Hello all,

I have a question regarding the MAX4623 (data sheet - http://experimentalistsanonymous.com/diy/Datasheets/MAX4621.pdf) On page 7 of the data sheet, it says:

Always sequence V+ on first, followed by VL[ogic], V-, and
logic inputs.

My question is, does that really matter? What I got from it was make sure you power the device up before sending it a signal.

Matt

Edit: Changed MAC4623 to MAX4623

 

Does it really matter? You read the instructions and ask if they matter?
Think about that for a moment.

 

It also mentions that schottky diodes can be used if the sequence cannot be guaranteed.
Possible cause may be latch up?
Max.

 

I'm just asking because I don't understand why it really would matter. My assumption is yes, it does matter for proper function, but why. I guess thats what my question should have been. Why does it matter? My only thought could be that improper start up can not allow the switching action to take place.

Matt

 

Figure one, internal protection diodes. If the power supply isn't up before the inputs arrive, the input signals will be shunted to either the power supply line or ground. In addition, some of these diodes are inherent to the manufacturing method. Triggering them could latch the chip in a shorted condition.

I call it the start-up sequence. You must account for what starts first when power arrives or you'll find chips locked in an SCR kind of short condition, a clock accumulator starting with a random number, an output pulse coming out before the inputs are even active. This is what reset pins and strobe pins are for, to hold the processing chips idle until they have stable power available.

 

12,

Thanks for the insight. My original thought was that things would be fine and work itself out with the chip, power was power. But now it sounds like race conditions where that's bad news bears.

 

A lot of times they do sort themselves out. Sometimes the first burst of noise out the output is irrelevant. But...If you don't even think about the start sequence, you're going to get caught eventually.

This even happens in analog design. There's a thread running right now about "speakers click during startup". The output stage was ready before the valid information arrived. Well, that's because the final amp is always powered. The information stage should be designed to be silent until valid information is available. No power-up pulses allowed.