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TPS92513: Customize EVM

na na78
Guru 16770 points
Part Number: TPS92513

Hi

Our customer is about to use TPS92513EVM with following specification.

Requirement:

Input : 10V - 30V

LED : Vf = 2.4V, If=700mA

Dimming type : Analog dimming

Questions:

1. 

I think the Fsw should be changed to lower frequency on EVM. 

So I would change R5 from 191K to 392K.  It means Fsw is 310KHz.

Is this change reasonable?

2.

Should any other change on EVM be required to meet our requirement?

3.

Is the analog dimming on EVM exeuted only by applying external voltage to IADJ?

Is it possible to left PDIM open?

BestRegards

  • 0
    TI__Mastermind 28655 points

    Hello,

    1)  Why do you think the Fsw should change?  The inductor ripple will go up but you will also be running at lower current so it should work fine, just wondering why?

    2)  Rcs can be raised to 0.43 ohm to get 700 mA at full Viadj.  Or Viadj can just be lowered to 1.26V externally.

    3)  Yes and Yes, PWM left open, it has an internal pull-up.

    Regards,

  • 0 in reply to Irwin Nederbragt
    Guru 16770 points
    Hi Irwin

    Thank you for your reply.

    Because I thought Ton would violate Ton(min) specification.

    If R(RT) = 191Kohm, Fsw can be ~598KHz.
    So, Ton can be calculated as Vout/(Fsw*Vin) = 2.4 / (598K * 30) = 134nsec.
    According to datasheet, Ton(min) = 140nsec typically.
    That's why I thought Fsw should be decreased.
    Regarding to 310KHz I offered, I considered margin.

    Is my understanding wrong?

    Do you think we don't need to make any change with EVM to meet our requirement?

    BestRegards
  • 0 in reply to na na78
    TI__Mastermind 28655 points

    Hello,

    Yes, you also have to add the diode in which is 0.7V but it can be a concern if you are dimming and the LED and diode are hot. So yes, you probably do want to lower the switching frequency.

    It should work as it is but you will have to drive Viadj or change the CS resistor to 0.43 to get 700 mA.

    Regards,

  • 0 in reply to Irwin Nederbragt
    Guru 16770 points
    Hi Irwin

    I'm sorry for inconvenience.
    Can I confirm your answer?

    1.
    Does changing inductance on EVM for decreasing switching frequency have bad impact?

    2.
    >you also have to add the diode in which is 0.7V but it can be a concern if you are dimming and the LED and diode are hot.

    What is the diode do you mean? Should we add it on EVM?

    BestRegards
  • 0 in reply to na na78
    TI__Mastermind 28655 points

    Hello,

    1)  No, not really.

    2)  The diode is the freewheel diode.  When the MOSFET is off the conduction path is The inductor, the LED and D2, the freewheel diode.  This makes the inductor see Vf of the LED and Vf of the freewheel diode.  If your LED is 2.4V and the diode is 0.7V the actual freewheel voltage is 3.1V.

    Regards,