TPS61061: Setting current limit

Alen Abraham Mathew

Part Number: TPS61061

Tool/software:

Hi Team,

Good day!

I am facing issues with setting the current limit for the design. As my understanding from the datasheet, we have pulled the ILED to GND and that should make the Vfb as 500mV.

From there, Rs=500mV/ I gives the resistance Rs.

In my design, we required the current limit to be set to 90mA (backlight LED with Vf=5.4(typ)), and hence chose 5.6Ohm resistance for Rs.

When I connected an Ammeter in series to the LED, I can see around 140mA of current.

Kindly support on this soon. Thanks.

7 months ago

0 Steven Li 7 months ago

TI__Mastermind 23190 points

Hi Alen,

Our expert is currently out of office for Chinese New Year Holiday. He will reply to you after Feb.5 when back to office. Thanks for your understanding.

Best Regards,

Steven

0 Patrick Yao 7 months ago

TI__Mastermind 34780 points

Hi Alen,

Could you please send me the schematic? And please also indicate how did you in series the multimeter, you can mark it in your schematic.

Patrick

0 Alen Abraham Mathew 7 months ago in reply to Patrick Yao

Prodigy 105 points

Hi Patrick,

Please find the section drawing with the LED and multimeter connections included.

Thank you.

Alen

0 Patrick Yao 7 months ago in reply to Alen Abraham Mathew

TI__Mastermind 34780 points

Hi Alen,

Have you measured the FB voltage?

And is the Vf=5.4V the total LED string voltage or a single LED voltage? If it is single LED voltage, please let me know the total string voltage.

Patrick

0 Alen Abraham Mathew 7 months ago in reply to Patrick Yao

Prodigy 105 points

Hi Patrick,

The measured Fb voltage came around 900mV.

I would like to make a correction. In order to test the backlight driver, instead of connecting the display directly, we used another LED for testing.(PN: LXML-PWC2). and its Vf = 2.9V. Only one LED is used, no string of LEDs. Kindly ignore the 5.4V Vf mentioned earlier.

Thank you.

0 Patrick Yao 7 months ago in reply to Alen Abraham Mathew

TI__Mastermind 34780 points

Hi Alen,

Because TPS61061 is a boost LED driver, so the output voltage should be higher than input voltage, if you only used one LED, that means the Vout is lower than VIN, so that the extra voltage will drop on FB.

I think if you in series more LEDs, this issue will be resolved.

Patrick

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TPS61061: Setting current limit