LSF0108: Using LSF0108 as level shifting for SWD

Yuhao Zhao

Genius 9810 points

Part Number: LSF0108

Tool/software:

Hi team,

Recently we are using LSF0108 with our on-board xds110(3V3) to get a 5V SWD port.

XDS_VCC = 3.3V, XDS_VBUS = 5V

However in some cases the SWD comms will fail

example 1 - SWD is fine when using jumper to connect on-board MCU
example 2 - SWD fails when using the dupont Line to connect external MCU
example 3 - SWD also fails when using the dupont Line instead of jumper to connect on-board MCU

Is there any concern when using LSF device as SWD level shifting?

6 months ago

+1 Clemens Ladisch 6 months ago

Guru 317260 points

Cables increase the capacitance, which reduces the maximum speed. Check the waveforms with an oscilloscope, and use stronger pull-up resistors. (But more pull-up current increases the V_OL of your devices, so there might be a limit on the cable length.)

0 Jack Guan 6 months ago

TI__Mastermind 40976 points

Hi Zhao,

In addition to Clemens' response, please note that the optimal performance of the switch is achieved by letting VREFB and EN pin shorted and pulled up through a bias resistor to XDS_VBUS.