Good afternoon.I am trying to launch an isoSPI isolation with the ltc6820 between a 3.3V microcontroller and an ltc6813. I am trying to set the appropriate values for pullups and capacitors. I have put 100nF capacitors and 1K resistors without success. In the datasheet there is no reference design. Can you help me?Thank you
Hi Framuga,
I have used the part in a reference design before, CN0410. The LTC6820 is used to convert the SPI signals into and isoSPI signal with the isolation of a transformer. The LTC6820's MISO and MOSI are open drain and would need external pull up resistors depending on the device being configured as master or as slave. If the device is on the master configuration then you need to provide a pull up resistor to MISO.
Here is the link to CN0410: https://www.analog.com/en/design-center/reference-designs/circuits-from-the-lab/CN0410.html
Hope this helps.
Regards,
Glenn
Good But I am trying to implement the solution without transformer. Isolation is possible by capacitors and pullup resistors. but I suspect that 1k pullups don't make it work. Thank you
This is the capacitive isolation indicated in the datasheet. The values of the pullup resistors on both sides of the capacitors are set at 1 K, but they don't seem to work with 100nF.
On the receive side, the resistors are set to ground.
On the Master side, do you have pull up resistors on the MISO line? Also what is the configuration on your SLOW pin of the LTC6820?
The slow pin is set to GND. I also have pull ups on the 2K master spi, both in MOSI and MISO.