WEBENCH® Tools/LMR16006Y-Q1: LMR16006Y Not showing as an option in Webench, when parameters seem to be within range

Bruno Saraiva

Guru 13040 points

Part Number: LMR16006Y-Q1
Other Parts Discussed in Thread: LMR14006

Tool/software: WEBENCH® Design Tools

Gents,

I have a few projects running properly with LMR16006Y, using the fixed 3V3 output version.

Trying to confirm a new design today, but Webench does not see it as a valid option for my parameters:

VIN: 9-36VDC
VOUT: 3.3V
Iout: 300mA
Ambient temp: 50oC

I wonder if this device is actually not suitable for that application? It is automotive rated and should be able to deal with 600mA per the datasheet, on an even wider input range...

Regards

Bruno

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

At the maximum input voltage the required on time is less than the specified minimum on time for LMR16006Y. That is why Webench does not see it as a valid option.

0 Bruno Saraiva over 7 years ago in reply to JohnTucker

Guru 13040 points

Hi John,
Thanks for the reply.
I am still confused - I started the Webench session directly from the products page, a few times with different parameters. The parameters are all "within specs" - and there is no "on time" field.
I tried a few combinations with lower Max VIN, but still did not see a valid project with LMR16006Y.
Further, I tried to look at the "Use Advanced Options" and seek such parameter, but could not find it there.
Is this "minimum on time" something related to the ramp up time?
Regards,
Bruno

0 JohnTucker over 7 years ago in reply to Bruno Saraiva

TI__Guru**** 191445 points

Minimum on time is not an input to Webench. The "on time" is the portion of the switching cycle when the high side FET is "on". For LMR16006Y, the on time can be calculated by Ton = Vout / (Vin * Fsw) where Fsw is the switching frequency. For Vin = 36 V and Vout = 3.3 V, the nominal on time is 43.65 nsec. Section 7.6 of the data sheet list the switching characteristics. It shows 80 nsec (typical) as the minimum supported on time. Webench checks for this when it creates designs. Also, it probably uses the maximum value for the switching frequency during that check. It will not produce a design if the minimum on time requirement is not met. There are several other checks it performs as well that may prevent a design even though the inputs seem to be within the device limits.

0 Bruno Saraiva over 7 years ago in reply to JohnTucker

Guru 13040 points

Hello John,

Thank you very much for the precise and really clarifying answer!

We are replacing the switcher by the X version of the same family, which by means of a slightly bigger inductor will be able to buck down to 3V3 at the full input range. And Webench is now happy.

Regards

Bruno

0 JohnTucker over 7 years ago in reply to Bruno Saraiva

TI__Guru**** 191445 points

You are welcome...yes, the "X" version switches at a much lower frequency so the required on time is quite a bit higher than the minimum. You should be good to go.

0 Bruno Saraiva over 7 years ago in reply to JohnTucker

Guru 13040 points

John,

While happy with the X design, I noted the option for LMR14006. That would make sense for us, because we actually won't need 60V input.

BUT running Webench for that part, I got surprised to see a "valid" project for the Y version. Here's the Webench link if it helps:
webench.ti.com/.../SDP.cgi

Looking into the datasheet, the min OnTime is even more strict for LMR14006 (table 6.6 shows 95ns).

Now, did I get back to square one on my understanding, or shouldn't webench block this result as well for the same initially posted reason?

Regards

Bruno

0 JohnTucker over 7 years ago in reply to Bruno Saraiva

TI__Guru**** 191445 points

For whatever reason, it looks like bench does not check LMR1406 for minimum on time. By hand calculation, the required on time is low. I'll post this question in the webench forum to see what they say...

0 Bruno Saraiva over 7 years ago in reply to JohnTucker

Guru 13040 points

Thanks. When you do, if you kindly paste the link here, I'll look up for future replies to that new post.
Bruno

0 JohnTucker over 7 years ago in reply to Bruno Saraiva

TI__Guru**** 191445 points

Yes, I'll let you know...they are usually pretty quick to answer.

0 JohnTucker over 7 years ago in reply to JohnTucker

TI__Guru**** 191445 points

Here is the link with the answer...

e2e.ti.com/.../2320366

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WEBENCH® Tools/LMR16006Y-Q1: LMR16006Y Not showing as an option in Webench, when parameters seem to be within range