I am using AD421BR on our transmitters as 4/20mA output IC. As stated in the
The DN25D FET transistor from Supertex1 meets all requirements for the FET.
Other suitable FETs include ND2020L and ND2410L, both from Siliconix.
These FET devices are all obsolete. Can you suggest a replacement part for the
The Infineon BSP129 can be used as an alternative FET. Note that the BSP129
Vgsoff voltage is quite low. Therefore, for correct operation, a 100kohm
resistor should be connected between FET gate and source (i.e. between AD421
Vcc and DRIVE).