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LP8860-Q1: Direct PWM +Hybrid Dimming

T Kishi
Genius 4425 points
Part Number: LP8860-Q1

Hi

My customer has question.

Is it possible to use LP 8860 in "Direct PWM Mode" + "Hybrid Dimming"?

The customer wants to do LED dimming frequency at 200 Hz.
⇒ We believe it is possible for Direct PWM Mode.
However, the resolution of customer's "PWM Input" is 0.1% (1000: 1) is the limit.
In contrast, the required SPEC is 0.02% (5000: 1).
Customers want to consider whether they can be realized by "Direct PWM Mode" + "Hybrid Dimming" to satisfy this.
Is it possible?

Best Regard

T Kishi

  • 0
    TI__Expert 4565 points

    Hi Kishi-san,

    First, direct PWM+hybrid mode is not supported.

    If customer wants to achieve 12 bit  resolution on output dimming, PWM input should be higher resolution than output resolution.

    So, output requirement is ~12 bit(5000 steps), PWM input steps should be higher than 12 bit resolution, so LP8860 can calculate output brightness level accordingly.

    If customer can use brightness register input instead of PWM input, input resolution will be 16 bit, and can support 12 bit output resolution.

    And if customer only cares about dimming ratio, not dimming resolution, usually, only hybrid dimming mode and min PWM out freq(4.88kHz) is used to achieve 5000:1 dimming ratio(not dimming resolution). For dimming resolution, current dimming resolution is max 12 bit due to LED current DAC limitation, so hybrid dimming will limit max resolution to 12 bit(4095 steps) for current dimming range, but PWM dimming range(low brightness) can have more resolution, and dimming ratio(max brightness/min brightness) can be bigger.

    Hope this helps,