Nanopower supervisor with programmable threshold
The Texas Instruments TPS3899DL01DSER is a nanopower supervisor — a Simple Reset/Power-On Reset IC that monitors a single voltage rail and asserts an active-low reset signal when the supply drops below a user-programmed threshold. The open-drain output stays low for a typical 40 µs after the rail returns, giving the system time to stabilise before the processor starts.
What the 40 µs timeout means for the design
A 40 µs typical reset timeout is fast — the supervisor releases the reset pin quickly after the supply recovers, so the processor or FPGA can begin code execution with minimal dead time. In a multi-rail system where sequencing matters, this short window pairs with a separate power-good signal rather than relying on the supervisor alone for hold-up. The threshold is adjustable via external resistors, which lets the same board layout accommodate different voltage rails by changing a divider pair rather than swapping the supervisor IC.