LM46002 - LED driver using SS/TRK pin

David Dean

Other Parts Discussed in Thread: LM46002, TPS92510

I'd like to use the LM46002 as an LED driver. The standard 1.01V is much higher than I'd want to have across a current sense resistor - my hope is that I can apply a fixed 100mV to the SS/TRK pin, and the part will then regulate FB to 100mV, but otherwise operate normally. Is that the case?

And if THAT works, I'd like to then control the voltage on the SS/TRK pin to implement a brightness control. Will the part follow the SS/TRK pin both up and down?

Any concerns about this? Or is this badly misusing the SS/TRK pin and will make the part mad?

over 8 years ago

0 Akshay Mehta over 8 years ago

TI__Genius 15810 points

There are a couple of different ways to do brightness control and also to have less than a volt at the FB pin to reduce the power dissipation in the sense resistor. Please refer to the reference design (www.ti.com/.../PMP10596) that showcases all those approaches.

Regards,
Akshay

0 David Dean over 8 years ago in reply to Akshay Mehta

Expert 2305 points

Thank you! That document was extremely helpful.

In addition to the LM46002, I am also looking at the TPS92510 - a dedicated LED driver, but also without built-in analog dimming capabilities. Would it be possible to add a similar circuit to bias the FB pin, and implement an analog dimmer?

0 Akshay Mehta over 8 years ago in reply to David Dean

TI__Genius 15810 points

Hello,

Unfortunately, I am not familiar with the TPS92510 as it is not part of the SIMPLE SWITCHER forum. You would have to ask that question in the LED forum.

Regards,

Akshay

0 David Dean over 8 years ago in reply to Akshay Mehta

Expert 2305 points

Could you explain the function of R10 in the LED reference design? It's the resistor between the analog dimming input and ground. I understand how the analog dimming input biases the FB node, but I don't see the function of that particular resistor.

0 Akshay Mehta over 8 years ago in reply to David Dean

TI__Genius 15810 points

The existence of R10 is just so that you can leave the jumper J2 open if you'd so like. This causes the actual LED current to be a little low becuase of some current flow in to that leg.
Regards,Akshay

0 David Dean over 8 years ago in reply to Akshay Mehta

Expert 2305 points

What would be the harm in leaving the jumper open if R10 was not present? Just leave the end of R6 floating, no current draw unless you want to use the dimming function?

0 Akshay Mehta over 8 years ago in reply to David Dean

TI__Genius 15810 points

The way it is configured, if jumper is always open and R10 is not present, there will be zero volts on top of the sense resistor translating to zero current. if you do not intend to use that mode of dimming, then just short out the jumper J2.
Regards,Akshay

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LM46002 - LED driver using SS/TRK pin