• TI Thinks Resolved

LP8860-Q1: Boost Adaptation and Short Detection using Single String

Part Number: LP8860-Q1

Hello,

we want to use all LED outputs shorted to maximize current in a single string configuration. LP8860 runs in display mode. According to table 10 of datasheet LED_STRING_CONF needs to be set to 101.

Question 1)

In Table 10 it says "Y/N" in section "Short LED String" under 101 for LED_STRING_CONF. In which cases is short detection possible ? I guess that usually two strings are compared using DRV_LED_FAULT_THR value in register 0x64 to detect shorts. However, here we have only single string.

Question 2)

What are the optimal values for DRV_LED_FAULT_THR, DRV_HEADER and DRV_LED_COMP_HYST in a single string configuration ? In our case we have 8 LEDs in series with Vf,total between 22V and 28V.

Best Regards.

  • Hi, Martin,

    Let us take a detailed look at this and reply you later.

    Thanks.
    Regards,
    Kenneth
  • Hi Martin,

    (1) The LED short fault is triggered if one or more outputs voltage is above DRV_LED_FAULT_THR and at least one LED output voltage is between DRV_HEADR and DRV_HEADR + DRV_LED_COMP_HYST. So if 4 outputs are shorted together, the 4 output voltages will be the same. So LED short fault cannot be detected.

    It says "Y/N' in the datasheet is because sometimes although "LED_STRING_CONF" is set to 101, the four outputs are not tied together. In that case, LED short can be detected.

    (2) DRV_HEADER and DRV_LED_COMP_HYST voltage usually depend on the output current, the thermal requirement, the maximum boost output voltage drop. You can select the minimum voltage at first, and increase the voltage if it cannot meet the requirement and thermal is also allowed.

    Best Regards,

    Shirley He