Nanopower supervisor with a 1V threshold and fast reset
The Texas Instruments TPS3899DL10DSER is a simple reset/power-on reset supervisor that monitors a single voltage rail at a 1V threshold and asserts an active-low, open-drain reset output. The 40µs typical reset timeout is notably short — it lets the downstream MCU or FPGA begin code execution within microseconds of the supply crossing the threshold, which matters for applications where the processor must come up ahead of a bus handshake or a safety watchdog window. The open-drain output allows the reset line to be shared with other supervisors or a manual reset button via a pull-up resistor.
What the 1V threshold and 40µs timeout mean for the BOM
The 1V threshold is set for monitoring a 1.0V core rail — common on modern MCUs, FPGAs, and SoCs. If your design uses a 1.2V or 1.8V rail, this part will assert reset prematurely; the TPS3899 family includes other threshold options for those voltages. The 40µs reset timeout is short enough that the supervisor will not mask a brief brown-out — if the rail dips below 1V for longer than 40µs, the reset fires. That is a feature for safety-critical systems that need fast fault reaction, but it means the supply decoupling must be sized to hold the rail above threshold during transient load steps.