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TPS92662-Q1: TPS92662

Michael Hope
Prodigy 50 points
Part Number: TPS92662-Q1
Other Parts Discussed in Thread: TPS92515, TPS92518, LM3409

Hello,

We are considering using this part in a camera-based system.

Each camera image requires about 200 to 300 usec for the exposure.

Different images at different times will require slight changes in brightness.

Because of the short capture time for each image, if the PWM cycle lines up such that the LED is OFF for a significant portion of the exposure, there will be a dark strip through the image.

How fast can the PWM cycle be run on these chips?

I already see that there is a maximum 10 bit dimming , so that will help set the minimum ON or OFF Time = (1 / 1024) * (1 / PWM_Freq).

-Michael Hope

  • 0
    TI__Mastermind 28655 points
    Hello Michael,

    I just want to make sure I understand what you are trying to do. The TPS92662 is not an LED driver but rather a bypass or open switch for multiple LEDs connected in series. It still requires a current driver that can change output voltage very quickly, like the hysteretic controllers TPS92515, TPS92518, LM3409. It is meant to be able to individually open or shunt LEDs in a string.

    Are you running one LED or multiple LEDs that all switch at the same time?

    Is you exposure time 200-300 us a range or does it need to be accurate within that window?

    Do you need to change the current amplitude in your LED/LEDs?

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 50 points

    There are 8 LEDs in a string, that are all switched off or on at the same time. They will each be adjusted to a slightly different brightness, to account for differences in the small lenses in front of each LED.

    Each LED and lens combination lights up a different part of the camera scene. There are small light baffles between each zone. The end result must be a camera image with 8 distinct zones, with completely even illumination in each zone.

    The 200 to 300usec exposure time is adjusted by the camera software as needed.

  • 0 in reply to Michael Hope
    TI__Mastermind 28655 points
    Hello Michael,

    So to adjust the current in each LED are you creating different PWM pulse widths for each LED? If this is the case I can see possibly using the TPS92662. WIth a register setting of fast the rise and fall times are 2 us for the TPS92662.

    If you have a series string and are switching all of the LEDS off or on at the same time the current in all LEDs will be the same, if you are not individually PWMing each LED.

    Which method are you planning on using?

    Best Regards,
  • 0 in reply to Irwin Nederbragt
    Prodigy 50 points
    The best we could do would be having different PWM duty cycles for each LED.
  • 0 in reply to Michael Hope
    TI__Mastermind 28655 points
    Hello,

    The TPS92662 can do that, with a 200-300 us pulse you will be limited on how many PWM cycles you can get but the resolution to adjust width can be fairly narrow. The limitation will be the rise and fall time as mentioned before at 2 uS each.

    Best Regards,