TPS92641: Question about 500:1 Analog dimming。

Hi Kazuya,

500:1 means the analog dimming ratio, which is the ratio of maximum output current over minimum output current when you are doing the analog dimming through the IADJ pin. This ratio is not only related to the IC itself but also related to the detailed application conditions.

The value of 500:1 is what this device can normally achieve based on general application conditions and well-designed external circuit components.

In some conditions, you may even achieve higher analog dimming ratio (possibly 1000:1), but the dimming linearity will be very poor when the output current is extremely small.

Best Regards,

Steven

Hi Steven,

Thank you very much for your reply.

According to the information from the customer, they don't use lower current range. So they don't care about lower current linearity.

In this case, can TPS92641 control LED analog current with 1000:1 step or more? (For example, 5mA step or less in case of Imax =5A)

Thank yo again and best regards,
Kazuya.

Hi Kazuya,

Kazuya Nakai59 said:

According to the information from the customer, they don't use lower current range. So they don't care about lower current linearity.

In this case, can TPS92641 control LED analog current with 1000:1 step or more? (For example, 5mA step or less in case of Imax =5A)

In this case, I think TPS92641 can control LED analog current with <= 1/1000 step.

Best Regards,

Steven

Hi Steven,

Thank you very much for your prompt reply.

I got an additional question from the customer as the below.

Could you please give me your reply?

[Question]
How much linearity does 500:1 analog diming have?
In other words, What is criteria of linearity error about 500:1 analog diming?

Thank you again and best regards,
Kazuya.

Hi Kazuya,

Sorry but there is no specific quantitative value for the linearity for this "1:500" dimming ratio.

Best Regards,

Steven

Hi Steven,

Thank you very much for your reply.

Could we ask you an additional question about analog dimming linearity?
The customer has the following question.

Q.
In higher ration using case like 1000:1 analog dimming, why does the current linearity become worse around lower grayscale?
They want to know the cause to design for better products.
Is the cause come from the offset voltage of internal ope-amp which connected to IADJ pin?

Thank you again and best regards,
Kazuya. 

Hi Kazuya,

I am currently out of office for Chinese New Year Holiday. I will reply to you on Feb.8 when I am back to office. Thanks for your understanding.

Best Regards,

Steven

Hi Kazuya,

I am back to office earlier than expected :)

Kazuya Nakai59 said:

Q.
In higher ration using case like 1000:1 analog dimming, why does the current linearity become worse around lower grayscale?
They want to know the cause to design for better products.
Is the cause come from the offset voltage of internal ope-amp which connected to IADJ pin?

The main cause is the input offset voltage of the error amplifier (EA).

Best Regards,

Steven