Input protection in a power path with high input capacitance

Tom Lightning

Other Parts Discussed in Thread: DRV8343-Q1

Hi,

I'm designing a 24V motor driver application and I have some problems by chosing the right input protection. So my application needs to withstand overvoltage events defined by the ISO 7637-2 standard. My idea is to put a TVS Diode at the very beginning of my supply input in order to clamp the overvoltages.

When I simulate the circuit the results show that the bulk capacitor (150µF) is so big that it takes up the whole energy of the overvoltage event. Thus the input voltage does not increase signaficantly and the breakdown voltage of the TVS diode will never be reached (so it is useless). The Problem with that is the high current flowing into the electrolytic capacitor (about 11A). I have the fear that the high current will significantly decrease the life time of the capacitor. Do you have any advice or ideas to deal with that problem?

Without input capacitance

With input capacitance

Tom

over 3 years ago

0 Bryan Marshall over 3 years ago

TI__Genius 10974 points

Hi Tom,

Thanks for your question. We will get back to you with a response in the next day or so as we have a few team members out on holiday..

Stay tuned.

Thanks!

Bryan

0 Tom Lightning over 3 years ago in reply to Bryan Marshall

Intellectual 305 points

Hi Bryan,

do you got something for me?

Tom

0 Aaron Barrera over 3 years ago in reply to Tom Lightning

TI__Mastermind 26046 points

Hi Tom,

The supply bulk capacitor you're using (150uF) suppresses the overvoltage event. You can always use a variety of bypass/bulk capacitors (10uF or greater) in parallel to divide the current and suppress a variety of frequencies, i.e. 10's of uF, 1's of uF, or 1-100nF.

My understanding is that the lifetime of electrolytic capacitors is determined mostly from temperature and operating voltage. If capacitors are not operating at their maximum temperature or rated voltage, then they should last longer. This is why we recommend capacitors for higher temperature ratings (such as X5R or X7R) and rated for 2x the motor operating voltage (i.e. 50V rated caps for 24V motor supply).

For more info, please check this training: training.ti.com/ti-precision-labs-motor-drivers-voltage-margin-and-bulk-capacitance

Thanks,
Aaron

0 Andrew Liu over 3 years ago in reply to Aaron Barrera

TI__Mastermind 18981 points

Thanks Aaron!

I believe this relates to Tom's other e2e post regarding DRV8343-Q1: https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1123339/drv8343-q1-robustness-against-overvoltage-events-in-a-24v-system/4174868#4174868

Hi Tom,

Another few resources regarding bulk caps:

Agreed w/ Aaron's statements above that the lifetime will mostly be affected by operating temp, and best way to counteract this is having multiple caps in parallel w/ misc values. current ripple is another variable mentioned in the Altium resource above.

Best Regards,
Andrew

0 Andrew Liu over 3 years ago in reply to Tom Lightning

TI__Mastermind 18981 points

Hi Tom,

Closing the thread for now due to inactivity - please feel free to reply/re-post if further assistance is needed. Thanks!

Best Regards,
Andrew

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Input protection in a power path with high input capacitance