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LM3410: LM3410XQMF/NOPB Not Making Voltage

Agatha
Prodigy 20 points

Part Number: LM3410

Hi, I'm using LM3410XQMF/NOPB in a simple application to power a 24V LED strip (target 22.5V, 500 mA). Unfortunately, the device does not seem to be switching; the output seems to be only the VIN rail passing through DC.

  • I have checked that VIN is getting power (from Li-Ion, 3.7ish V) relative to GND.
  • DIM is PWM generated from a 555 timer; I haven't checked the waveform yet but the average voltage (from voltmeter) looks plausible.
  • The PCBA was professionally assembled, so it's probably not due to damage.

The schematic for this section is attached:

Screenshot from 2026-01-14 15-28-10.png

Please help me figure out what I did wrong. Thanks!

  • 0
    TI__Expert 7760 points

    Hi Agatha, 

    Do you have a capacitor from Vin to GND? When a boost converter starts up, there is typically a large in-rush current which will cause the battery voltage (Vin) to droop below it's UVLO threshold. We recommend starting with a 10uF capacitor (with an appropriate voltage rating) to start.







    Can you please send us the full schematic and measure Vin during start up at the Vin pin?

    Also, please send me the following wave forms:

    Inductor current
    Switch node voltage
    Input voltage
    Output voltage



    This is what your scope shot should look like, the channels are labeled in the picture and I need the same time division:




    Best,
    Daniel Louis

  • 0 in reply to Daniel Louis
    Prodigy 20 points

    Hi thanks for the reply.

    Yes, there is a capacitor (C2) over Vin/GND, and it happens it's 10 μF. Though, it's about 25mm away, electrically.

    The schematic for the entire project is attached:

    I measured most of the requested traces:

    • Input voltage (VIN relative to device's GND) during startup (i.e. when the switch+pot R5 switches on and that GND falls) is a step function:

    The tiny downward spike about 200 μs after the rise is repeatable.

    The following transient is VIN (CH1) and SW (CH2) relative to board GND during startup. This was difficult to measure and varied qualitatively from run to run (also note different scales).

    • Inductor current (infeasible to measure on assembled board)
    • Switch node voltage (SW): measured at scales down to 500ns, but unable to detect any switching in steady state (trace is flat line at battery voltage)
    • Output voltage (after D3): measured at scales down to 500ns, unable to detect any activity in steady state (trace is flat line)

    Additionally, I measured the input DIM pin; this one works as I expect, a PWM signal that can be varied by switch+pot R5. Typical result:

  • 0 in reply to Agatha
    TI__Expert 7760 points

    Hi Agatha, 

    It is absolutely feasible to measure the inductor current on an assembled board. That is exactly how I took the wave forms above.Please see the image below.



    The dip at the Vin during start up is a concern and may be the culprit. are you using an electrolytic cap or a ceramic cap? Regarding placement, we recommend placing the capacitor right next to the pin as seen in the data sheet and 25mm is quite a distance and is definitely affecting it.



    I would like you to try and power our IC separately through a regulated DC power supply. Please connect a 10uF ceramic cap close to Vin and connect the DIM pin to VIN and lets see if it starts up. 

    Best,
    Daniel

  • 0 in reply to Daniel Louis
    Prodigy 20 points

    "It is absolutely feasible to measure the inductor current on an assembled board." ←Call it a skill issue on my part, but when I said "infeasible", I meant these sort of tests are not so easy for me. I don't have reflow capability (so I have to use a soldering iron; I ruined two boards trying this), let alone a fancy oscilloscope attachment (I mean, you see the photos of my oscilloscope output; this thing is two channels and from the bronze age).

    Trying a closer decoupling capacitor nearer is a good suggestion. I unfortunately don't have any SMT caps lying around. I included some but not enough test points on this board, so also it's difficult to access. Do you think a THT cap with one of the legs resting the IC is worth trying as a test? I could try that. I have ceramic up to at least 1μF X5R, and larger in electrolytic.

    I thought it might be useful to see the relevant area of the board. I've highlighted the IC, inductor, and cap, and the path connecting them of length about 2.5 cm. The cap is on the output of the battery charger, and the vertical part of the highlighted trace continues on to the battery.

    I think what might be most useful is if an error in the schematic can be ruled out. In particular, I think what I did for switching the right half of the circuit is dodgy; perhaps I should have switched the LED strip instead of the entire boost converter. I was trying to save power on the 555 and on leakage current, because this thing is battery-powered and off most of the time, but maybe the physical switch makes the startup voltages unstable?

  • 0 in reply to Agatha
    TI__Expert 7760 points

    As I mentioned previously, that is pretty far from the pin and can definitely cause problems.... your trace is even much longer than the physical distance of the cap to the board.

    I know this seems trivial, but is the right side of your schematic truly attached to ground? I see that ground is connected through that switch + pot.....

    I don't see any errors... have you checked for continuity? 

    I would really like to see the lm3410 circuit powered via a regulated power supply to determine if it is in fact the converter that is having the issues.

    the through hole cap will work. 

    A physical switch is fine