can a comparator pull down to a negative rail

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I would like to use a comparator so that it's output is either open drain (
or collector) or it's pulled down to its negative rail (Let's say -5V for m
y application) I've looked at a couple of comparators, and they have +Vin,  
-Vin, and GND pins... but from looking at the datasheets it doesn't look li
ke they can output their negative rail... am I right about this? if i am, t
hen what's the point of the -Vin input?

I was looking at the LT1011
http://cds.linear.com/docs/en/datasheet/1011afe.pdf

and the LM319
http://www.ti.com/lit/ds/snosbj2a/snosbj2a.pdf

much thanks!

Re: can a comparator pull down to a negative rail

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collector) or it's pulled down to its negative rail (Let's say -5V for my
application) I've looked at a couple of comparators, and they have +Vin, -Vin,
and GND pins... but from looking at the datasheets it doesn't look like they can
output their negative rail... am I right about this? if i am, then what's the
point of the -Vin input?
Quoted text here. Click to load it

You can just connect the "gnd" pin to -5.


--  

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

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Re: can a comparator pull down to a negative rail
On Mon, 6 May 2013 08:26:05 -0700 (PDT), panfilero

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collector) or it's pulled down to its negative rail (Let's say -5V for my
application) I've looked at a couple of comparators, and they have +Vin, -Vin,
and GND pins... but from looking at the datasheets it doesn't look like they can
output their negative rail... am I right about this? if i am, then what's the
point of the -Vin input?
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From p2 of the data sheet...

Supply Voltage (Pin 8 to Pin 4).....................36V
Output to Negative Supply (Pin 7 to Pin 4)
LT1011AC, LT1011C...................................40V
LT1011AI, LT1011I...................................40V
LT1011AM, LT1011M (OBSOLETE)........................50V
Ground to Negative Supply (Pin 1 to Pin 4)..........30V

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In both devices, "GND" is somewhat of a misnomer.  

In the LT1011, it's the potential that the output pulls down to, it
can be set equal to V-

Likewise in the LM319, though with slightly different range bounds.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: can a comparator pull down to a negative rail
On Mon, 06 May 2013 09:16:32 -0700, Jim Thompson wrote:

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What Jim said: "ground" is the reference for the output -- this is handy  
when your analog circuit is running off of differential supplies and your  
digital circuit is referenced to "0V".

Be sure to check the common-mode range of the inputs -- they may not go  
down to the V- rail (or, for that matter, up to the V+ rail).  If you  
need that, you must go looking for a rail-rail input comparator, or you  
must rearrange your input circuit to suit what you plan on using.

--  
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
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Re: can a comparator pull down to a negative rail
On Monday, May 6, 2013 11:37:20 AM UTC-5, Tim Wescott wrote:
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ahh ok, so I could set up my rails at +/-10V and tie my ground to -5V and should
be good to go then... great.

- thanks

Re: can a comparator pull down to a negative rail
Comparators like the LM319 (LM311, ...) would be better called  
"uncommitted transistor output".  Like the TL494 outputs, if you're  
familiar with it.  You can use it for pull-up (OUT to +V, output from  
"GND") or pull-down (normal), or whatever your imagination can come up  
with.

Other ones, made for specific logic levels (LM360, TTL level, comes to  
mind), may be more particular about voltages.  In the latter case, for  
example, obviously you need the analog supplies to be more than the analog  
input voltages (so you could do +/-5V for a [-3, 3V] range, say), and the  
output has to be referenced to whatever it connects to (i.e., +5V and GND,  
or insert-logic-level-here).  Consider: TTL, CMOS, LVDS, ECL...

Tim

--  
Deep Friar: a very philosophical monk.
Website: http://seventransistorlabs.com

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