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TPS61043: single led operation from coin cell battery

Alexander Alioshyn
Prodigy 170 points
Part Number: TPS61043
Other Parts Discussed in Thread: TINA-TI

I've got a red-colored led like the LS M67K or similar.

My goal is to drive such led from a single CR2032 battery with a voltage variation from 3 volts at the start of the battery life to 2 volts at its end.

Is it possible with the TPS61043?

Also I'd like to be able to dim the brightness of the led with the PWM signal from the controller.

Maximum current is 2mA and I'd like to be able to control it from about 100uA to full scale.

  • 0
    TI__Prodigy 600 points
    This Thread has been assigned and will be responded to in a short period of time.
  • 0 in reply to Rodney Jones
    TI__Intellectual 1985 points
    Hi,

    TPS61043 can operate as low as 1.8V, so this will work from 2.0V to 3.0V Vin. If you are going to connect PWM signal directly to the control pin, make sure the frequency is between 100Hz to 50KHz. You can also refer to chapter 9 for more ways of using PWM to control the brightness.

    Regards
    H L
  • 0 in reply to Hak-Leong Ng
    Prodigy 170 points
    Ok, I see. Then I've got another question. Is there any minimum current that the IC can regulate? Is it possible to regulate 100uA with the apropriate resistor?
  • 0 in reply to Alexander Alioshyn
    TI__Intellectual 1985 points

    Hi Alexander,

    In your previous post, you mentioned max current is 2mA, and you like to adjust the brightness from 100uA to full scale. If this is what you want, then you should have sense resistor at 126 ohms to have 2mA max, you can then use PWM with 5% duty cycle to adjust the brightness (average current) to 100uA.

    Can you tell me more about your application or how you intend to use the LED? if you only need to turn on an LED or blink an LED, TPS61043 will work for you. If you are using the LED as a source to trigger some machine via light sensor, you might have a problem with this approach. You will have a more stable output voltage if you have more LEDs in series, with only 1 single LED, output voltage will fluctuate quite a bit since the boost will either be in PFM or ON/OFF to provide you the average current you need.

    Regards

    H L

  • 0 in reply to Hak-Leong Ng
    Prodigy 170 points
    Hello Hak-Leong,

    Actually I try to develop a portable re-emission and luminosity test device for my colleague.

    We conducted some experiments and I have an updated data about currents. The lower limit is 5uA and the upper is about 1.5-1.6mA.
    So the LED should be lit constantly with some current flowing through it.

    Also the goal is to make the LED current as constant as possible. 10% of the fluctuation of the current will suffice.

    Does PFM mean pulse-frequency modulation? If so what are the possible problems with it? Can I implement two or more resistors connected from the LED through the microcontroller's gpio to the ground to be able to set the maximum current through the LED? Could such approach make the situation with PFM better?
  • 0 in reply to Hak-Leong Ng
    Prodigy 170 points

    By the way is there any SPICE or Tina-TI model of the TPS61043 available?

  • 0 in reply to Alexander Alioshyn
    TI__Intellectual 1985 points
    Hi Alexander,

    I don’t know about re-emission and luminosity test device. The reason I ask about your application is to determine if the LED is seen by human eye or machine vision. If the LED is seen by human eye, the fast ON/OFF switching of LED will fool the human eye and we will see a constant brightness as the duty cycle of the PWM changes. However, if a light sensor is used to sense the LED emission, the machine will be seeing pulses instead of a constant level.

    If you need a constant current going through the LED, you will not be able to use PWM driving the control pin. Even if you use the scheme in Figure 23, you are not going to get a constant current at low brightness, it will a string of current pulses that provides the average current for that brightness.

    I check through the list of Tina-TI model and I didn’t find TPS61043.

    Regards
    H L