SN65LVDS049 schematic.pdf Some percent of the SN65LVDS049 show this error:
Hello all,
We have a problem with an LVDS Driver and Receiver SN65LVDS049, where I would like to ask for your help. We are currently at the production start with a product in which this IC is used.
The Rin+ or the Rin- input of the device is low-impedance (approx. 10-20 Ohm) to 0V. Except this short circuit to ground, the SN65LVDS049 still works. However, the SPI signal transmission is very susceptible to interference from outside, because the common mode rejection no longer exists.
In order to find the cause of these defects, we applied an external voltage (+- 20V) to the Rin+ and Rin- pins to create such a defective input. We have not succeeded. It was not possible to create such a low input resistance. Is it possible that the SN65LVDS049 were already delivered defective? If no, how can such a damage occur and what can we do to prevent this damage?
Attached you find the circuit section with the SN65LVDS049. We have two identical pcb which communicate via an SPI bus, which is transmitted via these LVDS transmitters. One of these circuit boards is the master, the other circuit board is the slave. Switch S150 is used to determine whether a circuit board is master or slave. Therefore only two of the four SN65LVDS049 are enabled on each circuit board.
The cable length between the two circuit boards is approx. 4 meter. The clock frequency is approx. 4MHz. It is clear to us that the terminator resistor (220 Ohm) is not optimal because it is available both on the driver side (where it should not be) and on the receiver side. The effort to switch off the terminating resistor on the driver side was too big for us. The data transmission works good, except for the described defects.
I hope you can help us.
Best regards
customer
