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TPS92661-Q1: Can TPS92661 be used with boost converter?

Kazuya Nakai59
Guru 21515 points
Part Number: TPS92661-Q1
Other Parts Discussed in Thread: TPS92640, TPS92515, LM3409

 Hi guys,

 One of our customers wants to use TPS92661 for LED module dimming with a boost converter.

 But according to the Simplified System Schematic on page one of the device datasheet, it seems that TPS92661 shoud be used with a buck type constant current converter or controller.

 Could you please reply to the following questions?

Q1. Can TPS92661 be not used with a boost type constant current converter?

Q2. If Q1 answer is yes, why the device is not used with a boost converter,

 Your reply would be appreciated.

 Best regards,

 Kazuya Nakai.

  • 0
    TI__Mastermind 25500 points

    Hello Kazuya,

    The reason a buck converter is used is that is has continuous output current, and if it is a hysteretic device such as the LM3409, TPS92640, or TPS92515 it has extremely fast response to deal with the FETs opening and closing at high rates.

    A boost converter has discontinuous output current and cannot respond nearly as fast even if it is high bandwidth. There are also the cases when if enough FETs or shorted on the output that the output voltage is less than the input voltage you would have an input to output short through the boost converter inductor and diode which would be really bad. 

    A boost converter could work if the LED switching on/off frequency is slow enough, some over/undershoot is ok, and it never shorts enough LEDs to have the output voltage below the input voltage. If that is ok then sure, you could use a boost converter if it is designed for the wide operating range. But it will limit many operational parameters.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 21515 points
    Hello Clint,

    Thank you very much for your reply. I understood what you said.
    The customer wants to switch on and off LED TPS92661 with high frequency using TPS92661. So I will propose TPS40210-Q and TPS92515-Q to them.

    If Vin=12V, the number of white LED in series=11pcs (Vf=42V as the maximum), ILED=1A case, do you think that those devices are working without any big problem?

    Thank you and best regards,
    Kazuya Nakai
  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 25500 points

    Hello Kazuya,

    If you provide a voltage with a boost around 45V to 48V (or higher if needed) so that the TPS92515 can run like a buck as intended then yes, it can do this. That device was designed with shunt FET dimming, including a matrix, in mind. You will need to be careful with thermal management at such high voltage and power, it may just require using a relatively low switching frequency (you will not be able to switch at 1MHz for example).

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 21515 points
    Hello Clint,
    Thank you for your reply. Could I ask you an additional question?
    Can TPS92515 work well with 1kHz~10kHz PWM frequency using TPS92661?

    Thank you and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 25500 points

    Hello Kazuya,

    Yes, it is capable of 1kHz to 10kHz, it is designed for very fast PWM dimming.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 21515 points
    Hello Clint,

    Thank you for the reply.

    Best regards,
    Kazuya Nakai.