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TPS92692: TPS92692: Buck-Boost or Boost?

Josnei Silva
Prodigy 160 points
Part Number: TPS92692

I'm doing two projects using tps92692. I have a question if I should use them in the buck-boost or boost configuration?

Project 1:

Input:
Vin: (Min: 6V-Typ: 12V-Max: 16V)

Output:
3 LEDs in series
VLED: (Min: 2.75V-Typ: 3.25V-Max: 3.55V)
Vout: (Min: 8.25V-Typ: 9.75V-Max: 10.65V)
I LED output current: Typ: 1A - Max: 1.2A

Project 2:

Input:
Vin: (Min: 6V-Typ: 12V-Max: 16V)

Output:
2 LEDs in series, but sometimes only one will be active or both will be active. For this I will use a FET.
VLED: (Min: 11.6V-Typ: 13.6V-Max: 14.8V)

Vout with 1 LED active: (Min: 11.6V-Typ: 13.6V-Max: 14.8V)

Vout with 2 LEDs actives: (Min: 23.2V-Typ: 27.2V-Max: 29.6V)

I LED output current: Typ: 1A - Max: 1.2A

  • 0
    TI__Mastermind 18890 points
    Hi Josnei,

    For Boost regulator the output voltage has to be greater than input voltage at all time. For Buck Boost (Boost to Battery) the output can be less than or greater than the input voltage. Boost regulator in general has better efficiency than Buck Boost. The main thing you have to watch out for is not to exceed the voltage rating of the part for anything feeding back (65V).

    For your project 1, you should use the Boost to Battery.

    Project 2, you can use Buck Boost or Sepic. The main thing you have to worry about switching in and out the load for project 2 is the turn on and off time of the switch. You want to switch the loads in and out slowly so the loop can keep up with the regulation. For example when you have both LED's on and you switch to just one by shorting out the the other LED with a FET switch: If you switch too fast you will have high curent on the ON LED since output votlage on the output capacitor has to discharge since it has the previous high voltage on it.

    Based on you input voltage...Is this for an automotive requirement? If it is then you still have to worry about load dump voltage which can be a lot higher than 16V. So be sure that you do not exceed the 65V requirement.

    Thanks Tuan
  • 0 in reply to Tuan Tran74
    Prodigy 160 points

    Thank you Tuan.

    Because in Project 1 the boost to battery configuration must be used, if the output voltage can be higher or lower than the input voltage? Can I use the buck-boost setting?

    Would you have any examples of how to use the FET so that the time to turn the switch on and off does not affect the LEDs?
    The way I connected the FETs in the image would work? The values of the components have not been calculated yet, please consider only the red link that refers to the switch.

  • 0 in reply to Josnei Silva
    TI__Mastermind 18890 points
    Hi Josnei,

    This is a little bit beyond the scope for E2E. In general, your circuit will not work at all. VCC will always be lower than Vin so you will never be able to turn ON you Q2 FET if it's an N-Channel. I suggest you educate yourself on how FET's works and how to slow the switching times down.

    Thansk Tuan
  • 0 in reply to Tuan Tran74
    Prodigy 160 points

    Hi Tuan.
    I have two questions.

    1) Can I use the buck-boost converter for these output voltages?
    Vin: (Min: 6V-Typ: 12V-Max: 16V)
    Vout: (Min: 8.25V-Typ: 9.75V-Max: 10.65V)


    2) Could you use the Boost to Battery setting for these output voltages?
    Vin: (Min: 6V-Typ: 12V-Max: 16V)
    2 LEDs in series:
    Vout with 1 LED active: (Min: 11.6V-Typ: 13.6V-Max: 14.8V)
    Vout with 2 active LEDs: (Min: 23.2V-Typ: 27.2V-Max: 29.6V)

  • 0 in reply to Josnei Silva
    TI__Mastermind 18890 points

    Hi Josnei,

    Yes you can use the buck-boost for both 1) and 2).  Note that Buck Boost and Boost to Battery are the same topology.

    Thanks Tuan