Why is SHDN pulled up in MintyBoost and not in MAX756 specs?

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xinsight
 
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Joined: Wed Jul 25, 2007 11:14 am

Why is SHDN pulled up in MintyBoost and not in MAX756 specs?

Post by xinsight »

great project and documentation!

I've put the circuit together on a prototype board, and i'm getting 7.6volts.

I'm trying to understand how it works in order to debug.

I downloaded n the MAX756 spec sheet, and their "typical operating circuit" has pin 1 (SHDN) floating and Pin 5 (LB1) is at +3V.

The MintyBoost schematic (without low battery indicator) has pin 1 (SHDN) at +3V and pin 5 (LB1) floating.

Anyone know why this is? Will I damage the chip if SHDN and LB1 are both pulled high?

adafruit
 
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Post by adafruit »

LBI is just the low battery indicator
i dont think they leave SHDN floating, probablt they just say "to microcontroller" or something
you should copy the mintyboost schematic as it is tested correct.

xinsight
 
Posts: 5
Joined: Wed Jul 25, 2007 11:14 am

Post by xinsight »

yes, that makes sense to just ignore the two LBO/I pins if I'm not using the low battery indicator.

And i finally just got it that SHDN means "shutdown". And since it has a negation line over it in the specs, going low means shutdown. So, it needs to be high.

btw, I fixed my problem with getting 7.6v out instead of 5v. pin 3 (reference voltage output) wasn't actually grounded. whoops. fixed that and it works great.

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