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RLGeorge
Level 3
Level 3
10 likes given 10 questions asked 25 sign-ins

The TLE9853QX is configured in bi-directional design similar to the evaluation board.

My question is about repeatability, accuracy, of the CSA value after gain at ADC1_OUT_CH13. 

I have the PCB assemblies configured in a controlled environment where I can generate a fixed load current while operating the processor in Debug. I recorded A2D values while setting the load at fixed current values. I record the values in 5 Amp increments from 75 Amps to 165 Amps. The hand written values attached were recorded. I then repeated the test an hour later and all the values are 5% higher. What accuracy can be achieved? 

Will the TLE9853QX always generate the same A2D value at ADC1_OUT_CH13 on a particular TLE9853QX every time the same input value is applied in the same environmental conditions? Or, will the A2D value at ADC1_OUT_CH13 always fluctuate within the tolerances of the part each time?

I have not been able to achieve any A2D values close to the calculated values in the attached document.

In Config Wizard Channel 13  (CSA) is Calibration enabled. See attached.

Table 80 in the TLE9853QX data sheet list a 5% tolerance for differential gain, uncalibrated.

Enabling calibration in Config wizard leads me to Table 57 in the TLE9853QX data sheet. Are these tolerances listed for the values read at OP1 and OP2 or the ADC1_OUT_CH13?

Table 57 in the TLE9853QX data sheet values are for a gain of 40. Are the values the same when using a gain of 60?

I have attached a partial schematic of the current sense circuit for reference. Shunt is 1%, 200uOhms. 

Please provide any guidance possible guidance. I am only using the differential amplifier to protect the design from over current in the application and I need to know how to properly use the feature.

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1 Solution
Viswa
Moderator
Moderator
Moderator
10 likes received 50 solutions authored 100 replies posted

Hi

 

The output will be the same for the same voltage applied for the differential op-amp.

The minor difference in the offset measured may be due to fluctuations in the applied current and tolerance limits of the product.

Best Regards

View solution in original post

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3 Replies
Sahil_K
Moderator
Moderator
Moderator
First like given 100 solutions authored 250 sign-ins

Hi @RLGeorge ,

Could you kindly explain how did you select the RC filter (R8, R9, and C10) and shunt resistance (R1)? What does 2060 stand for in relation to the calculated value of 75A? Is it a voltage value in mV or an ADC count value? Please let us know what is the measured voltage in mV or Adc count value at zero amps.

Best Regards,
Sahil Kumar

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RC filter (R8, R9, and C10) Used the values in the proto board design.

R1 Shunt value was selected based on the operating load current range of our design.

2060 is the mV equivalent of 080C HEX.

No current flow value fluctuates. 05E2 HEX / 1506mV to 05F6 HEX / 1526 mV. Offset is 1500 mV. 

Further review when subtracting the attenuation of OPA (0.265) A2D HEX values are close to calculated values. An oversight on my behalf. 

Differential Gain amplifier has tolerance of 5%. Shunt is 1%. So, the design is +/- 6%.

The only question left is if I apply the exact same input voltage to the differential amplifier will I always get the same value out?

I originally thought I had the ability to use the current sense with precision and repeatability. I have seen that the differential amplifier output does appear to fluctuate when repeatedly reading the same input value.

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Viswa
Moderator
Moderator
Moderator
10 likes received 50 solutions authored 100 replies posted

Hi

 

The output will be the same for the same voltage applied for the differential op-amp.

The minor difference in the offset measured may be due to fluctuations in the applied current and tolerance limits of the product.

Best Regards

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