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Part Number: SN74CBT3251
I have a question regarding SN74CBT3251D:
1.The datasheet doesn't seem to specify what the Vout max is(when using a 5V supply), nor what the Vout min is.
In an application we're seeing the output voltage range to be 1.1 to 4.2V (when 0 to 5V is expected).
Is there something limiting the voltages a part from the I*R drop of the passing FET?
Since these are passive FET switches, Vout is not a valid spec since the voltage on the output of the switch is dependent on the input voltage and the on-state resistance of the FET.
There are three main architectures for bidirectional passive FET signal switches.
2) NFET in parallel with PFET
3) NFET with the gate biased by a charge pump
1) will pass signals from 0 V to Vcc - ~1V
2) will pass signals from 0V to Vcc
3) will pass signals from 0 V to slightly beyond Vcc
This application note selecting the right TI signal switch goes into more detail on the different switch types and the reason the on-state resistances are different.
The SN74CBTXXXX devices are the NFET type which means the on-state resistance gets increasingly high as the input voltage approaches Vcc. This is why you are only seeing about 4.2 V at the output with input at 5V and Vcc at 5V. If you would like to support 0 to 5V you will need to use the SN74CB3Q3251.
What are you connecting to the signal switch? You may also be interested in the new TMUX1208.
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In reply to Adam Torma:
In reply to Alberto Doronzo:
Alberto, The closet p2p device in a 16 pin SOIC package I found that will support voltages from 0 to Vcc is the SN74CBTLV3251. This device supply voltage goes up to 3.6 V. Thank you, Adam
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