Dual-rail supervisor for 3.3V and 5V systems
The two monitored thresholds are set at 2.93V and 4.55V, which correspond to undervoltage detection for nominal 3.3V and 5V rails respectively. When either rail drops below its threshold, the active-low open-drain output pulls low and holds the reset state for a minimum of 70ms after both rails recover.
The 2.93V threshold on the 3.3V rail gives roughly 11% undervoltage margin — tight enough to catch a sagging regulator before the downstream logic enters an indeterminate state, but not so tight that normal ripple triggers nuisance resets. The 4.55V threshold on the 5V rail provides about 9% margin, typical for supervisor ICs in this class. The 70ms minimum reset timeout is a standard duration for most MCUs and DSPs — it ensures the processor's internal POR and oscillator startup complete before the reset pin releases. If your design uses a part with a longer startup sequence, you may need an external capacitor to extend the timeout (the TPS3306 does not have a programmable timeout pin). The open-drain output allows wired-OR connection with other reset sources (manual reset button, watchdog timer) without contention — a common topology in industrial controllers where multiple fault conditions must assert reset.
The temperature range covers the full industrial envelope without requiring a higher-cost automotive-grade part.
Housed in an 8-pin SOIC (0.154-inch body width, 3.90mm width), the TPS3306-33DR uses a standard footprint that routes cleanly on a 2-layer board. The 1.27mm pin pitch is hand-solderable and inspectable — no hidden joints under the package.