UCC28950: TMIN range

Kenji Ohno1

Genius 5095 points

Part Number: UCC28950

Hi Team,

My customers are using RTMIN at 150 kΩ and I noticed that it exceeds the setting range of TMIN.

Perhaps it might be an effect, it seems to be transitioning to burst mode at heavy load.

I will attach a waveform, so I will ask for your view.

Also, if you change the operating frequency from 100k to 115kHz, this phenomenon will not occur.

Please tell me why.

I appreciate your support.

Best Regards,

Kenji

over 7 years ago

0 Michael Wu - HVC over 7 years ago

TI__Prodigy 90 points

Hi Kenji,

Thanks for your interest -- we will have someone look into this issue for you.

Regards,
Michael Wu

0 Colin Gillmor over 7 years ago in reply to Michael Wu - HVC

TI__Mastermind 25570 points

Hello Kenji-san

There is no problem for the IC if the RTMIN is 150kOhm. We had initially thought that 800ns (135k) was enough time for system applications and this is the reason we give 800ns in the Data Sheet - but it's not a hard limit so 150k is fine.

Can you let me know what the two waveforms are please ?

Thanks
Colin

0 Kenji Ohno1 over 7 years ago in reply to Colin Gillmor

Genius 5095 points

Hi Colin,

The waveform is the output voltage and output current of the phase shift circuit during continuous operation.
There is an action that is in burst for a moment during continuous operation.
I am investigating why such behavior will occur even though it is not light load.

I thought RTMIN was caused by 150 kΩ.
This operation stops occurring by decreasing RTMIN or increasing the frequency.
Please tell me your opinion on the cause.

Best Regards,
Kenji

0 Colin Gillmor over 7 years ago in reply to Kenji Ohno1

TI__Mastermind 25570 points

Hello Kenji-san

The waveforms are very strange indeed. Can you send me a schematic with the measurement points marked please - you can send them to me directly if you don't want to post them here - I'm at colingillmor@ti.com

The current waveform should be symmetrical around the 0A axis - but it clearly is not. There may be a problem with the gate drives to the primary side MOSFETs.

There may be a problem with the MOSFET driver circuit so I'd suggest that the customer check that the OUTx signals are being correctly delivered to the switching MOSFET gate.

Regards
Colin

0 Kenji Ohno1 over 7 years ago in reply to Colin Gillmor

Genius 5095 points

Hi Colin,

I appreciate your supports.
I got a waveform so I will mail it to you.

Best Regards,
Kenji

0 Kenji Ohno1 over 7 years ago in reply to Kenji Ohno1

Genius 5095 points

Hi Colin,

I mailed you.
I am waiting for a reply.

Best Regards,
Kenji

0 Colin Gillmor over 7 years ago in reply to Kenji Ohno1

TI__Mastermind 25570 points

We have taken this topic offline.

Regards

Colin

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UCC28950: TMIN range