LP8864-Q1: LED channel output behave as gradient process

Hi, Daniel

What is the meaning of each waveform? And what is the duty change from the first action to the next step.

Hello Zhiqian,

Please check the updated waveform as below.

Hi, Daniel

The slope function will make the brightness smoothly. If it is disabled, device will output current directly.

Hello Zhiqian,

I am FCE XIAMEN R&D CAI JINKAI

Thank you for your reply.

Now we follow the default configuration, can you tell me how to adjust it?

For example: Bit 7-5: 5h→0h?

What are the hazards after adjustment? Can you explain it briefly?

Thanks!

CAI JINKAI

Hi, Jinkai

Yes, change the Bit 7-5 :5h to 0h.

When change the brightness directly, it means a high ripple during the transient.

Hello Zhiqian,

I am FCE XIAMEN R&D CAI JINKAI

It has been confirmed that if USER_CONFIG1 is set as follows,

there is no brightness delay and the result  is OK.

①Bit7-5: 5h→0h

②Bit1: 1h→0h

Can you tell me what harm there is in changing this? We want to avoid other accidents caused by changing this.

Thanks!

CAI JINKAI

Hi, Jinkai

Boost output may needs time to change to target value, it may leads to unexpected action of the device, especially change from low brightness to high brightness.

Hello Zhiqian,

Does boost output refer to LED output? Can you explain it in detail?

After setting the register, from the actual measured phenomenon, there is no delay time.

What action is the action that causes the accident?

It is easy to cause an accident when changing from low brightness to high brightness?

Will it not happen when changing from high brightness to low brightness?

Thanks!

CAI JINKAI

Hi，Jinkai

It will not lead to a problem.

But when you change the low brightness to high brightness, the vf increased. And device needs time to increase boost output voltage to match high vf.

Hello Zhiqian,

How many will vf increase? Will it cause any abnormalities?
Is there a delay only when adjusting from low brightness to high brightness,
such as a 300ms delay in response? Instead of an immediate response?

Thanks!
CAI JINKAI

Hi, Jinkai

We recommend to use Slope function for our device.

A low brightness change to high brightness may effect the eye without slope function.

For analog dimming, a brightness directly change will lead to the LED vf change.

Hello Zhiqian,

Thank you for your reply.

Now our requirement is to cancel the Slope mode, and there is no delay in brightness change.
*So you can ignore the impact on the eyes, which is our requirement.

So disanble the Slope mode, and the LED vf will change immediately when dimming←This is the result we want.

Is my understanding correct?

Thanks!
CAI JINKAI

Hello Zhiqian,

Or, we can still use Slope mode as suggested,

but change the Slope time from the default 5h（200ms） to 1h（1ms）.

I think the effect can be achieved, and I will keep your suggestion.
What do you think?

Hi, JINKAI

If your purpose is to change the brightness immediately, yes you can disable the slope function or set it as 1ms.

May I ask why you doesn't want to use slope function?

Hello Zhiqian,

Thank you for your reply.
It will be set to 1ms.

Because customers want the brightness to change instantly when adjusting, and do not want a gradual change when visually.
If it is Slope mode, there is a gradual change when adjusting.
It is changed according to customer needs.

Thanks!
CAI JINKAI