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ONET1151L: Application with driver laser diode

David Huang
Intellectual 2285 points

Part Number: ONET1151L
Other Parts Discussed in Thread: ONET4201LD, ONET1101L

Hi Team

My customer is thinking about driving the following diode with ONET1151L.

U-LD-855062Ap.pdf

Is this application possible? The customer is planning on dimming with PWM.

Regards

  • 0
    TI__Mastermind 40033 points

    Hi,

    Can you share more details about the application?  Is this being used in a communications application?

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    TI__Intellectual 2285 points

    Hi Drew

    Thanks for the response!

    It's not for communication application.

    The end equipment is medical related, the customer simply wants a device to drive the current & voltage to appropriate value, and dimming the LED through PWM.

    Their requirements are as below,

    Can be controlled APC

    LD current can be changed

    PWM dimming control

    I'm aware that ONET is originally design for communications but can it also be used as driver for low energy LD?

    Also, do we have an EVM for this device?

    Regards

  • 0 in reply to David Huang
    TI__Mastermind 40033 points

    Hi David,

    Unfortunately, we do not have an EVM for this device.  Based on my understanding of this application, it seems like this should work.  With that said, this is definitely outside the intended use case for this device, so it's possible unexpected issues may be encountered.

    I have a couple questions regarding this application.  I'm not an expert when it comes to driving lasers, so please let me know if I have made a poor assumption.

    • It seems like laser brightness can be controlled with just bias current.  Why is bias current control and PWM control required?
    • Has the customer considered driving the laser with an adjustable current source and a switch for PWM control?  If so, what are the concerns with this sort of topology?

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    TI__Intellectual 2285 points

    Hi Drew

    Thanks for the response!

    PWM is there for lower brightness, for some use cases the customer needs very low brightness where with constant current the voltage will be lower than the threshold.

    The current source and switch would also work, but this would become a discrete solution. Adding APC to this will even further increase the cost and complexity of the system.

    Regards

  • 0 in reply to David Huang
    TI__Mastermind 40033 points

    Hi David,

    Thanks for the clarification on my questions.  I can see why the ONET1151L might be useful in this application.  Like I mentioned before, I think this should work, but this is outside of a typical use case.  I would recommend that the customer consider some sort of test platform for this part as a proof of concept prior to making significant investments into it.

    Thanks,
    Drew

  • 0 in reply to Drew Miller1
    TI__Intellectual 2285 points

    Hi Drew

    Adding some additional questions from the customer.

    1. Is adding GPIO signal to the Din pin possible for controlling?(Such as adding 3.3V to Din+ with Din- grounded) If not, could you advise a solution to covert the GPIO signal to differential?

    2. Could you let me know the difference between ONET1151L、ONET1101L, and ONET4201LD?

    Regards

  • 0 in reply to David Huang
    TI__Mastermind 40033 points

    Hi David,

    1) I have some concern about the customer application after further thought.  Regardless of differential vs single ended signaling, the input to this device is expected to be AC coupled.  This concerns me because a PWM signal is not DC balanced and the DC component will change over time.  Significant changes in the DC balance of an AC coupled high speed signal is not good.  I'm also concerned about device behavior for any extended periods of time when the laser is supposed to be on or off (without modulation).  When the input signal is AC coupled, this would mean that the differential voltage to the Din+/- would decrease to 0 in both conditions.  Apologies for any inconvienience, but based on my current understanding I would recommend considering another device.  Perhaps some discreate solution like I previously mentioned could be considered if you can't find a general purpose laser driver.

    2) There may be some additional differences between these parts, but an obvious difference is the recommended data rate:

    • ONET4201LD: 155-Mbps to 4.25-Gbps
    • ONET1101L: 2 Gbps to 11.3 Gbps
    • ONET1151L: 1 Gbps to 11.3 Gbps

    Thanks,

    Drew