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LP8556: LP8556 precisions upon power config

S C70
Prodigy 210 points
Part Number: LP8556

Hi, 
I intend to use LP8556, but I would need further information about correct usage of the device.
I would need to poweroff some stuff around for deeper low power mode, but I can' figure out some stuff in the datasheet.
- In Functional Block diagram @ page 12, a POR appears, but there is no other information about this. What are the electrical settings of the POR?
- Can the device have a EN/VDDIO greater than VIN ( min = 2.7V).
- Can it work it EN.VDDIO = 3.3V and  VIN=2.7V?
- What if EN_VDDIO = 3.3V and VIN = 0? Is there any risk?
- If VLDO falls below POR level, is the device reseted by the POR (µcut)
Thanks.

BR

 

  • 0
    TI__Mastermind 22745 points

    Hi Sir,

         1. For POR, it is an internal circuit and this doesn't affect your application, we don't provide every information about the internal circuit on datasheet since not all circuits affect application issue;

         2. Can the device have a EN/VDDIO greater than VIN ( min = 2.7V). ->Yes, the maximum voltage foe EN/VDDIO pins is about 6V, pay attention to this;

         3. Can it work it EN.VDDIO = 3.3V and  VIN=2.7V?-> Yes, but that depends on your real application specs, since for this low input voltage , it may can't output high power, and it may trigger internal current limit;

         4.What if EN_VDDIO = 3.3V and VIN = 0? Is there any risk?-> No risk, it will not work at all since there is no supply voltage, device will not start at all;

         5. If VLDO falls below POR level, is the device reseted by the POR (µcut)-> Yes, that's the internal circuit and protection;

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    Thanks for theses answers.
    For low power purpose, I'd need to know also if there could be leakage from EN_VDDIO to VDD if VDD = 0V?
    I had such issues with some level translator.

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

         No, for EN_VDDIO it only supplies some power for logic circuit and it doesn't have leakage to VDD pin. But I suggest if you want to lower power consumption, you can just pull down the EN/VDDIO pin as well when you disable the device.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    Could you please give me precision upon Overvoltage?
    Overvoltage is measured on VBOOST, but what is the value compared? Is that the VBOOST_MAX in register A9H?


  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

        Yes, that's right.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    On my board, I was trying to proceed to shutdown of the device, I had OVP triggered in status...
    I was suprised having such error.
    It is possible the ULVO disconnect first the load, and then the boost gets into OVP?
    The ULVO is said to shutdown the LED outputs and the boost...
    Thank sfor all your answers

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

        In which condition you get the OVP error? I don't understand your meaning.

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    Sorry, I forgot some setup description.
    On a board I implemented with LP8556, I try different configurations.
    I tried to switch off the VDD. 
    The result is that I have UVLO, but sometimes I also have OVC or OVP.
    I see why I'd have OVC.
    But I was more suprised by OVP, unless the load is disconnected and the boost is still active so that the capacitor are filled and the output voltage keep inscreasing. 
    I guess I'd need to check with the scope... but the phenomena is quite random...

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

         Usually the OVP occurs when there are some LED open or some channel open, But I don't understand why you switch off the VDD? Do you get those error when you switch off the VDD? 

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    In the current power topology, the power rail supplying the backlight is switched off for power saving consideration.
    The backlight is not the only one on this rail, so we need to switch everything off.

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

        Ok, understand, does that mean you have used separate two power rails for boost switch and VDD? If that is right, We suggest to power on VDD first and then boost voltage. If you have combined two power rails together, it is ok.

    Regards

    Sean

  • 0 in reply to S C70
    Prodigy 210 points

    Hi,
    Thanks for your answers.
    However, It seems I'm a little bit confused by the LP8556...
    I though the config in EEPROM was saved... I intended to modifiy the config...But it seems it is lost after power off...
    And reading the datasheet again, I notice that most of the time the storage is labelled as an EPROM, and sometimes as an EEPROM...
    What is it really?
    Is there a way to program it?
    THX

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

        LP8556 only has the EPROM which means it will lose the configuration information after power off. But there are some default version listed on datasheet section 8.6.2. you can check whether there is a default one may meet your requirement. Thanks.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    Ok, I saw these, but I intended tu use QFN package, but I did not understand the "recommended"...
    Note : the datasheet says EEPROM a couple of times.

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

         Just ignore that, We will fixed those later.

    Regards

    Sean

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

        Does my reply help your question? Since there is a long history question and reply, is there any other update information? 

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    Yes, it does help me understand the behavior of the LP8556.
    One last question please : I was now concerned with the Overvoltage issue. 
    I need to build a high lifetime product, and I was wondering about this overvoltage...
    My system has a 19 Vf Led. What Overvoltage limit shall I set? Does it has an impact on regulation?

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

         Considering the LED bing effect and headroom voltage(take 1V as the worst case) and add some margin. Usually, we set the (V_f+V_headrrom)*1.3=(19+1)*1.3=26V, so you can choose 30V as the OVP setting, it doesn't have an impact on the regulation.

    Regards

    Sean

  • 0 in reply to Sean Zhou
    Prodigy 210 points

    Thanks for all your answers.

    BR

  • 0 in reply to S C70
    TI__Mastermind 22745 points

    Hi Sir,

        Sure, thanks for choosing our LP8556.

    Regards

    Sean