140 ms reset timeout — system start-up timing
The MAX709LCUA+ is a single-channel voltage supervisor from Maxim Integrated that asserts a reset signal whenever the monitored supply rail drops below its 4.65 V threshold. Once the rail recovers above the threshold, the device holds the reset output low for a minimum of 140 ms before releasing it. This 140 ms timeout gives the supply rail time to settle and the processor time to complete its power-on reset sequence before code execution starts. The reset output is active-low, push-pull, so no external pull-up resistor is needed — it drives high when reset is deasserted.
4.65 V threshold — 5 V rail brown-out protection
The 4.65 V threshold is set for monitoring a nominal 5 V supply. It trips at roughly 93% of 5 V, which means the supervisor will assert reset before the rail drops far enough to cause logic errors or data corruption in 5 V logic. The 140 ms reset timeout is long enough to let the supply recover from a brief brown-out without cycling the system, but short enough that the system does not sit idle for an unnecessarily long time after a power-up. For designs that need a different trip point, the MAX709 family offers multiple threshold options.
The part is ROHS3 compliant.