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UCC28704: Selection of Primary Side Regulated (PSR) Fly-back controller

Danilo A.
Mastermind 24715 points
Part Number: UCC28704

Hi Team,

We would like to ask your help regarding the customer's inquiry below.

Background: I have used the UCC28704, but there is a problem: I need to reduce the impedance of the signal at Vs (pin 6), but I cannot do this because the impedance is set by the Line Sense Run/Stop Current requirements.

So what I am asking is: are there any PSR flyback controllers that use a different means to sense Vline (ie: do not use the Vs pin). Does there exist a Selection Guide for TIs range of PSR controllers?

Yes, I have read:
SLUA783–October 2016 "Troubleshooting TI PSR Controllers"
There is a very basic selection guide in Section 1 of that document (attached screenshot), but it is not sufficiently comprehensive.

Regards,

Danilo

  • 0
    TI__Expert 7080 points

    Hi Danilo,

    Transformer bias winding to sense input voltage is a low loss sense methods . that is to achieve a low standby power . Almost all of TI PSR flyback are used this method. You can search on TI.COM , there is a basic selection ways for you wanted controller. May i ask why you need to reduce the impedance of this signal on VS pin ?

    Thanks.

  • 0 in reply to Jaden Ning
    TI__Mastermind 24715 points

    Hi Jaden,

    Thank you for your response to our customer's inquiries. Here is the feedback of our customer.

    The reason is to ensure this signal is not disturbed by any capacitance that may be present at the Vs pin, from all causes, such as: PCB layout, component parasitics, and from probes that may be placed there only during manufacture and field testing (the latter is most important for automated testing).
    Also to reduce effect of external influences such as magnetically coupled signals, and dv/dt coupled signals.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Expert 7080 points

    Hi Danilo,

    Understand customer's concern. Just follow our design guide to setting VS pin resistors . and place the divider resistors close to VS pin . and don't place any ground plane under VS pin . in the way . there will no problem for the noise coupling.

    Thanks.

  • 0 in reply to Jaden Ning
    TI__Mastermind 24715 points

    Hi Jaden,

    Here is the response of our customer.

    Thanks, yes, we are well aware of how to layout PCB to ensure low stray C from any signal node to gnd.

    Can you please share any table that presents the PSR controllers which compares more of the features. What I am looking for is something that is similar to what I posted earlier, but much more comprehensive: ie: covers all of the product range and compares more of the features, such as ULVO thresholds, input V sampling method, max switching frequency, min-max duty cycle, if it has valley switching, etc.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Expert 7080 points

    Hi Danilo,

    I am sorry to say we don't have such table that you wanted. if customer has special requirements . please list it , then we can recommend the most suitable device. thanks.

  • 0 in reply to Jaden Ning
    TI__Mastermind 24715 points

    Hi Jaden,

    According to the customer

    "are there any PSR flyback controllers that use a different means to sense Vline (ie: do not use the Vs pin)."

    That is: the pin used to sense Vout is only used for that purpose and no other purpose.

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Expert 7080 points

    Hi Danilo,

    We don't have such device. thanks.