Hello,
My customer is evaluating use of 2x SN74CBT3125C in place of SN74CBT3257C due to space constraints.
Thanks,
Nitish
Hi Nitish,
For Ron the following parts have the following specifications:
SN74CBT3257C:
So Ron, for both devices is basically identical and there is no difference between the parts on Ron.
For Bandwidth, the parts don't have it spec'd, however there is a formula we can use to approximate the bandwidth of the switch.
The Formula for approximated -3dB bandwidth: f(-3db) = (R_L + R_on) / (2 * pi * (R_L * R_on) * (C_L + C_On). This is also explained in our precision lab video here.
The two components that come from the MUX is R_on and C_On. Since R_on is spec'd the same for both parts. That leaves C_On. C_On for the SN74CBT3257C is spec'd at 16.5pF while the SN74CBT3125C is spec'd at 12.5pF.
As an example:
For a load of 50pF and 50 Ohms in parallel using R_on = 3 Ohms the bandwidth is approximately as follows:
SN74CBT3125C ~ 900MHz and the SN74CBT3257C ~ 846MHz
However depending on how you are planning to implement the switch from a 1:2 configuration to 1:1 configuration, the load total bus capacitance on the output may be slightly higher when using the 2 SN74CBT3125C and this could degrade bandwidth.
Best Regards,
Parker Dodson
Hi Nitish,
Also to add. Switching times for the devices also vary slightly as shown below:
SN74CBT3125C:
SN74CBT3257C:
The switching time of the SN74CBT3125 is slightly faster with a lower max for Ten/Tdis.
Best,
Parker Dodson
