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TLC5941-Q1: TLC5941-Q1 failure

Julien Djn
Intellectual 840 points
Part Number: TLC5941-Q1
Other Parts Discussed in Thread: TLC5941

Hello,

We use the LED driver TLC5941-Q1 for an automotive application (LED display on an automotive dashboard).

First, we made an evaluation board to test the component (one TLC5941-Q1 driving five RGB LEDs). Our µC board is an external board and wiring with TLC5941 are made with ribbon cable.

Until recently the board worked good but for some days we experienced drivers failures, with something like VCC/GND short-circuit. When changing the driver, the board works correctly.

Looking at other e2e topic, I found that we shall not send SPI signals to driver when VCC is not supplied : is it still true (other topic was in 2012)?

If confirmed, we will now ensure to supply VCC before applying SPI signals.

Then, we have another problem : when driver is in error state, the XERR voltage is not 0V (more around 1.2V). In our board, we connected a LED and a 332 ohms resistor between XERR and VCC (+5V). We found this schematics in the TLC5941 evaluation board made by TI (not foundable anymore), leading to a current superior to 10mA, when the max current on XERR pin at low state is indicated to be max 1mA in the datasheet : do you think it can be the reason why XERR voltage is not 0V in error state ? Is it a possible reason for driver failure too ?

Thanks in advance for your help,

Best regards,

Julien

  • 0
    TI__Expert 5380 points

    Julien,

    Is the TLC5941-Q1 using for LCD backlight with local dimming?

    You are correct. Vcc should be added first, keep Blank High (add a pull up resistor), then sending the SPI command. As there is a path from SPI input to VCC, if Vcc voltage is lower than SPI input voltage.

    332ohm resistor is pretty small, recommend to keep the XERR current within 1mA. This should not be the reason for device failure, it may only broken the XERR pin because of the large current. 1.2V should be caused by the voltage drop flow through the MOSFET.

  • 0 in reply to Anda Zhang
    Intellectual 840 points
    Hello Anda,

    Thanks for your answer.

    Yes it is used with local dimming and dot correction.

    TLC5941 command signals are routed on our µC SPI I/O, whose are by default in pull-up state at reset. As pull-ups are made on VCC, can we consider it is ok for start-up (i.e. SPI input voltage will never be higher than VCC, as VCC supplies the µC). Or you recommend to add Schottky on SPI lines ?

    Ok for XERR current, we will increase resistor value.

    Then, we found why we burnt several drivers : on our board, the driver is directly supplied from a laboratory 5V power supply which is supplied by 230V/50Hz network. When another power supply (connected to the same electrical outlet) was switched on or off, it created some kind of EMC issues that provoked voltage spikes on 5V power supply output (until 8-10V during some µs), much higher than 6V max allowed by TLC5941. Since we avoided to switch on or off the other power supply, we didn't burn any other driver.

    In our final board, TLC5941 will be supplied from TPS7B6750-Q1 regulator. This board is not built yet, but we have another board that includes the same regulator. We made measures on 5V output while switching on or off the other power supply and found some spikes on 5V ouput. We fear these spikes burn again our driver if EMC issue appear on 230V/50Hz network (on labs tests, our board are always supplied from a lab power supply). Is this a real risk with TPS7B6750 supplying the TLC5941, or you think it shall not be a problem ?

    Thanks,
    Best regards,
    Julien