Analog Devices Inc./Maxim Integrated MAX6729KASDD3+

Overview

MAX6729KASDD3+ from Maxim Integrated is a triple-voltage microprocessor supervisory circuit in an 8-pin SOT23 package, monitoring VCC1 (4.625V threshold), VCC2 (3.075V threshold), and an auxiliary supply via RSTIN (626.5mV reference). It provides push-pull active-low reset (RST), power-fail input/output (PFI/PFO), manual reset (MR), and watchdog timer (WDI) with 35s startup and 1.12s normal timeout. Used in telecom power management to ensure reliable boot and brownout recovery.

For engineers reviewing the MAX6729KASDD3+ datasheet, MAX6729KASDD3+ pinout, MAX6729KASDD3+ application, or MAX6729KASDD3+ equivalent, key selection criteria include its triple-supply monitoring capability, guaranteed reset validity down to VCC1/VCC2 = 0.8V, push-pull RST output referenced to VCC1, PFO push-pull configuration, and 210ms (min) reset timeout period - all critical for multivoltage embedded systems requiring deterministic fault response.

Technical Context

The MAX6729KASDD3+ integrates three independent voltage comparators: one for primary supply VCC1 (factory-trimmed 4.625V threshold), one for secondary supply VCC2 (3.075V), and one for externally adjustable RSTIN (626.5mV internal reference). Its dual-mode watchdog uses a 35s minimum startup timeout followed by 1.12s minimum normal timeout, triggered by WDI edge transitions.

It features a push-pull RST output referenced to VCC1, a push-pull PFO output referenced to VCC1, MR with 50kΩ internal pullup to VCC1, and PFI comparator with 3mV hysteresis. Reset assertion is guaranteed while either VCC1 or VCC2 remains ≥0.8V, and supply current is 14µA (typ) at 3.6V.

Key Specifications

Pinout & Package

MAX6729KASDD3+ is housed in an 8-pin SOT23-8 package (2.0mm × 2.1mm × 1.25mm), optimized for space-constrained PCB layouts in portable and telecom equipment.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6728KA+T, MAX6729KASDD3+ eliminates external PFO pullup components and simplifies interrupt routing; versus TPS3808G33DBVR, it delivers full triple-supply supervision and integrated power-fail signaling in a single IC - reducing footprint, BOM count, and validation effort for complex multivoltage systems.

Availability

MAX6729KASDD3+ is available at Aetrix Electronics and suitable for telecom infrastructure, industrial PLCs, server management controllers, and medical imaging subsystems requiring stable component supply across extended product lifecycles.

Supply support for MAX6729KASDD3+ 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 in industrial, automotive, and communications markets.

The MAX6715–MAX6729 family delivers ultra-low-voltage, multirail supervisory circuits targeting space-constrained, high-reliability systems where deterministic reset behavior under brownout and multi-supply fault conditions is mandatory.

FAQ

What is the exact reset timeout period for MAX6729KASDD3+?

The MAX6729KASDD3+ has a minimum reset timeout period of 210ms, as indicated by the "D3" suffix in its part number. This is the guaranteed minimum duration for which the RST output remains asserted after all monitored supplies recover above their thresholds, MR returns high, or WDI resets the watchdog. The actual timeout may vary slightly with temperature and supply voltage but will not fall below 210ms across -40°C to +85°C.

Does MAX6729KASDD3+ support monitoring a negative supply voltage?

Yes, MAX6729KASDD3+ can monitor a negative supply using the PFI input with an appropriate resistor-divider network, as shown in Figure 3b of the datasheet. When the negative supply drops, PFI falls below its 626.5mV threshold and PFO asserts low. The circuit's accuracy depends on PFI threshold tolerance, resistor values, and VCC stability - design verification under worst-case conditions is recommended.

How does the watchdog timer in MAX6729KASDD3+ behave after power-up?

After power-up or any reset event, MAX6729KASDD3+ enters a 35s minimum startup watchdog mode. Only after the first valid WDI transition (rising or falling edge) within that period does it switch to the 1.12s minimum normal timeout mode. This prevents premature resets during lengthy firmware initialization while ensuring rapid hang detection once the system is operational.

Can MAX6729KASDD3+ operate with VCC1 = 1.8V and VCC2 = 1.2V simultaneously?

Yes, MAX6729KASDD3+ is fully specified to operate with VCC1 as low as 1.8V and VCC2 as low as 0.9V. Its reset comparators and internal logic remain functional, and the RST output is guaranteed valid as long as either VCC1 or VCC2 remains ≥0.8V. Supply current at these levels is typically 4–11µA, enabling use in ultra-low-voltage embedded systems.

What is the function of the RSTIN pin on MAX6729KASDD3+?

The RSTIN pin on MAX6729KASDD3+ is a high-impedance input for monitoring a third supply voltage. It compares the applied voltage against an internal 626.5mV reference; when RSTIN falls below this threshold, the device asserts RST. An external resistor divider sets the effective trip point - for example, a 100kΩ/10kΩ divider yields a ~6.9V threshold - enabling flexible auxiliary rail supervision without additional components.