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TS5A3167 Qc

Eric Raquette
Prodigy 250 points
Other Parts Discussed in Thread: TS5A4594, TS5A3167

Hello

I want to use this part in a sample and hold circuit with VCC=3.3V.

In the datasheet table for 3.3V supply Qc is typical 6pC, but  Figure 5. Charge Injection (QC) vs VCOM shows from -0.6 to +0.8 pC.

What is the correct figure typical and max?

  • 0
    TI__Mastermind 45350 points

    Eric,

    Thank you for bringing this to our attention.  I see that the datasheet is a little misleading.  This is most likely due to the electrical table value was taken over temperature and the graph on figure 5 maybe just at room temperature.  I will see if we can make this more clear.

    Thank you,

    Adam

  • 0 in reply to Adam Torma
    Prodigy 250 points

    Ok, the table does state that the number is at 25 degrees.

    I found that the TS5A4594 has much lower off leakage currents and lower Qc, so its a better part in this application.

    Maybe you could ask about the same difference in the table and graph in figure 5 for that part?

    Does the charge injection happen on both COM and NO/NC pin when the switch is opened?

    If it is only on COM i could connect the sample capacitor to the NO/NC pin instead.

    Thank you,

    Eric

  • 0 in reply to Eric Raquette
    TI__Intellectual 1465 points

    Hi, Eric,


    The charge injection would happen on both COM and NO/NC pins. It's measured by looking at the voltage difference on the load (CL) when the switch toggles. As this is a bi-directional switch, you can put your load on either the COM side or the NC/NO side. The result should be very similar.

    I agree with you the figure 5 looks pretty misleading. However, the typ charge injection spec of 6pc should be pretty accurate considering the lower Ron (0.9ohm) of the TS5A3167. The TS5A4594 has a high Ron, hence smaller parasitic caps and lower charge injection. As a rule of thumb, higher Ron==> lower charge injection; lower Ron ==> higher charge injection.

    We will try to figure out the root cause of figure 5. Thanks for bringing it to our attention.

    Thanks,
    David