Hi,

Trying to build a (overly) complicated LED lamp leveraging the LM3409 Constant Current driver from TI.
Bulding a HighBay type of LED lamp which requires a lot of power 50-60 Watt per LED (Cree XHP70.2).

My thinking was to design a PCB for each LED to make a simpler design in term of handling lots of power (which I'm not really comfortable with).

I control the TI chip via 5x different PWM signals. One per LED. So should be easy to scale up my power needs.

So for each board have pads VIN 16V, GND, PWM, LED+, LED-
I connect 16V + GND from my bench supply. Only one of the board have a PWM connected from an ESP32.
All three LEDs are connected via each PCB. Not in series.

There are five separate PCBs holded in place by a 3D printed case.
When I PWM control a SINGLE board with a PWM signal all three LEDs light up... What???

 

Thinking there is something I'm not fully understanding about the iadj PIN which is for analog dimming which i left floating

 

Used the datasheet simple app note as a starting point where IADJ is floating.

 

hi frippe,
Have you tried connecting a resistor to 0V, to check the effect it has on the other modules.?
E

Added link.
Have you seen these options?
https://www.google.com/search?sxsrf=ALiCzsZxwhfd47O1s_-OXAIAuWt5nm-TwQ:1670068279706&source=univ&tbm=isch&q=lm3409hv+evaluation+board&client=firefox-b-d&fir=PGgGwnoUGHFZzM%2Ch53f-8Iskr0J9M%2C_%3BG4DIz56Ht3H7uM%2Ct6a50muCTe4pGM%2C_%3BKfrUdrCopOLoxM%2CCk-NvnmYAlD9OM%2C_%3B8xIkb-cVQoJz6M%2CFxAJS4Y672V2BM%2C_%3BXcDjFkM5FMDoLM%2CaDcEqtVV8CBI6M%2C_%3BBWwV2KDxvvMPtM%2CL8OCzzqhDaSbCM%2C_%3BnJlLBwrbcEusDM%2Ce4yVKQ0K8uoQRM%2C_%3BLtGyKNYOS1sArM%2CFxAJS4Y672V2BM%2C_%3BoLLf8nb-2SnRlM%2CGApVDudCnds2nM%2C_%3BUX32xRG-YBzXGM%2CMDcNptiUwbAltM%2C_&usg=AI4_-kQVTy2-a1m-f9jewt8gArI5mPNwgA&sa=X&ved=2ahUKEwiM1r-Usd37AhVJTcAKHVWgA58QjJkEegQIDRAC&biw=1622&bih=891#imgrc=_1TptPhhsDZftM

 

Your diagram shows your MCU only being connected via one wire? It needs to share the same ground as your LED boards.

Is the EN pin on the other boards floating? Tie them to ground (use a resistor so that your PWM signal can overdrive it).

 

hi frippe,
Have you tried connecting a resistor to 0V, to check the effect it has on the other modules.?
E

Added link.
Have you seen these options?
https://www.google.com/search?sxsrf=ALiCzsZxwhfd47O1s_-OXAIAuWt5nm-TwQ:1670068279706&source=univ&tbm=isch&q=lm3409hv+evaluation+board&client=firefox-b-d&fir=PGgGwnoUGHFZzM%2Ch53f-8Iskr0J9M%2C_%3BG4DIz56Ht3H7uM%2Ct6a50muCTe4pGM%2C_%3BKfrUdrCopOLoxM%2CCk-NvnmYAlD9OM%2C_%3B8xIkb-cVQoJz6M%2CFxAJS4Y672V2BM%2C_%3BXcDjFkM5FMDoLM%2CaDcEqtVV8CBI6M%2C_%3BBWwV2KDxvvMPtM%2CL8OCzzqhDaSbCM%2C_%3BnJlLBwrbcEusDM%2Ce4yVKQ0K8uoQRM%2C_%3BLtGyKNYOS1sArM%2CFxAJS4Y672V2BM%2C_%3BoLLf8nb-2SnRlM%2CGApVDudCnds2nM%2C_%3BUX32xRG-YBzXGM%2CMDcNptiUwbAltM%2C_&usg=AI4_-kQVTy2-a1m-f9jewt8gArI5mPNwgA&sa=X&ved=2ahUKEwiM1r-Usd37AhVJTcAKHVWgA58QjJkEegQIDRAC&biw=1622&bih=891#imgrc=_1TptPhhsDZftM

Thanks for the advise @ericgibbs! Will try that tomorrow!
Well yes a lot of the layout from the eval board app note.... But not all. Will post back on my results.

 

Your diagram shows your MCU only being connected via one wire? It needs to share the same ground as your LED boards.

Is the EN pin on the other boards floating? Tie them to ground (use a resistor so that your PWM signal can overdrive it).

The ESP32 share ground but I left that out. EN pins are floating and that could be the reason I also see some initial flickering turning it on. I tried using a jumperwire placing one of the LM3409 EN pins to ground. No effect what so ever which is soo strange.

Will report back once I tried the resistor to ground. Or maybe I just connect all of the EN pins to the ESP32 directly. Not sure why I started out just testing one.

 

Top layer.

IADJ pin is left of the PWM pin which is clearly floating (U1) but hard to reach to "patch" if needed.

 

But the funny thing is that all three LEDs dim perfectly with that single PWM signal.... Not sure how it "travels" via either power or ground.