TPS54240: Skipping mode

Brian Wang0928

Part Number: TPS54240
Other Parts Discussed in Thread: TPS54140,

Team,

Is the criterion of skipping mode between TPS54140 and TPS54240 the same? Or they're not the same?

Since system requirement in customer side, the original TPS54140 is changed to TPS54240 however, as test result customer found the communication problem on MCU when TPS54240 is used.

In the waveform below, it looks the TPS54240 enter into Pulse Skipping mode, but TPS54140 is NOT.

Please help to clarify this issue, and offer suggestions. thanks.

TPS54140 Waveform:

SD300-> PH pin

TPS54240 Waveform:

Schematic:

over 1 year ago

0 Richard Fu22 over 1 year ago

TI__Mastermind 25260 points

Hi Brian,

Thanks for promoting the TPS54240 device.

I don't see the waveform for the TPS54140 device so can you also provide that?

It looks like the criteria for entering eco-mode is the same across both devices (COMP should be lower than 500mV). However, the specs of the error amplifiers are different for the devices since they were rated for different currents, so that may be the main difference. Can you provide the COMP waveform for both devices?

Regards,

Richard

0 Brian Wang0928 over 1 year ago in reply to Richard Fu22

TI__Genius 12960 points

attached the TPS54140 waveform

0 Richard Fu22 over 1 year ago in reply to Brian Wang0928

TI__Mastermind 25260 points

Hi Brian,

Thanks for providing the waveform. Were you able to get any waveforms of the COMP, VOUT, SW pin?

Regards,

Richard

0 Brian Wang0928 over 1 year ago in reply to Richard Fu22

TI__Genius 12960 points

Hello team,

Pls find the below waveform. Customer mentioned when TPS54140 is used, the MCU communication is ok. but TPS54240 is used, the MCU communication is abnormal.

In system topology, the 5V is converting to 3.3V for MCU bias power, and this MCU is communication with another system though SPI.

The measured voltage of COM pin are:

TPS54140:541mV

TPS54240:500mV

And both output rails of 3.3V are ok, not dropping out.

Could you help to double check it and how to improve it!

TPS54140

TPS54240

Regards

Brian

+1 Richard Fu22 over 1 year ago in reply to Brian Wang0928

TI__Mastermind 25260 points

Hi Brian,

Thanks for providing the waveform. I'm slightly curious about the stability of the converter. Since the spec of the internal error amplifier may be different, perhaps the compensation network will need to be adjusted. Do we have any stability plots comparing the two converters? Otherwise, I do not see any other thing that would need to be changed.

Regards,

Richard

0 Brian Wang0928 over 1 year ago in reply to Richard Fu22

TI__Genius 12960 points

Hello Richard,

1. When the TPS54240 is used, the output of 3.3V is stable. But it could make the MCU error, we still could not figure out?

2. What stability plot you want to see? Bode plot or output Ripple? Do you have any example? thanks.

Regards

Brian

0 Brian Wang0928 over 1 year ago in reply to Brian Wang0928

TI__Genius 12960 points

Please help on this critical issue with TPS54240.

Could design be able to share more details on design differences between both? As waveform we sent, is there abnormal behavior or not?

I'll also try to get PCB layout as well for team reviewing. thanks.

Regards

Brian

0 Richard Fu22 over 1 year ago in reply to Brian Wang0928

TI__Mastermind 25260 points

Hi Brian,

Sorry for delay in response. Please provide the Bode plot and layout if possible. The design looks correct schematic wise, but I think the difference is in compensation network values.

Regards,

Richard

0 Brian Wang0928 over 1 year ago in reply to Richard Fu22

TI__Genius 12960 points

Thanks. Could I send layout by email as it’s confidential?

0 Richard Fu22 over 1 year ago in reply to Brian Wang0928

TI__Mastermind 25260 points

Hi Brian,

Yes, that's fine. Let's close the thread here.

Regards,

Richard

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TPS54240: Skipping mode