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DLPA3005DPFD PWR3 not Connected

Other Parts Discussed in Thread: DLPA3005

We are using the DLPA3005DPFD and do not require the 2.5V output from the PWR3 LDO.  Because of this, we did not connect the PWR3_VIN and PWR3_OUT to anything and this has caused our system to now power up properly.  We connected the PWR3_VIN to 3.3V and this now allows everything to power up.  Based on the DMD Monitoring section of the datasheet, it appears as though the PWR3_VOUT is monitored and will generate an PG_Fault error if the 2.5V is not present.  Is this the reason why our system was not powering up?

Is the 2.5V used internally on the DLPA?

Is there any way to ignore this PG_Fault error and allow the system to power up?

With the modification to connect PWR3_VIN to 3.3V, we will have one input capacitor that is shared between PWR3_VIN and PWR4_VIN.  There is no output load on PWR3_OUT.  Because there is no load, is a 10uF input cap for both PWR3_VIN and PWR4_VIN sufficient?  Also, without a load, can we leave the PWR3_OUT floating and without 10uF output cap?

This mod would be limited to a small number of boards (30) and the questions I ask is to reduce the re-work and its complexity.  We will re-design our board to properly connect PWR3_VIN to 3.3V with an input cap and PWR3_OUT with an output cap.

  • Hi Chris,

    Welcome to the E2E forum and thank you for your interest in DLP® technology!

    Please allow me to look into this and get back to you by the mid of next week. 

    Regards,

    Lori 

  • Thanks for the update

  • Hi Chris,

    The PWR3 and PWR4 must have VIN supplied and a load on them. If the PWR3 and PWR4 do not come up correctly, then the SW will configure a fault and the DLPA3005 will not power up correctly. I don't think there is a supported solution to ignore the failure and allow the system power up. 

    The two auxiliary LDOs (PWR3 and PWR4) that can be used by an additional external application. 

    So, for your design, please connect PWR3 and PWR4 with VIN and properly load capacitor on them. For more details, please refer to the Reference designs section on the DLPA3005 page. 

    Thanks,

    Lori 

  • Are you positive a capacitor on the output is required even if we are not using the PWR4 outputs?  We have actually tried this and there does not seem to be an issue.  The main reason I want to confirm is because the modification to add this capacitor will definitely complicate the re-work more.

  • Hi Chris,

    It's possible to not apply the capacitor to PWR4_OUT if you don't use the PWR4 output and want to protect the component from voltage instability. However, we don't test the DLPA3005 without the decoupling capacitors applied to PWR3 and PWR4.

    Regards,

    Lori