Help increasing hysteresis of voltage detector

Thread Starter

GammaRay

Joined Jun 11, 2012
17
I built a circuit using the Seiko precision voltage detector p/n S80830CLA432, cmos version. The voltage detector reliably turns a mosfet on at 3.1v and off at 3.0v. However, I want to increase the hysteresis to at least .5 - 1 volt range. Already tried what I thought might work, so I'm turning to this forum for suggestions. Thanks in advance.

http://datasheet.sii-ic.com/en/voltage_detector/S808xxC_E.pdf
 
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#12

Joined Nov 30, 2010
18,167
You are going to have to make an external circuit to change the hysteresis. I don't know what you are trying to do so I can't imagine the circuit for you.
 

#12

Joined Nov 30, 2010
18,167
That's the basic shape of it if you have the insight to recognize R1 is in series with the voltage being detected, and the chip mentioned (CMOS version) has a push-pull output, so the pull-up resistor isn't necessary.

So much of interfacing this chip into your circuit depends on the details.
 

Thread Starter

GammaRay

Joined Jun 11, 2012
17
My application requires a voltage controlled switch turning on a mosfet at about 3.5v and off at about 2.5v. I realize there are many ways to accomplish this, but my primary goal is to find a method that has extremely/ultra low current consumption. I selected the S80830CLA432 voltage detector because it uses only 0.8uA current. The circuit works great in all respects except for the very narrow hysteresis. I added postive feedback and indeed it does increase hysteresis, the bad news (for my application) is that it also noticeably increases current consumption.
 

#12

Joined Nov 30, 2010
18,167
Well, there you have it. To do this in one stage requires multi-megohm resistors, and then you have to add capacitors to lower the noise sensitivity, and that causes time delays (which probably won't hurt anything), and you still can't do it in less than a microamp unless you are some kind of mad scientist brilliant.

There are a couple of those working here, but I still don't think it can be done in a couple of microamps.

Continuing: The fact that these are 3 legged devices and all of their operating current and load current come into play, you will have to custom make the circuit for each one. I'm thinking about using (2) of these devices or maybe a CMOS op-amp. IMHO, you can't get there from here.
 
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Thread Starter

GammaRay

Joined Jun 11, 2012
17
Mr. Chips. I revisited your positive feedback suggestion. Initially I found that adding R2 does increases hysteresis but at the expense of greatly increasing current consumption. Through a little tinkering I found that adding a 2nd resistor to the ground supply side of the voltage detector causes the current consumption to return to its normal rate. It's a balancing act, too much or too little resistance on either of the two resistors causes the current consumption to go way up, but a correct ratio seems to work well. Thanks for pointing me in the right direction. This is a good forum, glad to be a member.
 
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