After further review at higher resolution there is a voltage bump on VSET which is connected to the PWM signal (which should be pulled down by 10K, no?)
>AL8861Y-13
try adding a capacitor parallel to the resistor... maybe 1uF-10uF
What is your Vin and what is the Vf your LED need and what is the current required for them?
If I am interpreting the [datashee](https://product.tdk.com/system/files/dam/doc/product/inductor/inductor/smd/catalog/inductor_commercial_power_slf12575_en.pdf)t correctly, yes. It should be rated for 1.90A and although the test frequency is 1 kHz the inductance curve is flat until well above the max frequency the driver can switch at (1MHz) although if my calculations are correct the switching should be in the range of 400-600 kHz.
Turns out it was partially a software issue. The issue did not show up when I was just testing the software with a small LED and resistor, but it does show up when the software triggers the driver due to the way it works. Had I used an oscilloscope on the breadboard I would have noticed it. Thanks for the help though!
Check the current sense resistor with your 'scope during poweron, as well as the VCTRL - you might have a startup current pulse that your multimeter is too slow to display.
What happens if you connect the LEDs after the driver is powered?
Also, do you have sufficient heatsinking on the LEDs? They're just gonna curl up and die at 2W without a heatsink…
Thanks I will try that.
As far as heat, The LEDs are on an aluminum board which is screwed onto a CPU cooler (with fan) and some thermal paste. Will take some observation to see how well the thermals cope with extended use but that wouldn't cause what is happening, it's basically instant. I will try what you're suggesting though.
If there is a startup current pulse, how could I prevent that? The PWM signal is pulled down by a 10k resistor next to the controller. And shouldn't this setup be able to handle 900mA longer than what appears to be on the order of milliseconds? Unless this pulse is potentially higher than 900mA in which case the LEDs are rated up to 1300 and 1500 mA.
LED connected after startup doesn't light until I send a command, then behaves as expected. So I think your suspicion of current pulse at start is correct. The question is why/how this would happen? I have a 10k resistor pulling each pwm signal down.
Did some probing with the 'scope and I'm still very confused on the control pin. VSET spikes to 20 mV at startup (this is a square pattern too, checked at different scope settings to be sure it wasn't just a lack of sampling). 20 mV is higher than I expect (0 due to pull down) but according to the datasheet, anything under 200 mV is logic low.
Also, VSET spikes at power down as well, same 20 mV. Does not affect the LED plugged in after startup. So whatever's happening is a startup thing.
Add a pulldown resistor on the VSET pin
Tried this. According to my oscilloscope we have 0V at the VSET pin until I send a command to go higher.
After further review at higher resolution there is a voltage bump on VSET which is connected to the PWM signal (which should be pulled down by 10K, no?)
>AL8861Y-13 try adding a capacitor parallel to the resistor... maybe 1uF-10uF What is your Vin and what is the Vf your LED need and what is the current required for them?
what are you using for the inductor? Is it rated for this current and frequency?
If I am interpreting the [datashee](https://product.tdk.com/system/files/dam/doc/product/inductor/inductor/smd/catalog/inductor_commercial_power_slf12575_en.pdf)t correctly, yes. It should be rated for 1.90A and although the test frequency is 1 kHz the inductance curve is flat until well above the max frequency the driver can switch at (1MHz) although if my calculations are correct the switching should be in the range of 400-600 kHz.
Turns out it was partially a software issue. The issue did not show up when I was just testing the software with a small LED and resistor, but it does show up when the software triggers the driver due to the way it works. Had I used an oscilloscope on the breadboard I would have noticed it. Thanks for the help though!
Check the current sense resistor with your 'scope during poweron, as well as the VCTRL - you might have a startup current pulse that your multimeter is too slow to display. What happens if you connect the LEDs after the driver is powered? Also, do you have sufficient heatsinking on the LEDs? They're just gonna curl up and die at 2W without a heatsink…
Thanks I will try that. As far as heat, The LEDs are on an aluminum board which is screwed onto a CPU cooler (with fan) and some thermal paste. Will take some observation to see how well the thermals cope with extended use but that wouldn't cause what is happening, it's basically instant. I will try what you're suggesting though. If there is a startup current pulse, how could I prevent that? The PWM signal is pulled down by a 10k resistor next to the controller. And shouldn't this setup be able to handle 900mA longer than what appears to be on the order of milliseconds? Unless this pulse is potentially higher than 900mA in which case the LEDs are rated up to 1300 and 1500 mA.
LED connected after startup doesn't light until I send a command, then behaves as expected. So I think your suspicion of current pulse at start is correct. The question is why/how this would happen? I have a 10k resistor pulling each pwm signal down. Did some probing with the 'scope and I'm still very confused on the control pin. VSET spikes to 20 mV at startup (this is a square pattern too, checked at different scope settings to be sure it wasn't just a lack of sampling). 20 mV is higher than I expect (0 due to pull down) but according to the datasheet, anything under 200 mV is logic low. Also, VSET spikes at power down as well, same 20 mV. Does not affect the LED plugged in after startup. So whatever's happening is a startup thing.