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LM3429: TOF CAMERA's LED DRIVER Schematic Problem Review

Part Number: LM3429

HI Subhash Chandra Sadhu

Test environment

OPT8241-CDK-EVM kit is used and IR LED circuit is in use Refer to attached circuit

OPT8241-CDK-EVM Using the firmware for the built-in laser and adjusting the Voxel SDK parameter without firmware modification.

- OPT8241-CDK-EVM OPT9221 ILLUM_N Signal line R99 1K Installed R101 does not use open processing ILLUM_P signal

LED DRIVER Schematic Problem Review

1. Circuits PL7 and ZD1 do not use LED DRIVER but 20V as power supply separately. The LED is driven without any problem.

    However, when 20V is input using LM3429 LED DRIVER, the switching noise is heard and the IR_LED_OUT voltage shakes.

Thank you Subhash Chandra Sadhu6330.tof_sch_170327.pdf

 

17 Replies

  • In reply to Subhash Chandra Sadhu:

    hi Subhash
    I've been doing a lot of LED lamp design in the meantime. In particular, we have developed automotive lights using TI LED drivers. For example, headlights, work lights, etc.
    So, considering the heat that Subhash was worried about, we designed the LED PCB by applying metal PCB from the beginning and also made a heat sink for heat dissipation.
    The LM3429 power input is designed and calculated as SFH4715S_OSRAM IR_LED 1S_6P VF_2.9V_1000mA at 12V input. The output current is 1.7A [20.4W]
    If I connect the ILLUM_EN signal from the opt8421 to the LM3429 nDIM pin, why do I hear switching noise?
    For example, if you connect another PWM signal [beacon], you will not hear any sound.
    The value of the pix_cnt_max parameter that Subhash advised has changed. So the switching sound is getting smaller. But the sound did not completely disappear.
    What is the cause? may be difficult, but I need help with Subhash.
    Thanks
  • In reply to Subhash Chandra Sadhu:

    hi Subhash

    I've been doing a lot of LED lamp design in the meantime. In particular, we have developed automotive lights using TI LED drivers. For example, headlights, work lights, etc.

    So, considering the heat that Subhash was worried about, we designed the LED PCB by applying metal PCB from the beginning and also made a heat sink for heat dissipation.

    The LM3429 power input is designed and calculated as SFH4715S_OSRAM IR_LED 1S_6P VF_2.9V_1000mA at 12V input. The output current is 1.7A [20.4W]

    If I connect the ILLUM_EN signal from the opt8421 to the LM3429 nDIM pin, why do I hear switching noise?

    For example, if you connect another PWM signal [beacon], you will not hear any sound.

    The value of the pix_cnt_max parameter that Subhash advised has changed. So the switching sound is getting smaller. But the sound did not completely disappear. 

    What is the cause? may be difficult, but I need help with Subhash. Thanks

  • In reply to Subhash Chandra Sadhu:

    In reply to Subhash Chandra Sadhu:

    hi Subhash

    I've been doing a lot of LED lamp design in the meantime. In particular, we have developed automotive lights using TI LED drivers. For example, headlights, work lights, etc.

    So, considering the heat that Subhash was worried about, we designed the LED PCB by applying metal PCB from the beginning and also made a heat sink for heat dissipation.

    The LM3429 power input is designed and calculated as SFH4715S_OSRAM IR_LED 1S_6P VF_2.9V_1000mA at 12V input. The output current is 1.7A [20.4W]

    If I connect the ILLUM_EN signal from the opt8421 to the LM3429 nDIM pin, why do I hear switching noise?

    For example, if you connect another PWM signal [beacon], you will not hear any sound.

    The value of the pix_cnt_max parameter that Subhash advised has changed. So the switching sound is getting smaller. But the sound did not completely disappear. 

    What is the cause? may be difficult, but I need help with Subhash. Thanks

  • In reply to MINSU PARK:

    Hi!

    Sorry for delaying this.
    The sound that you hear is coming because some large value capacitor has its voltage changing a lot or some large value inductor has its current changing by a large value. This happens because the capacitors/inductors expand and contract a little whenever their voltage/current change. If they expand and contract, they create sound waves in air at the frequency of expansion or contraction.
    If the nDIM pin is switched at frequencies which are in human hearing range, approx. 20Hz to 20kHz, you will be able to hear the sound from the PCB. So when you try to inject a PWM signal into the nDIM pin you may not hear anything because of its frequency. Can you tell us the frequency of the nDIM pin?

    Regards,
    Subhash

    3D ToF Product Landing Page

  • In reply to Subhash Chandra Sadhu:

    Hi Subhash,
    I also have acoustic noise problem, the frequency of ILLUM_EN is 60Hz@15fps and 120Hz@30fps.
    How could I do to improve the noise?

    Regards,
    Eric
  • In reply to Eric Chen27:

    Hi Eric,


    Here is a post which explains how to reduce the sound from the capacitors: 

    Regards,
    Subhash

    3D ToF Product Landing Page

  • In reply to Subhash Chandra Sadhu:

    Eric, Minsu Park,

    Please let us know if following the guidelines helps reduce the sound.
    These guidelines are specific to the ceramic capacitors whose voltage changes a lot.

    Regards,
    Subhash

    3D ToF Product Landing Page