Dear TI Support,
our company develops electronics for LED luminaires. We use a lot of TI chips.
We encountered a problem with the matrix controller TPS92661-Q1 on our aluminium-core light engines: The lowest LED of the string (on negative/GND input of the current source, between pin 36 and 37) of 12 LEDs is flickering - in a way which normally cannot be programmed. This means, in some of the periods the controller turns on the lowest LED for a short time (shorter than one clock pulse).
The phenomenon exists not on all layout versions – however these light engine layouts are pretty similar. It depends clearly on if the aluminium core is connected to GND or not. If the core is floating, no flickering occurs. (Due to EMC reasons the alu cores of the light engines must be connected together and to GND.) We already measured the control signals, these are OK. As I wrote above, the ON-pulse is so short, this cannot be programmed for that length. Maybe it is a bootstrap issue. (Increasing the capacitor value doesn’t solved the problem.)
At the pictures You can see two periods which should look identical, but they are different. The one LED is turned on, where it should remain off.
The next picture shows the Vf of one LED (the lowest in the string).
The cursors marking one period. This means, the controller turns the LED in some periods two times on! (Programmable: only one time.)
Of course, we could provide You our light engines to test them – we think this would be the fastest way to find out what causes the flickering. (I may not post the layouts here.)
Many thank in advance for Your response!
Peter H.
