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TPS61195 fault/status code meaning

Dan Andersen
Genius 11460 points
Other Parts Discussed in Thread: TPS61195

My customer is using the TPS61195 in a backlighting application.  They are trying to determine a system fault signal to indicate a bad backlight and had the following questions:

1.      BL_STAT: What is this bit mean? If the BL_STAT = 0  does it indicate a bad Backlight driver? If the BL_STAT = 1 indicates a good Backlight driver (NO Faults)?

2.      2_CH_EN and 1_CH_EN : What this bits mean? Are this the LED strings fault? Which faults (ex. Open, shorts, etc.)? What happens to BL_STAT and FAULT bits when the CH_EN reports a fault?

3.      FAULT: What is this bit mean? If the FAULT = 1  does it indicate a bad Backlight driver? If the FAULT = 0 indicates a good Backlight driver (NO Faults)?

The datasheet is a little light on details for these.  It is not clear if BL_Stat changes on fault conditions.  Also, the Fault indicator seems to indicate "any fault except LED open and short occurs"... so this only toggles on thermal shutdown and overcurrent?  Is a short condition the same as overcurrent?

Thanks,

Dan

  • 0
    TI__Prodigy 320 points
    Hi Dan,

    * BL_STAT bit
    BL_STAT=0 has two cases.
    1) Fault: LED open/short or OCP or thermal shutdown
    2) Normal operation: backlight block is off (BL_CTL=0 or PWM duty 0%)
    BL_STAT=1 means backlight driving works well.

    * 2_CH_EN, 1_CH_EN bits
    If 2_CH_EN and 1_CH_EN are non-zero, then it represents both cases - LED open or short status.
    In this case, BL_STAT should be 0 but FAULT could be 0 or 1. Please note that FAULT=1 is not related with LED open and short condition.

    * FAULT bit
    FAULT=1 : All fault case except LED open and short
    FAULT=0 : If backlight block is off (BL_CTL=0 or PWM duty 0%), then FAULT could be 0 because OCP is not operated yet. And FAULT could be 0 in case of LED string fault (open or short).

    * Over current vs LED short
    Over current is detected on PWM input. LED short condition is detected on current sink.

    Best regards,
    Milo
  • 0 in reply to Milo Kim
    TI__Genius 11460 points

    Thanks, Milo.

    We have a table to summarize the fault states - not sure if it was an early TI table or customer generated (I can't seem to find this in our documentation).  Given your information above, this would seem correct - but please review and confirm/correct:

    It would seem like the fault logic is like this:

    If bit 3=0 and bit 0=1 then there is a real fault (regardless of other bits).

    If bit 5 or bit 4=1 then there is also a real fault (LED open or short)

    Thanks,

    Dan

  • 0 in reply to Dan Andersen
    TI__Prodigy 320 points
    Hi Dan,

    Yes, correct.
    However I'm not sure specific conditions of fault detection in the table is still valid or not - we may need to ask IC design team.

    Best regards,
    Milo