TEA2017AAT reference design UM11613

[bluespark]

Hi,

I have a few questions about the reference design described in the document UM11613:

• The gates of the transistors Q5 and Q6 are driven using a totem pole formed by Q10 and Q11. The 12V power of this totem pole comes from the linear regulator implemented around Q12, from the power supply AUX. This AUX supply comes from an auxiliary winding of the transformer. How can the LLC start switching at startup, as the AUX supply (and thus the 12V supply) is not available yet, as the LLC hasn’t started?
• The coil of the relay RL1 (used to short the NTC inrush limiter) is powered by VDD: where does this power come from?
• After the linear regulator implemented around Q12, there is a 12.1V, what’s its use?

Thanks for your help.

Kind regards, 

bluespark

[bluespark]

Dear Jozef,

Thanks for your answer. The start-up mechanism using the HV current source is indeed well documented.

But I still don't fully understand the implementation in UM11613 which is quite different: the HV current source charges the SEPIC capacitor, which allows the TEA2017 to start switching the GATEPFC pin, in order to raise the Vboost voltage above its threshold, allowing the LLC to start. But in order for the Vboost voltage to raise, Q5 and Q6 have to be turned ON and OFF, which is done using the totem pole formed by Q10 and Q11.

 

The 12V used to supply power to the totem pole is created by a linear regulator from the Vaux voltage. Vaux is the result of the auxiliary winding of the transformer T1. The PFC needs this 12V voltage to switch the gates of Q5 and Q6, but this 12V doesn't exist because LLC hasn't started yet.

 

 

About the other questions, I still don't see what is the use of the 12.1V in the linear regulator section of the schematics, and the VDD voltage used to power the relay coil is nowhere to be found in the schematics.

What am I missing?

Kind regards, 

bluespark

[JozefKozon]

Hi Guillaume,

there is also a PFC driver connected to the Gate of the Q6. I think this turns on the Q6 before the 12 V from the Auxiliary winding is available for the Q10, Q11 totem pole connection.

With Best Regards,

Jozef

[JozefKozon]

Hi Guillaume,

the TEA2017 contains internal HV start-up source. At the beginning the TEA2017 is supplied from the DRAINPFC. Only later, when the switching starts, the auxiliary winding is used to supply the TEA2017.

With Best Regards,

Jozef