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A
AlexandrG
Visitor II
October 22, 2024
Solved

STUSB4700 - constant output switching

  • October 22, 2024
  • 1 reply
  • 1534 views

We are using the STUSB4700 in our PD implementation as a source. We have encountered an issue where it seems like the output is constantly switched on/off/on/off with about 500ms on, 200ms off timing.

Below is the schematic which connects to a USB type C connector and a SoM. Please note that we are aware that PD_1V2 should not be connected to the gates of the power FETs and we have patched this on the board we are testing with. Also, to make sure there is no interference from the SoM, the reset and alert line have been cut as well.

AlexandrG_0-1729577539449.png

So to summarize the behaviour:

  1. The input voltage is 5V and seems stable when no device is connected.
  2. We connect a USB PD enabled sink device through USB and see that the PD negotiation is working. The output is shortly as expected and device is charging.
  3. After about 500ms, the VBUS_EN_SRC is released which forces the fets to open and the output drops to 0V.
  4. After about 500ms this cycle repeats.

The input voltage seems stable for the most part with about a 1.4V drop when the fets are switched. Limiting inrush current eliminates the drop but doesn't eliminate the issue. The picture below shows the input in yellow and output in pink:

AlexandrG_4-1729578119498.png

 

Please note that when we connect a NON PD device, the controller does output a stable 5V ~500mA. Once there is any communication everything fails.

 

We also have access to the I2C registers but didn't find anything useful through that.

 
    This topic has been closed for replies.
    Best answer by NBALL

    Hello

    So the behavior is correct: by default, STUSB4700 will advise 5-9-12-15-20V to USBPD sink.

    If contract is done on 9V for example, stusb4700, thru is monitoring feature, will expect to see voltage increasing to 9V. If not, issue is detected and that's why vbus_en_src is released.

    If you want to operate only at 5V, I suggest to use STUSB1700 which is 5V only.

    To keep stusb4700, you need to change NVM: change number of PDOs from 5 to 2 (this is the min).
    On PDOs I suggest to setup 5.1V for example (as it should not advise 2 times same voltage).
    Best regards

    Nathalie

    1 reply

    N
    NBALL
    ST Employee
    October 22, 2024

    Hello

    Vs description you are providing, it seems that voltage does not raise as expected so that stusb4700 detects a monitoring issue which explains VBUS_EN_SRC going high.
    I do not see in the schematic how PD_GPIOx nets are connected to power supply, in order to change the regulation point and output correct voltage, vs negotiation done and I suppose that there are PDOs above 5V

    Can you please provide this part of schematic ?

    Best regards

    Nathalie

    A
    AlexandrGAuthor
    Visitor II
    October 22, 2024

    Hi Nathalie,

    Makes sense, we might be missing something in that regard.

    The PDOs are all left on default.

    The GPIOx are all floating and connected to testpads. This is the full schematic:

    AlexandrG_0-1729582335382.png

    We are not using the GPIO configuration as as of now we do not expect to be using voltages above 5V.

    N
    NBALLAnswer
    ST Employee
    October 22, 2024

    Hello

    So the behavior is correct: by default, STUSB4700 will advise 5-9-12-15-20V to USBPD sink.

    If contract is done on 9V for example, stusb4700, thru is monitoring feature, will expect to see voltage increasing to 9V. If not, issue is detected and that's why vbus_en_src is released.

    If you want to operate only at 5V, I suggest to use STUSB1700 which is 5V only.

    To keep stusb4700, you need to change NVM: change number of PDOs from 5 to 2 (this is the min).
    On PDOs I suggest to setup 5.1V for example (as it should not advise 2 times same voltage).
    Best regards

    Nathalie

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