Two-rail voltage supervisor in a 5-pin SC-70
The MAX6739XKVD7-T is a multi-voltage supervisor from Analog Devices that monitors two supply rails: one at a fixed 1.575V threshold and a second adjustable input that lets you set the trip point with an external resistor divider. It asserts an active-low reset output when either monitored voltage drops below its threshold, then holds the reset for a minimum of 1.2 seconds after all rails recover — long enough for the downstream processor's oscillator and PLL to stabilise before the core starts executing. The reset output is push-pull (totem-pole), so it drives the processor's reset pin directly without needing an external pull-up resistor. The SC-70-5 package (also listed as SOT-353) keeps the footprint small — useful in space-constrained designs like portable instruments, sensor nodes, or multi-rail embedded systems where board real estate is tight.
What the thresholds mean for your power-up sequence
The fixed threshold of 1.575V is set for monitoring a 1.8V nominal rail — a common core supply for low-voltage ASICs, FPGAs, or memory. The adjustable second channel covers the other rail at whatever voltage you need (e.g. 3.3V, 2.5V, or 1.2V), configured by two resistors. This dual-monitor approach catches a brownout on either rail before the processor sees corrupted logic levels. The 1.2s minimum reset timeout gives the main regulator time to settle after a fault clears, preventing a rapid on-off-on cycle that could stress the load.
Note that this part is RoHS non-compliant per the manufacturer's declaration. If your BOM requires RoHS-10 or REACH compliance, verify the exemption or consider an alternative from the MAX6739 family that carries the lead-free suffix.