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HOW TO set LP8556 BOOST TO 22V AND CUREET 20mA VIA I2C

user4858020
Prodigy 10 points
Other Parts Discussed in Thread: LP8556

I don't  know  how   to   set  LP8556  BOOST TO  22V AND  CUREET  to  20mA  VIA  I2C  ，can  you  tell  me  which  regester need to write ，and  the  detailed  value ？

  • 0
    TI__Expert 4915 points

    Hi,

    In the LP8556 datasheet, you can find each variable and it's corresponding register address. Below, I've referenced each setting by it's variable name for simplicity.

    To configure the output voltage to 22V, set:

    • VBOOST_MAX = 100
    • VBOOST_RANGE = 0

    For the current setting, I'm assuming you talking about the maximum LED current. To configure it to 20mA, set:

    • CURRENT_MAX = 011

    Thanks,

    Mitchell

  • 0 in reply to Mitchell
    TI__Expert 4565 points

    Hi,

    I'm an apps engineer works for LP8556.

    Mitchell's explanation is correct.

    A couple of things to add are:

    1. VBOOST_MAX can be 101b(25V) if you need 22V boost output

    2. CURRENT_MAX = 011(20mA) as recommended, and CURRENT[11:0] = FFFh

    In order to control output LED brightness, there are a few dimming modes. Pure current mode, pure PWM mode, and mixed mode.

    This can be selected by PWM_TO_I_THRESHOLD(addr A4h).

    Pure current mode : once you set max current as above, and control brightness with I2C or PWM input, LED current will change at 100% duty

    Pure PWM mode : current value will stay at max value all the time, and PWM duty will change with brightness

    mixed mode(adaptive dimming) : current mode dimming at high brightness and switch to PWM mode at low(switch point set) brightness. This will give you advantage of light efficiency at high brightness and high enough current to turn on LED correctly at low brightness.

    Hope this helps,