• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 488 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS92515: How to controll and check the peak to peak inductor ripple?

dao hop
Prodigy 200 points
Part Number: TPS92515


Hi everyone,

I'm working on a project about LED Light Source and use the TPS92515 IC.

I expect our product can reach the 98, 99% accuray and the product has the dimming function.

I have some questions:

1, How can I confirm the Vcst? Could I measure this voltage between 2-sides of the sense resistor?

2, Why the accuracy when using VCC to charge Coff is less than when using VLED (Vout) to charge Coff?

How can I know or measurement the VLED? (with dimming, ex 50% duty and without dimming - that means 100% duty)?

Thanks and Regards

  • 0
    TI__Genius 17720 points

    If you are targeting for 98, 99% accuracy, then you need to do additional calibration, either TPS92515 or other device. 

  • 0 in reply to Xiaoguang
    Prodigy 200 points

    Hi Xiao,

    Thank you for your reply

    Could you explain for the calibration? what do I need to do?

    And do you have any answer for the my above questions?

    Regards,

  • 0 in reply to dao hop
    TI__Genius 17720 points

    TPS92643 can achieve +/-4% accuracy that you may look into it, however, it's still far from your expectation. 

    For calibration, common way is to monitor output current using high precision current sensor, compare it with reference and then fine tune the output current with PWM/analog dimming etc. 

    For example, you may refer to battery test system like www.ti.com/lit/wp/slpy010/slpy010.pdf

    About your question ,

    1. Yes, you can measure it. 

    2. Generally VCC range is much wider comparing to VLED, which causes frequency changing and ripple current. Not understand about your last question. Certainly you can measure VLED voltage. 

  • 0
    Prodigy 200 points

    Hi Xiao ,

    Due to VLED affects the Imax. So I want to determine this value.

    But when I measure the VLED by DM during TPS92515 working (at the anode of LED), the waveform is pulse. So I want to know how we can determine VLED?

  • 0 in reply to dao hop
    TI__Genius 17720 points

    Hi, Dao,

    TPS92515 controls output current that you expected. VLED is affected by current, and you may check it in LED datasheet. VLED is also affected by other factors like temperature and devices variance.  

    For LED, it's key to control LED current to change brightness. What's your purpose to determine VLED? 

  • 0 in reply to Xiaoguang
    Prodigy 200 points

    Hi Xiao,

    1, I think to have better accuracy in the controlling and calibration, I have to have VLED. I thought same the above your suggestion, I checked VLED follows its datasheet. VLED is depended Imax , not the output current, right?

    2, I'm trying to test with shunt FET dimming to archive better dimming. I see that the temperature of TPS92515 is very high. This is caused by the low effeciency when shunt FET is turned on, right?

  • 0 in reply to dao hop
    TI__Genius 17720 points

    1. Why you need to know VLED? What is your purpose? Generally, we don't care about VLED unless diagnostic feature (LED open/short/ Single LED short etc) is required. 

    2. No, I don't think so. When shunt FET is on, TPS92515 high side FET duty cycle is smaller, power loss is less than shunt FET off status. You may need to check power loss for the design. like conduction loss, switching loss etc.  

    May i know what your application is? What is the spec and LED part number? why you need such high accuracy? Thanks.  

  • 0 in reply to Xiaoguang
    Prodigy 200 points

    Hi Xiao,

    1, The toff and delta Ip-p are depended the VLED. I wanted to know VLED to compare between the theory and the fact. The currently, to do the calibration, I use the multimeter to know Imax so I don't need VLED information any more.

    2, I found the reason the temperaturer of TPS92515 is high during using shunt-FET dimming. I used the small value of Roff when VCC charge the Coff (FET is on), so the switching frequency is quite high. So the loss power is increased.

    We're developing the LED Light Source for spectrometer. So the accuracy and high frequency of dimming are what we need.

    Thank you very much.

  • +1 in reply to dao hop
    TI__Genius 17720 points

    You are welcome! 

    If no more question, i will close this thread in 24 hours. thanks.