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AMC1300: multiple series-connected supercapacitor cells using the AMC1200/AMC1300

Ynouss DIALLO
Prodigy 20 points
Part Number: AMC1300
Other Parts Discussed in Thread: AMC1200, AMC3330, AMC1311, INA146, AMC131M03

Tool/software:

I am working on a project to measure the voltage across multiple series-connected supercapacitor cells using the AMC1300 fully differential isolation amplifier. The first cell in the stack has a voltage of 60V, and I chose the AMC1300 due to its high common-mode voltage (VCM) tolerance, which seems suitable for this high-voltage application.

Application Description

  • Objective: Measure the voltage across each supercapacitor cell in a series stack with Balancing resistor in parallel.

  • Configuration: I plan to connect the AMC1200s in a daisy-chain manner for the differential inputs:

    • The VINN pin of the first AMC1200 (component 1) is connected to the VINP pin of the second AMC1200 (component 2), and so on, to reference each cell's voltage relative to the next.

    • Each AMC1200 is intended to measure the differential voltage across one cell.

  • Setup:

    • The first cell is at 60V relative to ground.

    • Each AMC1200 is powered with isolated supplies (VDD1 = 5V, VDD2 = 5V, with proper isolation between high-side and low-side grounds).

Issue Encountered

In simulation (using a SPICE model of the AMC1300), the configuration does not work as expected:

  • The simulation shows an unrealistically high power dissipation of approximately 11 kW, which is clearly incorrect.

  • The measured voltages across the cells are not accurate, suggesting an issue with the input configuration or common-mode voltage handling.

Questions

  1. Is my proposed configuration (VINN of one AMC1200 connected to VINP of the next) valid for measuring voltages across series-connected supercapacitor cells? If not, what is the recommended approach?

  2. Could the high power dissipation in simulation be due to improper handling of the common-mode voltage, given the 60V on the first cell? Does the AMC1300 require additional components (e.g., voltage dividers or clamping circuits) to manage such high VCM?

  3. Are there specific design considerations or reference circuits for using multiple AMC1300s in a high-voltage series stack application?

  4. Could the simulation issue be related to the SPICE model or simulation setup? Are there known limitations or settings I should check?

Additional Details

  • The supercapacitor cells are expected to have voltages in the range of a few volts each, but the stack starts at 60V for the first cell.

  • I am using the AMC1300 for its isolation and high VCM tolerance, as specified in the datasheet

  • The simulation tool is SPICE model from TI.

Any guidance on the correct configuration, simulation troubleshooting, or reference designs for this application would be greatly appreciated. Thank you in advance for your support! Do no hesitate to recommand me anoither device that could do the job.

Best regards,

  • 0
    TI__Intellectual 2451 points

    Hello, 

    thank you for sharing a detailed and well written summary of your project!

    Please note that the very high common mode rejection comes from the fact that the high voltage side of the isolation amplifier is isolated from the secondary side over a capacitive barrier (data are transferred digitally). 

    The high voltage side (group of pins VDD1, GND1, INP and INN) can't withstand any high common mode. It must stay withing the supply rails. 

    When you look at the diagram, you see that you power ports are shorted together. The top amplifier U10, pin GND1 is connected to 0 so does the bottom one. This means, when you start sweeping the voltage V15, the voltage on INP, INN of U10 becomes way higher than VCC1. The internal body diodes of the circuit open and the current is not limited. In real life, the part would explode. 

    Also, the AMC1300 has the input only 250mV. Use better AMC1311 or AMC0331 with the resistor divider. Use AMC3330 if you want integrated power (easier to use).

    Attached is a quick diagram of what I think the circuit should look like. Please try it in spice first.

    Best regards,

    Jiri Panacek,

    Systems Applications Engineer

    Sfrsq037.em25061116210.pdf

     

  • 0 in reply to Jiri Panacek85
    Prodigy 20 points

    Thank you for your quick response. If I understand correctly, your reply suggests that each AMC1300 requires its own isolated power supply for the high-side (VDD1) in this configuration. Is that correct?

    Unfortunately, our design cannot accommodate multiple isolated power supplies due to space and cost constraints. Additionally, while the AMC3330 is a good fit for this application, its power dissipation is too high for our requirements (we need 52 components).

    Could you recommend a fully differential isolation amplifier that would allow the use of a single power supply (or shared power supply) for multiple devices in a series-connected supercapacitor cell measurement setup? Alternatively, are there any design techniques or TI reference designs that could help minimize the number of isolated power supplies while maintaining measurement accuracy?

    Thank you for your assistance!

  • 0 in reply to Ynouss DIALLO
    TI__Intellectual 2451 points

    This is correct, you would need independent isolated power supplies in this case. 

    I am thinking of different solutions for your problem:

    #Option1: The adaption of BQ devices for battery management systems. This is what automakers use for monitoring cells. 

    https://www.ti.com/battery-management/monitors-balancers/products.html#1498=Automotive&2192=Stackable%20(built-in%20interface)&

    https://www.ti.com/battery-management/monitors-balancers/overview.html

    However, I do not know much about this portfolio. If you find any part there interesting, please start a new E2E thread and use this part as a label. It goes to my colleagues (on the other side of the world) and they should be able to answer your question.

    #Option2:

    Using an integrated difference amplifier with very high common mode range (INA146 as an example).

    https://www.ti.com/amplifier-circuit/difference/overview.html

    This is a non-isolated solution. If you then need a galvanic isolation, you could use a device such as AMC131M03 (communicates over SPI) which is practically a 3-channel isolated AD converter. 

    #Option3:

    Create a difference amplifier yourself using a standard rail to rail input/output opamp (e.g. OPAx911 family) and precise resistors (depends on the accuracy you want to achieve).

    Again, if you like a specific part other than AMC***, please start a new E2E thread as the system automatically forwards it to the right engineer as I am an expert only for the AMC devices. ;-)

    I hope this helps, 

    Best regards, 
    Jiri