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TPS92520-Q1: Output clamp diode questions

Part Number: TPS92520-Q1

Hi Team,

Could you possible help to check if customer could remove the output clamp diode which we recommend in datasheet?  Since currently, customer with 100nF output capacitor and with 7m cable from LED+ and then short the cable to ground, it shows now minus voltage in VLED+ side without the clamp diode, so, customer is considering remove the output clamp diode, but not sure if there still has some risk here.

Could you possible help to share some comments under what kind of test condition or design condition would there see a minus voltage in output side? Thank you very much for your help to confirm.

Best regards


  • Hello Jie,

    We recommend the protection diode to clamp the negative voltage that can be seen by our part when there is a fast short at the LEDs that have harnesses between the buck output and the load.  This is especially important when the harness used are fine gauge wires that have large parasitic inductances.  Here is circuit representation, which is already covered in the datasheet.


    From the circuit we can see that if the short is sufficiently fast, like a hard short, then we can have ringing on the output due to the LC tank on the output.  This ringing is a function of the parasitic inductance, resistance, capacitance, operating condition (output voltage and current setpoint), the control loop bandwidth, and the impedance of the short (which controls the speed of the short).  Depending all all these variables, you may or may not need the diode to protect against the ringing.  Most customers that do ECUs don't know what the load looks like so they can't assume it won't cause a problem and need the diode to protect the device.  Here is an example of a short applied to an output without the protection diodes.

     You can see that the output is approximately -4.5V, which exceeds our abs max specifications, which isn't allowed.

    This will violate our specifications and can damage our parts.  If they can ensure the negative voltage never exceeds the abs max specifications then they can remove the diode, but that is their choice and they are putting themselves at risk of failure.  We do not recommend it because generally the output parasitics and type of short is not well controlled or defined for most applications.  

    -Francis Houde