Maximum REXT and CEXT values that can be used with 74LVC1G123 ?

Jitender Misra

We want to use 74LVC1G123 to derive a High going pulse of width close to ten seconds.

Going by the Calculations in the datasheet , there is no limit provided on the values of REXT and CEXT . Per my requirement i need to use either

1. 1M ohm resistor with a 10uF capacitor OR

2. 10M ohm resistor with a 1uF capacitor

My question is that whether these kind of REXT/CEXT values can be used with 74LVC1G123 and in fact whether it is possible to acheive this value of pulse width using 74LVC1G123

Regards

Jitender

over 7 years ago

0 Clemens Ladisch over 7 years ago

Guru 243790 points

Both would work.

You have to figure out which components have better tolerances, or are less affected by external noise, or have lower leakage, or are cheaper.

0 Jitender Misra over 7 years ago in reply to Clemens Ladisch

Prodigy 150 points

Thanks Clemens, but what one part of my question was whether 10 second type of timing pulses can actually be derived using 74LVC1G123 ? since in datasheet of 74LVC1G123 there are no graphs which show timing values in the range of greater than 1 second and datasheet specifically does not set any limit on the highest allowed values of REXT and CEXT!

0 Clemens Ladisch over 7 years ago in reply to Jitender Misra

Guru 243790 points

There is no upper limit on REXT or CEXT.

But if the capacitor's leakage current is as high as the charging current, or if the resistor's resistance is higher than that of some random dirt on the PCB, your circuit will not behave as you expect it to.

Logic

Logic forum

Maximum REXT and CEXT values that can be used with 74LVC1G123 ?