LDC1101: Length of SPI connection for reading and setting registers.

Michael9q

Part Number: LDC1101
Other Parts Discussed in Thread: SN74AUC125

Hello there,

I would like to ask for recommendation of connection distances of entire sensor system?

As recommended in multiple LDC manuals it is best to place capacitor as close as possible to sensor coil. LDC should be also as close as possible to LC circuit. Ideally on the back of the coil. L to C max 1", LDC to LC max 1".

How far can be place MCU which sets registers and receives data from LDC? SPI runs at 8MHz. I know that SPI is mainly for short distance, the closer the better but would it work reliably with shielded cables even on distance +-3 fl ? Here is the schematics:

Thank you.

Best Regards,

Michael

over 5 years ago

0 Scott Bryson over 5 years ago

TI__Mastermind 21360 points

Michael,

Thanks for your question. As you point out, higher transmission rates become more difficult at increasing lengths. The maximum distance you can achieve will depend on a number of design factors such as impedance matching and routing techniques to limit coupling with other signals on your PCB. You will want to carefully consider these as you plan your design. Another option would be to insert serial buffers periodically to help limit reflections and maintain signal integrity. You might consider using a device such as SN74AUC125.

There are a handful of documents that may prove useful when considering your design that could help limit the need for extra components and give you a bit more guidance what can be achieved when driving SPI signals:

Extending the SPI Bus for Long Distance Communication:

http://www.ti.com/lit/an/slyt441/slyt441.pdf

Extending SPI and McBSP with Differential Interface Products

http://www.ti.com/lit/an/slla142/slla142.pdf

How to Extend an SPI Bus Through a Differential Interface

https://e2e.ti.com/blogs_/b/analogwire/archive/2015/02/13/extending-spi-with-differential-signaling-technology

High Speed Layout Guidelines

http://www.ti.com/lit/an/scaa082a/scaa082a.pdf