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Original question:

LM5170EVM-BIDIR: Decrease High Voltage Port

LM5170EVM-BIDIR: Jumper Setup for ISETA Analog Control

Justin Quattlebaum
Prodigy 60 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170

Hello,

I have now received the LM5170EVM board and am trying to test it with a nominally 12.8V battery. This battery has a 5Ah capacity and 2.5A constant current limit during charging. I am trying to test the buck mode of the converter with 26V on the high voltage port from a lab power supply with the current limited to 2.5A and a constant current set with ISETA. I am able to control the current with a resistor divider providing a voltage within the range of 0-.1V to keep the current below 2A. I understand that certain parts can be changed out to get a more accurate conversion for the output current. However, the current seems to be clamped at 1A even when the voltage at the ISETA pin should be setting it higher. I will attach a picture with my jumper settings to make sure I have not set the board up incorrectly. I am enabling the board with a microcontroller and using it to set EN1, DIR, CH1. I am using an analog voltage from the second channel of the lab power supply to adjust ISETA. 

Thank you for your time.

  • 0
    TI__Mastermind 21720 points

    Hi Justin,

    Thanks for reaching out with your questions and for using the LM5170 EVM.

    I have a few questions/comments 

    1. What is the voltage that is being placed on the ISETA pin?

    2. I would also suggest pulling the UVLO pin( J31)up to 5V with an external supply.

    To improve the accuracy of the average current the current sense resistor can be changed appropriately. The voltage drop across the current sense resistor is 50mV when ISETA is equal to 2.5V. For example if you wanted to have 2.5A correspond to the full range the (ISETA = 2.5V) the current sense resistor will need to be 20mOhm.

    Please let me know if you have have any questions.

    Thanks,

    Garrett

  • 0 in reply to Garrett Roecker
    Prodigy 60 points

    Hi Garrett, 

    Thank you for your reply.

    1. The voltage I am using at ISETA is between 0-.1V.

    2. When you say UVLO pin, which pin of the three do you mean? I see on the schematic that (1) is grounded (2) is connected to the UVLO -> j-17 pin 5 / Enable and (3) is connected to the other EN1 and EN2 for master enable, as well as DIR to set Buck Mode. Is this correct? 

    I am working on setting up the PWM control for ISETD but have not completed the code yet. I am still in a testing phase. The accuracy of the current is not as much important as getting a range of current from 0-2.5A, unless the sense resistor being too inaccurate is what could be causing the issue. If you could clarify on pulling up the J31 pin I will try that and see if it helps.

    Thank you again for your time, I appreciate the help.

    thanks,

    Justin 

  • 0 in reply to Justin Quattlebaum
    TI__Mastermind 21720 points

    Justin,

    Regarding the UVLO pin make sure that there is 5V on pin 2 of J31. This should ensure the LM5170 is enabled and 3.3V and 5V bias rails are active. I would suggest only having channel one (EN1=1, EN2=0) enabled as the current is considerably under the maximum current level of the EVM. 

    Let me know if you have any questions.

    Thanks,

    Garrett

  • 0 in reply to Garrett Roecker
    Prodigy 60 points

    Hi Garrett,

    I finally got the current sensing resistors in (they were on back order) and switched them out. I have the same setup as before and can confirm that the bias rails are active (3.3V and 5V) as well as I am getting the correct voltage at ISETA. However, the current is not flowing in either direction (buck or boost). Is there a common part that could have failed somewhere along the way that I can check? Or do you have any other suggestions for me to try and get this working?

    Thanks,

    Justin

  • 0 in reply to Justin Quattlebaum
    Prodigy 60 points

    Hello,

    After further testing, I have come to the conclusion that phase 1 of the converter is not functional. However, when phase 2 is enabled, the converter operates as expected with just one phase. I can only assume that a part was damaged within the phase 1 circuit. For my use case this is not an issue as I only need one phase. Thank you for your help!

    Justin