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TPS563209: Protection against short circuit

Hamid Ahangari
Prodigy 40 points
Part Number: TPS563209
Other Parts Discussed in Thread: TPS560200, TPS56339

I've implemented a 12V to 5V buck converter using TPS563209 which works fine from no load to full load.

I've also tested the over-current protection function and it seems to work, but in the event of a short circuit (in 5V to GND), TPS563209 fails almost immediately and never recovers from that.

Is over-current protection enough to protect against short circuit or do I need to add something else to the circuit?

If the short circuit is an issue with TPS563209 , is there any similar IC (500mA output current is enough) with added short circuit protection capability?

Best regards,

Hamid Ahangari

  • 0
    TI__Expert 4035 points

    Hi Hamid,

    Typically buck device has a minimum on-time limitation, the high-side MOFET need turn on at least the minimum on-time. When output was short to GND, the inductor current would increase quickly. Please check your inductor's saturation current, if the saturation current is very low, inductance would dropped quickly after inductor saturated. That means the current rising slew rate would be very high. Typically, you need the saturation current higher than the device supported current if you want to do the output hardshort test with no damage to the IC.

  • 0 in reply to Ryan Hu (BSR-MV)
    Prodigy 40 points

    Hi Ryan,

    Thank you for your respond, that was really helpful. I wasn't considering the inductor's saturation current in that situation. It was around 1.5 A as i was using lighter loads around 500 mA. I will use a lower rating device such as TPS560200 for that matter.

    Best regards,

    Hamid Ahangari

  • 0 in reply to Ryan Hu (BSR-MV)
    Prodigy 40 points

    Hi Ryan,

    I've tested your theory and this time I used an inductor with higher saturation current than TPS563209 rating. Again, the over-current limit works perfectly, but when I connect the Vout to GND, the device fails immediately. 

    Best regards,

    Hamid Ahangari

  • 0 in reply to Hamid Ahangari
    TI__Expert 4035 points

    Hi Hamid,

    Just as I mentioned above, most of the buck converter has the damage risk in theory. The peak current is determined by the minimum on-time, inductance and input voltage.  What's the inductance in your test?

  • 0 in reply to Ryan Hu (BSR-MV)
    Prodigy 40 points

    Hi Ryan,

    I used a 10 uH inductor, with a saturation current of around 7 A.

    I guess I don't understand why such a sophisticated IC doesn't come with short-circuit protection, as this scenario happens a lot of times in real world situations.

    Best regards,

    Hamid Ahangari

  • 0 in reply to Hamid Ahangari
    TI__Expert 4035 points

    Hi Hamid,

    The key factor is the TPS563209 has a longer minimum on-time and has only valley current controlled, has no peak current cycle-by-cycle limit function. There is nothing more we can do to avoid the damage. Maybe you need a part with shorter minimum on-time and better has peak current cycle-by-cycle limit function. You can try with TPS56339, P2P with TPS563209. Asking sample from TI.com.