LM76005-Q1: Trouble with startup simulation

Jeffrey Tieman

Part Number: LM76005-Q1

Tool/software:

I am trying to simulate the LM76005-Q1, but I can't get an output voltage. In every sim I run (OrCAD Pspice - both a "manual" circuit drawn from the Webench output and the provided "Buck_Startup" simulation, TI Tina) the output starts to rise, gets to 10s of mV, then decays back down to zero.

I am using the spice model at:

https://www.ti.com/lit/zip/snvmby2

(linked from https://www.ti.com/product/LM76005-Q1?bm-verify=AAQAAAAJ_____8fTa_keYhmTmva1SwA0WGUvDzFl-qrNJvFK07CVmHQm5PkVZEmSuGYlXE5_SUy8nFYdAie8_vgUeOAuIZ6KLf-wGizuYXQhtjSe_aR7YZQUXjElMtRIN7HxsJHP15Qks9dp6DV0K10f9lpqoh1kR9YAsIL8HCZ6LD62dwHchqW1kLm-t83pi4d1kGNIxx0gYmYMXBeucnXFm-N3RcejJUTsvc8wchujbu2VwiqIXo4gPRypk1Mc_nb0NgoBG_hmbcUBZFRgqEIqT7_qnX3jiLxQC4pTLexc8vI9p84H3P2vIf1QkzoDTzdvQmI-#design-tools-simulation)

I am unsure what I am doing wrong, but need to be sure when I design the board, the circuit works.

over 1 year ago

0 Jeffrey Tieman over 1 year ago

Prodigy 20 points

some images of setup and results.

0 David Baba over 1 year ago in reply to Jeffrey Tieman

TI__Mastermind 40410 points

Hello Jeffrey,

I followed the link you provided above; I copied the folder onto my local drive, out of the download folder. I ran the simulation using PSPICE for TI.

Does the simulation run OK without modifying it? if not suggest downloading PSPICE for TI, which is free.

Hope this helps.

David.

0 Jeffrey Tieman over 1 year ago in reply to David Baba

Prodigy 20 points

PSPICE for TI isn't working at all... I finally got it to load, but it won't let me create a simulation profile to run. I don't know if this is because I'm using OrCAD X (Pspice for TI is asking to update to a "174" library, which is suspiciously close to 17.4 - the old version of OrCAD).

The simulation does NOT run without modification (speaking of the simulation provided in the link above). It behaves the same way as described above... looks like it is about to start as it runs up to several mV before decaying back down to 0.

+1 EricLee over 1 year ago in reply to Jeffrey Tieman

TI__Guru 66801 points

Hello Jeffrey

Please 1) download https://www.ti.com/lit/zip/snvmby2, 2) Unzip the file 3) open' LM76005-Q1_TRANS.OPJ' 4) run simulation as it is.

And then, would you please let us know whether you can simulate it successfully or not ? If not, please let us know the error message.

-EL

0 Jeffrey Tieman over 1 year ago in reply to EricLee

Prodigy 20 points

That worked. I looked to see what was different and noticed the "maximum step size" simulation parameter was set to 20ns in the recommended file, whereas in the simulations I've been running it was left blank to let Pspiice "pick" the value. Setting the maximum step size to 20ns in my other sims has resulted in them working.

0 EricLee over 1 year ago in reply to Jeffrey Tieman

TI__Guru 66801 points

Thanks for choosing TI. Please feel free to contact us if you have any question.
-EL

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LM76005-Q1: Trouble with startup simulation