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SN74LVC1G66: Max. on-state switch current question

Denis Varlamov
Prodigy 10 points
Part Number: SN74LVC1G66
Other Parts Discussed in Thread: TS5A3166

Tool/software:

Hello, 

I have a question regarding the use of SN74LVC1G66 analog switch.  We are looking to replace a onsemi part number NC7SZ66M5X that is going obsolete and the SN74LVC1G66 looks very promising.  There is, however, one part of specification that looks off.  The maximum ON-state switch current in the datasheet is specified at +/-50mA. The original onsemi part has a maximum sink current specification of 128mA. 

We are using this part to reset the voltage on a low value capacitor through a resistor.  I wanted to make sure that this lower rating isn't going to be an issue.  I am concerned because we may be exceeding this number but very briefly.  I can provide more details along with some scope captures.  

Thanks,


Denis. 

  • 0
    TI__Mastermind 28968 points

    Hey Denis,

    If you exceed the rating you'll likely damage the device. We do typically have some extra headroom on these specs but it isn't much and I can't recommend exceeding and can't guarantee any performance at that point. 
    Depending on your definition of brief, a brief pulse over may not actually damage the device but that would be a risk you'd have to assume and verify on your end if it's an issue.

    Could you limit the current in any way? Or would a device like TS5A3166 work here? It can handle the current just note that while the RON is about 1ohm but the capacitance would be a little higher (13pF in the 1G66 vs 35.5pF in the 3166). Also comes in the SOT-23 package (TS5A3166DBVR) so would still be a drop-in to the original OnSemi device.

    Let me know if that works

    Thanks!
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 10 points

    Hi Rami,

    Thanks for the quick reply!  The current pulse is on the order of 120mA peak, but it decays to zero in less than 20ns.  We have a 390pF cap being discharged through a 10Ohm resistor.  For what it's worth, the SN74LVC1G66 seems to work just fine and I haven't seen any problems with 30 boards I tested.  

    The TS5A3166 looks good overall.  I am getting some samples of the part.  I am also investigating if the higher capacitance is going to be an issue in our application.  

    The TS5A3166 shows an on-state peak current spec of 400mA for 1ms with less than 10% duty cycle.  Is there a similar peak current spec for the SN74LVC1G66? 

    Thanks,

    Denis. 

  • 0 in reply to Denis Varlamov
    TI__Mastermind 28968 points

     Hey Denis,

    We unfortunately don't have that spec on the 1G66. That being said, seeing your 120mA peak for 20ns, I'll provide a TI answer and a more general engineering answer. From a TI perspective we can't guarantee anything past the datasheet specs and won't be able to definitively say whether the 1G66 can support it or not. However, from my personal engineer perspective 120mA at 20ns is an extremely fast pulse and I would be extremely surprised if the device has issues, which seeing how you're saying you haven't seen issues across 30 boards, it only furthers my confidence in that statement.

    Thanks,
    Rami