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TPS92200: PCB Trace impedance affect on Sense Resistor of TPS92200D1DDCR and LM3414MRX/NOPB

Mohamed Obaid
Prodigy 20 points
Part Number: TPS92200
Other Parts Discussed in Thread: LM3414,

Tool/software:

Dear Texas Instruments Support Team,

I am currently working on a project involving the control and driving of UV LEDs using the TPS92200D1DDCR LED driver. This driver requires an external sense resistor to set the LED current. However, in my application, the PCB layout is constrained to a single layer, and the trace impedance added to the sense resistor is significantly affecting the overall LED current, leading to a reduction in the output power of the UV LEDs.

To overcome this, I searched for LED drivers without the need for an external sense resistor and found the LM3414MRX/NOPB. However, I noticed that the block diagram of the LM3414MRX/NOPB includes an internal sense resistor. I am concerned that this internal resistor might still be influenced by the trace impedance in the same way as the external resistor in the TPS92200D1DDCR, leading to similar issues with LED current and output power.

I would like to request your expertise in understanding the following:

  1. Trace Impedance Effect on LM3414MRX/NOPB: How does the trace impedance on a single-layer PCB affect the internal sense resistor in the LM3414MRX/NOPB, and what impact does this have on the LED current regulation?

  2. Solutions for Mitigating Trace Impedance Issues: Are there any recommended solutions or design guidelines for minimizing the effect of trace impedance when using these LED drivers? Specifically, I am looking for methods to drive UV LEDs without experiencing current reduction due to trace impedance, ideally without using an external sense resistor.

  3. Alternative Solutions: If the internal sense resistor of the LM3414MRX/NOPB is also susceptible to trace impedance issues, could you suggest alternative LED driver ICs or design approaches that would be more suitable for driving UV LEDs in my application without being affected by trace impedance?

Thank you for your assistance. I look forward to your guidance on resolving this issue.

Best regards,

Mohamed Obaid ,
QUANTTRONIX LLC

  • +1
    TI__Genius 17705 points

    Hi Mohamed,

    Please refer to my comments below:

    Mohamed Obaid said:
    Trace Impedance Effect on LM3414MRX/NOPB: How does the trace impedance on a single-layer PCB affect the internal sense resistor in the LM3414MRX/NOPB, and what impact does this have on the LED current regulation?

    In general, the trace impedance will also affect the current output accuracy of LM3414, in the same manner as TPS92200 if the PCB is not designed well.

    Mohamed Obaid said:
    Solutions for Mitigating Trace Impedance Issues: Are there any recommended solutions or design guidelines for minimizing the effect of trace impedance when using these LED drivers? Specifically, I am looking for methods to drive UV LEDs without experiencing current reduction due to trace impedance, ideally without using an external sense resistor.

    Please use Kelvin connection for the sense resistor.

    Mohamed Obaid said:
    Alternative Solutions: If the internal sense resistor of the LM3414MRX/NOPB is also susceptible to trace impedance issues, could you suggest alternative LED driver ICs or design approaches that would be more suitable for driving UV LEDs in my application without being affected by trace impedance?

    You can try TPS92200 with Kelvin connection for the sense resistor and see if it helps.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 20 points

    Hi Steven ,
    Thank you for this guidance ,
    I couldn't find any Kelvin connection resistor in range of 220 - 270 mOhm .Any recommendation for 4- terminal kelvin connected resistor in range of 200-300 mOhm ?

    Best Regards,
    Mohamed

  • +1 in reply to Mohamed Obaid
    TI__Genius 17705 points

    Hi Mohamed,

    I do not think it is necessary to use a 4-terminal kelvin connected resistor. A normal 2-terminal current sense resistor should work here. Since TPS92200 is a low-side current-sensing device, you should use Kelvin connection to the point of the sense resistor which is connected to the FB pin. For GND point of the sense resistor, you should make your GND trace / plane as thick / large as possible to minimize the voltage drop on it.

    Best Regards,

    Steven

  • 0 in reply to Steven Li
    Prodigy 20 points

    Thank you Steven

  • 0 in reply to Mohamed Obaid
    TI__Genius 17705 points

    Hi Mohamed,

    You are welcome. I am going to close this thread. Feel free to contact me again if you have any further question.

    Best Regards,

    Steven