TPS7A85: TPS7A85 design mismatches between webench and datasheet

Hey Lu,

I'm looking into the webench error. The graph in the datasheet is labeled as Vin-Vout, the one from webbench is in input voltage. they both line up the same when you do the math.

Thanks,

Vahnroy

Hello Vahnroy,

Thank you for your prompt response, I still have some confusion, please advise:

1. For my application, "a 1.5V input and 1.2V/3.6A output design by using TPS7A8500RGRR", the input voltage 1.5V is allowed by datasheet while not allowed by webench:

• these are the evidences in datasheet:

you can see in fig.23/24 above, I draw a RED LINE to indicate where the 1.5V inpit is, both of them show VDO at 1.5V input is under 300mV(Iout=4A higher than 3.6A), which means 1.2V output is OK;

the other one is as above in chap."6.5 Electrical Characteristics" which indicates a possible VDO for 1.4V Vin is 215mV, and so 1.5V Vin is likely under 300mV too.

• now this is what it looks like in webench:

I type in the params above then click "open design", and the error pops up:

so the webench warms that input voltage is NOT ok, when I change the Vin to 1.55V, the webench can launch normally:

so there is some mistake between datasheet and webench, what do you think? Which result should I follow?

2.

• When set the Vin=1.55V as above and do the design in webench, the "Safe Operating Area" chart X-Axis shows up as below in EXPORT label:

I download data of this chart by "save as -xlsx" option, and the data is:

seems like webench simulate a max allowed input voltage for Iout=3.6A is 1.55V.

• and this is what I can get from datasheet:

I draw some lines to split 0.25~0.5V(Vin-Vout, it's VDO) equally, and can estimate that for a VDO=0.3V the Iout is above 3.6A, which conflicts the result in webench.

So which results can I follow indeed, thank you.

attach my SCH:

Hey Lu.

Can you try changing ambient temperature to 25 and rerun the design.

Thanks

Vahnroy

Hi Vahnroy,

Thank you for the response. And this is the 25 deg. ambient temp input, keeping the other inputs as my application requires:

Now the webench remains warning me, just like the 30 deg. situation:

so I have to change the input to 1.55~1.57V, and the webench launches:

while in this situation, the "Safe Operating Area" chart data seems like no change from yesterday:

Can I just assume that this is just a webench issue and ignore, and use 1.5V input as datasheet?

Thank you for your support.