• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 62 subscribers
  • Views 398 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TPS92513HV: IADJ cannot be adjusted to less than 20%

Roy Chen52
Intellectual 395 points
Part Number: TPS92513HV

Dear Sir,

   We have a LED current can't be adjusted IADJ to drop 20~30% issue. LED current SPEC adjustment range= 90mA~9mA(100%~10%),Frequency: 150kHz,the PDIM is a enable LED on/off function. If device start up to adjust IADJ 60~70% stable current status can drop to 10% LED current (9mA) , If device start up IADJ setting under 30% it can't continue drop to 10% range will be keep at 30% (current 28mA) refer waveform. Normally status current must adjust up to 60% then go down 10% it's ok. Is there a suggestion to improve?

Thank you!

  • 0
    TI__Mastermind 28655 points

    Hello,

    What is your LED stack voltage?  Are the notes on the schematic accurate?  LED_+48 is 48V input?  Driver_65mA+ is really up to 90 mA?

    A quick calculation using 150 KHz for the switching frequency and Vled at 24V shows this to run discontinuous.  I would first try increasing the switching frequency or increase the inductor value to see if there is a change.

    The filter pole for Iadj is 16 KHz, is this okay for your design?

    From the datasheet:

    "Analog dimming is also most accurate when the device is in continuous conduction mode (CCM). If the highest accuracy possible
    is desired during analog dimming, size the inductor so that 1/2 the peak-to-peak inductor ripple is less than the
    minimum LED current to remain in CCM. The IADJ pin should be decoupled with a 10 nF capacitor to ground. A
    1 kΩ resistor should be used between the ISENSE pin and RISENSE to protect the pin in the event RISENSE opens
    or there is a transient due to one or more LEDs shorting."

    Best Regards,

  • 0 in reply to Irwin Nederbragt
    Intellectual 395 points

    1.What is your LED stack voltage? 12 Leds , 36v

    2.Are the notes on the schematic accurate? Yes! LED_+48 is 48V input? Yes.

    3. Driver_65mA+ is really up to 90 mA? typical 65mA(typ) / 75mA(max)

    We have tried to adjust frequency down to 150KHz. It is better but only can approach 20% range.

  • 0 in reply to Roy Chen52
    TI__Mastermind 28655 points
    Hello,

    I asked another engineer for some suggestions. He stated to try increasing the switching frequency to 300 Khz by cutting Rt in half, 375 Kohm. I would also suggest trying a much larger inductor value just to see if it works.

    Best Regards,