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ULN2003LV: Hot plug - output burn

Part Number: ULN2003LV
Other Parts Discussed in Thread: ULN2003A

Dear,

I developed a circuit that use the ULN2003LV. They outputs are directly connected to a connector.

The other side of circuit (plug side) has a bridge diode and optcoupler (low current consumption).

The problem reported by my client is the burn of driver at the moment the plug is plugged.

My question is: The ULN2003LV has no protection for inrush current on they outputs? If I put a serie resistor in each output is possible to correct this issue?

Thank you.

  • Hi Clkunde,

    If my understanding is correct, then the outputs of the ULN2003LV are connected to a connector that supplies power to another circuit with optocouplers and a bridge diode.

    A few questions on the failure:

    1. Are the outputs of the ULN device active when the plug side is connected? If not, then does the device fail before turning on or after?

    2. I'm not sure what you mean by "inrush current protection". When the outputs are enabled (pulled to ground) then they activate without a controlled/slow discharge to ground. When the outputs are turned off, the output pins are left floating.

    3. Is power being supplied by the plug side? If not, then why would the act of connecting the plug side have an impact on the UN2003LV?

    4. How strong are the loads on the plug side? Do you expect transients over the abs max ratings of the ULN2003LV? If you suspect transient current draw to be an issue here, then the resistors in series may help.

    Thanks,

    Alek Kaknevicius

  • Hi Alek.

    Yes, you understood my issue. I just forgot to say that beyond a circuit with optocouplers, sometimes are connected another circuit with relays (I believe the problem happens with this circuit).

    Answering your questions ....

    1 - Yes. The output probably is enabled when the operator change the circuit. I verified that some drivers has all outputs burned and another times just the channel is burned.

    2 - I understood how the driver provide the current. I believe that I need to provide a implementation to control de current when the plug is connected with the hardware energized (Hot plug).

    3 - Yes. The function for ULN in this case is a power supply.

    4 - I took care to not exceeds the max current. By the way, the current limit is 100mA per channel, right? 700mA in all outputs, is it?

    Thank you for while Alek,

    Claudio Kunde
  • Hi Claudio,

    Your understanding of the max current is correct, the device can support 100mA/channel for a total of 700mA. I also agree with your assessment to "provide a implementation to control the current when the plug is connected with the hardware energized (Hot plug)". Based on your description, it sounds like this is the problem. 

    Because the device is on during the connection, I suspect that the hotplug event is causing high voltage and/or current transients that are exceeding the maximum limits of the ULN2003LV device.

    Have you considered trying the ULN2003A? This device can support up to 50V and also has 7 channels that can support even greater than your 700mA requirement. This device may be able to withstand the hotplug event.

    The other solution would be to keep the ULN2003LV outputs off until the plug side has been connected, then turn on the outputs.

    Thanks,

    Alek Kaknevicius