LM5069: LM5069 Design Calculator REVC 2

Joseph Fearon

Part Number: LM5069
Other Parts Discussed in Thread: LM5066,

Tool/software:

Copy of LM5069_Design_Calculator_REV_C_2001.xlsx

Hi Please can you help with attached design tool. The problem I am having with the calculator is how it derives the min power limit. The suggested min power limit is unrealistically high (1.2kW) and I don't understand what's driving that value to be so high in the design. As a result the SOA margin is extremely low and there are lot's of RED cells!

Can you advise how to get over this problem please. I've attached the file for reference.

Thanks

1 month ago

0 Kunal Goel 1 month ago

TI__Guru 56860 points

Hi Joseph,

I will check and get back on this.

Regards

Kunal Goel

0 Joseph Fearon 1 month ago in reply to Kunal Goel

Prodigy 20 points

Ok thanks. I've found the formulas tab in the spreadsheet. The power limit is dependent on the value of Rs the larger Rs the smaller the power limit value. We are using 250uR due to the high current in the system we can't make this value any bigger due to power dissipation. So I'm stuck on how to overcome this issue. Any help would be appreciated.

0 Kunal Goel 1 month ago in reply to Joseph Fearon

TI__Guru 56860 points

Hi Joseph,

As long as you do not do SOA violations you can go with 1.2kW limit. Can you check LM5066 device als?.

Regards

Kunal Goel

0 Joseph Fearon 1 month ago in reply to Kunal Goel

Prodigy 20 points

Hi Kunal,

I'm using 7x IPB017N10N5LFATMA1 in parallel it's a very good spec Mosfet. RDSon MAx is 1.7mR. Looking at the SOA it's hard to tell. The fault time is 0.26mS and the circuit breaker current max is ~250A. So if I divide total current by 7 then each MOSFET must handle 35A for 260uS. Looking at the SOA it should be ok what do you think ?

What do you mean by device als ?

Thanks.

0 Kunal Goel 1 month ago in reply to Joseph Fearon

TI__Guru 56860 points

As far as calculator confirms within soa we are good to go. I meant you can also check lm5066 device.

0 Joseph Fearon 1 month ago in reply to Kunal Goel

Prodigy 20 points

That's the problem the calculator has a lot of red cells and the 'margin' is too low. I've tried to change the variables as much as I can to reduce the errors but I can't overcome this issue of the power limit ? Can you help with this ?

0 Kunal Goel 1 month ago in reply to Joseph Fearon

TI__Guru 56860 points

Let me go through this.

Regards

Kunal Goel

0 Joseph Fearon 1 month ago in reply to Kunal Goel

Prodigy 20 points

Hi Kunal Any updates/ suggestions.

Thanks

0 Kunal Goel 1 month ago in reply to Joseph Fearon

TI__Guru 56860 points

Hi Joseph,

It shows violation during startup. What is actual load cap? Will 1ohm load also be present?

Regards

Kunal Goel

0 Joseph Fearon 1 month ago in reply to Kunal Goel

Prodigy 20 points

The Load Capacitance is unknown. The load is a DC motor Controller. The load capacitance is high and causes high inrush current hence need to use LM5069. The worst case Load could potentially be a dead short on startup if the motor controller was to fail short.

0 Kunal Goel 1 month ago in reply to Joseph Fearon

TI__Guru 56860 points

Okay. Let me check again.

0 Kunal Goel 29 days ago in reply to Kunal Goel

TI__Guru 56860 points

Hi Joseph,

The main violation is showing during startup because of powering up 1ohm within certain time. I think that is not the actual scenario. Can you help fill this one? It has some changes for correct estimation.

LM5069_Design_Calculator_REV_D_Rakesh.xlsx

Regards

Kunal Goel

Power management

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LM5069: LM5069 Design Calculator REVC 2