RD9Z1-638-4Li-SW Current measurement

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RD9Z1-638-4Li-SW Current measurement

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Contributor I

Hi all

I’m working with the demo software provided by Freescale for RD9Z1-638-4Li-SW. I’m finding it when I reading the current measurement register (ACQ_CURR) there always something wrong (I think).Because when there is no load (only the board) I also see the current result is almost 200mA(the board consume is probably 20mA).

  1. Is there some offset in the ACQ_CURR when I reading it. How can I get the really result or when the board is reset what is the result of the ACQ_CURR(it is 0xFFFFFF ?).
  2. How Can I understanding the register ACQ_AHC? What is the unit of the register?  How is the register increasing ? eg. When a current (150mA) runs one minute, I read the ACQ_AHC register increased 7690884.what is the meaning of the number 7690884?

Thanks for all answer!!!

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Contributor I

Hello!

I am using the MM912_637, but I am experiencing the same problem.. I always see an offset of around 150mA when comparing to the current value on the multimeter.

I am doing the calibration procedure and I am not being able to fix it. Does anyone could help me?

Maybe I am using the wrong configuration for the current ACD or doing the wrong procedure for the calibration.

Thank you,

Marina

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NXP Employee
NXP Employee

Hi Marina,

can you provide more details on your setup (schematics, where do you apply what, etc..)?

W.

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Contributor I

This is my setup:

setup.png

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NXP Employee
NXP Employee

Marina, is the Chassis side floating? How does the current reading look like if you short Chassis to Battery Minus?

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NXP TechSupport
NXP TechSupport

Hi,

I am just adding here Wolfgang’s answer to keep this thread consistent:

Depending on your setup you should see either ~0mA or ~35mA (typical current consumption of the board - no balancing, no additional loads).

Items to check:

  • in your setup is the current consumption of the board measured (flowing accross the shunt)
  • measure the acctual current consumption of the board
  • have you used the calibration values provided on the back of the shunt (sticker)

The Ah counter basically sums up all CSENSE measurements: AHC = SUM(CURR).

I expect in your setup the CSENSE is continuous running at 1KHz data rate. Which for 1 minute would be 60000 samples which are accumulated. So the average current Iaverage = SUM(CURR) / number_of_samples = 7690884/60000 = 128mA

Regards,

Tomas

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Contributor I

HI ,

i use my board  to measure voltage and current,but its value are increase all the time.Is there something wrong with my schematic or my program(KT9Z1_638_CAN_demo).Design1.PNG

KT9Z1_638_CAN_DEMO.PNG

Thank you.

Best regards,

H YW

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Contributor I
  • the current flowing accross the shunt(100uΩ​)
  • I want to measure the acctual current consumption of the board (no additional loads)
  • I used it.
  • connection.jpgwhen my Power GND connect to the CHASIS the current register was read as 0xFFFF94. when my Power GND connect to the BAT- the current register was read as 0xFFFF76(the result is always changing).The number of 0xFFFF94 is right,is it related to the hardware?
  • Thanks for the answer of Ah counter.
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NXP Employee
NXP Employee

Hi,

You state that the 0xFFFF94 is right, why?

You measured:

  • 0xFFFF94 (is -106 mA) in the Power Supply GND -------  BAT- terminal   (Ishunt = Iload)
  • 0xFFFF76 (is -136 mA) in the Power Suply GND ------> CHASSIS terminal (Ishunt = Iload - Isup)

With Iload = 0A, we can see that the Isup is about 30 mA (delta between both) and that we have a offset error of ~100mA. What values did you have on the Shunt sticker?

Did you measure Isup with an ext. Multimeter?

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