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TS5A23157-Q1: Input logic high at IN1 for 3.3v system

Kuo Guo
Prodigy 130 points
Part Number: TS5A23157-Q1

Hi TI:

We found the VIH-min is V+*0.7(2.31V) for 3.3V supply.

In fact we used 1.8V in IN1 pin,that can also to select NO to COM.

Can we use 1.8V in IN1 pin to select channel in 3.3V system?

What is the risk of it ?

 

Thanks!!

  • +1
    Guru 317460 points

    The actual switching threshold is likely to be near V+/2. But there is no guarantee, so it is possible, especially at extreme temperatures, that a signal below VIH does not switch high.

  • +1
    TI__Guru 52492 points

    Hi Kuo,

    As Clemens mentioned the actual switching threshold will be closer V+/2 but there are two main reasons why you should stick to the values listed in the datasheet.

    1. This level isn't guaranteed across temperature and operating ranges of the device- so using a lower than spec'd control voltage could cause a switch to not properly switch during operation. 

    2. High Power Consumption + Risk to Damage part. This part (and other parts with a 70% * V+  VIH(min) and 30% * V+ VIL(max)) work best when the control voltage is at V+ or GND as at that point the supply current will be lowest. Supply current will increase dramatically as the control voltage increases from ground and will peak ~V+/2. This extra supply current isn't a concern from an operational point of view if operated where a low signal is between 0V and VIL(max) and a high signal is between VIH(min) and V+ as the increase in supply current will just add to the total power consumed by the system. However when the control voltage is in-between 30% * V+ and 70% * V+ the supply current will increase dramatically and could potentially cause the current from V+ to GND spec to be violated and could damage the part.  For this part in particular it is +/-100mA as the max current from V+ to GND. 

    Please note that when the control voltage is transitioning from a low level to a high level the time spent between 30% and 70% of V+ is typically not long enough to cause any real issues with the device for most applications (if there is a very slow rise and fall time due to an RC or something similar on this pin it could also cause similar issues). The real issue is holding a control voltage between 30% and 70% of V+ as this will increase current consumption to the point of possible damage.

    If you have any other questions please let me know!

    Best,

    Parker Dodson