OPA172: OPA172 – Internal series resistor 2.5k ohm in each IN-/IN+

GaryC

Part Number: OPA172
Other Parts Discussed in Thread: LM324

May I know the OPA172 has a internal series resistor 2.5k ohm in each IN- and IN+?

We had try to short IN- to ground (base on figure 46). We find OPA172 has higher short current than LM324. Do you have any suggest why they have this difference? Thanks

BR,

Gary

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi Gary,

GaryC said:
We had try to short IN- to ground (base on figure 46).

I have no idea what you mean. Can you elaborate on this, please?

Kai

0 Ron Michallick over 4 years ago

TI__Guru**** 157336 points

Gary,

The answer to why OPA172 input pin current is high should be clear from the drawing you provided. Yes there are resistors inside.

The answer to why LM324 input pin current is zero should be clear from the application note. There are only diodes from IN to VS-, no diodes to VS+, no diode to other input

Design Guidelines for Devices with LM324/LM358 Cores

+1 Ron Michallick over 4 years ago in reply to Ron Michallick

TI__Guru**** 157336 points

Gary, the resistor inside may be less than 2.5k. Here is a input current versus input difference voltage chart.

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OPA172: OPA172 – Internal series resistor 2.5k ohm in each IN-/IN+