How to read datasheets
Which is the correct way to read a power MOSFET's safe operating area (SOA) graph?
- AThe DC line is outermost, and for pulsed operation, the shorter the pulse, the more strictly it is limited compared with DC
- BThe boundary is set only by the absolute maximum ratings of VDS and ID, so it does not change with pulse width or case temperature
- CShorter pulses allow higher power, and most graphs are for 25 °C single pulses, so derate according to temperature
Show answer and explanation
Answer: C. Shorter pulses allow higher power, and most graphs are for 25 °C single pulses, so derate according to temperature
The SOA is a log-log graph with VDS on the horizontal axis and ID on the vertical axis, showing the combinations of voltage and current at which the device can be used without damage. The boundary is set by the RDS(on) limit, the current rating, the thermal (power) limit and so on; the thermal limit relaxes as pulse width shortens, so multiple lines such as 10 µs, 1 ms and DC are drawn. Most graphs are for a case temperature of 25 °C and a single pulse, so derate them for the actual temperature and repetitive operation. This is especially important when operating in the linear region, as in inrush-current limiting circuits.