LM5069: schematic review_Huaqin

Hi Rakesh,

the customer update their design, there may be some changes to the operating parameters

please help review the design calculator, many thanks

LM5069_Design_Calculator_REV_C_PA5713.xlsx

Hi Meng,

I see current level has increased to 97A. With this, the power loss in Rshunt is 7.6W if we use LM5069.

I suggest to consider LM5066 as it offers lower sense voltage and is preferred for high current applications. Can you fill https://www.ti.com/lit/zip/snvr507 and send me for review.

Best Regards,

Rakesh

Hi Rakesh,

I have three questions need your comments:

question1

The customer current design's TDC is 61A but there would be 97A peak current which would last for at most 2ms. So what value should they use to calculate the Rshunt?(for the design calculator part 1, what the maximum load current should they use? 61A or the 91A). the customer's current proposal is to fill the maximum load current at 61A , the calculated Rshunt is 1 mohm, but they use the external divided resistor to make the actual effective Rshunt 0.46mohm to make the actual current limit 97A. if this works, can they use just one 0.5mohm Rshunt and use the external divided resistor to make the actual effective Rshunt 0.46mohm. I would attach the final version for your review.

LM5069_Design_Calculator_REV_C_PA5713_0.5.xlsx

question 2

For the external soft start circuit, why we can make the Tblank smaller than the Tss with the external soft start circuit? when there is a external soft start circuit, what would be different for the SS capacitor? there still would be a constant current source to charge the SS cap,right?  I try to find the answer from the application note below, but there is no a detailed discrption on this? why the Tblank can be smaller than the Tss?

Effects of Gate RC Soft Start in Hot Swap Controllers.pdf

Question3

for the Cin, what is the recomended value and how is it calculated?

for the TVS, is there any selection guide or application note we can provide to the customer?

Hi Meng,

A1) Since 97A peak current last for 2ms, we need to set the minimum current limit above 97A. you can use 0.5mohm Rshunt without any external resistor divider. But you can have placeholder for resistor divider in schematic and layout to use in case needed later.

A2) If we use soft-start, Tblank and Tss are independent. The gate drive current is constant and as you increase SS cap, the slew-rate reduces which reduces the FET stress during startup

A3) Typical Cin of 0.1uF is recommended for hot-swap application 

Please refer https://e2e.ti.com/blogs_/b/powerhouse/posts/selecting-tvs-diodes-in-hot-swap-and-oring-applications and Power Electronics article, “TVS Clamping in Hot-Swap Circuits.” for TVS selection guidelines

Best Regards,

Rakesh

Attaching the updated design sheet

 8863.LM5069_Design_Calculator_REV_C_PA5713_0.5.xlsx

Hi Rakesh,

Thanks for the detailed reply!!

For the question two, why when we use the external soft start, the Tblank and the Tss are independat and we don't have to limit the Tblank > Tss, is there any detailed explanation on this?