LM7171: How to understand the input and output swing

Venkatesh P17

Part Number: LM7171
Other Parts Discussed in Thread: OPA320,

Hi TI Team,

1) How can we understand the input and output swing of this op amp if my supply voltage is other than ±5 or ±15

Because, in datasheet it is mentioned only for ±5 or ±15 supply

2) In datasheet, the output swing is specified positive value as minimum and negative value as maximum, how to understand this? (page no. 5 and 7)

3) If I configured the device with the supply 0V for V- and 12V for V+, What will be my input an output swing?

Thanks,

over 4 years ago

0 Michael Steffes over 4 years ago

Guru 47485 points

Well the I/O swings are really the required headroom to the supplies and do not change with supply settings, here you go - some background info.

https://www.planetanalog.com/author.asp?section_id=3404&doc_id=564967

0 Karan Kotadia over 4 years ago in reply to Michael Steffes

TI__Genius 16725 points

Hi Venkatesh,

Has you issue been resolved by what Michael has provided? If not here are some videos explaining input and output limitations:
training.ti.com/ti-precision-labs-op-amps-input-and-output-limitations-1

Thanks!
-Karan

0 Venkatesh P17 over 4 years ago in reply to Karan Kotadia

Intellectual 895 points

I have seen those op amp videos already. Here my question is I can't understand the I/o swing from the datasheet of this device . And I want to know the I/o swing at(i) 12V single supply (i)12 and -5V dual supply.

Thanks,

0 Venkatesh P17 over 4 years ago in reply to Karan Kotadia

Intellectual 895 points

Hi Karan,

Lets take example of OPA320, its datasheet shows its Vcm will be from (V-)-0.1 to (V+)+0.1 and output swing is 10mV to 45mV from the rail, so from this we could calculate i/o swing directly

But in case of LM7171, the swing mentioned in datasheet is specified only for +/-15V and +/-5V only, that also confusing like negative value as Vmax and Positive value as Vmin for output swing [Page No5 and 7]

With this detail how can I calculate my application specific i/o swing? [Lets take my examples (i) +12V and GND (ii)+12V and -5V]

Please help me to understand this, kindly correct me if I misunderstood

Thanks and Regards,

0 kai klaas69 over 4 years ago in reply to Venkatesh P17

Guru 140200 points

Hi Venkatesh,

I do not see any confusion. The "max" labeling merely comes from the minus.

In your case with the LM7171 the output swing is up to 15V - 12.7V = 2.3V from the rails, for a 1k load.

Kai

0 Michael Steffes over 4 years ago in reply to Venkatesh P17

Guru 47485 points

Ok Venkatesh,

In my parametric databases, the amplifier swings are all set up as headrooms, then you simply use that number to subtract from any supplies to generate the available I/O ranges - here is the LM7171 slice

0 Venkatesh P17 over 4 years ago in reply to Michael Steffes

Intellectual 895 points

Thanks Michael,

This is really good information.
So can I conclude my input swing is from 1.65 to 10.344V and my output swing will be 2.1V to 9.9V if the supply is +12V and GND?

If yes, this resolved my issue,

Thanks and regards,

0 Michael Steffes over 4 years ago in reply to Venkatesh P17

Guru 47485 points

Correct, of course you have to keep your external set up to stay inside those limits.

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LM7171: How to understand the input and output swing