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BQ24610EVM: Is it good to include a TVS diode for the BQ24610EVM circuit layout?

Part Number: BQ24610EVM
Other Parts Discussed in Thread: BQ24610

Hello,

I have a question about TVS diodes for use in the standard BQ24610EVM circuit layout.

Would it be good to connect a TVS diode at the connector of the ACPWR pin? I made provision by putting pads (DO-214AC pads) which allows Wurth Electronik 400W TVS diodes to be placed.

At the moment I have 26V unidirectional TVS diodes available with me, but I can get a 24V version too.

My connection to the circuit is a medically approved PSU which provides 24V DC at 6.25A.

Our best guess is the customers would be connected and disconnected the system at least 2 to 6 times a day, and worst-case scenario to never disconnect the system from the PSU for a 1 year or 2.

My question is would it be good to include the TVS diode (product code from Wurth is: 824500261) for these scenarios?

I have attached a diagram to explain where the TVS diode is going.

Best regards

Mo  

  • Hi Mo,

        The TVS diode and snubber circuit (R1/R2, C2) are trying to accomplish the same thing, to clamp the voltage overshoot due to ringing when you plug in an adapter. TVS diode has the advantage of accurately limiting the peak voltage to its rating, while snubber circuits might need a little trial and error with values to fine tune the suppression effect. Snubber circuit does have added leakage current (I wouldn't imagine too considerable) but also does help smooth out the frequency of oscillations. The biggest downside of TVS is the much higher cost and board area that is required compared to a snubber circuit. It is good you have the footprint to add in the TVS if needed.

  • Thank you Kedar,

    I have two more questions:

    1) Would you say 26V TVS diode be a better option by going 2V above the rated voltage,or  is better than the 24V TVS version which is the same voltage as my supply?

    2) The good thing is, the cost of the TVS diode is acceptable for us.  Would it be good to add it with the snubber circuit, or would having both counteract each other and have unforeseeable issues?

    Thank you

    Best regards

    Mohammed Al-Amin

  • Hi Mo,

      26V rated would be better as when TVS diode is clamping voltage (maybe if power supply is equal to TVS diode clamping), current is shunted through the TVS diode (usually this would only be during the transient, but if your input power supply is the same voltage as TVS diode clamping, I am not sure if it would continuously be shunting a little current), so you would see a little more power loss across the TVS, as opposed to when you have a little headroom. When TVS is not clamping there is only a little leakage current through the diode and it appears as an open circuit. The main aim is to protect against transient voltage spikes (on plug-in) so this headroom is ok as 26V is under recommended operating condition of 28V for BQ24610. There is no issue with having both the snubber and the TVS diode, and this is just added protection for you.