What this supervisor does on your board
It asserts a reset signal on power-up and holds it active for a minimum of 140 ms after the supply crosses the adjustable/selectable threshold, giving the system time to stabilize. The active-high, push-pull output directly drives the reset input of most MCUs, FPGAs, or SoCs without needing an external pull-up resistor.
140 ms reset timeout — what it buys you
For a typical MCU with a startup time of a few milliseconds, this provides ample margin. If your design uses a fast-starting FPGA or a processor with a short power-on reset window, the 140 ms delay is conservative but harmless — the supervisor simply holds reset a bit longer than needed. No external timing capacitor is required; the timeout is fixed internally.
Active high output — check your logic polarity
The MAX6839XSD0 asserts a logic high on the reset pin during power-up and fault conditions. Many processors expect an active-low reset, so verify the polarity of your target device's reset input before specifying this part. If your design requires an active-low signal, look for the active-low sibling in the same family. The push-pull output stage can source and sink current, so it drives CMOS and TTL inputs cleanly without an external resistor.
Housed in an SC-70-4 (also known as SOT-343), this part occupies minimal board area. The four-pin footprint is standard for simple supervisor ICs, making it straightforward to route on a dense PCB.
However, note that the part is marked RoHS non-compliant — it contains lead (Pb) in the solder finish or die attach. This limits its use in new designs bound for RoHS-regulated markets (EU, California, etc.) unless an exemption applies. If you need a RoHS-compliant alternative, Maxim offers functionally similar supervisors in the same family — check the active-low or adjustable-threshold variants for lead-free options.