596uA input bias current on LM6132?

You aren't providing enough white space in your message for those with less than perfect eyesight

martin

Dead? Are you SURE that Vin < Vdd ??

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

[snip]

Try posting your schematic on a.b.s.e or post a link to your schematic. Can't really tell what your problem is without a schematic.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Okay its in pdf format at

Current > >

:

You don't know how to identify the chip's pins.

Nope! Output is railed trying to force inverting input node to +3.5V asked for by non-inverting input. Where are you measuring? My guess is that inverting input pin is at ~604mV.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

You couldn't get 1/2 ma into that terminal with a sledge hammer.

Check your pinout and use a series resistor to connect the ni input, not a yard of loopy meter leads.

Bypass the supply terminal. Don't apply low impedance input signals when power is not on.

Then decide what you want the ouput to be, within the supply rail's capabilities.

RL

Believe me, I'm not a newbie at this, and I have tried all of those things. I put 5V onto a 10k resistor and the other leg of the resistor has a scope probe. As soon as I touch the resistor to the ni/+ input of the opamp, the voltage drops from 5 to 3 or 4 .Something is WACK here. Am I going crazy? I'm going to try a totally different opamp just to make sure I am still on planet earth

If you're not a newbie, then look at

figure 2. Now you can explain us why it so. If you can't then... I guess you'll have to extend somewhat your definition of newbie :-)

If that current is a pb to you, then you have no choice but to change the opamp model.

--
Thanks,
Fred.

Sounds like the input protection circuitry is kicking in youve probably got 0.6v or so accros the input because the output cant drive the (-) input high enough the feedback network as its limited by the supply.

Colin =^.^=

You need to find a different type of opamp. BTW, this is an example of why it's a good reason for IC manufacturers to include schematics with their chips. NSC doesn't give you a full schematic, but they do describe a special feature of the input stage, see figure 2, as Fred Bartoli suggested. If your source impedance is low enough, you can drive a great deal of current into the + input if it's more than +/-0.6V away from - input. This is an intentional LM6132 feature, meant to increase the slew rate for large input-signal errors, as shown in figure 1. The current to accomplish this comes from the input pin. We're sorry, but you need to choose a different part.

--
 Thanks,
    - Win

Try learning to read first... study the replies to your post, study the schematic, apply MATH, etc ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I thought thats where figure 2 was leading. Thanks for the help everyone!

Thanks Win!

FWIW, the spice model in circuitmaker does not show this behavior, which made things even more confusing. My fault for not reading the datasheet in more detail.

Asa

It's Figure 2 in the data sheet.

You also missed that your configuration, as posted, would rail the OpAmp EVEN if it didn't include cross-couple slew-boost devices.

I mentioned this before. I suspect you don't understand the fundamental rule of OpAmps... while in their linear (fed back) region, the loop forces Vin- EQUAL TO Vin+

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

I'll let you figure this out. Hints:

Your resistors are programming the op amp to act like an amplifier with a voltage gain of 200/33, or a voltage gain of about 6.

You're feeding 3.5 volts to the input.

Sooo the poor op amp is trying to put out _____ volts..

But your Vcc is only ___ volts.

So the output is only rising to ____ volts.

So the voltage fed back thru the 200K resistor is at pin 2, only ____ volts.

So the voltage difference between the input pins is ____ volts.

An op amp is usually designed to be operated with the inputs within ___ microvolts of each other.

If you bias an op-amp at ___ times the expected input difference, the input bias current specs will be ______ .

A kind of Socratic dialogue, I'm pretty sure you can fill in the blanks with a little thought.

There you go...lead 'em by the nose ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

thanks. this isnt how the opamp is actually used in the circuit. this is how i wired it up to isolate the bias current paths.

Jim Thomps>