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LM2759 LED Driver Control

keunyong jung
Prodigy 20 points
Other Parts Discussed in Thread: LM2759

Hi,

I wonder why can't control output current and timeout duration in using LM2759.

I have designed circuit that is same circuit in datasheet.

I have succeed that write/read register(addr : 0x10, 0xa0, 0xb0, 0xc0) by I2C  communication. 

It can change LED control mode.

But I can't control Flash/Torch current and Flash Timeout Duration. (addr : 0xa0, 0xb0, 0xc0)

Although the register of this address are set value, current is never changed. ( measure to DMM, oscilloscope )

I want to know that is exact method and control current(led brightness).

Sincerly.

  • 0
    TI__Intellectual 1940 points

    Hello,

    I have a few questions that will help me understand the situation better.

    • So to confirm, you can put the device in torch or flash and see the LED turn on at some current level.  
    • After you disable the LED, are the values found in the registers the same as they were before enabling the device?
    • Are you using Strobe to control the flash?
    • Are you using a power supply or a battery to power the flash?  If it is a supply, what input voltage and what is the current limit on the supply?
    • When the LEDs are on, if you move the input voltage around, does the current in the LED stay the same?

    The more information you can provide is appreciated.  Scope photos showing the behavior with different current and time out settings could be useful.

    Thanks.

    Greg

  • 0 in reply to Greg Lubarsky
    Prodigy 20 points

    Hi,

    I reply your questions.

    •So to confirm, you can put the device in torch or flash and see the LED turn on at some current level.  

    •After you disable the LED, are the values found in the registers the same as they were before enabling the device?

    - When I have checked LM2759 registers, it is always worked that write/read registers normally.

    Also registers maintain setting value when I turn off the LED(Shutdown mode (addr : 0x10, value : 0x0 )).(not change)

    •Are you using Strobe to control the flash?

    - I use both Strobe and Tx pin. But I have not changed state

    ( it's state is always Tx = 0V or 5V(Low or High), Strobe = 0V (Low) (=> Current I2C programmed state))

    •Are you using a power supply or a battery to power the flash?  If it is a supply, what input voltage and what is the current limit on the supply?

    - I used 5V-3A DC adaptor.

    •When the LEDs are on, if you move the input voltage around, does the current in the LED stay the same?

    - I can't check it because I used 5V DC Adaptor. It maybe stay the current when I move input voltage (5V -> 3.3V ==> brightness was same nearly).

    I hope that help your understanding as this answer.

    Thank you.