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TPS92692EVM-880: Can EVM be modified for buck configuration?

Viktorija Cecil
Mastermind 18111 points
Part Number: TPS92692EVM-880
Other Parts Discussed in Thread: TPS92692, TPS92691, TPS92512

Team, 

Can EVM be modified for buck configuration?

Vin - 48V,

Vout 32V-35V

Thanks

Viktorija

  • 0
    TI__Mastermind 18890 points

    Hi Viktorija,

    Yes it can be.  You will need to modify it with jumper's and cut ect. but it's possible.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    TI__Mastermind 18111 points

    Tuan, can you provide more detailed guidance on what changes would need to made?

    Can the EVM handle the 48V input voltage? It seems the only problem is C8 (50V too marginal for 48V). All other components (input and output capacitors have 100V).

    If there is a better way to evaluate device performance in described buck configuration - please let me know. 

    Thanks

    Viktorija

  • 0 in reply to Viktorija Cecil
    TI__Mastermind 18890 points

    Hi Viktorija,

    Please follow the Buck configuration of TPS92691 in figure 27 of the data sheet (page 18).  There is a typo on the schematic, the CSP and CSN is reversed on Rcs feedback. The TPS92691 is the predecessor to the TPS92692 so the configuration should be similar.  There are design equations in the TPS92691 data sheet for the Buck.

    Since you are with TI, I believe that you are familiar with some of these fundamentals of voltage and current ratings ect.  If not then you can asks more questions offline via my email.  As I mentioned before, there will be cut, jumpers and 'dead bugging' of parts but it's possible.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Prodigy 20 points

    Hi Tuan

    Thanks Tuan. ViktoriJa has asked this question for me.

    TPS92691 pin DDRV is referenced to PGND (supposed to drive 0-7.5V). TPS92692 pin PDRV is refernced to CSP and supposed to drive CSP to CSP-7V.

    Using buck LED driver of TPS92691 for TPS92692: In order to drive Q2 I need drive referenced to Q2/source. PDRV cannot do it.

    My LED driver input/output needs:

    Input 48V DC

    Output: 32V -  38V.

    What configuration would you recommand?

    1. It seems I cannot use Buck-Boost (Figure 37 page 26 in the data sheet). CSP and CSN pins will see voltage of sume of input and output (48V+38V=86V) that is greater than maximum alowed (65V).

    2. Use SEPIC (Figure 38 page 26 in the data sheet)

    3. or Boost (figure 36 of data sheet with changes):

    • Add output capacitor to GND.
    • Delete Qm and Ris (it seems it will function without).

    Moshe

  • 0 in reply to Moshe Levi
    TI__Mastermind 18890 points

    Hi Moshe,

    1.  For your requirement you cannot use a Buck Boost as you mentioned...the voltage will be greater than the allowed maximum of 65V.

    2.  You cannot use the boost since boost requires that output voltage be greater than input voltage.

    3.  You can use SEPIC but for your application the Buck is the best choice in term of component cost and efficiency.

    What application is this for and how much output current do you need?  Does it need PWM dimming and does it need to pass EMI like automotive application?  I assume that this is to drive LED.  Please let me know and maybe there's a better part for your application.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Prodigy 20 points

    Hi Tuan

    Thank you for the fast reply.

    1. I do not understand the limitation of output voltage to be greater than input in boost configuration (it does not damage the chip). I have used the simulation file "TPS92692_Boost_Design_Calculator.xlsx" and it does not show any error.
    2. SEPIC DC/DC converter is normally used when the output voltage may be higher, equal or lower than input voltage. This is not my case: output voltage is alwas lower than input voltage. There is no calculator XLS file for SEPIC.
    3. My application:
      1. curing in 3D printing machine.
      2. Output current is estimated to be maximum 2.5A.
      3. I need dimming.
      4. PWM diming may be needed. Because PWM may have different effect (on curing) than linear dimming, I prefer to add this option.
      5. It is not an automotive application.
    4. Is there a better part for my application?

    Thanks Moshe

    .

  • 0 in reply to Moshe Levi
    TI__Mastermind 18890 points

    Hi Moshe,

    Based on your application the TPS92512 Buck regulator would be a better choice.  You will need a BUCK regulator not a BOOST.

    Any Boost regulator, the output has to ALWAYS be greater or equal to the input (subtract the Diode voltage drop).  This is a fundamental for Boost regulator.  If the FET is not switching then the output will be the input voltage thru the inductor and diode (subtract the Diode voltage drop).  You might need to read up on this if it does not make sense to you.  Below is a link for that.

    www.ti.com/.../slva061.pdf

    Thanks Tuan