - especially in telecom, computing, and industrial control.

FAQ

What is the exact reset threshold voltage for VCC1 and VCC2 on the MAX6721UTLTD3-T?

The MAX6721UTLTD3-T has factory-trimmed reset thresholds of 4.625V (±125mV) for VCC1 and 3.075V (±75mV) for VCC2, as defined by the "LT" suffix per Maxim's Reset Voltage Threshold Suffix Guide. These values are measured under standard conditions (TA = +25°C, VCC1/VCC2 ≥ 0.8V) and maintain 20ppm/°C tempco across -40°C to +85°C. The MAX6721UTLTD3-T guarantees valid reset assertion even when either supply drops to 0.8V.

Does the MAX6721UTLTD3-T support monitoring a third voltage rail?

No, the MAX6721UTLTD3-T is a dual-voltage supervisor and does not include the RSTIN input required for adjustable third-rail monitoring. That feature is present only in MAX6719/MAX6720/MAX6723–MAX6727 variants. The MAX6721UTLTD3-T provides dedicated PFI input for power-fail detection but cannot configure it as a third reset threshold - PFI drives PFO independently without reset timeout or latching behavior.

What is the function of the WDI pin on the MAX6721UTLTD3-T and how is it timed?

The WDI (watchdog input) pin on the MAX6721UTLTD3-T monitors µP activity via rising/falling edges. After any reset event, it enters a 35s minimum startup timeout; the 1.12s minimum normal timeout begins only after the first valid WDI transition occurs within that window. The MAX6721UTLTD3-T asserts RST if WDI remains static beyond these periods, with 100ns glitch rejection ensuring noise immunity. WDI thresholds are 0.3×VCC1 (low) and 0.7×VCC1 (high).

Can the MAX6721UTLTD3-T drive a reset line directly without an external pullup resistor?

No - the MAX6721UTLTD3-T features an open-drain RST output and requires an external pullup resistor to VCC1 (or another logic rail) to establish a valid HIGH state. Typical values range from 10kΩ to 100kΩ depending on bus capacitance and rise-time requirements. This architecture enables wired-OR connection with other reset sources, unlike push-pull variants such as MAX6722UTLTD3-T which do not require external pullups.

How does the power-fail input (PFI) differ from the reset inputs on the MAX6721UTLTD3-T?

The PFI input on the MAX6721UTLTD3-T connects to a dedicated comparator with the same 626.5mV internal reference as RSTIN (in supported variants), but its output (PFO) deasserts immediately when PFI rises above threshold - with no reset timeout period. Unlike VCC1/VCC2 monitoring, PFI does not trigger RST assertion; it provides standalone early-warning signaling (e.g., to initiate firmware save routines) while leaving reset timing fully governed by supply voltages and MR/WDI events.