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SN74LVC1G123: Is there a version with inverted output?

user6067694
Prodigy 80 points
Part Number: SN74LVC1G123
Other Parts Discussed in Thread: BQ25121A,

Hi,

I have an application where an external switch is continuously pressed when in operation and released when not. It is powered by a battery which in turn is controlled by a BQ25121A. Unfortunately, to switch the BQ25121A active, a high signal has to change to low and then to high again. Since my external switch only manages to go from high to low, I need to have a logic element in between which pulls the line high after switching on the BW25121A. Switching it off is then done over I2C with a microcontroller.

If I use the SN74LVC1G123 to create the temporary change in voltage, I only can switch from low to high and back to low again. It is maddening but I cannot find an equivalent part which switches in an inverted way. Why does TI insist on accepting only high-low-high in their battery controller when at the same time all logic parts only switch low-high-low? And please do not tell me to add an inverter. The multivibrator should be doing the right thing from the get-go.

Regards, Peter

  • +1
    Guru 317360 points

    The /MR input is designed to be connected to a push button, not to a logic circuit. Active-low is is the most common polarity for this.

    The output polarity of the 74xx123 is active high for historical reasons, und must stay this way for backwards compatibility. There is no market large enough for a separate active-low model, so your only choice is to add an inverter.

  • 0 in reply to Clemens Ladisch
    Prodigy 80 points

    Dear Clemens, thank you for your fast response! I was afraid that there is no better solution. Other battery controllers do indeed work with a low-high-low signal, for example the ST STBC02. However, it only tolerates 16V and gets fried by non-compliant USB chargers which output 20V without enumeration. That is why I settled on the BQ25121A. And I cannot go with the pushbutton signal by itself.