Analog Devices Inc./Maxim Integrated MAX6728KALTD3

Overview

MAX6728KALTD3 from Maxim Integrated is a dual-voltage microprocessor supervisory IC monitoring VCC1 (primary supply) and VCC2 (secondary supply), with power-fail input (PFI)/output (PFO), manual-reset (MR), and watchdog timer (WDI) functions. It asserts an active-low open-drain RST output when either supply drops below factory-trimmed thresholds (VTH1 = 4.625 V, VTH2 = 3.075 V), maintains reset for 210 ms (min), and operates from -40°C to +125°C in an 8-pin SOT23 package. Used in telecom power systems to ensure clean boot and brownout recovery.

For engineers reviewing the MAX6728KALTD3 datasheet, MAX6728KALTD3 pinout, MAX6728KALTD3 application, or MAX6728KALTD3 equivalent, key selection criteria include dual-supply threshold accuracy (±1.5% over temperature), guaranteed reset validity down to VCC1/VCC2 = 0.8 V, PFI/PFO power-fail signaling with 2 µs delay, 1.12 s (min) normal watchdog timeout, and 14 µA typical supply current at 3.6 V.

Technical Context

The MAX6728KALTD3 integrates two independent voltage comparators for VCC1 and VCC2, each with factory-trimmed thresholds (4.625 V and 3.075 V respectively), 20 ppm/°C tempco, and 0.5% hysteresis. Its internal reset timeout timer is fixed at 210 ms (min), and it features a dual-mode watchdog with 35 s (min) startup period and 1.12 s (min) normal timeout.

It includes a dedicated PFI comparator referenced to 626.5 mV, driving an open-drain PFO output with 2 µs propagation delay, and supports manual reset via MR (internal 50 kΩ pullup to VCC1). All logic inputs (MR, WDI, PFI, RSTIN) accept CMOS-compatible levels, and outputs are guaranteed functional down to VCC = 0.8 V.

Key Specifications

Pinout & Package

MAX6728KALTD3 is housed in an 8-pin SOT23 package (JEDEC MO-178AA), with 0.65 mm pitch, 2.9 mm × 1.6 mm footprint, and 1.1 mm max height. Pin 1 is marked with a dot; device orientation follows standard SOT23 pin 1 indicator.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6728KALTD3, MAX6729KALTD3 offers identical supervision logic but simplifies interface design with push-pull RST, while TPS3808G33DBVR reduces feature set and package size at the expense of dual-supply and power-fail capability - making it viable only in constrained single-rail applications.

Availability

MAX6728KALTD3 is available at Aetrix Electronics and suitable for telecom infrastructure, industrial control, and automotive ADAS applications requiring stable component supply, extended temperature operation, and AEC-Q100–qualified reliability.

Supply support for MAX6728KALTD3 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 demanding industrial, automotive, and communications applications.

The MAX6715A–MAX6729A family delivers ultra-low-voltage, multi-rail supervision with integrated watchdog and power-fail detection - engineered specifically for high-reliability embedded systems where supply integrity directly impacts functional safety.

FAQ

What is the exact reset timeout period of the MAX6728KALTD3?

The MAX6728KALTD3 has a guaranteed minimum reset timeout period of 210 ms. This is the minimum duration the RST output remains asserted after all monitored supplies (VCC1 and VCC2) rise above their respective thresholds, MR returns high, or the watchdog is cleared. The actual timeout may vary slightly due to process and temperature, but never falls below 210 ms across the full -40°C to +125°C operating range. This value is fixed by the "D3" suffix in the MAX6728KALTD3 part number.

Does the MAX6728KALTD3 support monitoring a third voltage rail?

No, the MAX6728KALTD3 does not support a third monitored voltage. Unlike variants such as MAX6723A–MAX6727A, it lacks the RSTIN input pin required for externally adjustable auxiliary voltage monitoring. Its supervision is strictly limited to VCC1 (4.625 V threshold) and VCC2 (3.075 V threshold), plus PFI-based power-fail detection. For triple-voltage monitoring, consider MAX6723KALTD3 or MAX6727KALTD3 instead of MAX6728KALTD3.

What is the function of the PFI and PFO pins on the MAX6728KALTD3?

The PFI (Power-Fail Input) pin on the MAX6728KALTD3 is a high-impedance comparator input referenced to an internal 626.5 mV threshold. When the voltage at PFI falls below this level - typically set via an external resistor divider from a monitored supply - the PFO (Power-Fail Output) pin is driven low. PFO is an open-drain output that deasserts immediately upon PFI recovery, with no timeout delay. This enables real-time power-fail alerts for firmware-driven shutdown sequences, distinct from the timed RST assertion.

Can the watchdog timer in the MAX6728KALTD3 be disabled?

Yes, the watchdog timer in the MAX6728KALTD3 is disabled by leaving the WDI pin unconnected. An internal 200 nA current source detects the floating state and disables watchdog functionality. If WDI must be routed on the PCB, it should be tied directly to GND or VCC1 through a ≥1 MΩ resistor to avoid unintended activation. Driving WDI with logic signals enables the dual-mode watchdog: 35 s (min) startup period followed by 1.12 s (min) normal timeout - both fully supported in MAX6728KALTD3.

What package type and pin count does the MAX6728KALTD3 use?

The MAX6728KALTD3 uses an 8-pin SOT23 package (JEDEC MO-178AA), measuring 2.9 mm × 1.6 mm with 0.65 mm lead pitch. It is RoHS-compliant and lead(Pb)-free. This 8-pin variant accommodates dual reset outputs (RST and RST2), PFI/PFO, WDI, MR, VCC1, VCC2, and GND - unlike the 5- or 6-pin versions of the MAX67xxA family. The "KA" in the part number explicitly denotes the 8-pin SOT23 package for MAX6728KALTD3.