• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 1044 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS63060 to drive LED

Paul Breakfield
Prodigy 80 points
Other Parts Discussed in Thread: TPS63060, TLV431

I am using the tps63060evm to try and evaluate the tps63060 in constant current mode. I would like for the voltage to adjust variably to what the led needs while supplying a constant current.

I am initially wanting to test in boost mode with a 4.2v Li-ion battery, but I would also like to explore bucking with 8.4 (2x Li-ion batteries) as well.

I would like to explore several output currents. Starting with 500mA and then trying increasing currents and hoping to find the maximum working currents in buck and boost.

The documentation on the evaluation board seems sparse, how do I set it to output in constant current mode? Thank you!

  • 0 in reply to Chris Glaser
    Prodigy 80 points

    Thanks Chris, 

    I hadn't seen that article.

    Paul

  • 0 in reply to Paul Breakfield
    Prodigy 80 points

    Some thoughts about the PDF...

    It contains three circuits:
    "Circuit 1"- TPS630x0 and a shunt resistor (very poor efficiency and high thermal dissipation due to shunt's power loss);
    "Circuit 2"- improved version of "1" but the output current is not constant because it partially depends upon the diode's forward voltage;
    "Circuit 3"- improved version of "2" but with the need of an external voltage reference which adds more components.
    Moreover none of the three proposed circuits is adjustable nor supports a grounded load.

    I believe the TPS is capable of this. I would like to drive a single "led" from a handheld Li-ion (4.2v in boost from a single or 8.2v in buck from two Li-ions) preferably with the body as the ground.

    My maximum voltage out woud be right around 6v with a minimum of 2v.  Obviously anything below 4.2v would be in buck only.

    I need precise constant current with very little and very short startup current spike and preferably less than 5% ripple. So at 2A I would like to have less than 100mA ripple current, otherwise I have to lower overall current to the diode so that my upper peak of ripple doesn't significantly go over my led's maximum current.

    Also, getting back to my original question... How do I get the evaluation module to output in constant current mode? Do I need to add on to it in order to make this work?
  • 0 in reply to Paul Breakfield
    TI__Guru**** 150660 points

    The app note contains several circuits for using these ICs as LED drivers.  You can pick any one of them or come up with one of your own.  The EVM would need to be modified to the circuit that you want to implement.

    Unfortunately, it's not easy to get your grounded LED.  When driving an LED, you need to regulate current not voltage.  To regulate current requires sensing the voltage across a shunt resistor and then driving the FB pin with this voltage.

    How do you plan to adjust the LED current?  What signal do you have for doing this?  Circuit 3 simply uses an analog voltage to do the dimming.  This is one possible signal you might have.  If you add an RC filter to a PWM output, then you also have an analog voltage.  So, this dimming method works with almost all commonly used dimming signals.  A TLV431 is a simple way to create an analog voltage and its voltage can be adjusted by tuning one of the resistors (i.e. potentiometer).