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Original question:

Dimmable LED Driver for Video Recording application

LED driver selection

Liu Yang
Expert 8965 points
Other Parts Discussed in Thread: LP8556

Hi Team,

We are using LP8556 LED driver. it seems that has noise issue.
1. we are looking for pure current controlled (Analog based ) LED driver
2. it should be non-switching regulator type LED driver to suppress switching noise.
3. input is 5V. we don't need more than 5V supply for LEDs. PWM is input.
4. we can controll each channels of LED driver by programming.
5. required minimum 3/4 channels and maximum LEDs in a channel is 3
6. LEDs should glow off, when we give Zero duty cycle of PWM.
7. Maximum current per channel should be at 100mA.
8. it is used in medical endoscopy. so LED driver should have camera application. not back light LED driver.
9. should have medical standard.
For white balancing, we need each channel control through programming

Beat Regards,
Tom Liu

  • 0
    TI__Genius 13001 points

    Hi Tom,

    For customer requirements, we have no proper device at present.

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 70 points

    Hi Robin,

    Can you elaborate more on which point is hard to satisfy accordingly to find proper LED Driver. so that we can rearrange them. In LP8556, we are combining two sink channel in order  to get maximum 100mA. But it has switching noises and also it is back light LED driver. ( it has enable feature on each channel by programming. it is okay to control each channel if we did not find any individual control over channels). if you found any suitable one to avoid such issue, it is highly appreciated to assist us on that

  • 0 in reply to AMEENU RAHMAN
    TI__Genius 13001 points

    Hi,

    LP8556 has 325kHz, 625kHz and 1.25MHz boost switching frequency option and the slew rate can also be configured, are these methods helpful for noise issue?

    Besides, if you are very careful about the switching noise, then the only choice is linear topology. Pls.  refer to tps92630, tps929120 and tps92638.

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 70 points

    Hi Robin,

    These all three LED drivers are purely based on PWM dimming control. we need pure current (analog dimming) control like in LP8556 (In that, high value of PWM input will give maximum current to channel and minimum value will give zero current, it means LED should turn off completely. Hence, we can control LED brightness uniformly in accordance with  the PWM input.). if it has Dynamic headroom voltage control, it will fit as best. 

    Best Regards,

    Ameenu

  • 0 in reply to AMEENU RAHMAN
    TI__Genius 13001 points

    Hi,

    If your must need analog dimming, it's necessary that the output current change is continued?

    BR,

    Robin

  • 0 in reply to Yuting Shao
    Prodigy 70 points

    Hi.

    Because of noise issue in PWM dimming scheme, we need PWM to analog controller instead of traditional direct PWM dimming (Analog brightness control LED driver) in order to get proper noiseless working. i would like to add one more observation to your point of view, that is , when we use  AL3065, Dimming Control 1) Direct PWM Dimming Control - Has noise issue 2) PWM to Analog Dimming Control  - Led does not get switch off completely . LED will glow even for 0 duty cycle 3) DC to Analog Dimming Control - It is limited control range and we didn't see the brightness LED glowing.

    Regards,

    Ameenu

  • 0 in reply to AMEENU RAHMAN
    TI__Genius 13001 points

    Hi,

    If you don't need change the analog output current continuously, then you can configure the external resister (REFI, REF) of TPS92638 and the output current has four level.

    We don't have linear topology, analog dimming, multi-channels LED driver. 

    BR,

    Robin