LM3697: Low LED current tolerance in Exponential mapping control

Tiger Yeh

Part Number: LM3697

Hi,

Some questions for the LED current tolerance and would like to check with BU.

1. According to datasheet, the first line spec in captured below is around 10% tolerance and the 2nd line is +3.4% ~ -3.2%.

They are all in 20.2mA LED current, so this is confusing me what is exactly tolerance spec.

Please help to clarify.

2. My customer application will use exponential mapping control and the brightness will be less than 2014brightness code.

That means the LED current is very low for the brightness requirement of <1nits brightness backlight lighting.

Could you please provide the low brightness tolerance spec to me (brightness code between 0 to 1024 at full scale= 20mA)?

3. If LM3697 is not suitable for low LED current (6uA) application, please help to suggest alternative part.

Thanks and Best regards,

Tiger

0 Patrick Yao over 1 year ago

Hi Tiger,

1. The -3.4%~3.2% is at VIN=3.6V, and the below line is at VIN from 3V to 4.5V. You can find this description above the EC table.

2. The accuracy at LED current 500uA is -8.5%~8.5%.

3. LM3697 supports the minimum LED current 6uA.

Patrick

0 Edison Wang over 1 year ago in reply to Patrick Yao

Hi Patrick,

May I know how to achieve min LED current 6uA(typ) in exponenitial mode ?

Base on Equation(1) and (2)

Use 8bit and full scale current=20.2mA, the min current will be 16.75uA (brightness code = 1)

Use 11bit and full scale current=20.2mA, the min current will be 16.35uA (brightness code = 1)

And the min current will be 16.29uA even brightness code = 0

Thanks and Best regards,

0 Patrick Yao over 1 year ago in reply to Edison Wang

Hi Edison,

You need to adjust the full-scale LED current as well.

Patrick

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