Three-rail supervisor in a five-pin SOT
The LTC1728HS5-5#TRMPBF from Analog Devices is a multi-voltage supervisor that keeps an eye on three supply rails at once. It monitors thresholds at 3.086 V and 4.675 V, plus a third adjustable input for whatever other rail you need to watch. The open-drain, active-low reset output pulls low for a minimum of 140 ms when any monitored voltage drops below its threshold, then releases after the timeout once all rails are good. That three-in-one package saves board space and a couple of external comparators on a multi-rail design.
What the thresholds mean for your rails
The fixed 3.086 V threshold is a natural fit for a 3.3 V rail — it trips at roughly 93.5% of nominal, which is a common undervoltage detection point for logic supplies. The 4.675 V threshold suits a 5 V rail, tripping at about 93.5% as well. The adjustable input lets you set any threshold down to 0.6 V with a resistor divider, so you can monitor a 1.8 V or 2.5 V rail alongside the fixed ones. That covers the typical power tree in a mixed-voltage system without needing a separate supervisor per rail.
Temperature range and where it goes
Rated for -40°C to 125°C, this supervisor works in industrial enclosures, outdoor telecom cabinets, and under-hood automotive zones where the ambient swings hard. The TSOT-23-5 package is small enough for space-constrained PCBs but still hand-solderable for rework. The open-drain output lets you wire-OR multiple supervisors or pull up to a different voltage than the monitored rails, which is handy in mixed-logic designs.
Lifecycle and sourcing reality
ROHS3 compliant.