XTR111, how to protect the external MOSFET transistor?
Hi Alex,
Page 14 of the XTR111 datasheet gives some very good information on protecting the external MOSFET. Figure 37 shows two implementations of current limiting in order to protect the MOSFET. If you are concerned that a transient or ESD event may damage the MOSFET a zener diode between the gate and source of the MOSFET is a suitable protection option.
John Caldwell
Analog Applications Engineer
PA Linear Apps
Hello John!Thanks for the answer!Than use of the MOSFET-transistor is caused? Why it is impossible to apply the bipolar-transistor?Me protection against ESD interests. Whether one diode zener for protection of the MOSFET-transistor will suffice? It can be necessary to protect a drain-source in addition? Application of supressor instead of diodes zener will be more effective?
Alex,
The XTR111 was designed specifically to operate with an external P-MOSFET, therefore its gate-drive circuitry is not suitable for a PNP bipolar transistor. Generally, the thin gate oxide layer of MOSFETs is the structure that is most vulnerable to ESD discharge. If a P-MOSFET is selected with a VDS rating well above your loop supply voltage I would not expect a protection diode to be necessary across the drain/source, however there is always the potential for inductive flyback in a transient condition and a diode would help prevent these from damaging the FET. TVS's may provide superior protection in your application however remember to consider the leakage current through any added protection circuitry as it will contribute error in your current loop.
John, thanks for the answer!