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LM3549: Solution selection for keyboard

Hardy Xue
Expert 3640 points
Part Number: LM3549
Other Parts Discussed in Thread: LP5036

Hi Team,

My customer would like to find a solution for gaming keyboard. The LED spec is as below picture. LM3549 is that I found the solution closest to the customer's needs. But its minimum output current is 107mA. It means that the customer cannot adjust to a darker brightness. Is it correct? If yes, do we have better solution can provide to customer?

Best regards,

Hardy 

  • 0
    TI__Genius 9255 points

    Hi Hardy,

    Parallel LEDs will lead to unbalanced current distribution. 

    Would you like to provide more information?

    • input/output voltage
    • how much LEDs do you want to drive
    • the output current range of each LED
    • which LED function does the customer want to achieve?
    • ...

    Best Regard

    Monet Xu

  • 0 in reply to Monet Xu
    TI__Expert 3640 points

    Hi Monet,

    Update LED sepc picture and information is as below.

    • input/output voltage
      5Vcc
    • how much LEDs do you want to drive
      R: 12 pcs parallel, G: 12 pcs parallel, B: 12 pcs parallel
    • the output current range of each LED
      0mA - 30mA
    • which LED function does the customer want to achieve?
      Like breathing light, backlight color soft change..

    Best regards,

    Hardy

  • 0 in reply to Hardy Xue
    TI__Genius 9255 points

    Hi Hardy,

    According to your information, I think LP5036 is a better choice.

    LP5036 is a 36 channels 12 BIt PWM ultra-low quiescent current I2C RGB LED driver. Operating voltage range is from 2.7V to 5.5V and the maximum current can be choose between 25.5 and 35mA. The LP503x has a 29 kHz,12-Bit PWM generator for each channel, as well as channel/module independent color mixing and intensity control, formerly called brightness control registers to enable vivid LED effects with zero audible noise. Users can benefit from the device’s ultra-low shutdown Iq Power Saving Mode, while designers will appreciate the incredibly straightforward software coding of the LP503x’s three programmable R/G/B banks.

    Best Regard

    Monet Xu

  • 0 in reply to Monet Xu
    TI__Expert 3640 points

    Hi Monet,

    Thanks for your reply.

    Due to customer's LED which connect each color LEDs together, there are only 3 wires for R/G/B. Could we connect every 12 channels for one basic color like below? 

    out1-out12 are connected for red LED.

    out13-out24 are connected for green LED.

    out25-out36 are connected for blue LED.

    Best regards,

    Hardy

  • 0 in reply to Hardy Xue
    TI__Genius 9255 points

    Hi Hardy,

    Does the customer mind too much wires between LEDs and output pins? Could you please check with customer?

    We don't suggest that connect too much output pins together to drive parallel LEDs which may lead to unexpected shock. The little difference between LEDs will cause the unbalanced current distribution in each LED, so the brightness of each LEDs may vary. When using this program, we can't control the RGB LEDs individually.

    Best Regard

    Monet Xu

  • 0 in reply to Monet Xu
    TI__Expert 3640 points

    Hi Monet,

    Thanks for your reply.

    I have checked with customer and whey will change application for Individual LED driver. I will check other solution. Thank you.

    Best regards,

    Hardy