Hello,
We have a project in which QTB QBTO46-UVA LEDs are used. We arrange the LEDs as a 6x4 array and use TI LED driver chip TLC5947 to implement constant current drive.
I need your help. I have 2 questions:
1. We use TLC5947 4 outputs. each output drive 6 LEDs, the nominal LED VF is 3.5V, So 6 LEDs is 21V, VLED = 21V. If we apply VLED 21V, it seems to be constant voltage drive, no constant current drive. And I don't see any feedback (in side the chip?) to stabilize the current. Would you please educate me ?
2. Our customer needs to have LED fault notification when LED burnout. 6 LEDs are serial together. When one LED is burnt out, The LED is in OPEN state or SHORT state? Is there still current flowing the 6 LEDs. I need this information to design our fault detection circuit. Should I detect the voltage cross the 6 LEDs (the total voltage is less then normal voltage if the burnout LED is SHORT) or the current flowing the 6 LEDs (no current if the burnout LED is OPEN)?
By the way, the customer doesn't want to use a microcontroller, so no SPI interface and no grayscale .
Thanks.
Regards;
Chang
Chang