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LM3642: How to enable torch mode correctly

user4979989
Intellectual 2800 points
Part Number: LM3642

Hi team,

My customer is trying to enable torch mode by changing register(0x0A) to 0x02 (torch).

1. They tried to send (0x0A) to 0x02 (torch), but the LED is not lighted up, then they read back register 0x0B is 0x05.

2. They tried to send (0x0A) to 0x01 (indicator), then send (0x0A) to 0x02 (torch), the LED will be normal, and LED pin is 2.6V, OUT pin is 4.14V.

Does this mean hardware circuit/components are fine?

How do we set to torch mode correctly?

Please help to advise then we can check if there is something wrong.

Regards,

Allen

  • 0
    TI__Mastermind 22745 points

    Hi, Sir,

         In Torch Mode, the current source (LED) is programmed via the Current Control Register. Torch Mode is activated by the Enable Register and/or by Enabling the part in TX/Torch pin configuration. Once the Torch Mode is enabled the current source will ramp up to the programmed Torch current level. The Ramp-Up and Ramp-

    Down times are independently adjustable via the Torch Ramp Register. Torch Mode is not affected by Flash Timeout.

         So for Torch mode, you just need to send 0x02 to reg 0x01. I suggest you try again and make sure the communication is right and the hardware is correctly connected.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    TI__Intellectual 2800 points

    Hi Sean,

    I think the communication and hardware are fine.

    Because customer can enable torch mode by enabling indicator mode first then enabling torch mode, but he can't enable torch mode directly.

    To enable torch mode, besides sending enable register, is pulling up TX/TORCH pin also needed?

    Or torch mode can be done through enable register only?

    We read back the 0x0B is 05, which means LED or VOUT short and Timeout flags are 1, is there any clues and what we can check next?

    Thank you.

    Regards,

    Allen

  • 0 in reply to user4979989
    TI__Mastermind 22745 points

    Hi Allen,

        Technically sating, it should enter Torch mode when you write enable register only. Since I don't have the LM3642EVM on my hand now, I suggest you request an LM3642EVM to test on our EVM to verify this phenomenon:http://www.ti.com/tool/lm3642tlevm

    Regards

    Sean

  • 0 in reply to user4979989
    TI__Mastermind 22745 points

    Hi Sir,    

         I have tested with our EVM, when I sent the 0x02 to reg0x0A, it entered into torch mode and light up the LED as below:

         

       

     I suggest to check the I2C communication and you can also apply our EVM and test again.

    Regards

    Sean

  • 0 in reply to user4979989
    TI__Mastermind 22745 points

    Hi Sir,

        How about your update? Does my reply has resolved your problem yet? It should enter Torch mode when you just enable that reg.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    TI__Intellectual 2800 points

    Hi Sean,

    Customer connects LED pin to load switch then to LED, there is 1uF in load switch input, 1uF in output. (that means 2uF in LM3642 LED pin to GND)

    After removing 2uF capacitor, torch mode can be enabled normally.

    Regards,

    Allen

  • 0 in reply to user4979989
    TI__Mastermind 22745 points

    OK, that's the good news.