TINA/Spice/TPS40210: Departing from the operating TI model, I modified some parameters and the design doesn't work

Hi Guillermo,

I'm looking into this question. Have you tried increasing the soft-start capacitor to help limit the in rush current? What is the ISEN pin voltage when the current limit is triggered?

Thanks,

Garrett

Hi, Garret

Yes, I tried a greater cap on SS to reduce the startup ramp and I had the same failing result.

Please take a look a the attached TINA file. I started from a well functioning TI example (slum492.tsc) and I progressively changed one component at a time, to detect when and why the problem arised.

Changing the feedback, the output voltage was changed to 24V and it worked.

Changing the load resistor, it was augmented from 8ohms to 29 ohms, and it worked.

With the input voltage VIN (designated as VG1 in the TINA file) at 10V it worked fine, but when I changed it to 15V the simulation failed.

I don't understand why, and mi reasoning is as follows:

1) The converter operates in discontinuous mode, where with a fixed load the discharge time (when the inductor transfer energy to the output filter+load) is constant, and also the inductor's peak current.

2) A higher VIN voltage only means that TON will be shorter, so this is not a problem associated to continuous/discontinuous mode changes.

3) The fact that the same circuit operates OK with VIN=10V shows that this is no a problem on SS start ramp, since in this case the output voltage goal is achieved.

May you help me? I need this circuit operating with this fixed load resistor powered with 24V, but with an input voltage ranging from 15V to 28V.

Thanks a lot

Guillermo (I apologize my english mistakes, I usually speak spanish)

slum492a4.TSC

Hi Guillermo,

I am looking into this and will get back to you.

Thanks,

Garrett

Dear Garret,

I guess I've tried everything and still the simulation fails.

Have you detected any wrong component or it is a TINA simulation bug?

I'm a bit anxious because I'm afraid of manufacturing a malfunctioning system ...

Thanks a lot

Guillermo

Note: I plan to use the TPS40210-EP version