TPS61178: Question Asking

Jason Ciou

Expert 3600 points

Part Number: TPS61178

Hi team,

My customer have some question on TPS61178.

CH1 Vin; CH2 Vout; CH3 SW ;CH4 EN

Below is the test specification:

Vin: 4V

Vout:5V

Iout: 2.5A

Frequency:1MEG HZ (steady state)

When the system start up, customer see the SW waveform is discontinued (red circle), is this normal? what's the root cause to make this phenomena.

over 2 years ago

0 Jason Ciou over 2 years ago

TI__Expert 3600 points

Hi team,

Anyone could help?

Jason

0 Yichen Xu over 2 years ago in reply to Jason Ciou

TI__Expert 4760 points

Hi Jason,

This is a typical startup waveform. Could you measure the startup waveform like this? You may zoom in for both pre-charge state and soft start state.

0 Jason Ciou over 2 years ago in reply to Yichen Xu

TI__Expert 3600 points

Hi Yichen,

If the start up behavior is not the same as EVM, what's the next step.

Jason

0 Yichen Xu over 2 years ago in reply to Jason Ciou

TI__Expert 4760 points

Hi Jason,

We can check layout for further analysis.

0 Jason Ciou over 2 years ago in reply to Yichen Xu

TI__Expert 3600 points

Hi Yichen,

Let me ask my customer to provide the layout file, thanks.

Jason

0 Yichen Xu over 2 years ago in reply to Jason Ciou

TI__Expert 4760 points

Hi Jason,

We need to check the behavior first. Could you provide waveforms like the typical waveform and zoom in it for both precharge and softstart state? And please label every curve. Because I can not see much useful information in your previous waveform.

0 Jason Ciou over 2 years ago in reply to Yichen Xu

TI__Expert 3600 points

Hi Yichen,

Please see below waveform.

Jason

0 Jason Ciou over 2 years ago in reply to Yichen Xu

TI__Expert 3600 points

Hi Yichen,

update the question.

1.) My customer want to know how to make sure the soft-start phase is the period from 1.1 × VIN to the setting output voltage.

2.) SW doesn’t continue during the start up, is this normal?

...

Jason

0 Yichen Xu over 2 years ago in reply to Jason Ciou

TI__Expert 4760 points

Hi Jason,

Yes, soft-start phase is the period from 1.1 × VIN to the setting output voltage.

From the waveform, EN is connected to Vin, right? The main issue is that Vin falls at startup. The most possible reason is that the impedance of your input trace is high so the voltage drop caused by inrush current is large. You need to add a bulk capacitor at input side. Optimizing the layout and make the input trace short and thick could fix the issue too.