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Original question:

[FAQ] TPS23758: Difference between TPS23758 and TPS23755

TPS23758: Pin treatment between TPS23755 and TPS23758

Shunsuke Nagata
Genius 12460 points
Part Number: TPS23758
Other Parts Discussed in Thread: TPS23755, , TPS23753A

Hi, team,

My customer will check TPS23755 and TPS23758 for linearity in PSR solution.

Could you please let me know how to treat each PINS in PSR? Customer doesn't want to change PCB layout for this evaluation (prefer to same layout if possible.)

- PIN 7 :
APD(TPS23758) : Connect 48V adapter via resister divider
AUX_D(TPS23755) : Is it possible connect 48V adapeter via resister divicer in PSR solution? or should be OPEN

- PIN20 : 
TST (TPS23758) : OPEN
AUX_V(TPS23755) :  Is it possible to OPENin PSR solution?

Is there anther treatment for TPS23758 and TPS23755?

Regards,
Nagata.

  • 0
    TI__Mastermind 21320 points

    Hello Shunsuka Nagata,

    One good place to understand how pins are used in a design is our EVMs. 

    The only one that really changes because of PSR is the TPS23755 used with an adapter on the secondary side. However, this challenge is present whether the design is PSR or SSR. 

    The TPS23755 is designed to have the auxiliary power be on the secondary side, and thus be 12V. The TPS23758, however, does primarily support auxiliary power at the input (42V-57V). 
    If wanting to OR at the primary with you will need an external FET solution. However, at that point I might as well suggest the TPS23753A. We can discuss this offline!

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    TI__Genius 12460 points

    Hi, Michael,

    Thank you for your support. Could you please let me know detail about each device?

    His condition are
    - Wil not use secondary side AUX supply detection
    - 12V out ( doesn't require secondary side synchronous)

    If user design his pcb based on TPS23755 EVM,  can the board be useful for TPS23758 without changing layout?

    I guess AUX_D and AUX_V of TPS23755 are for secondary side AUX Supply detection, AUX_D is for input from feed back and AUX_V is current source input for opto-coupler with Raux. These pins are not used in the case user doesn't use secondary side feed back. If user replace to TPS23758 from TPS23755 on same board, APD of TPS23758 can get power which may rise 1.5V from RTN via Raux and detect AUXILIARY POWER.  Then TPS23758 and TPS23755 can work on same board which is referred to TPS23755EVM.

    Is my understanding correct?

    Regards,
    Nagata.

  • 0 in reply to Shunsuke Nagata
    TI__Mastermind 21320 points

    Hello Nagata,

    No these parts are not interchangeable. The reason is the TPS23755 supports diode rectified flybacks, and the TPS23758 supports synchronous flybacks. Although they are the same package and nearly pin-to-pin compatible, they do not support the same topology, so just swapping the parts will not work. 

    We have also found that syncrhonous flybacks are optimized in 5V output designs, and the diode rectified flybacks are optimized for 12V outputs. So designing the TPS23758 in a 12V output design is not impossible, but not recommended. 

    Please refer to this FAQ for the differences: 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments 

  • 0 in reply to Michael Pahl
    TI__Genius 12460 points

    Hi, Michael,

    Thank you for your support.

    Could you please let me know about TPS23755 solution?

    If user doesn't use secondary side AUX supply detection, can he AUX_V leave open? Or should it connect to FB via RAUX?

    Regards,
    Nagata.

  • 0 in reply to Shunsuke Nagata
    TI__Mastermind 21320 points

    Hello Nagata,

    If the customer is not using secondary side adapter then AUX_V should be connected to RTN. Please see the IC block diagram. AUX_D can be left open since it is internally pulled up. 

    Again, TPS23755 does not support primary side auxiliary power. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments