The MAX6369-MAX6374 from Maxim Integrated (now part of Analog Devices) are pin-selectable watchdog timers that supervise a microprocessor's activity. The µP must toggle the watchdog input (WDI) within a set window; if it does not - because the software has hung in a loop or crashed - the watchdog times out and the WDO̅ output pulses, which is wired to reset or interrupt the processor. The MAX6369 is the open-drain WDO̅ version. MAX6369KA+T is the RoHS ("+"), tape-and-reel ("T") option in 8-pin SOT23.

The defining feature is pin-selectability. Three inputs - SET0, SET1, SET2 - program both the watchdog timeout period and the initial startup delay, each selectable from 1 ms to 60 s, by tying the pins to GND, V_CC or leaving them open. This means the timing is set in hardware with no external resistor or capacitor, and - unlike a one-time-programmed part - it can be changed without a power cycle. One SET combination disables the watchdog entirely for debugging.

It is built for always-on, battery-friendly supervision. The supply current is just 8 µA, and the part needs no external components - the timing is internal. The startup delay gives the system time to initialize on power-up before the watchdog begins counting, so the µP can take charge cleanly. The MAX6369 runs from +2.5 V to +5.5 V over the automotive -40 °C to +125 °C range in a miniature 8-pin SOT23 (the KA/V+ option is AEC-Q100 qualified).

Note: Values are taken from the Maxim MAX6369-MAX6374 datasheet. The exact timeout/startup-delay set by SET0-SET2 is per the datasheet's selection table; confirm against the latest official documentation before committing a design.

MAX6369KA+T ships in the 8-pin SOT23 (package outline 21-0078) - the miniature surface-mount body that lets a watchdog with no external timing parts sit beside the processor in minimal area. The layout is simple: tie SET0/SET1/SET2 to the levels for the chosen timeout, route WDI from a clean point in the µP's main loop, pull up the open-drain WDO̅ to the logic rail, and bypass V_CC. The package image is shown below.

The 8-pin SOT23 carries the watchdog input/output, the three SET inputs and the supply (per the MAX6369-MAX6374 datasheet):

• Pin 1 - WDI: Watchdog input; the µP must transition it within the timeout, or WDO̅ pulses.
• Pin 2 - GND: Ground.
• Pin 3 - N.C.: No connection; leave unconnected.
• Pin 4 - SET0: Set Zero - selects startup delay and watchdog timeout (with SET1/SET2).
• Pin 5 - SET1: Set One - timeout/startup-delay select.
• Pin 6 - SET2: Set Two - timeout/startup-delay select.
• Pin 7 - WDO̅: Watchdog output (open-drain, active-low pulse); needs a pull-up resistor.
• Pin 8 - V_CC: Supply, +2.5 V to +5.5 V; bypass to GND.

Within the MAX6369-MAX6374 family the variants differ by output type and timing range - the MAX6370 is the push-pull WDO version of the MAX6369. Related supervisory and power-management parts are below.

Selection Tips: Choose the MAX6369 for a pin-selectable watchdog with an open-drain WDO̅; step to the MAX6370 for a push-pull output, or other family members for different timeout ranges. Pair it with a supervisor (MAX6368) for reset/battery-backup, an LDO (MAX604) and a reference (MAX6071/MAX6063) to complete the system's housekeeping.

Maxim Integrated, now part of Analog Devices, Inc. (ADI), built the MAX6369-MAX6374 to give designers a watchdog whose timing is set by pins, not external parts - so a single SOT23 covers a wide range of timeout and startup-delay needs, changeable without a power cycle.

ADI maintains the datasheet, the SET0-SET2 selection table, and the WDI-service and layout guidance for the family - the documentation behind a robust watchdog design.