Four-rail voltage watchdog in a SOT-23-6
The MAX6339BUT from Maxim Integrated is a multi-voltage supervisor that monitors four supply rails simultaneously. It tracks three fixed thresholds at 2.19 V, 3.08 V, and 4.63 V, plus one adjustable input for a custom voltage, all in a six-pin SOT-23-6 package. The open-drain, active-low reset output asserts when any monitored voltage falls below its threshold and holds for a minimum of 140 ms after all rails recover — enough time for most power supplies and system clocks to stabilise before the processor starts. Rated for the industrial temperature range of -40°C to 85°C, this part fits into outdoor telecom cabinets, factory automation controllers, and any board where multiple supply rails need a single-package supervision solution. The SOT-23-6 footprint keeps the board area small, and the open-drain output lets multiple supervisors share a common pull-up resistor on a shared reset line.
Thresholds and the adjustable channel
Three of the four monitored thresholds are factory-set: 2.19 V, 3.08 V, and 4.63 V. The fourth channel is adjustable via an external resistor divider.
Reset timing and output drive
The 140 ms minimum reset timeout is long enough to ride through a brief brown-out without a false reset, but short enough that the system does not sit idle for a quarter-second after the rails come up. The open-drain output sinks current when the reset is asserted; you supply the pull-up resistor to the logic supply.
Lifecycle and compliance note
One catch: the part is RoHS non-compliant, so it is not suitable for new designs that must meet the EU RoHS directive. For legacy boards or military/aerospace projects where leaded solder is still specified, that is not a blocker — but a BOM reviewer should flag it if the assembly house requires RoHS.
Sourcing and availability
This part is sourced through independent distribution channels. Because it is an active part with no LTB risk, it can be specified into a production BOM with confidence that the supply chain will support it for the foreseeable future.