SLYT834 March   2023 ISOUSB211

 

  1. 1 Introduction
  2. 2 Existing implementation of OTG USB applications
  3. 3  On-the-go operation
  4. 4 Implementation of isolated OTG
  5. 5 Demonstration of OTG with ISOUSB211 EVM
  6. 6 Scenario A: Isolated OTG module connected to a USB-drive (bus-powered)
  7. 7  Scenario B: Isolated OTG module connected to a laptop (host)
  8. 8 Demonstration
  9. 9 Connect phone to laptop
  10. 10Connect phone to USB-drive
  11. 11Summary

4 Implementation of isolated OTG

#FIG_OBQ_XK1_MVB shows that the isolated repeater needs to have flexibility for any side to operate as host or peripheral. During operation, the isolated repeater introduces a 15-kΩ pull down at power up. The side that provides the external 1.5-kΩ pull up will establish the connect. The other side, which assumes the host role, introduces the internal 1.5-kΩ pull up in the repeater to mirror the downstream connect. The end plugged in with the micro-A plug takes on the initial A-device role and the end plugged in with the micro-B plug assumes the initial B-device role. After the initial role assignment, HNP has a defined set of transitions in a scenario where the devices wish to exchange roles: the initial A-device suspends the bus and initial B-device transitions to wait-for-connect state by disconnecting the 1.5-kΩ pull up and enabling the 15-kΩ pull down. As the lines are now in SE0 state, the A-device takes up the peripheral role and establishes a connect by enabling its internal 1.5-kΩ pull up resistor. The bus now reflects a J-state which gets detected as a peripheral connect by the initial B-device, which now assumes the host state. The 5-V VBUS is sourced by A-device, irrespective of the roles determined by HNP.

Figure 4-1 Block diagram of a self-powered Isolated on-the-go module.