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Isolated RS232

Calum Mackinnon
Genius 4155 points
Other Parts Discussed in Thread: LP2981, TRS3232E, TRS3232

I’m looking for a 3.3V or 5V to RS-232 with isolation and ESD protection. The current design used 2x ADUM7441’s for isolation, MAX845/xfrmer/LP2981 for isolated +5Viso, and MAX3160E for 232/485, plus TVSs – fair amount of board space. All the circuitry I just listed drops may 85-90mA on the input non-isolated +5V. I only need RS-232 and board space looks to be at a premium. I looked up ADI’s ADM3251E which fits the bill but draws 110mA to 140mA, possibly adding to the power supply. Do you have a better solution?

Calum

  • 0
    TI__Mastermind 28265 points

    Calum,

    please see below my suggested circuit. total curren consumpiton at 3.3V should be less than 40mA. For the transformer I have just given the turns ratio. However, in conjunction with a German transformer manufacturer we are currently developing a new low-cost, small form factor transformer with 2.5kVrms isolation. Samples will be available by end of August. So far the efficiency measured in the 20 to 40mA range is between 80 and 83%.

    regards, Thomas 

  • 0 in reply to Thomas Kugelstadt
    TI__Guru**** 150106 points

    Thomas,
    Thank you for the circuit and development efforts.

    For better ESD protection the TRS3232 can be upgraded to a TRS3232E.

    Regards,
    Ron Michallick