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TIDA-00364: Number of parallel mosfets required for 5W drive

kalyanraj durairaj
Prodigy 30 points
Part Number: TIDA-00364
Other Parts Discussed in Thread: CSD19536KCS, CSD19535KCS,

Hi,

I am currently working on the 48V,5kW PMSM motor inverter drive. 

I am trying to implement the same system with through hole mosfets. Now we are considering the CSD19535KCS,CSD19536KCS parts for hardware implementation.

if we consider CSD19535KCS part,it can carry a continuous current of (as per the datasheet) 133A. Our requirement is 133A continuous current and overloading current of 250A for 2min, switching frequency :20kHz. 

For this we are planning to use 3 Mosfets in parallel. 

In this configuration, we are getting 3.53W(Rds_on: 3.6m ohm) conduction loss and 10.64W (rise and fall time assumed as 100ns each)switching loss per FET. So the total inverter power loss is around 255W. 

we are getting junction temperature of 76.34 deg cel for  maintaining the inside air temperature of 65 deg cel.

But in the application note I can see 5 parallel mosfets (200A rated)  are used for 5kW inverter system. May I know How you are choosing number of parallel mosfets for this application? 

For our specifications, Is 3 parallel mosfets are sufficient for optimum operation?

Looking for reply at earliest.

Thanks & Regards,

Kalyanraj D

  • 0
    TI__Mastermind 38320 points

    Hello Kalyanraj,

    Thanks for your interest in TI FETs. I was not involved in the design of TIDA-00364 and I am not certain what drove the decision on the number of FETs. Typically, performance targets such as efficiency/power loss and maximum junction temperature of the FETs during normal operation and under fault conditions will determine how many FETs are required for the application. A big part of this is how the FETs are cooled. For thru-hole FETs in TO220 packages this is usually done by attaching them to a heatsink or chassis to provide conductive cooling. I am going to send this over to the team who worked on the TIDA-00364 design to get their inputs.

  • 0 in reply to John Wallace1
    Prodigy 30 points

    Hi John,

    Thanks for the fast response and involvement in my query.

    Yes,you are correct. we are planning to attaching the mosfets to a chassis for natural cooling. 

    At overload condition( 250A,we are getting 12.5W(Rds_on: 3.6m ohm) conduction loss and 20W (rise and fall time assumed as 100ns each)switching loss per FET. So the total inverter power loss is around 585W, and junction around 91 deg cel.

    I am waiting for the response from your design team.

    Once again thanks for shown interest on my query.

    Regards,

    Kalyanraj D

  • 0 in reply to kalyanraj durairaj
    TI__Prodigy 640 points

    Hi Kalyanraj,

    I understand that the system requirements are 133A continuous current and 250A overcurrent for 2 mins. What is the maximum ambient temperature that the system should operate in? Also, please provide some information on the thermal system - thermal resistance of heatsinks/ chassis. You have mentioned natural cooling - does this mean there is no forced air or liquid cooling?

    The maximum current that the FET can handle and the number of parallel FETs needed depend a large extent on the cooling system and maximum ambient temperature requirements. Also, please note that Rds_on increases as junction temperature increases and hence conduction losses will be higher as the device junction temperature increases.

    Regards
    Siva