Dual-channel digital isolator with 15Mbps open-collector outputs
The Renesas NEPOC PS9821-2-F3-AX is a dual-channel optocoupler in an 8-SOIC package, designed for galvanic isolation in digital interface applications. It provides two independent isolation channels with open-collector outputs, supporting a data rate of 15Mbps and an isolation voltage rating of 2500Vrms. The part operates from a 2.7V to 3.6V supply on the output side and accepts DC input on the LED side with a typical forward voltage of 1.65V.
15kV/µs common-mode transient immunity — what it means for motor-drive and inverter designs
The PS9821-2-F3-AX specifies a minimum common-mode transient immunity (CMTI) of 15kV/µs. In a motor drive or inverter stage, fast-switching IGBTs or SiC MOSFETs can couple kilovolt-per-microsecond edges across the isolation barrier. A CMTI rating below the system's dV/dt risks data corruption or latch-up on the output side. At 15kV/µs minimum, this part handles the transient environment of most industrial drives and power converters without needing external filtering or a higher-rated isolator.
Open-collector output — pull-up resistor selection and bus interface
The open-collector output stage on each of the two channels sinks up to 25 mA per channel. This output type requires an external pull-up resistor to the supply rail (2.7V to 3.6V) to define the logic-high level. Propagation delay is specified at 75ns max for both low-to-high and high-to-low transitions, with rise and fall times of 20ns and 5ns typical. For a 15Mbps NRZ data stream, the pull-up value should be chosen to keep the RC time constant well under one bit period — roughly 33 ns at 15 Mbps — which typically lands in the 330Ω to 1kΩ range depending on bus capacitance and supply voltage.