CSD18543Q3A: Gate driver selection and circuit (ORing)

Daniel Miller

Part Number: CSD18543Q3A
Other Parts Discussed in Thread: LM5022, LM5050-1, LM7480-Q1

Having selected the CSD18543Q3A as my switch I need assistance with the supporting connections. I have a 3.3V microcontroller that I want to control the MOSFET. The application is to switch between two external voltages - 32VDC and 40VDC, current ranging from 5ma to 3A. The thermal environment should tolerate at least 75C.The power supplies are using LM5022 designs that already use this switch which is why I want to use it again.

My intent is to have one of the two voltages constantly connected to the load, via a diode (https://www.smc-diodes.com/Products/Discrete/Schottky-Rectifiers/SBRD10200) and switch the other voltage in as required for system function. Can you assist with selecting the appropriate driver and supporting passive devices for a complete solution? A schematic would be helpful.

over 1 year ago

0 Don Dapkus over 1 year ago

TI__Guru**** 189399 points

Our office is currently closed for the US year end holidays. We will reply to your request shortly.

Best regards,

Don

0 John Wallace1 over 1 year ago

TI__Mastermind 31385 points

Hello Daniel,

Thanks for the inquiry. The CSD18543Q3A requires a minimum Vgs of 4.5V to guarantee on resistance. We do not recommend driving the gate with only 3.3V as the on resistance can vary widely as shown in the Rds(on) vs. Vgs curves as shown on page 1 of the datasheet. Based on your description, this is an OR'ing application with the FET configured as a high side switch (i.e. source floating with respect to GND). If this is the case, then the gate must be driven at least 4.5V higher than the input voltage. Something like the LM5050-1 might be a good option for controlling the FET. Please take a look and I will reassign this thread to our power switches applications team.

Best Regards,

John Wallace

TI FET Applications

0 Daniel Miller over 1 year ago in reply to John Wallace1

Prodigy 40 points

Thank you. Would the following be correct?

0 Praveen GD over 1 year ago in reply to Daniel Miller

TI__Guru 57737 points

Hi Daniel,

LM5050-1 drives FET in Diode orientation i.e. N-FET Source connected to the input and Drain connected to the output. In this orientation, the Body diode of the FET will be forward biased when Vin > Vout. So, when Vin > Vout even when the FET is turned OFF using the 'OFF' pin of LM5050-1, there will be flow of forward current through the body diode. So, in order to control the flow of Forward Current, you need a controller which can drive the FET in load switch orientation which is reverse to that of diode orientation (i.e. N-FET Source connected to the output and Drain connected to the intput).

You would need reverse current blocking Functionality + Forward current control. So, the right controller to use would be LM7480-Q1.

0 Daniel Miller over 1 year ago in reply to Praveen GD

Prodigy 40 points

I don't quite understand how to use this correctly. Would I be using two of the LM7480-Q1 controllers and four MOSFETs? Can you show me how these would be wired?

0 Praveen GD over 1 year ago in reply to Daniel Miller

TI__Guru 57737 points

Yes, you would need two of the LM7480-Q1 controllers and four MOSFETs as shown below to achieve reverse current blocking Functionality + Forward current control on each power rail.

Please refer to below documents for more understanding on Power Switches:

Power management

Power management forum

CSD18543Q3A: Gate driver selection and circuit (ORing)