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TPS27S100: Reverse Current Protection options

Part Number: TPS27S100

Section 7.3.4.7 of the TPS27S100 datasheet discusses Reverse Current Protection and offers either a series diode or a GND network.

In my application, reverse polarity is not a concern (I have protection elsewhere) so the GND network is not helpful. Instead, the primary source of reverse current is when the supply drops out rapidly and the load still has a large charged capacitor, that wants to discharge backwards through the switch (essentially the supply shorted scenario offered in the datasheet).

Others have pointed out that a series diode can be costly in terms of power wasted to heat. The lowest Vf diode I could find was ~410mV, which will produce a constant 1.6W of heat for a 4A load. This seems ridiculous when I am designing in a low Rds switch, that is only going to consume 1/4 of that power without the diode.

So, my question is, can I use an anti-parallel diode instead (shown in the figure below)? I could not find a spec. on the forward voltage of the TPS27S100 body diode, but assuming it is greater than 450mV (Vf of FSV15100 @ 4A), then the FSV15100 should carry the majority of the reverse current instead of the body diode, right?

Thank you,

   Daniel

  • Hi Daniel,

    As you mentioned, the condition could be assumed similar to short to supply.

    I also assume that in this case the EN pin is pulled low as well to avoid any situation where reverse current tries to flow through the Power FET.

    In this situation, the DC reverse current that can flow through the device in a short to supply is specified as 2A.

    I think such a system could work but I think using an input capacitor to slow down the voltage drop would be more beneficial. Do note that the device is not meant to discharge a heavy cap load on the output but rather the output load should be the main discharge path. 

  • Shreyas,

    Thank you for your quick and detailed reply.

    Daniel