SN74AXC4T774: SPI Series Resistor placement

Vibhu Vanjari

Genius 11900 points

Part Number: SN74AXC4T774

Hello,

I am using this part for SPI voltage translation.

In order to drive the SPI lines at maximum power I read that series resistors can be placed at the driver to match the impedance of the lines.

My setup includes a master (MSP), level shifter and then the slave. In case of the signals running from the master to the slave (MISO, SS, CLK) should these series resistors be placed near the MSP or near the level shifter?

Thanks,

Vibhu

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 316690 points

Series resistors are used to reduce ringing caused by the output driver's impedance being lower than the line impedance. Therefore, they must be placed directly at the output pin. See [FAQ] What happens when I connect a logic device's output to a 50 ohm transmission line?

You should place resistors at the beginning of any trace that is long enough, which can be between the MSP and the shifter, or between the shifter and the slave, or both.

Logic

Logic forum

SN74AXC4T774: SPI Series Resistor placement