TPS4812-Q1: TPS4812-Q1 Switching from positive current to reverse current I2t capacitor trips fault

Philip James

Part Number: TPS4812-Q1

Tool/software:

Dear TI support,

We're using the TPS4812-Q1 device and want to allow current in both directions.

In the forward mode everything is working fine. The device trips at the maximum current setting (48amps), and short circuit is working properly.

When we try to switch the current direction by slightly increasing the voltage above the battery source we see the I2t capacitor integrating voltage and tripping the fault and shutting down the the device.

Is there any insight or possible suggestions you can offer to solve our issue?

Thank you,

Philip

2 months ago

0 Timothy Logan 2 months ago

TI__Mastermind 34905 points

Philip,

First- are you using I2T? If not, you can actually use the TPS48121-Q1 variant and simplify the design.

Assuming you are using I2T, could you comment on the value of your RSNS resistor? Also, when you induce the reverse current does the I_DIR pin toggle low?

Best Regards,
Tim

0 Philip James 2 months ago in reply to Timothy Logan

Prodigy 30 points

Yes, the I2t pin is being used (cap value of 4.7uF). Rsns= 0.3 mOhms, Rsetf = 300 Ohms and Rsetr = 3.48 Ohms. We changed Rsetr to 270 Ohms and are getting better results.

0 Philip James 2 months ago in reply to Timothy Logan

Prodigy 30 points

Why in the worksheet (excel worksheet from TI) does it recommend such a low value for for RsetR? This causes the reverse current to immediately trip the fault condition?

0 Timothy Logan 2 months ago in reply to Philip James

TI__Mastermind 34905 points

Hello Philip,

Could you send your version of the calculator that is giving you such a low value for RsetR? You are correct- the RsetR value should be higher... so if there is an issue with the current calculator we would want to address it.

Best Regards,
Tim

0 Philip James 2 months ago in reply to Timothy Logan

Prodigy 30 points

It's the TPS4812/1212-Q1 Design Calculation Tool. I downloaded the file back at the beginning of April.

0 Sarah Raines 2 months ago in reply to Philip James

TI__Expert 8100 points

Hi James,

No problem! Can you send us the zipped version you are using with the filled out values? It will help us see where your numbers and threshold calculations are coming from.

If you can also send us a schematic it we can review that also and make sure we are not missing anything here.

Thanks,

Sarah

0 Philip James 2 months ago in reply to Sarah Raines

Prodigy 30 points

Sarah, Attached is a compressed (zip) file of my worksheet. We're looking to allow 40 amps in reverse direction. Thank you...TPS4812 exl.zip

0 Sarah Raines 2 months ago in reply to Philip James

TI__Expert 8100 points

Hi Philip,

Thank you very much. I took a look. Looks like you have not adjusted cell D25.

This should be 40A and then your RSETR should be more accurate.

Let me know if I can help further!

Thank you,

Sarah

0 Philip James 2 months ago in reply to Sarah Raines

Prodigy 30 points

Sarah, If I change Max reverse current to 40A, then I get an error for RserR. It references that RsetR must be lower than RIMON_max (which it is). RIMON_max is 40.22k Ohms and RsetR_max is suggested to be 150.823 Ohms. See image attached.

0 Philip James 2 months ago in reply to Philip James

Prodigy 30 points

There still is an issue with the spreadsheet value as pointed out above.

+1 Sarah Raines 2 months ago in reply to Philip James

TI__Expert 8100 points

Hi Philip,

Yes it looks like the conditional formatting does not take into account the difference between kohms and ohms. Ill work on correcting this. In the meantime please use the value calculated and ignore the error.

Thanks,

Sarah

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TPS4812-Q1: TPS4812-Q1 Switching from positive current to reverse current I2t capacitor trips fault