TMUX1574: Pull up resistors on SPI lines with Mux

Joel Brown

Part Number: TMUX1574

When using TMUX1574 to connect SPI from Microcontroller to two devices are pull-up resistors required on the SPI signals on each device?

If there are no pull up resistors then the SPI signals to the un-selected device will be floating.

This diagram is from the datasheet:

Also is it possible to use two TMUX1574 to connect four SPI devices to a microcontroller as shown below?

SEL and EN signals will be controlled by port bits on microcontroller.

over 1 year ago

0 Nir Gilgur over 1 year ago

TI__Expert 8445 points

Hello Joel,

Regarding your first question, since the TMUX1574 doesn't have internal pull-up/down resistors on the GPIO pins. I do recommend connecting pull-down resistors on the SPI signal lanes in order to prevent unpredictable behavior that may happen when they are left floating.

For the second question, yes two TMUX1574 can be connected to 4 SPI devices. Since the device is a 4 channel 2:1 mux.

If you have any more questions or concerns please let me know and feel free to look into our FAQ about SPI Muxes: https://e2e.ti.com/support/switches-multiplexers-group/switches-multiplexers/f/switches-multiplexers-forum/1064277/faq-what-analog-switch-multiplexer-should-i-use-for-spi-applications-3-4-wire-spi-qspi-or-ospi

Thanks,
Nir

0 Joel Brown over 1 year ago in reply to Nir Gilgur

Prodigy 240 points

Thanks for the response. But it seems like pull up resistor would be more appropriate on CS# signal since that is the inactive state.

0 Nir Gilgur over 1 year ago in reply to Joel Brown

TI__Expert 8445 points

I recommended a pull-down resistor specifically because it is easier to implement. But there is no difference between the two, a pull-up resistor will work as well.

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TMUX1574: Pull up resistors on SPI lines with Mux