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TPL7407LA: Transistors Damaged When Installed on Vehicle

Jacob Anderson56
Prodigy 20 points
Part Number: TPL7407LA

Application We have chosen the Texas Instruments TPL7407LA to drive groups of LEDs for an automotive lighting solution. The TPL7407LA inputs are connected to +12 VDC input signals to trigger the TPL7407LA’s outputs to turn on. These outputs are sinking current from groupings of automotive LEDs through the TPL7407LA.

INPUTS

BRAKE-IN +12VDC signal from vehicle's mechanical brake switch

TURN-IN +12VDC signal from vehicle's electronic flasher switch OR thermal hazard switch (depending which is enabled)

REVERSE-IN +12VDC signal from vehicle's mechanical reverse switch

PARK-IN +12VDC signal from vehicle's mechanical headlight switch

GND Vehicle's ground

COM Connected to 9V rail. 9V rail is also providing power to LED groupings.

OUTPUTS

BRAKE-PARK-LED-GND (O1/O2) LED common ground from brake light LED grouping

TURN-ON  Connected to micrcontroller pin. Pullup resistor to 5V rail installed to preventing floating. 5V rail also connected to microcontroller power supply pin.

REVERSE-LED-GND LED common ground from reverse light LED grouping

BRAKE-PARK-LED-GND (O6) LED common ground from brake light LED grouping. Resistor inline used to dissipate power and ultimately lower LED grouping's brightness.

Issue When applying power to the TPL7407LA on the test bench, the TPL7407LA inputs and outputs work just as expected. Power from the test bench is supplied by a generic adjustable power supply set at 12.5 VDC in this scenario. The TPL7407LA sinks a maximum of approximately 1.0 A total when all inputs into the TPL7407LA are activated with the given +12 VDC inputs.

When installing our product on a vehicle, testing goes mostly as expected except for the scenario where more than one of the +12 VDC inputs into the TPL7407LA goes high. The vehicle provides the switched +12 VDC power input triggers via mechanical OEM vehicle switches (brake light push button switch, turn signal electronic flasher, hazard thermal flasher, etc).

We notice that when multiple transistor are activated (typically from both the brake and the turn +12 VDC signal inputs), then after the lines are deactivated - upon the next activation of the lines, all outputs are activated no matter which singular transistor is activated. I believe this is a symptom of a damaged transistor array and we are unsure why this condition is occurring.

We have since ordered an automotive grade ULQ2003AQDRQ1 equivalent to see if this part is more resilient than the TPL7407LA for this application, but it is still very bizarre to us why this transistor array would be damaged in this type of environment.

What are we doing incorrectly in this application that is causing damage to this transistor array?

  • 0
    TI__Genius 10855 points
    Hi Jacob,

    Thanks for reaching out on E2E!

    Can you provide me with more details on the transition to the vehicle platform? Are these LEDs far away from the TPL7407LA, and thus have longer cables? If so, there is inherent inductance in longer cables that could be introducing inductive ringing into the wires. This could be potentially exceeding the absolute max current per channel.

    Can you capture any oscilloscope shots of the device, including the current entering the device and toggling the inputs?

    Thanks,
    Arthur Huang
  • 0 in reply to Alpha H
    Prodigy 20 points
    Hi Arthur,

    The TPL7407LA is placed on the same circuit board as the LEDs. The connection to the LEDs from the TPL7407LA is relatively short, 1-3 inches approximately via PCB traces.

    The PCB itself is connected to the vehicle's wiring harness using a 12" copper stranded 14 AWG wire adapter harness.

    The only variable that I can see is the power source. The test bench uses a simple voltage generator vs the vehicle using the vehicle's 12v battery and mechanical switches to turn on the inputs.

    We do not have oscilloscope captures at this time.
  • 0 in reply to Jacob Anderson56
    TI__Genius 10855 points
    Hi Jacob,

    It would be great to get some oscilloscope captures when you're switching the multiple channels on/off. I'm curious to see if switching multiple channels on at the same time is causing an overcurrent event in the device that could potentially be damaging it.

    Other than that, I don't see any immediate concerns with your schematic. To confirm, all the of the LED channels are connected to the same 9V supply as the COM pin? This is all eventually coming from the 12V battery?

    Thanks,

    Arthur Huang