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LP8556: Dimming resolution

Pjs
Intellectual 880 points
Part Number: LP8556

HI, 

I'm looking to use the LP8556 to dim some discrete LEDs at low brightness and so am particularly keen to understand the dimming resolution available. 

1) There's mention in the first page of the datasheet that says "LED current sinks can be set with the PWM dimming resolution of up to 15 bits" but then I can find no mention of achieving 15-bit dimming either via current or PWM control? Can you clarify what this means? I'm looking for an effective dimming resolution of at least 14-bits ideally at a 1khz refresh or faster.

2) If I want to dim the LEDs without using a PWM signal and use I2C control only, how do you dim the LED outputs? Am I right in thinking you set a value in the 8-bit brightness register and the adaptive mode control will either dim with current control if the 8-bit value is above PWM_TO_I_THRESHOLD or PWM if below?

3) Can you achieve additional PWM resolution by setting the CURRENT and CURRENT_MAX registers dynamically and then also setting the brightness BRT register?

Thanks

  • 0
    TI__Mastermind 22745 points

    Hi Sir,

        1. 15bit resolution is achieved by 12bit I2C regs(reg A0H and A1H) + 3bit dithering(Section 8.3.2.10 on datasheet).  For your application, 14bit as 1kHz is very challenging. It is so challenging to do this with PWM dimming mode, We suggest to use I2C dimming mode.

        2. If you only use the I2C to dimmming , you need to update A0H and A1H;

        3. You mean you want o change the maximum current of each channel to achieve high dimming ratio?, I think this onlyimproves dimming ratio, not resolution,

    Regards

    Sean