TPS54360-Q1: Softstart behavior

Hello Egon,

Can you provide a schematic? I would like to make sure the device is properly connected. There is typically a delay from the time a VIN and VOUT begins to rise. Can you provide another waveform with EN pin included?

Thanks,
Alejandro

Hello Alejandro,

The EN pin is open circuit.  Do you still want a ograph showing it?

Is the typical delay you mention rated in the datasheet?

Best regards

Egon

Egon,

Yes, please. Additionally, please probe the switch-node. I would like to take a look at the start-up characteristics. (VIN, VOUT, EN, SW).

Thanks,
Alejandro

Hello Alejandro,

my customer replays:

 We can do that.  Before I do, is there anything in the datasheet that speaks to a delay after the application of VIN?

How long does it take for the clock to get started and established? 

Thanks.

Best regards

 Egon

Egon,

The datasheet does not provide this info. I have reached out to the team for more info in regards to this phenomena. For the meantime, we wanted to look at some waveform to try and make sense out of it.

Thanks,
Alejandro

Hi Alejandro,

attached the scope pictures you ask for.

In addition the customer has following question:

Is there an under voltage lockout on the gate drive?

Best regards

Egon

Hi Egon,

Thanks for this waveform. It is very helpful.

When comparing the waveform you provided with the ones found in datasheet or user's guide, I noticed that there is a delay between VIN rise and VOUT start to rise, and also sometimes a delay between EN rise and VOUT start to rise.

I don't have a definite answer, but I believe it might have to do with the UVLO threshold. If EN is floating, which that's the case in this application, there is some delay for the internal pull-up to rise to the threshold.

I am waiting to hear back from the team internally. So, I will get back to you with further information as soon as possible.

Thanks,
Alejandro

any update?

Hello 5t34m,
Still waiting to hear back from the team internally. I will get back to you as soon as possible.

Regards,
Alejandro

any update

Hi 5t34m,

No updates. We have further reached out to Design Engineer. I will get back to you as soon as I have any updates.

Thanks,
Alejandro

Hello all,

this thread is now open for 4 weeks. My customer asks me every day for an answer.

Our TPS54360 is not the only DC/DC converter on the market. We have here strong competition from MPS and ADI.

Best regards

Egon

Hi Egon,

I understand. I have been following up with Design team internally but unfortunately the response has not been quick.

Regards,
Alejandro

Hi Egon,

At least a 540μs delay is expected between EN High and COMP active. Plus, some additional delay can be caused by the following:

1. Starting from VIN vs EN Startup varies the delay within the internal circuits.
2. The capacitance on COMP is adding more delay. This creates a longer time from EN to switching as the COMP voltage needs to charge up the switching threshold before switching can begin.

Regards,
Alejandro