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OPA2333: Keeps shorting out

June 13, 2017, 4:59 am
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Part Number:OPA2333

Hello.

Im making a temperature measuring project. We are using an OPA2333 and it keeps shorting out. We have shorted 2 now. They both work for about 30min and then the power supply goes into current limiter.

This is our circuit where the PT100 is set to the maximum resistance we want. Vss = +5v. Vcc = -5v.

The biggest annoyance is no one here can see why its shorting out (nothing seems wrong with out pcb). So i thought maybe some of you could explain why?

We have one OPA2333 left, and would like to solve this problem before we try it.

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LMP91000: LMP91000_Wrong Schematic in Datasheet

June 13, 2017, 9:41 am
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Part Number:LMP91000

I have an LMP91000, and I want to communicate with it using I2C communication. In the datasheet, on page 26 Figure 33, it says that SDA of microcontroller should be connected to SCL fo the sensor, and SCL of microcontroller to SDA of the sensor. Is it a typo, or I should indeed connect it as such? 

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OPA379: OPA379

June 14, 2017, 1:50 am
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Part Number:OPA379

We are interested to use either OPA379, OPA348 or OPA314 in a battery operated device

Is there any information with respect to distortion 2nd, 3rd harmonics, THD and IM and how to minimize it.

We are operating these devices at frequencies up to 400KHz

Thanks for the help

 

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LMV771: Specs and Distribution, offset voltage and bias current

June 14, 2017, 7:06 am
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Part Number:LMV771

Dear Specialists,

My customer is considering LMV771.
He has question about deviation of some specs.

Could you please advise?

---questions---

Acccording to the Lecture Manual of TI Precision Labs of Op Amps(P.5),
typ value of Offset Voltage and TCVos is within +/- one sigma.
The device is OPA350.

Could you please see attached file.

(1)Is the bias current specification ± sigma like the offset voltage?

In case of LMV771, Vos(typ) is 0.3V, TCVos(typ) is 0.3V,Input offset current(typ) is -0.1pA and Input offset current is 0.004pA,
these specs are ± sigma. Are these correct?

(2)Which is LMV771, CMOS or Bipolar?

A post of E2E listed below says, calucration to total Vos is different from CMOS and Bipolar.

CMOS is root mean square, Bipolar is SUM.

(3)When I also consider bias bias current, could I think same as (2).

---

I appreciate your great help in advance.

Best regards,
Shinichi

(Please visit the site to view this file)

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Constant Voltage source Design

June 14, 2017, 9:47 am
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Hi,

I need to design a constant voltage source of .7V output. The requirement is like for testing I will be injecting a voltage of "0 to 1.2V-100ma" at the output of my constant voltage source.

At that time also the output of my voltage source should be  constant.What I understood is my constant voltage source should have a capacity to sink 100ma.

May I know how to approach this Problem.

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OPA350: Unity gain OPA350 oscillates when driving 10 ft. Coax Cable

June 14, 2017, 11:02 am
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Part Number:OPA350

Hi,

A unity gain OPA350 is driving a 10 ft RG-58 cable terminated in an AC-Coupled 50 Ohm input spectrum analyzer.

A circuit schematic is pasted below. The OPA350 is powered by a +5V single supply. ALA_MID is at 2.5V.

The two inputs that are summed are outputs of a high-gain 200 kHz and 300 kHz band-pass filter.

In addition to the desired signals, the spectrum analyzer is showing an oscillation at 109-112 kHz of significant amplitude.

When the output is connected to a nearby scope (2 ft of coax), there is no oscillation.

Another clue is that when the inputs to the summing amp are reduced, there is no oscillation.

Placing 100 ohms in series with the OPA350 output eliminated to oscillation, but 50 ohms had no effect.

Any insights would be appreciated.

Thanks

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TLE2062: Output Impedance when both Power Rails are Grounded

June 14, 2017, 1:24 pm
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Part Number:TLE2062

My customer is asking the following about the TLE2062:

I am using the TLE2062AMDREP in an application where, in certain circumstances, I ground the VCC  and VCC– rails in order to guarantee that the output is driven to zero. I had made the assumption that when I do this the output pin goes high impedance, but lab tests have shown that is not the case. Can you provide any more information about the impedance of the output with respect to the rails when there is no voltage applied?

I am wondering if maybe the impedance path I am seeing has to do with any ESD protection diodes. I am not sure if those are shown in the equivalent schematic in the datasheet (D1 and D2), or if those were omitted for clarity.

I cannot tell from looking at the diagram where the current path would be other than the feedback circuits that would be used in the circuit. Can you go into detail to answer the customer’s questions.

Thanks for your help with this!

Richard Elmquist

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OPA356: Unexpected output

June 14, 2017, 3:15 pm
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Part Number:OPA356

Hi,

I've got a weird output when feeding an oscillating signal into the OPA-356, hoped somebody could clear it up for me.

Please see the schematic attached to this post.

I've got a 1KHz signal (Vmin = -0.31V, Vmax =  4.08V). I'm using a voltage divider to lower the altitude of the signal (to Vmin = -0.20V, Vmax =  2.43V), and then I'm feeding this signal into the op amp, OPA-356. I've set the gain to 1.22 (using 2.2k and 10k resistors), so theoretically the output should be between about 0V and about 3V. However, I'm getting the oscillations between 0V and 7V. I attached the oscilloscope readings to the post.

Can somebody please explain me why this is happening? I assume that the problem is with the fact that I'm feeding an oscillating signal into the op amp, cause the op amp is amplifying straight 0V or 2.4V signals perfectly. The purpose of all this is to get the output between about 0 and 3V. How can achieve that? And what am I doing wrong? 

Many thanks in advance.

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LOG112: High reliability requirement

June 14, 2017, 4:33 pm
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Part Number:LOG112

LOG112AIDR  is Catalog (commercial) Part, we are looking for the automotive or Mill-Spec grade alternative part. Also Does TI offer any additional screening to increase the long term reliability?  Our requirement is 25 years life time of the parts at 45 C surrounding temp.

  

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Instrumentation amplifier input offset

June 15, 2017, 9:15 am
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Hi

I m working on an aplicaiton which measure low amplitute differential signals ( 500 nV-10 uV) from a low impedance source.

Could anyone tell me if the imput voltage offset of the amplifier (1 uv in the best case) is a hard limitation that canot be surpassed?

many thanks in advance

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LMH730033: What are the connectors on this eval board

June 16, 2017, 4:44 am
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Part Number:LMH730033

Hi

There is no bom with this eval board and input output connectors appear to be sma size but with smaller diameter pins.

Rather than guess would it be possible to know the connector type for this eval board.

Peter

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TINA/Spice/LMV861: LMV861 amplifier at 17 MHz frequency

June 18, 2017, 3:20 am
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Part Number:LMV861

Tool/software:TINA-TI or Spice Models

Dear sir, please answer

I need a buffer for  signal matching with generator (please, see attach). Generator: Frequency = 17 MHz,  Um=0.5V 

I made circuit in TINA-TI, but oscilloscope doesn't  work (please see picture in Word). The multimeter seems to be working.

I need Ku=2 for amplifier. Generator's load must be 10k & 10 pF.

Will this circuit work?

TIA

Sincerely

Vladimir Naumenkov 

(Please visit the site to view this file)(Please visit the site to view this file)(Please visit the site to view this file)

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Calculating of the CMRR of a voltage controlled current source

June 18, 2017, 4:34 am
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Hello

I want to determine the CMRR of a VCCS.

I found some useful about the CMRR in the blow topic:

https://e2e.ti.com/blogs_/b/analogwire/archive/2013/11/06/what-you-need-to-know-about-cmrr-instrumentation-amplifier-topologies-part-3

a simple voltage to current converter is like below:

but usually there is some mismatch between the resistors so we can add a unity gain buffer like below to improve the CMRR:

my question:

what happen to the CMRR if I want to modify the above circuit like below:

 

anyhow we have an unity gain at the Vx point but I have concerned about  the output impedance seen by this point.

what should I do if I don't want to remove the modified stage? is it nessecery to modify the Rx?

How should I calculate the CMRR of the VCCS?

 

Regards

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OPA4277: Current consumption calculation

June 19, 2017, 2:59 am
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Part Number:OPA4277

Dear Team,

Can you please share me how to calculate current consumption information of TXB0108PWR.

Regards,

Prasanna G

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Best Instrumentation Amplifier for high impedance source

June 19, 2017, 2:46 pm
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I need to design a couple  of differential input pre- amplifiers for a high impedance electrochemistry potential type of measurement. The target impedances of my circuitry are 10 megOhm and 100 megOhm or greater (both).. the differential signal range is about 1 volt.. The frequency of the  signals is DC to 4 Khz.  This is a battery operated system with 20v battery.   The output is going to a National instruments DAQ with 24 bit sampling at 10Khz (1 meg Ohm input impedance).  Other features I would like are over-voltage protection, and ESD input protection,, obviously I will need to filter RFI .

Which IA should I choose and any recommendations on the circuitry would be nice. This is a new realm for me and I am not experienced with the tricks of dealing with high impedance signals.  

Thanks, Robert

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ISO122: Operating Junction temp

June 19, 2017, 8:49 pm
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Part Number:ISO122

Hi team,

 

In ISO122, it spec max junction temp as 150C and storage temp as -40 ~ 125C. Is this correct?

I supposed the max junction temp should be less than or equal to max storage temp?

 

If the max junction temp is 125C, could we update the ISO122 datasheet to truly reflect it?

 

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OPA827: OPA 827

June 19, 2017, 11:42 pm
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Part Number:OPA827

Hello

I have a general question on JFET input op amps. 

What are the main disadvantages or limitations to JFET opamps for precision applications?

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OPA333: OPA333

June 20, 2017, 1:28 am
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Part Number:OPA333

Hi，engineers!

I configure OPA333 voltage follower, providing  reference voltage for two ADCs (AD7768)。But  I found that however the feedback RC or ouput compensation resistor(R259) tuned, the OPA333 is in oscillation，the feedback resistor R260 tuned from 110KOhm to 1MOhm, the amplitude of oscillation can be attenuated, but could not be suppressed completely .I am appreciated for your ideas.

 

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TLE2022A-Q1: Current consumption

June 20, 2017, 3:48 am
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LM321: Why my LM321 output can't approach GND?

June 20, 2017, 9:01 pm
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Part Number:LM321

Dears,

I used LM321 to design a difference input amplifying circuit, when the input is about 0V, but the output can't received the datasheet rating, When the input oV~2.4mV,the output is 40mV, but the datasheet is 20mV. whether is relation with the PCB layout or other design parameters? Could you kindly give me some sugeestion? Thanks!

My SCH as below,

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