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ONET1151L: The laser can not emit light when the fault enable bit FLTEN is set to 1

Harrison Wang
Intellectual 280 points
Part Number: ONET1151L

We use ONET1151L to drive Laser in optical module.It works normally when the fault enable bit FLTEN is set to 0,but the laser can not emit light when the fault enable bit FLTEN is set to 1.

We try to write 11001010,11101010,10001010 to the Register 0(0x00) of ONET1151L,the fault always exist.Then we change the value to 10000010 writen to the Register 0,the fault is removed.

Why is this happening?What else do we need to set up when the fault enable bit FLTEN is set to 1?

  • 0
    TI__Guru* 93670 points
    Hi Harrison,
    I believe - based on values you are using - bit 3 is always set so fault is enabled(11001010,11101010,10001010 ) until you write 10000010 - bit 3 is set to 0'b - disabling fault detection. As far as I can see, this is normal.

    To determine what caused this fault, you can try the followings:
    1). Set MONPFLT, DMONP, and DMONB to low. For example set reg 0x0A[2:0]= 000'b.
    2). Next enable FLTEN by setting reg 0x0[3]=1'b.
    3). Do you see fault trigger?
    Then you can enable MONPFLT, DMONP, and DMONB one at a time to figure out which condition caused fault.

    Regards,,nasser
  • 0 in reply to Nasser Mohammadi
    Intellectual 280 points
    Thanks.Now we have sloved the fault issue when the fault enable bit FLTEN is set to 1.But we found the read value of Ibias current and Imod current was not zero.Why is this happening?
    The datasheet showes that If the fault conditions occur, and the fault enable bit FLTEN is set to 1, the ONET1151L device responds
    by setting the bias current or the modulation current to 0.
    So do the actual phenomenon contradict the specification in datasheet?
  • 0 in reply to Harrison Wang
    TI__Guru* 93670 points
    Hi Harrison,

    Could you please run the following experiement:
    1). Please confirm when there is no fault condition, then there is optical eye and we are drivig the laser.
    2). When we are in step #1, let's raise modulation current and confirm modulation monitor current reads accordingly.
    3). Then cause fault again.
    4). At step 3, do we now read the new modulation current?
    Regards,,nasser
  • 0 in reply to Nasser Mohammadi
    Intellectual 280 points

    Thanks for your suggestion.But We still read the bias current and modulation current maintain the original value(not zero) by your step.

    We only want to know which status bit can be changed while ONET1551L go to flaut except the FLT pin because the MCU have no enough I/O port to connect with the FLT pin?

    If none,how can we make the MCU know that ONET1551L go to flaut?

  • 0 in reply to Harrison Wang
    TI__Guru* 93670 points
    Hi Harrison,
    Other than FLT pin, the only fault indication that I can think of is to set ADCSEL pins to read photodiode current or bias current and then compare these versus the settings you've used to declare fault.
    Regards,,nasser