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LP5569: Clock synchronization between two LP5569

Bruno Lau Costa
Prodigy 150 points
Part Number: LP5569

Hi there,

My team just received a new custom board that has two LP5569, intended to drive 6 RGB LEDs. We observe that clock synchronization is needed since, for LED animations of period greater than some seconds, LEDs from one driver start getting out of phase with respect to the other. Thus, we connected the two CLK pins, as shown in datasheet Figure 122.

LP5569 number 1 has CLK pin configured as output, driven by internal 32kHz oscillator used as clock source
LP5569 number 2 CLK pin is input.

Problem:

LP5569 number 2 doesn't work when its clock is configured as input. When configured as output, it works normally (but desynchronization occurs). 

In BOOST-LP5569 (Dev Kit), the code with synchronization works. We saw that it has a pull-up resistor in CLK traces. 

Question: Is this CLK pull-up mandatory for synchronizing two or more LP5569? We couldn't find such info in the datasheet. 

Any help in solving this issue would be appreciated.

Thank you,

Bruno

  • 0
    TI__Genius 9255 points

    Hi Bruno,

    Please refer to the Figure 19 in the datasheet of LP5569 which provide the reference design of synchronizing multiple devices using the clock generator. An pull up resistor to Vin is necessary due to the pin's type.

    If it is convenient you can provide the schematic of your design and I will help to check.

    Best Regard

    Monet Xu

  • 0 in reply to Monet Xu
    Prodigy 150 points

    Hi Monet, thanks for the quick response

    Oh yes, we had seen Figure 20 before. Nevertheless, as our device is low power and we didn't find it written in the datasheet that such pull up was mandatory, we opted for not using such component :(  
    I removed the CLK pull-ups in two BOOST-LP5569 EVM and I noticed the same behavior as in our custom board (driver number 2 stops working). The problem seems to be not having this resistor, indeed.

    Is there a way to internally enable a pull up for this pin?

    Best regards,
    Bruno

  • 0 in reply to Bruno Lau Costa
    TI__Genius 15776 points

    Hi Monet, please help to keep following this case.

  • 0 in reply to Bruno Lau Costa
    TI__Genius 9255 points

    Hi Bruno,

    When the CLK pin is configurated to be the output pin, it is necessary to series a pull-up resistor for generating high level.  The type of this pin is an Open-drain output. There is no internal way to enable a pull up for this pin.

    Best Regard

    Monet Xu