Interpreting specs
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Chip Amps Amplifiers based on integrated circuits

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
 22nd March 2014, 01:20 PM #1 akis   diyAudio Member   Join Date: Jul 2008 Interpreting specs I am looking at various datasheets and was trying to understand the terminology and the implications around "input common mode range" or similarly worded terms. For example I am looking at the TLE2072. In the absolute maximum ratings it says: Differential input voltage range = Vcc+ to Vcc- (note: Differential voltages are at the noninverting input with respect to the inverting input). How am I meant to interpret this ? I can see two options. Option A: You are free to apply any voltage to the Vin+ and Vin- as long as it is between Vcc+ and Vcc-. Option B: You can apply any voltage to Vin+ and Vin- as long as Vcc- <= (Vin+ - Vin-) <= Vcc+ Option A practically means do what you like with the inputs unless you have some voltages exceeding your rails somehow. Option B is way more loose and restrictive at the same time. It implies I can apply any voltage I like to the inputs, even if I exceed the rails, as long as the difference between the two inputs is between Vcc+ and Vcc-. As a practical example of the implication of Option B, if I had a +/- 15V rails, I would be able to apply 50V to Vin+ and 45V to Vin-, since the difference is only +5V. I would also be able to apply 10V to Vin+ and -25V to Vin-, since the difference is only -15V, within the range. Further down the datasheet we read the "recommended ranges". There for example it says that the voltages applied at the inputs must stay within -11.9V and 15V for a +/- 15V rails. I interpet this to mean "do what you like as long as any of the two inputs do not fall outside of those two values". But in that case I could be violating the Option B above, because the differential input may then get outside the limits. Suffice to say that on the simulator I have not managed to reproduce weird behaviours , eg phase reversals at the output when input voltages fall outside the recommended ranges. I might try it on breadboard though. Could someone please explain this to me ?
DUG
diyAudio Member

Join Date: Jan 2003
Quote:
 Originally Posted by akis I am looking at various datasheets and was trying to understand the terminology and the implications around "input common mode range" or similarly worded terms. For example I am looking at the TLE2072. In the absolute maximum ratings it says: Differential input voltage range = Vcc+ to Vcc- (note: Differential voltages are at the noninverting input with respect to the inverting input). How am I meant to interpret this ? I can see two options. Option A: You are free to apply any voltage to the Vin+ and Vin- as long as it is between Vcc+ and Vcc-. Option B: You can apply any voltage to Vin+ and Vin- as long as Vcc- <= (Vin+ - Vin-) <= Vcc+ Option A practically means do what you like with the inputs unless you have some voltages exceeding your rails somehow. Option B is way more loose and restrictive at the same time. It implies I can apply any voltage I like to the inputs, even if I exceed the rails, as long as the difference between the two inputs is between Vcc+ and Vcc-. As a practical example of the implication of Option B, if I had a +/- 15V rails, I would be able to apply 50V to Vin+ and 45V to Vin-, since the difference is only +5V. I would also be able to apply 10V to Vin+ and -25V to Vin-, since the difference is only -15V, within the range. Further down the datasheet we read the "recommended ranges". There for example it says that the voltages applied at the inputs must stay within -11.9V and 15V for a +/- 15V rails. I interpet this to mean "do what you like as long as any of the two inputs do not fall outside of those two values". But in that case I could be violating the Option B above, because the differential input may then get outside the limits. Suffice to say that on the simulator I have not managed to reproduce weird behaviours , eg phase reversals at the output when input voltages fall outside the recommended ranges. I might try it on breadboard though. Could someone please explain this to me ?
There are absolute maximums and when these are exceed the IC may be damaged.

From data sheet:

absolute maximum ratings over operating free-air temperature range (unless otherwise noted)†
Supply voltage, VCC+ (see Note 1) . . . . . . . 19 V
Supply voltage, VCC− (see Note 1) . . . . . . −19 V
Differential input voltage range, VID (see Note 2) . . . . . VCC+ to VCC−
Input voltage range, VI (any input) . . . . VCC+ to VCC−
Input current, II (each input) . . . . . . . . . . . ±1 mA
Output current, IO (each output) . . . . . . . ±80 mA
Total current into VCC+ . . . . . . . . . . . . . . . . 160 mA
Total current out of VCC− . . . . . . . . . . . . . 160 mA

The other term you have seen is "common mode input voltage range". This is for normal operation.

As for "Differential input voltage range", in a normal feedback operational amplifier circuit (that does not enter into output clipping) you will not have to worry about this as the differential input is 0V.

If you were to use it as a comparator then this number is important as some op-amps have diode clamping (protection) on the inputs.

Not all op-amps exhibit phase reversal and I am not knowledgeable in simulations to say whether or not the sim would demonstrate this in an op-amp that has this characteristic.

Hope that helps.
__________________
Doug We are all learning...we can all help
"You can't stop the signal, Mal. Everything goes somewhere..."

peufeu
diyAudio Member

Join Date: Mar 2001
Location: Lyon, France
In fact the absolute maximum ratings say :

Quote:
 Differential input voltage range, VID (see Note 2) : VCC + to VCC – Input voltage range, VI (any input) : VCC + to VCC – Input current, II (each input) : ± 1 mA
The second line makes your option B impossible. The opamp does not have specific circuits for correctly handling voltage over the rails anyway.

So it becomes :

Option A: You are free to apply any voltage to the Vin+ and Vin- as long as it is between Vcc+ and Vcc-.
New Option B: You can apply any voltage to Vin+ and Vin- as long as Vcc- <= (Vin+ - Vin-) <= Vcc+ and both inputs are between Vcc+ and Vcc-

Option B is entirely contained in option A then.

Now, in normal use, even if the output clips or is shorted to ground, the differential voltage will not exceed option B. It could exceed it if the output is shorted to one of the supplies, or if the opamp is used as a comparator, which is a bad idea anyway.

So it doesn't matter a lot...

> Further down the datasheet we read the "recommended ranges".
> There for example it says that the voltages applied at the inputs must stay within
> -11.9V and 15V for a +/- 15V rails.

"Absolute maximum ratings" means that the device is not guaranteed to survive above those ratings.

"recommended ranges" and "operating conditions" is the range where the device will operate to specification.

Between the two, the device will survuve, but it will misbehave, you can get phase inversion, etc.

Many opamp models only include stuff like frequency response, noise, and offset, not what happens outside the normal operating range, since that would mean simulating the complete opamp circuit, with all the details, which the manufacturer is probably not going to share. So it is unlikely this will show up in simulations.

Last edited by peufeu; 22nd March 2014 at 01:55 PM.

 22nd March 2014, 02:17 PM #4 akis   diyAudio Member   Join Date: Jul 2008 AH OK somehow I completely missed the "Input Voltage Range" which indeed restricts the inputs to within the rails. Still that leaves me with a problem however, "New Option B" is limiting the voltage between the two inputs to half the supply. For example if Vin- is -10V and Vin+ is +10V, there we have a problem as the differential input now is 20V, which is 5V outside the limits. And these were the absolute maximum limits, which means we will likely destroy the op-amp ?
 22nd March 2014, 02:31 PM #5 DUG   diyAudio Member   Join Date: Jan 2003 Location: mississauga ontario canada "if Vin- is -10V and Vin+ is +10V," This would not happen in a linear amplifier mode but would happen if you used the op-amp as a comparator...the output would be as close to the +ve rail as it could go. I am not sure why you would want this in your audio chain. But to your question: If your supply was +/- 5V then you would need a new op-amp. If your supply was +/- 15V then the output would be very close to +15V. The op-amp would not be destroyed. Got to go do some exercising. Bye for now. __________________ Doug We are all learning...we can all help "You can't stop the signal, Mal. Everything goes somewhere..."
 23rd March 2014, 07:55 PM #6 akis   diyAudio Member   Join Date: Jul 2008 Thanks to all who replied. I ran some tests and indeed I observed phase reversal when the voltage at any of the inputs was outside the recommended range.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Holton Precision Audio         CSS         Dx Classic Amplifiers         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post jimjimmyjimjim Multi-Way 5 26th September 2013 07:52 PM fringy75 Full Range 6 19th April 2013 06:46 PM GeeVee Solid State 16 10th January 2008 12:05 PM getafix Multi-Way 6 12th October 2003 12:52 AM Super Everything Else 39 22nd September 2001 03:53 PM

 New To Site? Need Help?

All times are GMT. The time now is 04:08 PM.