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How to use LP8555 Evaluation board?

Liang Zhang
Prodigy 40 points
Other Parts Discussed in Thread: LP8555

I bought a LP8555 evaluation board and now don't know how to use it.

1 :  connection--J5，J11，J4(PIN2，3) have jump caps. I connect an external 5V to J7. LED+ is connected to boostA and LED- is connected to LEDA1,LEDA2....

2:   USB virtual com port driver is installed sucessfully and the software already recgonized the connection.

3:   I tried many different options but the LEDs cann't be lighted up. I measured and find there is 5V between boostA and PGND, 3V between LEDA1 and PGND. But there is no voltage between boostA and LEDA1.

4:   The LED's normal working condition is 3V, 8mA. I tried single LEDs and LED strings.

The evaluation board user guide is not very clear. Is there any other guide files or could someone explain the mehod detaily? Thanks very much.

  • 0
    TI__Expert 4565 points

    Hi,

    If you're using only 1 LED between boost A and LED1, then LED short fault can be triggered due to high headroom voltage(voltage between LED1 and GND), which is normally less then 1V or so. Min boost output voltage of LP8555 is 6~7V and if you use only one LED per LED channel, 6V-3V = 3V will be applied to LED1 and LED fault is triggered. Can you try 2 or more LEDs in series per string(LED channel)?

  • 0 in reply to Sung Ho Yoon
    Prodigy 40 points

    Thany you very much!

    I use 3 LEDs per string and they can be lighted up.

    But does the six channels of same group(like LEDA) always work at same state?

    I want to control the six LED strings sperately. But the "LED string enable" seems not work. 

    Can i control each channel seprately? At least on/off and brightness adjustment would be better.