Power Management for Solar Panels

Hi Raymond,

Thanks for your interest in TI FETs. I was not involved in the TIDA-00640 reference design. Can you share more details about the application and the requirements for the CSD18532Q5B: max voltage, continuous current, short circuit current and any inrush when the switch turns on. Also, how do you plan to drive the FET? I'll have to estimate the steady state power dissipation to make sure the package can handle it. Also, need to check SOA during turn-on and turn-off. I'm including links to some useful information on SOA and power dissipation capability of TI FET packages.

How to choose the right power MOSFET or power block package for your application

Other Parts Discussed in Post: CSD17581Q5A When starting a new design, engineers are often overwhelmed by the number of package options for power metal-oxide semiconductor field-effect transistors ( MOSFET…

By John Wallace1 over 6 years ago in Technical articles > Power management

Hi John,

Thank you for getting back.

I want to use this MOSFET as a switch on the way to a 600W solar panel.
It is installed on the hot / plus wire of the solar panel and is used as a rapid shutdown switch.

The current is about 10A, Max and the voltage may be 10V - 90V, worst-case.

The gate driver is a logic level driver that is controlled by the microcontroller. 

By looking at Gate Charge, it seems the device can be turned fully on at 5V.

Please share your thought and let me know should you require more information.

Regards,

Raymond Koosha

Hi Raymond,

The CSD18532Q5B has a maximum VDS rating of 60V. If it needs to support 90V, then you should consider a FET with maximum VDS rating of 100V. The CSD18532Q5B has on resistance specified down to a minimum VGS = 4.5V and will work with 5V gate drive. Please note, in a high side switch application, where the drain is connected to the input voltage and the source is connect to the load (i.e. source not grounded), you must provide a gate drive voltage that is greater than the input voltage by at least 4.5V. That is because the drain and source are at roughly the same voltage when the FET is turned on. If you need to use a higher voltage FET, all of our 80V and 100V devices have a minimum VGS = 6V at which on resistance rated. You must provide VGS >=6V or we cannot guarantee the on resistance of the FET. If you do need to go to a 100V FET, then I would recommend the CSD19533Q5A or CSD19531Q5A which has lower on resistance but is higher cost.

For SOA, I need to know the turn-on and turn-off timing of the FET. It seems like you're trying to turn it off pretty fast if there is a fault condition.

Hi John,

I am going for CDS19531Q5A to be on the safe side. In that case, I have to boost the 5V to 6V for the gate.

This is how I will connect it so please advice if you see something unusual.

1. The Source and Drain of MOSFET are connected along the Hot OR positive wire.
2. The gate is connected between the Gate and a Gate drive that generates 6V. I will use a 100 Ohms resistor in series to the gate to limit the inrush current to the gate.

3. Is there anything else that I need to consider?

As you have rightly guessed, this is a switch that is ON during the operation and should turn OFF in an emergency.
The ON and OFF times are 10ms or less.
The drain current is about 10A and the voltage between drain and source is 90V. This is the worst case.

Also, for your information, this MOSFET will be used in Series and Parallel PV strings .

Please do not hesitate to ask any questions you might have.

I have looked at Fig 10 of the Datasheet about SOA but would appreciate an explanation.

Thanks,

Raymond Koosha

Hi Raymond,

Thanks for the update. Please see attached. Is this how you plan to use the FET? Is the gate driver referenced to the source of the FET (i.e. floating gate drive) or it referenced to ground? How are you deriving the gate drive supply and is it referenced to ground or isolated? I just want to make sure you're driving the FET correctly. As mentioned in my previous response, the gate must be driven at least 6V higher than the input voltage for the CSD19531Q5A. Can you share the part number for the gate driver you're using? I'd like calculate or simulate the switching times to verify operation within SOA.

Please refer to the blogs in my earlier posting for more information on SOA and hot swap (very similar to your application). We can use Figure 10 to verify the FET is operated within the SOA limits. For a given pulse width, we can determine the SOA drain current for a given drain-source voltage. The FET can support can support higher power operation at shorter pulse widths. 

TI makes hot swap and high side switch controllers such as the LM5066 which provide the gate drive and protection features note available in simple gate drivers. It's good up to 80V. I'd have to check to see if we have anything to support up to 90V.

High_Side_Switch.pdf

Hi Raymond,

Thanks again for your interest in TI FETs. Following to see if I have adequately answered your questions and your issue is resolved. I will wait another day and if I do not hear back from you, I will close this thread.

Hi John,

Thank you so very much for your response.

I will simulate the schematic with the part and see how it functions.

Is there a simulator engine on Ti website that I can run simulation on?

Best Regards,

Raymond Koosha