MC33772 Current measurement diagnostics

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MC33772 Current measurement diagnostics

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Susan_1
Contributor I

Hello,

When reading the #MC33772B safety manual, the following questions need to be confirmed: 

1. How to obtain the diagnostic threshold for current measurement function for #MC33772B? 

2. Whether the pack controller modify the current measurement diagnostic threshold?

3. How can the current measurement diagnostic threshold be converted into a certain current value(mA or A)?

 

Thank you in advance!

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diazmarin09
NXP TechSupport
NXP TechSupport

Hello,

I hope all is great with you. Thank you for using the NXP communities.

Please review the response from our specialist  below:

  1. Do you mean A) the value of the Hardware threshold TH_ISENSE_IC mentioned in the datasheet, or B) the value of the Software threshold in normal mode? 

The answer is in both cases application specific, there is no general answer. If case A, then the threshold TH_ISENSE_IC - represents the value of the voltage drop across the micro-shunt valid for the sleep mode only. The resolution is 1.2 uV/LSB, therefore the max representable value equals (2^12-1)*1.2 uV = 4914 uV. Assuming Rshunt = 100 uohm, max current is Ishunt_max=  4914 uV/Rshunt  = 49.14 A, while current resolution is Ires = 1.2uV/Rshunt = 12 mA. In sleep mode I would expect a very low value of the current threshold, where such value may represent an anomalous current consumption due to a defect. If case B, then the current threshold value in normal mode depends more on the max allowed current for the power inverter module. It may be a very high value.

  1. Is always the responsibility of the Pack Controller modifying the threshold vale. If case A, the pack controller sends a value to the TH_ISENSE_IC register, if case B, the value is entirely under the domain of the Pack Controller (I expect a temperature dependent threshold value).
  2. I think I answered at point 1.

 

I hope this information helps.

Regards,

David

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