I am working on a project to use 4 Texas Instruments TLC5940 16 channel LED drivers to control a total of 64 one-meter RGB LED strips. The TLC5940 sinks a constant current when an output channel is on, and this current is set by reference resistor R(IREF). I am using R(IREF)=2K ohms for an ouput channel current sink I(REF) of 20mA.
Here is a drawing of my output stage:
V(LED) is 12V and R(PU) is 470 ohms. When the TLC5940 pulls 20mA across the 470 ohm resistor, 12V drops by 0.02*470=9.4V to 2.6V. This switches the p-channel MOSFET on, providing power to the LED strip.
Here is an Eagle schematic of my circuit:
This circuit works perfectly when just a single such circuit is used to control 1-16 LED strips. When I connect the TLC OUT-1 from the first such circuit to the TLC in of a second such circuit (as specified in the TLC5940 datasheet , the second TLC5940 begins to overheat and malfunction. If I use this second circuit by itself it operates well.
I suspect that I am somehow sinking current from the first circuit thru the TLC5940 in the second circuit, and somehow exceeding the power handling capacity of this second TLC5940.
Any ideas about what might be wrong with my design, or how I might further test to identify the source of the problem?
Thank you in advance for any assistance!!
Here is a drawing of my output stage:
V(LED) is 12V and R(PU) is 470 ohms. When the TLC5940 pulls 20mA across the 470 ohm resistor, 12V drops by 0.02*470=9.4V to 2.6V. This switches the p-channel MOSFET on, providing power to the LED strip.
Here is an Eagle schematic of my circuit:
This circuit works perfectly when just a single such circuit is used to control 1-16 LED strips. When I connect the TLC OUT-1 from the first such circuit to the TLC in of a second such circuit (as specified in the TLC5940 datasheet , the second TLC5940 begins to overheat and malfunction. If I use this second circuit by itself it operates well.
I suspect that I am somehow sinking current from the first circuit thru the TLC5940 in the second circuit, and somehow exceeding the power handling capacity of this second TLC5940.
Any ideas about what might be wrong with my design, or how I might further test to identify the source of the problem?
Thank you in advance for any assistance!!