TLV172: Input impedance and input bias current

Hirotaka Matsumoto

Part Number: TLV172
Other Parts Discussed in Thread: TLV2172, OPA172, TINA-TI, OPA2172, OPA191

Hi all

Would you mind if we ask TLV172?
Could you refer to the file "20171217_TLV2172.pdf"?

2705.20171217_TLV2172.pdf
20171218_TLV172.TSC

Our customer could confirm this using actual circuit.

In case of voltage follower, there is no problem.

We need this reply as soon as possible.
We appreciate your help always.

Kind regards,

Hirotaka Matsumoto

over 8 years ago

0 Ron Michallick over 8 years ago

TI__Guru**** 174826 points

Hirotaka-san,

This device has a VID (IN+ - IN-) voltage limitation.

Input current will flow, if inputs are at different voltages.

0 Hirotaka Matsumoto over 8 years ago in reply to Ron Michallick

Guru 27605 points

Ron san

Thank you for your reply!

TINA-TI simulation, there is no voltage drop using OPA172.
These devices also have a VID (IN+ - IN-) voltage limitation.
As your recognition, does it occur voltage drop the same as TLV172?
Our customer guess that TLV172's transient current response is inferior to OPA172.

And then "Input current will flow, if inputs are at different voltages."
->It means that if inputs difference are more than ±0.5V(input protection diode's VF), input current will flow, right?

Kind regards,

Hirotaka Matsumoto

0 Ron Michallick over 8 years ago in reply to Hirotaka Matsumoto

TI__Guru**** 174826 points

Hirotaka-san,

OPAx172 and TLVx172 both have input to input diodes. Yes a difference over 0.5V will cause input flow.

Here is input current measurements (OPA2172) where one input is held at 2V (red current) while the other input (white current) is swept from 0V to 4V

0 Ron Michallick over 8 years ago in reply to Ron Michallick

TI__Guru**** 174826 points

Hirotaka-san,

For input current modeling the TLVx172 model is superior to OPAx172 model.

0 Ron Michallick over 8 years ago in reply to Ron Michallick

TI__Guru**** 174826 points

Hirotaka-san,

OPA191 is not my device, however section "8.3.1 Input Protection Circuitry" in data sheet suggests no diodes between inputs at all.
Therefore, it will work better in this application.

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TLV172: Input impedance and input bias current