Other Parts Discussed in Thread: TS3A44159
We are trying to utilise a TS3A27518E to switch a uSD card (com channel) between either our own controller (NC channel) or a camera's SD slot (NO channel) so that we can read photos back from the SD card when required.
With slower uSD Class 4 cards, everything works fine for a variety of cameras (and a clock speed of up to 50MHz) proving that the hardware connections are fine. However, for HC-I bus cards, the circuit is failing when it tries to switch clock/data lines from 3.6v to 1.8V and ramp up the clock speed to 100MHz. Although the tracks are short and a ground plane is used, my guess is there is too much parasitic capacitance as viewing the clock signal shows that the clock sometimes has a reduced amplitude of 1.0v (down from 1.8v) and also has a DC bias. I was considering using a low forward voltage schottky diode to remove the DC bias but this will also introduce a phase delay that I suspect would be too much at 100MHz. Has anyone had any success in using this type of switch for low voltage (1.8V) and high speed (100MHz) SD signals? I was wondering if I should have used two TS3A44159 devices instead as that has a lower R(on) of 0.3 ohms.
Although the circuit board allows for pull-ups, no pull-up or pull-down resistors are used on the data lines.
RHS screenshot: Ch1 is input to switch, Ch3 is the output.
Appreciate any ideas anyone might have to resolve this.
Thanks!!
Paul