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LM61460-Q1: Protection against Reverse Current

Filipe Satake
Intellectual 1760 points
Other Parts Discussed in Thread: LM61460-Q1

Hello,

Regarding LM61460-Q1, is there any protection against reverse current when the OUTPUT voltage is higher than the INPUT voltage?

If not, what phenomenon could happen, and what kind of solution can we use to avoid it?

Best regards,

Filipe Satake

  • 0
    TI__Guru 57555 points

    Hello

    Usually it is not a good idea to allow voltage on the output of a regulator when the input is zero volts (or even floating in some cases).  This condition could be caused by a very large output capacitor that is charged when the input is removed, or some kind of active load suppling a voltage.  There is a diode between the drain(VIN) and source(SW) of the power MOSFET inside the converter.  With a voltage on Vout, and the input held at zero volts, there will be a path from Vout to Vin through the inductor and this diode.  Even if the input is floating, a current will flow and try to charge the input caps, possibly to a high voltage due to resonance with the caps and the inductor.  This phenomenon has been seen in the past under some conditions.  Allowing current to flow through this diode can cause a parasitic to turn on or even damage the diode.  Since it is not a "true" diode but a parasitic formed when the MOSFET is constructed on the die, it is not designed to take current for more than a few usec, or so.  One way to avoid this issue is to use a diode from input to output to provide a path for the output capacitors to discharge around the device.  A Schottky diode with cathode connected to Vin and anode connected to Vout can be used.  Please also see app note SLYT689 and SLVAE57 for more information.

    Thanks