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DCR010505 does not start when using to isolate RS232

Stefan Pindera
Prodigy 20 points
Other Parts Discussed in Thread: MAX232, DCR010505

I have used DCP010505 to isolate RS232 circuit, it means that isolated circuit was: MAX232 with capacitors and two ISO7221 and nothing more. It has worked well when RS232 cable from PC was connected to the circuit before power was on to the circuit.

I have thought that better choice is to use DCR010505 instead of DCP010505 and I did it. When I power on this circuit, and RS232 cable is connected to PC, it does not wake up (DCR010505 output voltage = 0V). When I disconnect RS232 cable from PC and connect it again to PC, DCR010505 wake up and work OK.

It is big problem because when there is short break down of the power, someone have to go and disconnect  and connect again RS232 cable it is not acceptable.

Perhaps I have to add something to the circuit or go back to DCP010505.

Please help me to solve this problem.

Stefan Pindera

  • 0
    TI__Mastermind 38230 points

    Stefan:

    The likely reason for the no +5Vout output when connected to RS232 , but has +5V when disconnected is there is an apparent (-) voltage  on the Vout bus.

    One method is attached. Add  a resistor  or zener diode by-passing the internal LDO when (-) voltage is applied  to the positive bus during start-up  is likely to eliminate the start-up  operation.

    The zener diode clamp is the preferred method for applying a low possible voltage when (-) Volts is present .

    My direct e-mail is tguerin@ti.com

    DCRnegative voltage busclampcircuit.pdf
  • 0 in reply to Tom Guerin
    Prodigy 20 points

    TOM,


    Thank you very much for your support, when I attached the 5V6 zener diode and 1uF capacitor, according to ‘DCRnegative voltage busclampcircuit.PDF’ it works pretty well!

    Best regards.

    Stefan Pindera