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UC1708: ENABLE line on UC1708; bypassing capacitor values for "VIN"

Kenneth Aquino
Expert 1330 points
Part Number: UC1708


Two questions:

1.  I'm operating the UC1708 from 12 volts.  I want to keep it permanently enabled.  Can I tie the EN pin to 5 volts to keep it permanently enabled?  Do you recommend leaving it open in order to permanently enable it?

2.  The data sheet shows a 47 uF tantalum and a 10 uF ceramic used as bypass caps for the VIN pin. The UC1708 in my app is driving a MOSFET with 2200 pF Ciss. Do I really need the 47 uF tantalum?  Is the 10 uF ceramic good enough?

  • 0
    TI__Mastermind 29105 points

    Hey Kenneth,

    1. I would suggest tying EN to 5 Volts to keep it permanently enabled. I would not leave it open.

    2. It is possible that 10 uF is fine, but what must to be taken into account is the amount of charge the device needs to supply. What needs to be looked at is how much charge that the device will supply to the FET to fully turn on the gate and how long that time will take. You can then look at the voltage change at the input and see if you are okay with that voltage change in your design. Another thing to consider is only using ceramic capacitors can cause trouble with input voltage stability if the power supply providing the 12 V is too far away either on board or with cables.

    Thanks,

    Daniel