5.6 V Zener in DO-214AC — board-level shunt regulation
The Microchip SMAJ4734AE3/TR13 is a 5.6 V Zener diode in the DO-214AC (SMA) surface-mount package, rated for 2 W continuous power dissipation. The ±5% tolerance on the nominal voltage means the actual breakdown falls between 5.32 V and 5.88 V — tight enough for a reference rail or input clamp where the downstream regulator can absorb the spread.
Impedance and leakage — what they mean for the bias point
Maximum Zener impedance (Zzt) is 5 Ohms at the test current — the dynamic resistance at the knee. A 5.6 V rail loaded with a few mA sees the output shift by roughly 5 mV per mA of load change, which is acceptable for a simple shunt regulator but not for a precision ADC reference. Reverse leakage is 10 µA maximum at 2 V reverse bias, well below the self-heating threshold in a high-impedance divider.
The DO-214AC package with a copper pad under the cathode tab sets the thermal resistance — the 2 W rating assumes adequate board copper for heat spreading. In a dense layout, derate based on the actual trace area and adjacent component heating.