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DRV8801 nFault when supplying VBB

masahiko shimizu

Replies: 7

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I am using DRV8801EVM and sense resister changed from 0.2ohm(default) to 2.2ohm.

I meet issue when VBB voltage is supplied to EVM.
Issue is nFault is every time Low out put when VBB voltage is supplied to EVM.
But DC motor can operate.
Why does this issue occur? Could you solve this issue?

[Starting procedure]
1.EVM connects to PC and GUI starting up.
-> nFault is High

2.Voltage is supplied at 18V by Stabilized power supplies.
-> nFault is Low

3."Enable motor" bottum is ON.
-> nFault is Low, but Motor can operate.

Best regards,
Shimizu

Expert 8885 points

Milan Rajne
- Sep 8, 2014 4:51 AM
Shimizu,

nFAULT is a status signal only and H-bridge can operate even with nFAULT low till VBB down to 8V. But definitely, we need to find the reason why nFault is asserted low. Can you provide little more inputs?
1. Does this behavior is observed with higher Rsense =2.2ohm or present even with 0.2ohm?
2. even if you are applying 18V, Just to double check, measure VBB voltage level at device pin in EVM, if it is below VBBNFR (typically 12V), nFault may be low.
3. Are you making sure in all conditions with Rsense=2.2ohm i.e. in start-up transients/steady state motor running, current is limited such that it does not generate voltage across Rsense higher than +/-500mV?
4. It would be good to capture the transient scope shot nFAULT in starting as VBB rises, to see at what point n-FAULT is asserted low.
Best Regards

Milan-Motor Application Team
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masahiko shimizu
- Sep 8, 2014 1:25 PM
In reply to Milan Rajne:

Hi Milan

Thank you for your support.
I chacked your question.
Please see the attached file.
But I am going to trying tommorow in case of Rsence=0.2ohm.

Best regards
Shimizu

sample.xlsx
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masahiko shimizu
- Sep 9, 2014 5:56 AM
In reply to masahiko shimizu:

Hi Milan

Thank you for your support.

I checked the case of Rsense = 0.2ohm.

But the results is same as the case of Rsense=2.2ohm.

Please see the attached file. ->"Rsense=02.ohm" tab in xlsx file.

I think that VOUT+pin in waving when 18V is supplied.

Is internal FET motion normal?

Best regards,

Shimizu

sample.xlsx
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Milan Rajne
- Sep 9, 2014 9:11 AM
In reply to masahiko shimizu:

7563.Vout+ripple.pptx

Shimizu,

Thanks for conducting the experiment and providing experimental waveforms. So now it’s clear that nFault is not triggered by Rsesne value. As you pointed out that Vout+ output goes in to ripple condition and its effect is more predominant figure 4.

Refer to attached pircture, with Rsense=2.2, there is huge ripple on Vout+ during high/on conditions. It looks like that due to ripple, minimum voltage level is ~12V which is close to VBBNFR level and may be causing nFault trigger. In order to confirm, can you please simultaneously capture the VBB, Vout+ and Vout- (keeping all channels at 10V/Div) at motor running condition?

Unfortunately, I do not have EVM with me at present, I have ordered couple of them but it’s going to take 4-5 days to get EVM. Meanwhile, if you have another EVM, you can repeat the same experiment, to remove any possibility of device or any component damage on present EVM.

Best Regards

Milan-Motor Applicaiton Team

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masahiko shimizu
- Sep 24, 2014 12:47 PM
In reply to Milan Rajne:

Hi Milan

Thank you for your support.

I confirmed VBB, VOUT+ and VOUT- at motor running condition.
Please see the attached file.

I will get a new EVM tomorrow.
I will try it tomorrow.

Best regards
Shimizu

VBB,VOUT+,VOUT-.pptx
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Milan Rajne
- Sep 25, 2014 5:09 AM
In reply to masahiko shimizu:

Shimizu,

Thanks for capturing the waveforms. It's clear that Vout+ output is not correct, it has ripple even though VBB is clean.

Looks like H-bridge for Vout+ is not functioning properly. Test with new EVM, and I hope you will not see the issue,

Meanwhile here, I tested new EVM and it is working absolutely fine.

Best Regards

Milan-Motor Application Team

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masahiko shimizu
- Oct 1, 2014 2:31 PM
In reply to Milan Rajne:

Hi　Milan

Thank you for your support.
I confermed nFault signal with new EVM.
This board operated normally.

Thanks a lot.

Best regards
Shimizu
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