I am using adm2582 in one of our application , in datasheet of the IC it is explicitly mentioned that pin 16 should not be connected to pin 14 & 11 . I am just curious why ? also what are the repercussion if we connect pin 16 directly to 14 & 11 ? what are its worst outcome .
Thanks & Regards
ADM2582E eliminates the need to design an isolated DC-DC power supply circuit for the isolated RS-485 transceiver. There are minimal design requirements for this integrated solution, but we have included this recommendation so that switching noise from the integrated isolated DC-DC circuit can be filtered before connecting to the PCB bus-side ground. This is because the PCB acts as an antenna for this noise, resulting in radiated emissions, and also connecting pins 16 and 20 directly to pins 11 and 14 will allow the switching noise to couple to the data transmission section of the IC (iCoupler + RS-485 transceiver).
Pin 16 and Pin 20 should be connected directly to the bus-side ground plane of the PCB.
Hello Conal ,
Thank you for your reply it was indeed very helpful , so to my understanding if we directly connect the Pin 11 & 14 to Pin 16 & 20 it will only cause EMI/EMC issue. Will it affect the other side of transceiver port or damage the port ?
Thank you .
You're correct, pins 11, 14, 16 and 20 can be connected together per the pin naming (all GND2) and the part will operate and function normally, it's just not optimal from an EMC perspective.
User guide UG-916 for EVAL-ADM2582EEMIZ evaluation board has guidelines to pass EN 55022 Class A with ADM2582E on a two layer PCB (in fact with 3.3V Vcc, and a high-voltage discrete capacitor across the isolation barrier, Class B limits can be met on a two-layer PCB).
User guide UG-044 for EVAL-ADM2582EEBZ evaluation board has guidelines to pass EN 55022 Class B limits with ADM2582E on a four-layer PCB (implementing a small overlap in internal layers for embedded stitching capacitance in the PCB).
Lower data rates or ADM2587E will also be lower emissions.