5 Demonstration of OTG with ISOUSB211 EVM

#FIG_PT4_KL1_MVB demonstrates the isolated USB-OTG implementation using on-board components. The circuit includes ISOUSB211 isolated high-speed USB repeater, SN6505 5-W push pull transformer driver and ISO6721 dual-channel digital isolator to implement the isolated USB-OTG operation. As highlighted in the previous section, it is necessary for the isolated USB solution to allow any side to be upstream- or downstream-facing for USB-OTG application. This flexibility is allowed by ISOUSB211 which has automatic role-detection making it straightforward for any side to assume the upstream or downstream role based on which side detects a 1.5-kΩ pull-up first. ISO6721 transfers ID information across the isolation barrier from the connector to the OTG module. V2OK signal from ISOUSB211, which indicates if VBUS2 is available, is fed to USB_DET pin of the OTG module. USB2.0 standard mandates that a device should not introduce pull-up on the DP/DM lines unless VBUS is present. The OTG module controls the internal pull-ups based on the USB_DET status. The switch in the power path between the secondary side’s low-dropout regulator (LDO) output to the connector’s VBUS for controlling power delivery is based on the type of device connected to the module. The OTG Module drives the VBUSON signal, in case an off-chip source needs to power up the connected device. This controls the switch between the secondary side LDO’s output to connector’s VBUS.