What four rails does the MAX6339KUT watch?
The MAX6339KUT is a 4-channel multi-voltage supervisor from Analog Devices that monitors up to four supply rails and asserts a reset signal when any monitored voltage falls below its threshold. Two channels have fixed thresholds at 2.19 V and 2.93 V; the remaining two are adjustable via external resistor dividers, letting you set custom trip points for non-standard rails like a 1.8-V core or a 3.6-V I/O supply.
What does the 140 ms reset timeout mean for system boot?
The 140 ms minimum reset timeout holds the system in reset long enough for all monitored supplies to stabilize after power-up, then releases the reset to start the processor. This prevents the CPU from trying to execute code while the 2.93-V or adjustable rails are still ramping — a common failure in multi-rail designs where a fast-starting 3.3-V rail is ready before a slower 1.8-V rail has settled. The SOT-23-6 package keeps the PCB footprint small — six pins for four voltage inputs, ground, and the open-drain reset output — so it fits in tight layouts where a larger supervisor would force a board spin.