I'm designing a RS-485 communication device for CE & UL standard certifications. My test standard is ±2KV (IEC61000-4-5). We have In-house lab test facility with ESD, EFT, Signal line surge generator, etc., For my various protection circuit, I can't able to pass the test more then ±1.5KV. Please review my circuit & share your commands.
The attached waveforms & test run procedures are below..,
2kv_sig_pos (2kv signal surge positive)
04.gdt_bu_2k (bourns GDT parallel with surge generator)[measured across A & GND point]
05.gdt_bk_2k (brightkings GDT parallel with surge generator)[measured across A & GND point]
06.gdt_bu_tvs_2kv1 (bourns GDT & SMAJ6.5CA TVS diode parallel with surge generator)[measured across A & GND point]
07.gdt_bk_tvs_2kv1 (brightkings GDT & SMAJ6.5CA TVS diode parallel with surge generator)[measured across A & GND point]
08.gdt_bk_tvs_2kv_ab (brightkings GDT & SMAJ6.5CA TVS diode parallel with surge generator)[measured across A & B point (differential)]
09.gdt_bk_res_tvs_2kv_ab (brightkings GDT, 10ohms resistor(between GDT & TVS) SMAJ6.5CA TVS diode parallel with surge generator)[measured across A & B point (differential)]
As per bourns "RS-485 PORT PROTECTION EVALUATION BOARD1" design notes, I changed my design as GDT, TBU(series), TVS. But this configuration also doesn't help me. The waveform similar to GDT+Resistor+TVS configuration.
Measurement tools are,
Oscilloscope (Agilent DSO-X 3014A, 100MHz)
Active differential probe (Pintek DP-150 PRO)
Surge generator (EMC Partner TRANSIENT 3000)
RS-485 Transceiver (MAX485)
GDT ( Bourns 2030-23T & brightking 2RL230M-6)
TVS (Vishay SMAJ6.5CA)
Regards
Udhay