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LP5562: Driving two RGB LEDs

Part Number: LP5562
Other Parts Discussed in Thread: LP5523, LP5569

Hello,

as the title says, is it possible to drive two LEDs from LP5562? I just don't want to use a bigger chip like LP5523 due to size constrains. Each channel of the RGB LED consumes around 8mA on average. Since LP5562 can sink up to 25mA on each channel, I though there should be no problem, but double checking wouldn't hurt. (see attached schematics for reference)

And the second question: would the efficiency be better of worse (due to Peak Efficiency (%)) if I would use LP5523 and drive each LED separately? 

Kind Regards,

Den 

  • Hi,
    Yes, you can connect two LEDs in one channel but these two LEDs will turn on/off at the same time. If you don't need control two LEDs separately, no problem.
    Thanks,
    BRs,
    Rosley
  • Hi Rosley,

    I have another question on the same subject.

    I know there is always a problem when you connect LEDs in parallel. One of the LEDs might draw slightly larger current than the other, then it become hotter and draws even more current, becomes hotter until it fry itself. Then it propagates to the other LEDs.

    I also know that there is a away to prevent this with a current sources and since we have a current source (or sink) here which is controlled by PWM, how should I set it up (or even if I can or not?) so that the LEDs will both work normally?

    Kind Regards,
    Den
  • Den,
    I don't know how to use the current source to prevent current unbalance. Could you attach a SCH to explain your idea?
    Thanks,
    BRs,
    Rosley
  • hi Rosley,

    I think I confused it with the current mirror solution, which I don't want to use since I don't have space for additional components. So as it seems at this point there are only two solutions, either to take an IC with more available pins or connect the LEDs in series. However, it is impossible to do it with an RGB LED which has one anode, i.e. I have only one solution and it is to take an IC with multiple pins. I am looking into LP5569 since it has the lowest Iq, apart from that they all seem to be similar. 

    regards,
    Den

  • So as it turned out I will have to use two LP5562 ICs. Hence I have two questions: 

    1 - the i2C address selection pins should be connected to GND or VCC. In case of VCC, do you need a pull-up resister?

    2 - I don't want to use uVias so I've set the address selection pins so that I can fan out ADDR_SEL0 (Pin B2), through CLK_32K, which is set to GND in my case. (see the attachment). This way B3, B2 and A3 are all connected to the GND. It should be fine, but I still would like to double check that there won't be any signal integrity problems since now all signals go out through A3 which is a CLK signal. 


    Kind Regards,
    Den

  • Den,
    1. A pull-up resistor is required for each I2C pin.
    2. I think it is OK to connect it like this.
    Thanks,
    BRs,
    Rosley
  • Dear Rosley,

    I'm not asking about i2c interface itself. please read the sentence! The ADDRESS pin which I tie to VCC do I need a resistor in series for it or can I just connect it to the VCC? (to change the address of the IC).

    Regards,

    Den

  • Hi,
    Sorry for misunderstanding. If you connect pin to VCC, no need resistor and just connect it directly.
    Thanks,
    BRs,
    Rosley