Beyond datasheet curves

Perform worst case analysis with missing datasheet information

RAPHTON enables high technology actors to save an invaluable amount of time during their development phase. What do they remember from this? A precise evaluation of their products’ performance in record time.
This is what Marc Marmouget, hardware expert at STEEL ELECTRONIQUE explained to us…

Our needs

STEEL ELECTRONIQUE is a high tech company that has most of its activities in the space industry, working with majors actors like Thales Alenia Space, Airbus Defence & Space, CNES, ONERA, CEA, …

As part of a development of a power supply board for a space application, we used Raphton Analyzer software to check the performances of a voltage limiter stage.

This stage aims to limit the value of voltage delivered to the equipment in case of failure of the switching power supply, a major function for the safeguarding of the mission. The delivered current range is 100mA to 2A.

Limits of the datasheet compared to the constraints

The main technical constraint is the very low dropout voltage tolerance for the output voltage. This design is based on a voltage limitation performed by a P-MOS transistor.

The objective was to find the best component to minimize the RDS (ON) of the transistor and thus make the output voltage the least sensitive as possible to inrush current.

The selected transistor is an IRHLNJ797034 from International Rectifier. Its RDS (ON) is only 72mΩ at 22A, then probably a very low RDS (ON) between 100mA and 2A. Unfortunately it is impossible to calculate from the component datasheet where curves only start at a VDS of 100mV.

Normally, a prototype would have been necessary to characterize the component behavior in the current range, and for the desired temperatures, before adding it into the equipment schematic.

RAPHTON, the solution for precision

Thanks to Raphton and its modeling technology, the component model has operating characteristics that are representative of the real component. Raphton can therefore extrapolate the curves and provide accurate results. Even when there are only 2 temperatures provided by the manufacturer and the currents we are interested in are out of the graph.
Using Raphton, the RDS (ON) values of the transistor were calculated for the extreme currents and the operating temperature to validate the design before manufacturing the electronic board. The test campaigns showed that Raphton’s results were good.

Marc Marmouget