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CSD18511KCS: MOSFET Selection for high current

Sv
Intellectual 500 points
Part Number: CSD18511KCS
Other Parts Discussed in Thread: CSD17573Q5B, CSD17570Q5B, CSD18531Q5A, CSD18533Q5A, CSD18543Q3A, CSD88537ND, CSD18535KTT, CSD18540Q5B, CSD18536KCS, CSD18536KTT

Tool/software:

Hello Team,
We are looking for some high current MOSFET for one of our products.
Hope your team can help us on this.

The MOSFET driver we are using will be TPSI3050 in the following configuration.

1). The high current can be bidirectional so we are using back to back MOSFETs.
2). The VGS voltage will be 10V.
3). Low RDSon is needed.
4). Low ON capacitance between the D-S pins.
5). The continuous current will be just above 40A and will be 100% time ON.
6). We cannot parallel multiple MOSFETs because of the space constraints in the PCB
7). Most MOSFET datasheet/vendor sites says their MOSFET is able to carry hundreds of amperes. But when we dig deep into the datasheet, we can see some conditions like package limited, or silicon limited or not meeting the SOA.
8). Can anyone suggest a MOSFET for our application?.
9). Is there any method to measure the RDSon of the MOSFET. In the datasheet of some MOSFETs (CSD18511KCS) the RDSon will be marked as 2.6mOhms.
Is there any method to measure the RDSon using multi meter.
When we measure the resistance across the drain and the source we get the resistance as 300mOhms.
But when we measure the voltage drop across the VDS and when I divided it with ID, i got the RDS as 200mOhms.



We have another application in the same board with continuous current of 15A.
Can you suggest another MOSFET for this application.
Looking for your reply.

  • 0
    TI__Mastermind 36140 points

    Hello Sv,

    Thanks for your interest in TI FETs. What is the maximum input voltage to the b2b FETs? You mention the CSD18511KCS which is a 40V N-channel FET in TO220 thru-hole package. Is 40V adequate MOSFET breakdown voltage for your application? Is TO220 the preferred package or would you prefer a SMT MOSFET in D2PAK or 5x6mm SON package? Please see the links below for more information on how TI tests and specs maximum continuous and pulsed currents for our FETs. The first blog explains the various continuous current ratings in the datasheet including package limit and silicon limit. Because of the low on resistance, it is very difficult to measure Rds(on) of a MOSFET using a multimeter. You would need to make a 4 wire resistance measurement with kelvin connections to the drain and source. A two wire resistance measurement will not be accurate because of the resistance of the test leads, solder joints and PCB resistance from the measurement points to the actual FET terminals. Measuring the voltage drop across the FET when it is on is also challenging because of the parasitic resistance. Rds(on) is 100% tested in production at the conditions defined in the FET datasheet. Please keep in mind that Rds(on) has a positive temperature coefficient and increases at higher case/junction temperature as shown by the characteristic curves in the MOSFET datasheet. TI has a number of Excel-based FET selection tools including a load switch tool that allows the user to input their requirements and compare up to 3 different TI FET solutions. It is available for download at the third link. I prefilled out the attached spreadsheet with some assumptions for your application. Please review and let me know if you have any questions.

    https://www.ti.com/lit/pdf/ssztcp0

    https://www.ti.com/lit/pdf/SSZTCJ6

    https://www.ti.com/tool/LOAD-SWITCH-FET-LOSS-CALC

    LOAD-SWITCH-FET-LOSS-CALC_Rev2_Sv.xlsm

    Best Regards,

    John Wallace

    TI FET Applications

  • 0 in reply to John Wallace1
    Intellectual 500 points

    Hello John,
    Thank you for your reply.
    Following are our application requirements.

    1). The high current can be bidirectional so we are using back to back MOSFETs.
    2). The VGS voltage will be 10V.
    3). The maximum switching voltage is 12V (peak can be up-to 24V)
    4). Low RDSon is needed.
    5). Low ON capacitance between the D-S pins.
    6). The continuous current will be just above 40A and will be 100% time ON.
    7). We cannot parallel multiple MOSFETs because of the space constraints in the PCB
    8). SMD package is preferred more.
    9).

    For the second application, the continuous current is 15A and the maximum voltage can be up to 48V.


    looking for your reply

  • 0 in reply to Sv
    TI__Mastermind 36140 points

    Hello Sv,

    Thanks for the updated information. For 24V peak input voltage, you should be able to use a 30V FET. I'd recommend the CSD17573Q5B, 30V N-channel in 5x6mm SON package. The conduction loss for each FET at 40A is about 2.3W at TJ = 100°C and increases to about 2.6W at TJ = 125°C. If the power dissipation is too high, the upgrade path to a lower on resistance FET is the CSD17570Q5B which is lower Rds(on) and reduces the conduction significantly to about 1.5W at TJ = 125°C. For 48V, you should be able to use a 60V FET and I would recommend the CSD18533Q5A, 60V N-channel FET in 5x6mm SON package. Estimated power loss is about 1.8W. A lower cost, higher Rds(on) option is the CSD18531Q5A with estimated power loss of about 2.4W. Let me know if you have any questions.

    Best Regards,

    John

  • 0 in reply to John Wallace1
    Intellectual 500 points

    Hello John,
    Thank you for your reply.
    We have 7.5A, 15A, 20A, 30A, 40A and 60A lines in our design.
    All are 100% time ON.
    We cannot parallel MOSFETs to carry higher current because of the space constraints.
    Because of the space limitations, we cannot parallel multiple MOSFETs.
    The MOSFET driver we are using is TPSI3050.
    The output voltage of the driver is 10V and we can use the driver TPSI3052 for higher Gate voltage (15V).
    All the signals are 48V rated. (in the previous post I said the 60A lines are 24V only).
    After considering cost, PCB space and everything, we are planning to use a dual N Channel MOSFET for 7.5A lines.
    1). Can you please suggest any 7.5A continuous current rated, dual channel MOSFET with maximum switching voltage of 48V.
          a). Low RDSon
          b). Low ON state capacitance
          c). Low ON state capacitance
          d). Low PCB footprint
    2). We are planning to use the same MOSFET for 15A, 20A and 30A lines.
    Can you please suggest any 30A continuous current rated, N channel MOSFET with maximum switching voltage of 48V.
          a). Low RDSon
          b). Low ON state capacitance
          c). Low ON state capacitance
          d). Low PCB footprint
    3). For 40A and 60A lines will be using some high current MOSFET. The switching voltage will be 48V.
    We can use same MOSFET for 15A and 60A if they have small footprint since because we can reduce the BoM cost if we have same components.

    The MOSFET CSD18533Q5A is suggested for 15A high current at 48V


    But I cannot determine how we derived at this conclusion.
    Can you please explain this?.

    Looking for your reply

  • 0 in reply to Sv
    TI__Mastermind 36140 points

    Hi Sv,

    Just to confirm, all of the lines require 48V (not 24V as in your previous email). With that in mind you will need to use 60V FETs at a minimum. Driving the FETs with VGS = 10V should be fine. There is no need to drive VGS to 15V.

    1. For a dual, 60V NFET, there is the CSD88537ND in SO8 package. The conduction loss per channel at 7.5A is about 0.85W at TJ = 25°C and increases to around 1.2W at TJ = 100°C for a total of 2.4W which is pushing the capabilities (~2W max) of the SO8 package. We do not have any better dual FETs for this application. An alternative is to use two of the CSD18543Q3A in 3.3x3.3mm SON package. It reduces the conduction loss to 0.87W at TJ = 100°C which is well within the capabilities of the package.
    2. For 15A, 20A & 30A, I'd recommend the CSD18540Q5B. Conduction loss is about 2.8W at 30A & TJ = 100°C The alternative is to go to a larger D2PAK device such as CSD18535KTT with about 2.6W conduction loss.
    3. I do not have a recommendation for a single 60V or higher FET that can handle 60A. The power loss will be too high. For 40A, a D2PAK or TO220 FET is required and I would recommend CSD18536KTT which is also available in TO220 as the CSD18536KCS.

    All of my recommendations are based on power loss in the device when it is on. SOA becomes a consideration during switching transitions when there is voltage across the FET and current thru it. If you know the switching times, we can evaluate SOA. If there is a lot of capacitance on the output side, then controlling turn-on is important due to inrush current to charge the capacitors.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Intellectual 500 points

    Hello John,
    Thank you for your reply.
    Thanks for the suggestions on the MOSFET.
    Regarding the switching of the MOSFET. I can say, they are for continuous ON application.
    But regarding the 40A or 30A signals, 100% current can flow when we turn ON the MOSFET.

  • 0 in reply to Sv
    TI__Mastermind 36140 points

    HI Sv,

    Thanks for the update. I am off for the Fourth of July Holiday and will follow up with you next Monday when I'm back in the office.

    Thanks,

    John

  • 0 in reply to John Wallace1
    TI__Mastermind 36140 points

    Hi Sv,

    Following up to see if you need any additional assistance from me. Please let me know.

    Thanks,

    John

  • 0 in reply to John Wallace1
    Intellectual 500 points

    Hello John,
    Thank you for your reply.
    The 100% current will flow through the MOSFET when it is turned ON and the current can flow through the MOSFET for 2-3 hours.