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TIDA-010208: MOSFET circuit maximum load current

Ian Kelly2
Prodigy 50 points
Part Number: TIDA-010208
Other Parts Discussed in Thread: CSD18536KCS, TIDA-010247, BQ76952, BQ76942

Tool/software:

Hi,

If the high-side driver MOSFET circuit from TIDA-010208 was placed on a PCB with much thicker tracks (like 1.5mm copper sheet) could these two sets of three MOSFETs safely handle a 200A load? What if all 6 main MOSFEETs were replaced by CSD18536KCS (in TO-220 package) as they would be easier to fix?

What changes would be needed to each of the gate driver circuits to drive six MOSFETs in parallel?

Many thanks,

Ian

  • 0
    TI__Intellectual 1940 points

    Hi Many,

    I am afraid 6 MOSFETs can't handle 200A load because large MOSFET conduction loss. You need to add more MOSFETs to achieve this(maybe ten pairs - 20 MOSFETs and above).  You also need to optimize the driver circuit for stronger driving capability.

    You can find reference circuit in TIDA-010247 schematics.https://www.ti.com/tool/TIDA-010247 

    BRs

    Kian

  • 0 in reply to Kian Lin
    Prodigy 50 points

    Hi Kian,

    Thank you for the quick response.

    Having three CSD18536KCS in parallel would give a drain source resistance of about 0.43mR which is only 0.86mV at 200A and a reasonable power of 17W?, <6W per deice, assuming the gates are fully saturated (which they should be with the gate drain voltage limited to 16V by the 16V Zenors). Please can you help me understand why this isn't enough?

    Using more FETs would lower this power loss (thus increasing efficiency) I have just found the document "Multiple FETs with the BQ76952, BQ76942 Battery Monitors (Rev. A)" (https://www.ti.com/lit/an/sluaa09a/sluaa09a.pdf), which is easier to understand than TIDA-010247 since I'm only using a single battery monitor (not two stacked together).

    Could someone please suggest suitable PNP transistors for Q30 & Q31 for the circuit in figure 5.2 on page 9, as that's much closer to the circuit we already have?

    Many thanks,

    Ian

  • 0 in reply to Ian Kelly2
    TI__Intellectual 1940 points

    Hi Ian,

    You should notice the Junction-to-Ambient thermal resistance of CSD18536KCS. 6 watt loss would lead to ~370oC temp rise which is unacceptable. Typically, I suggest <1W per piece but it depends on customer's thermal design.

    Ian Kelly2 said:
    Could someone please suggest suitable PNP transistors for Q30 & Q31 for the circuit in figure 5.2 on page 9, as that's much closer to the circuit we already have?

    I am not sure what's the part number of the PNP transistors. MMBTA56LT1G could work here.

    BRs

    Kian

  • 0 in reply to Kian Lin
    Prodigy 50 points

    Hi Kian,

    So if only three CSD18536KCS (TO220 package) are used, but are mounted to a 2'C/W heatsink (with good airflow) would that be okay? i.e. the only problem is heat.

    Thank you for the quick answer!

    Best regards,

    Ian

  • 0 in reply to Ian Kelly2
    TI__Intellectual 1940 points

    Hi Ian,

    Yes, it could be better if you can dissipate the heat. The only problem is heat, Our AFE can easily drive three FETs.

    BRs

    Kian

  • 0 in reply to Kian Lin
    Prodigy 50 points

    Thank you for your help!