SN74CB3T16212: Maximum data rate support

Hi Rahul,

Would you comment on two more details?

1. What are the voltage levels at NOR flash side and CPU side? Are both 3.3V?

2. What is the fastest required data rate?


If you can draw me a block diagram, that will be super helpful for me to understand how 48 wires connected.

All signal will be on 1.8V IO standard bidirectional and I think SN74CB3T16212 support 1.8V IO as mentioned in the datasheet.

1. All are 1.8V NOR & CPU & FPGA.

2. Max Data rate would be per pin would be 20-25MHz? How much fastest data rate it support?

Connections are shown below:-

Hi Rahul,

Thanks for this detailed drawing. Are you open to TI's SN74CBT16232? It is a 16-channel 2:1 switch.

At your NOR Flash side, you have (26+16) wires. Then, three SN74CBT16232 should be good enough to handle it. It is very cost and board space effective.

The supply voltage is required 5V while the signal passing though can be 1.8V logic. I do not know if your design is okay with 5V supply.

Actually, in my system there is no 5V supply if I use  SN74CBT16232 then I have to generate 5V.

Another thing lets see if I generate 5V also in my system.

Please confirm whether this IC requires clock input also for the selection or S0 & S1 inputs are sufficient because i dont want to use clock input.

What is the maximum data rate supported by this?

and second thing if I use five SN74CB3T16212 IC then what are the limitation except cost & board size? 

Hi Rahul,

I would hesitate to use SN74CB3T16212 to pass 1.8V logic because the input and output of this device is not linear. It has build-in level shifting feature. It will be very convenient for rail-to-rail input/output. However, in your case, you want to use 3.3V supply while 1.8V logic passing through.

For control logic and circuit simplicity, if you can generate 5V in the system, SN74CBT16390 will be a good candidate, though it also has 16 channels.

Another 3.3V bus switch I really like is SN74CBTLV16292. It has 500 Ohm internal pull down resistor. Once your processor and FPGA do not need to access Flash. SN74CBTLV16292 can pull down your Flash's interface so that high impedance nodes in your circuitry can be avoided. However, it is only 12 bit. We also have 5V version of this type of device. It is SN74CBT162292

Power sequencing between these bus switches and your other chips is not a concern because they have a feature that while Vcc is 0, the I/O voltage is allowed to be non-zero.

Channel bandwdith was not characterized for these bus switches. I normally use Ron and Con to esitmate the 3dB bandwidth. It should be above 100MHz.