BQ79606A-Q1: Use only as electrical interface

Hi Achim,

Thanks for your question!

Just to clarify the device capabilities: because the stack devices can be INDIVIDUALLY read ("single device read" in the protocol description), you can choose to ignore specific devices in the stack when doing reads/writes. In this way, you can completely ignore a device (make it "transparent"). It will simply pass the data from its low-side COMM lines to its high-side, and vice versa. This inherently means though that the devices are listening/responding by passing on the data.

However, it is important to note that to initially communicate with the devices, you must auto-address the entire stack of devices. This will require directly communicating to each device.

Also, to answer your last question, TI does not offer a dedicated interface IC for the COMM bus (as the devices are meant to be only connected to one another over the COMM lines).

As a follow-up question, is there any reason that transformer isolation does not suffice, as a replacement for the optical isolation suggested in your image? Our devices support transformer isolation between devices on the COMM lines, which may ease your design significantly!

Regards,

Vince

Hi Vince,

Thank you for your response.

The optical link is sadly required, since the transceivers main purpose is to transport signals into and out of shielded test chambers during EMI and EME tests, without carrying in noise from the outside.

When using the BQ79606 inside a transceiver would it make sense to configure it as a stack or as a bridge device? Assuming a base device is also present at the bottom of the stack (as shown in the image). Configuration as a bridge device does sound preferable as it would not react to any stack read/write command frames that may get sent over the bus.

As an alternative interface for the COMM Bus do you think an RS485 Interface would be compatible, provided the bus idle state is detected separately?

Regards,

Achim