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TPS65920 - USB VBUS current issue

Tudor-Cristian G.
Prodigy 20 points
Other Parts Discussed in Thread: TPS65920

Hi,

 I am working with a TPS65920 connected to a single USB port. I am having problems with the current supplied by this device. Under no load conditions, VBUS is stable at 5V but once I connect a USB key for example, VBUS drops down to 0V. I tried different USB devices and the same issue comes up.

I read the TPS65920 can supply 100mA on the VBUS line, so I took a variable resistor and connected it on the VBUS output.

On the failed units I get the following:

3.00 Kohms  5.00V  (1.6 mA)
2.00 Kohms  4.97V  (2.5 mA)
1.50 Kohms  4.80V  (3.3 mA)
1.10 Kohms  4.57V  (4.1 mA)
1.01 Kohms  0V        (0 mA, +5V USB offline)

On a good unit I can go all that way down to 50 ohms and the output will be stable at 5V. At this stage, I measured 91mA. I am going to try to connect an external 5V supply to VBUS.

I saw three different batches of chips having these problems. Does anyone know why this happens?

Thank you in advance.

  • 0
    TI__Genius 15100 points

    Hi,

    Havent seen this before. The readings you show for the failed units - is this when you connect the USB key or it is the variable resistance that you keep chaninging in steps to see the current behavior?

    Can you check the register bit that turns on the VBUS supply - DRVVBUS, before and after you see this behavior. I wanted to see if something in sw or hw forces this bit to go to '0' and shut down the internal charge pump.

    If you are trying with external 5V then make sure you disable the internal charge pump.

    Let me know what you find out.

     

    Regards,

    Gandhar.

     

     

  • 0 in reply to Gandhar Dighe
    Prodigy 20 points

    Hi Gandhar,

    First of all, thank you for your reply.

    Those readings were taken with a variable resistor box connected to VBUS and the USB cable+key removed.

    I dont have software access to disable the internal charge pump. I still tried though. Having an external 5V, 100mA supply turned out to work and the USB is detected properly. But removing the external supply caused the USB to lose power.

    I believe there is an issue with a control bit, but I am not familiar with this chip.

     

    Regards,

    Chris.