UCC14141-Q1: How to design single RLIM?

Cody,

From the UCC14141-Q1 data sheet, equation 9 is used when the UCC14141-Q1 is configured for either dual positive or dual negative outputs. If this is the configuration you desire, you need to determine the maximum current needed for the VOUT2 output or IVOUT2_max as it is referred by equation 9. 

For example, a popular dual positive output configuration is to set up for VOUT1=15V, VOUT2=5V, where VOUT1 would be the voltage rail required to bias the gate driver and VOUT2 could be used to bias the isolated side of a digital isolator (commonly needs isolated 5V) or some other low power 5V circuitry on the iso side. For the main VOUT1=15V, the power calculation is straight forward as P=Q*V*F, For the VOUT2=5V output, IVOUT2_max will be the addition of all bias currents connected to VOUT2. Add the total power required for VOUT1 and VOUT2 and make sure the UCC14141-Q1 can support based on max ambient temperature and corner cases of input voltage.

Regards,

Steve

How to calculte RLIM(R3) in UCC14141EVM-068? Could you take this EVM to make an example for me? I want to learn about how to select Ivout2_max.

Thank a lot

Cody 

Cody,

The EVM is not configure for dual positive output voltage and so the function of RLIM in the EVM is not the same as you've been asking for dual positive outputs. For the dual positive output configuration, the value of IVOUT2_max will be unique according to whatever circuitry you are connecting as a load to VOUT2.

Also, the EVM is configured as a dual split capacitor output, VDD-COM=+18V and VEE-COM=-4V which is common for IGBT and SiC gate driver bias. The calculation of RLIM in this case can be found using the Excel Design Tool downloaded from the UCC14141-Q1 landing page here.

UCC14141EVM-068 is configured as (c) below:

Regards,

Steve

Dear Steve,

I knew this Excel and tried. This Excel didn't tell me how to select Iout2_max, it just told me the available range of RLIM, I want to learn about this EVM and how to select R3(475R). 

Thanks a lot 

Cody

You select R3 by following the recommendation from the Excel calculator. As you mentioned, the Excel tool does not describe how to calculate Iout2_max. You need to determine Iout2_max based on the total load. It is not possible for the the Excel tool to calculate the total load. I would recommend to order the EVM (if not done already) and then you can learn by using it in the lab and comparing to results given by the Excel tool using various design inputs.

Steve

I applied UCC14141 on my power stage. Now, it could work already, I want to learn about how to select RLM correctly, and how to determine Iout2_max, could you take a MOSFET and Gate Driver (UCC21530)  to make an example, let me learn about your calculating procedure,

Cody