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OPA3S328: Question on ton/toff

Sunny Qin
Expert 4890 points
Part Number: OPA3S328
Other Parts Discussed in Thread: TMUX1308

Hi team,

Why ton/toff of OPA3S328`s internal switch is so slow:

It need 1~2 uS, but for general MUX device, even low cost one, like TMUX1308, it only need tens of nS for ton/toff:

So I am wonder if OPA3S328 can suit for some fast switch circuit, like 1MHz switch enable signal to make the internal switch on and off?

Thanks.

Regards, Sunny

  • 0
    TI__Guru 52426 points

    Hello Sunny,

    The integrated switches on the OPA3S328 are intended for programmable gain amplifier or programmable gain transimpedance amplifier applications. 

    As you have mentioned, there are differences between the TMUX1308 and the OPA3S328 switch turn on and turn off behavior.  The TMUX1308 feature break-before-make switching.  In a standard multiplexer application, this feature prevents two inputs from connecting (or shorting) while the multiplexer is switching.  In contrast, the internal switches of the OPA3S328 feature the opposite make-before-brake switching.  In the OPA3S328, the previous switch does not change to high-impedance state until the new switch is closed, with a typical delay where both switches are closed for a short period of time.  This is done to avoid the amplifier going into an open-loop or open feedback state while switching gains on a programmable gain amplifier application.  The OPA3S328 datasheet discuss the switch behavior on section 7.3.3.  

    If the application above requires fast-switching between two signals in less than 2µs with break-before-make switching, as featured on the TMUX1308 multiplexer, the OPA3S328 internal switches are not suited for this system, since this is different criteria than the intended OPA3S328 application.

    Thank you and Regards,

    Luis