OPA725: Impedance of IN+ & IN-

Antony Lin

Part Number: OPA725
Other Parts Discussed in Thread: LM358, TS321

Hi,

Customer board is using OPA725 for battery ADC purpose as below. When both V+ & V- are 0V, they found the voltage level of IN+ is around 0.62V. We'd like to ask, when V+ is 0V(not supplied), what is the impedance of IN+ & IN-?

Thanks!

Antony

over 5 years ago

0 Collin Wells over 5 years ago

TI__Guru 62085 points

Hello,

There are internal ESD diodes from each input to the supply pins (V+ / V-) which are conducting when an input voltage is applied while the supply pins are connected to GND.

There are very few modern products without this ESD cell architecture so the best option will be to prevent the input signal from reaching the IN+ pin of the amplifier while the V+/V- pins are connected to GND, or to place a large resistor in series with the IN+ pin so the input current is minimized.

The LM358/324 are some of the few high voltage products that do not include ESD cells to V+.

0 Antony Lin over 5 years ago in reply to Collin Wells

TI__Genius 13480 points

Hi Collin,

THanks for your reply. Do we have any part like LM358/324 (do not include ESD cells to V+) but have the same pin definition and package as OPA725? It seems not, right?

Antony

0 Antony Lin over 5 years ago in reply to Collin Wells

TI__Genius 13480 points

Hi Collin,
THanks for your reply. Do we have any part like LM358/324 (do not include ESD cells to V+) but have the same pin definition and package as OPA725? It seems not, right?
Antony

0 Paul Goedeke over 5 years ago in reply to Antony Lin

TI__Mastermind 30600 points

Hi Antony,

Are you looking for pin-to-pin compatibility on the 8-pin SOIC or the 5-pin DBV package?

-Paul

0 Antony Lin over 5 years ago in reply to Paul Goedeke

TI__Genius 13480 points

Hi Paul,

Customer is asking for SOT-23 package of OPA725.

Antony

0 Paul Goedeke over 5 years ago in reply to Antony Lin

TI__Mastermind 30600 points

Hi Antony,

I wasn't able to find anything in our catalog, sorry. Like Collin said, you're probably better off placing a large series resistance or preventing the signal from getting to the inputs.

-Paul

0 Paul Goedeke over 5 years ago in reply to Paul Goedeke

TI__Mastermind 30600 points

Hi Antony,

I did have one more look in our portfolio and found the TS321 which should work for your application and comes in the SOT-23 package.
www.ti.com/.../samplebuy

Best,
Paul

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OPA725: Impedance of IN+ & IN-