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TPS92642-Q1: Led driver for 1A/10us pulses

DanielC
Prodigy 50 points
Part Number: TPS92642-Q1
Other Parts Discussed in Thread: TPS922052, TPS92515

Tool/software:

Hello,

I'm looking for a current-controlled led driver for pulsed operations with the following specs

  • PWM dimming: 10-50kHz, with duty cycle limited from 100% (always on) to 20%. In any case, the minimum pulse duration is 10us. Typical operation patterns are: [Always-ON mode] or [20us ON + 40us OFF].
  • Rise and fall time < 2us
  • Edge-to-egde delay (PWM control to Led current) < 2-3us
  • Peak current from 0.2A to 1.0A, set by an external resistor
  • 1 led series with total Vf (forward voltage) from 5V to 20V, depending on the LED type and count (several configurations are to be supported with the same driver)
  • Supply voltage 24V
  • Pcb area available for the driver including all necessary components: 15x22mm

We are considering two solutions

  1. Low-side linear led driver. A step-down DC/DC is used to lower the input voltage close to Vf, but up to 3V headroom is necessary due to LED tolerances. The driver has to dissipate up to 3W + its drop at 1A. We have not found suitable devices in TI's portfolio. Is there any?
  2. Buck driver. More efficient than the linear but pulses have unwanted ripple and may be difficult to meet the timing requirements.
    We've found three candidates:
    - TPS92642: package is a bit large but LED's cathode is grounded and would help the board layout
    - TPS922052: VSON package is small but an external diode is required and LED's anode is not grounded
    - TPS92515: maybe too large pcb area required

Which would you recommend to better meet the timing specs and have low LED current ripple?

Do you have other parts to advise?

Feel free to ask further details, if needed.

Thank you and kind regards

  • 0
    TI__Genius 11685 points

    Hi Daniel,

    These are very strict requirements. Is the application characterization of optical sensors?

    I'm not sure if you will be able to achieve 10-50kHz PWM dimming with an automotive LED driver with high linearity. The TPS92642 is a closed loop current mode control so the bandwidth is limited.

    The TPS92515 is controlled off-time which can respond faster but you may require shunt-FET dimming instead of PWM dimming for better speed and linearity.

    The TPS922052 belongs to the display lighting group. I will move this post to the display lighting forum to comment on this device. They may have a more optimal solution as this doesn't seem to be an automotive application.

    Regards,

    Zach

  • 0 in reply to Zach Olson
    Prodigy 50 points

    Hello Zach,

    Thank you very much for your reply. 

    Let me just point out that although the PWM frequency is high, the dimming ratio is limited.

    • The most demanding scenario is at 50kHz, with a 10us ON, 10us OFF pattern (1:2 dim ratio).
    • The target operating condition is 16kHz with 20us ON, 40us OFF (1:3 dim ratio).

    Let's see if the lighting forum can help. Maybe they can also advise a linear solution, which could be faster. In this case, a controller with an external FET could be an option. 

    Best,

    Daniel

  • 0 in reply to DanielC
    TI__Mastermind 30291 points

    Dear Daniel,

    Pls allow me some time to check with EVM board and I will give you feedback by end of this week. Thank you!

    BRs

    Lucia

  • 0 in reply to Lucia Gao
    TI__Mastermind 30291 points

    Hi Daniel,

    I sent you the test result of TPS922052 by email. Thank you!

    BRs

    Lucia