USB Selective Suspend Compliance Test - KBA84678

Question: How to ensure that the enCoRe MCU based USB devices pass the USB selective suspend compliance test?



To conserve power, USB devices automatically enter the Suspended state when the device senses that there is no USB traffic for a specified period. All devices must ‘suspend’ if bus activity has not been observed for 3 ms time. In Suspend mode the current consumption should not be more than 2.5 mA.

To ensure that enCoRe MCU based USB devices comply with this, follow the steps below:

  1.   Configure the unused pins on the enCoRe MCU to High impedance analog mode.
  2.   Configure the sleep timer for 2 ms. Check the USB bus activity every 2 ms. If there is no activity on the bus for more than 3 ms, put the device into Sleep mode.

Cypress enCoRe MCUs pass the test for USB compliance, and the selective suspend current is less than 2.5 mA.

For selective suspend current test procedure, follow this link.