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TPS25741EVM-802: PS_RDY not sent if 12v offered but not requested

Part Number: TPS25741EVM-802
Other Parts Discussed in Thread: TPS25741, TPS25740,

I have the EVM connected to a tablet device for testing purposes. The device only accepts 5v and 20v profiles. 

The EVM is setup as follows:

24v input

J3 set to H2  (20v @3A)

/EN12V link NOT fitted so NO V2 (No 12v)

J4 set to P2 (default 65W)

with this setup, the device will accept and charge at 20v as expected.

Here is a capture of the power delivery traffic. As you can see, PS_RDY is sent to the device after about 300mS from capabilities message send. All good..

If we now remove the /EN12v link on J3 to allow 12v to be offered we no longer get the PS_RDY message even though the device has not requested 12v, it has requested V3 (20v)

Here is the capture. As you can see the device performs a hard reset after about 500mS. This process cycles indefinitely.

I have scoped the EVM and the DC-DC is being set to 20v (20.62v) as expected when the device requests 20v but the TPS25741 does not seem to be sending the PS_RDY message when the 20v becomes stable.

Any ideas please


  • Hi Trevor,

    The TPS25740EVM can be set to advertise 5V,12V,and 20V by the following connections:

    • J3 set to H2 ( enables 20V at IMAX of 3A) 
    • EN12V in J3 header set to HIGH (no shunt installed - default; enables 5V and 12V) 

    I might be misunderstanding, but for the first scenario you have the EN12V shunt installed and the PS_RDY message is sent correct? 

    Only when you uninstalled the shunt on EN12V, there was no PS_RDY? 

    I'm currently looking through your PD traffic message and will get back to you on this issue.


    Jimmy Hua

  • Hi Jimmy,
    Original post was slightly incorrect. The EN12v link is FITTED so that 12v is NOT advertised for the first set of trace data. I also have a design on the bench which is using the TPS25740 which has opposite polarity for this pin, this caused the confusion.
    Our design is showing the same issue with no PS_RDY signal.

    Although you say that the EVM802 only supports 2 voltages due to the layout of the PCB (your reply on my other post), as far as I can see the EVM will support the 3 voltages for the following reasons:
    1/ CTL1 is connected to DC-DC2 and does set the DCDC to produce 20v when PDO request is 20V.
    2/ The links allow all three voltages to be advertised (confirmed by data analyser).

    Could you explain to me how or why the EVM does not support all three voltages?

    I will run further tests on our PCB design (TPS25740) which uses only one DC-DC converter and no PFET. We also don't see the PS_RDY being sent.


  • Hi Trevor,

    Please take a look at the TPS25741EVM-802 Evaluation Moduel User Guide. In section 1.1, it references the EVM's supported features of 2 output voltage selection. The TPS25741 IC itself is capable of sending USB Type C PDO of 5V,12V, and 20V but the EVM is not configured for such use case.

    Jimmy Hua

  • Hi Jimmy,

    I think the data sheet should be a bit clearer in stating that if using GDPG for selecting a 2nd source then it is not possible to also use the CTL1/2 lines to control the 2nd source voltage to provide V2 and V3.

    It seems you can only use all 3 voltages in the non-mux mode.

    Just as well my design doesn't use the power muxing feature.


    Trevor Emerson