• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 615 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

UCC21520: UCC21520: Failure mode where VDDA/VSSA short together

UCC21520: The VDDA and VSSA are frequently getting shorted

Peeyush Tekriwal
Prodigy 80 points
Part Number: UCC21520

Hi, I am developing an LED control board using the UCC21520. However, as soon as I brought up my first board and started testing, after some time the VDDA and the VSSA are getting shorted. The VCCI is maintained at 5V and the INA/B are at 3.3V. I am not able to understand the reason for this. Please help.

  • 0
    TI__Genius 10652 points

    Hi,

    How did you determine VDDA/VSSA shorted? could you share your schematic here and any data or scope you have of the short event you are witnessing?

    Best

    Dimitri

  • 0 in reply to dimitri james
    Prodigy 80 points

    This is the main circuit for the UCC21520. We are using it to drive an Industrial Tree light which is being controlled by an Ubuntu system. We were driving the IC with:

    VCCI = 5V

    INA/B = 3.3V

    VDDA/B = 24V


    After a few runs the output of the UCC21520 got shorted. It has happened thrice now and we don't have any idea why is this happening.

    Also, is this a good application for this particular IC? We are starting to doubt our selection of this IC as this is mainly used for driving HV MOSFETS and we are using it to drive Low Power LEDs (30mA) with a large duty cycle (500ms - 1000ms)

  • 0 in reply to Peeyush Tekriwal
    TI__Genius 10652 points

    Could you share where REDLIGHT / YELLOW light is connected to? Was the LED burned out after the shorting issues?

    Is that connected directly or you have resistor in series with LED? Because a low power LED doesn't need 24V, the only voltage drop i see is the 40v schottky

    Peeyush Tekriwal said:
    Also, is this a good application for this particular IC?

    Not really, for one, this IC can support way higher drive currents than you need. Secondly, there is no currently limiting resistor that i can see.

    To drive a simple LED, you dont need this IC. You can use a general purpose buffer or even BJT circuit which is much easier!

    Best

    Dimitri

  • 0 in reply to dimitri james
    Prodigy 80 points

    Hi,

    So in the schematic right after the 40V schottkey the RED and YELLOW LED modules are connected. These modules have their own current limiter and are connected through pluggable connectors and mounted over manufacturing machines. The LED module has a power consumption of around (24Vx0.01A) per colour panel.

    The main idea behind using these ICs was to get isolation between our control system and the factory supplied power supply which will be used to drive these modules.

    After the short the IC stopped giving out any output. The VDDA and VSSA was shorted together, and VDDB, VSSB and OUTB were shorted together.

    I am guessing there is some protection element missing in the circuit due to which even by a slight disturbance the internal MOSFETs are getting damaged.

  • 0 in reply to Peeyush Tekriwal
    TI__Genius 10652 points

    I am not exactly sure about the exact cause for the failure, especially because the current is very low. for each. Unless you are driving many many LEDS in parallel for 1s on-time ( you mentioned it was a LED string for tree lights) on all LED and you are drawing current on the order of amps, the IC will overheat and damage as it was not designed to this. That is one possible cause.

    It wasn't clear from your earlier message, If your use case is to source current to many LEDs in parallel simultaneously, you should not use the device because the internal mosfet are not designed for sustained currents, this would need to drive a Lowside FET (or highside, with a redesign of supply) that can take the current for such a time.

    If by isolation, you mean about taking care of the level-shifting requirement from your 5V to 24V, know that this is not a requirement for an isolated gate driver because the power planes do not need isolation such as for safety, and the Grounds won't be seperated anyways.

    To take care of levelshifting, the BJT circuit will work a s level shifter from 5v input to 24V with just a 5V. We also have non-isolated gate drivers that would work to drive a highside or lowside MOSFET like a load-switch for a string of many LEDs. Isolated will work, but for this application, its not required. Rough rule is, <600V working voltage you can choose a non-iso gate driver.

    If you have any questions further please let me know.

    Best

    Dimitri