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[FAQ] TPS2546: EL_9 certification test J D- voltage.

Expert 3465 points

Replies: 2

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Part Number: TPS2546

If a standalone battery charging device (TPS2546) is used on a downstream hub/host port with  CDP mode enabled, then the USB 2.0 Hub/Host Downstream Port Test J portion of the compliance testing will fail.  This occurs because the test conditions mimic the disconnected CDP state and cause the TPS2546 to increase the voltage level on DM.  The standalone battery charging device is not aware that a test J packet is being sent.  The failure shows up as D- line measuring ~20mV when the D+ line is driven high.  

There is no Impact on end-user, the problem will only occur when the Test J mode is forced during compliance testing.

This is not a real world failure.  This can be verified by forcing the TPS2546 out of the disconnected CDP state. If a Test J failure occurs on a battery charging enabled port, use a header to short DP and DM on the test fixture for 1-2 seconds and rerun the test.  This forces the battery charging device out of the disconnected CDP state and allows the test to pass.

2 Replies

  • Hi Win,

    May I know this test method is permitted by USB-IF?

    ""This is not a real world failure. This can be verified by forcing the TPS2546 out of the disconnected CDP state. If a Test J failure occurs on a battery charging enabled port, use a header to short DP and DM on the test fixture for 1-2 seconds and rerun the test. This forces the battery charging device out of the disconnected CDP state and allows the test to pass.””

    Best regards,
    Daisy Yang
  • In reply to user4773197:

    Yes this method is permissible

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