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LM3643: What’s the functions of TORCH Polarity bit of TEMP Register?

Part Number: LM3643

Hi, Team

I am studying on LM3643 flash driver. But I have confusion on What’s the functions of TORCH Polarity bit of TEMP Register? Could you help to explain on it?

Thank you very much.

  • Hi, Team
    Could you help to give some comments?
  • Hi,

    The TORCH polarity bit is relevant only when the TORCH/TEMP pin is configured as TORCH pin.
    Then, if this bit is set to '0', Torch mode will be enabled when the Torch pin is pulled high and disabled when pulled low.
    Then, if this bit is set to '1', Torch mode will be enabled when the Torch pin is low and disabled when pulled high.
    The polarity of the Torch pin can only be changed if the device is not already enabled (as explained in the note below the register table).

    I hope this clarifies it.

    Best Regards,
    Angelos Tsiros
  • Hi, Tsiros
    I tested it in the LM3643 EVM using a wire connected with TORCH Pin, touching the wire to VIN pad and GND pad, and found that when the TORCH polarity bit is set to '1', Torch mode will be enabled when the Torch pin is low and disabled when pulled high. But after touch the wire about more than 20 times between GND and VIN, the led wouldn't turn on again. Then i need to change it to torch mode in PC software again, and set the TORCH polarity bit again. In this way, it will work again.
    Could you help to explain why need to re-setup after more than 20 times changing of TORCH Pin between GND and VIN?

    Thank you very much.
  • Hi,

    This should not happen. I'm suspecting that at some point you introduce a low, wide enough spike at Vin and the device goes into power on reset (all registers are reset to their default values). You can read all registers when the LM3643 stops torching to verify my suspicion. Can you instead of using a wire use a toggling (relatively clean) signal at the Torch pin? A function generator could do it.

    Regards,
    Angelos Tsiros
  • Hi, Tsiros
    A function generator really can do it when I tested again today. It seems a low, wide enough spike at Vin cause the problem but when read register, the register keeps the same. Maybe the IC works in unknown state. Anyway, this question is close.
    Thanks.