LM317L: Regarding waveform at startup and startup period

Daisuke Higa

Genius 4315 points

Part Number: LM317L
Other Parts Discussed in Thread: LM317

Hi support team.

My customer asked about startup waveform and startup period.

They are considering using it in the constant current circuit of the LM317.

The current and voltage waveforms at startup were measured in the test circuit.

We also performed simulations using PSPICE for TI.

Since the results were significantly different from the actually measured waveforms, we have received inquiries regarding the reason.

Could you please give me some advice on the different reasons?

There is also a large discrepancy between simulation and actual measurement results regarding startup time.

Simulation: 60us(Green trace)

Actual:340us(Red trace)

I would like to know the approximate time it takes for the Vout voltage to rise.

Do you know how long it will take?

[Simulation Circuit]

[Simulation waveform]

[Actual waveform]

Best regards,

Higa

over 1 year ago

0 Josh Nachassi over 1 year ago

TI__Expert 5231 points

Hi Higa,

I wouldn't really follow the simulation as the best indicator if you manually tested it yourself. I am still curious about that rise of Vout in the scope shot you sent me. Something looks a little off, it seems to have some step and then rises non linearly. Can I see your schematic for this application?

Thank you,

Josh Nachassi

0 Daisuke Higa over 1 year ago in reply to Josh Nachassi

Genius 4315 points

Hi Nachassi-san

I attach the schematics as below.

Best regards,

Higa

0 Josh Nachassi over 1 year ago in reply to Daisuke Higa

TI__Expert 5231 points

Hi Higa-san,

Thank you for the schematic, after reviewing further all looks good and so does the schematic.

Hope this helps and please let me know if you have any further questions.

Thank you,

Josh Nachassi

0 Daisuke Higa over 1 year ago in reply to Josh Nachassi

Genius 4315 points

Hi Nachassi-san

Sorry for repeating, my inquiry is as below.

I would like to know the approximate time it takes for the Vout voltage to rise.

Do you know how long it will take?

I think that the rise of the output depends on the output impedance of the device as far as the waveform is concerned.

Therefore, it is difficult to estimate the startup time using only the external circuit.

Best regards,

Higa

0 Josh Nachassi over 1 year ago in reply to Daisuke Higa

TI__Expert 5231 points

Hi Daisuke-san,

Since it's an older part and it is being used in constant current configuration there is no data supporting rise time in this configuration. Are you trying to compare the calculated time to the time you are receiving?

Thank you,

Josh Nachassi

0 Daisuke Higa over 1 year ago in reply to Josh Nachassi

Genius 4315 points

Hi Nachassi-san

you said;

Are you trying to compare the calculated time to the time you are receiving?

-> Yes. I have no choice but to use that method.
Is there another way?

Best regards,

Higa

+1 Josh Nachassi over 1 year ago in reply to Daisuke Higa

TI__Expert 5231 points

Hi Higa-san,

I wouldn't compare the two as the startup of the device in simulation might not be the most accurate. There is also not really a lot of characterization regarding this spec in the data sheet and the part is very old, so it is hard for me to assist you with the rise time in constant current configuration.

I would not be worried if you notice your rise time differ from that in the simulation though.

Hope this helps please let me know if you have any further questions.

Thank you,

Josh Nachassi

0 Daisuke Higa over 1 year ago in reply to Josh Nachassi

Genius 4315 points

Hi Nachassi-san

Thank you for your support.

I understood.

Regards,

Higa

0 Josh Nachassi over 1 year ago in reply to Daisuke Higa

TI__Expert 5231 points

Hi Higa-san,

Glad I could help. Have a great day.

Thank you,

Josh Nachassi

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LM317L: Regarding waveform at startup and startup period