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TINA/Spice/OPA197: Difficulty with convergence issue in modeling + in stability analysis

December 21, 2017, 12:13 pm
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Part Number:OPA197

Tool/software:TINA-TI or Spice Models

Hello,

I'm in the process of trying to model a unity gain follower using the OPA197 with various load capacitances but am running into some issues with TINA. Note that I'm a hobbyist, not an EE, so I apologize in advance for any dumb questions!

First of all - in the attached file "opa197 unity gain", which is just the simple unity gain follower circuit, I am getting the error "Convergence problem. Check the analysis parameters".  I'm not sure exactly why its having difficulty with the circuit as it seems pretty basic...

Secondly, in the attached file "opa197 unity gain stability analysis", I've attempted to follow the instructions in this tutorial in order to get look at the phase margin for the circuit (). However, The curves that are being generated look very strange, and the baseline open loop gain seems to start from -50db... I'm not certain as to why the curves are coming out wrong (see attached image). Can anyone give me a hand?

Thanks so much in advance..

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Op Amp with a Common-Mode Voltage that can go 200~300 mV below the Negative Supply

December 22, 2017, 8:50 am
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Hello team,

I am looking for an Op Amp where the VCM can go somewhere in between 200 and 300 mV below the Negative Voltage Supply, and it should apply over a temperature range -40°C to 85°C

Other relevant specs: BW can be as low as 1 MHz, Supply Voltage is 3.3 V, Offset Voltage < 1 mV, RRIO.

I found OPA342 at 300 mV (as well as a few others at 200 mV), but they only spec the VCM for TA = 25°C

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Medical current source

December 23, 2017, 10:32 am
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I want to make a device for medical purposes.

I need a PWM on the frequency of 100kHz currents within ± 0.05mA ~ 2mA with the ability to adjust it using a DAC.

Electrodes are connected to the ear of the patient, I tried to create a skin model:

I have three schemes but they all work not as I would like.
I need to get the best possible signal shape without overshooting and ringing.
What can I change to get the best result? Maybe I should use other op-amp?

1)

2)

3)

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LMC6482: Unable to get 700mA constant current

December 24, 2017, 2:39 am
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Part Number:LMC6482

Hi, I'm designing a Bio-Impedance Analyzer for which I need a current of 700mA at 50kHz and 100kHz. I have implemented the Howland current source using LMC6482, but I'm unable to get a constant current at the output. Is there a resistance combination that can get the desired value or is there any other issue? 

This is my circuit 

 

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LMP91200: About some design questions...

December 25, 2017, 12:02 am
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Part Number:LMP91200

Dear Sirs,

Here are some questions from my customer. Attached is their schematics.

Please help to input your comments.

Thanks.

1. while the ph probe did not attached, the readout ph value will be 0 or 14 sometimes.

what voltage should be for Vout/Vocm while no ph probe attached?

The AVref=5V in schematics.

2. While measuring ph of water in vats, the Vout/Vocm=0V, that means ph value is 14. If customer take same water of vats and put in smaller container, the ph we get is 7.2

Is there anything wrong with it or affect by something? 

Since there are old/new version of LMP91200.(difference is removed temperature sensor function), does it cause by this change? 

3. Is there any recommended additional schematics for ph probe or LMP91200 to enhance signal or reduce noise?

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OPA615: OPA615 DC restoration and video amplification

December 25, 2017, 10:01 pm
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Part Number:OPA615

Hi ! I am currently working with a PAL based composite video. The video has 0.5-1V peak to peak amplitude and 15 MHZ bandwidth. I want DC restoration and a gain of +2V/V. How can it be done with OPA615 ?

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TINA/Spice/OPA615: Output dropout, peak-holding circuit simulation

December 25, 2017, 11:06 pm
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Part Number:OPA615

Tool/software:TINA-TI or Spice Models

Hi all, this inquiry is from the deyisupport (Chinese version of E2E community):

Using the OPA6165 to do the peak-holding, the schematic uses the figure 48 in the datasheet without the negative peak-holding as the attachment show. When input a 60ns pulse, the output voltage has a a few hundreds of mV dropout at the falling edge of the input pulse. Please help with the question, thanks.

(Please visit the site to view this file)

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Pre-amplifier is needed for ADS1198 front-end in EEG application?

December 26, 2017, 12:51 am
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Hello everybody,

I intend to use a ADS1198 front-end for my EEG acquisition application. I have read the datasheet that the ADS1198 has a maximum gain up to 12. However the EEG potential is typically ranges from 10uV to 100uV. So, in order to meet the ADC input requirement, should I amplify the signal 100 times before feeding it into the ADS1198?

Please give me an advise about this confused thing.

Thank you in advances!

Hau Nguyen.

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TL441: AC component lost after passing logarithmic amplifier

December 27, 2017, 8:30 pm
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Part Number:TL441

Hi,

I am trying to build a lock-in amplifier. This amplifier needs to operate at 3.58MHz, sine wave. I use TL441 as the logarithmic amplifier, TL592B as the linear amplifier, then the reference signal and the test signal input into the multiplier AD734. Because the tested signal is too low, I have to use two levels of amplifiers. However, after passing through TL441, the AC component in the tested signal was lost. Can any TI Specialist or any friend in E2E community provide any advice on solving this issue? Or TL441 cannot be applied to this range of frequency.

Thank you in advance,

A TI user

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INA826: Instrumention Amplifier gets damaged

December 28, 2017, 7:40 am
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Part Number:INA826

Hello,

i am developing an constant current source. The following picture shows the concept.

The current is given by dividing the DA-Converter-Voltage with one of the resistor values (SHUNTS). Which resistor is activated is controlled by an microcontroller. Also the DA-Voltage ist controlled by the microcontroller. The Current flows through P$1. The INA826 has a supply voltage of 30 V DC, Rg is not connected, so the gain is 1. Pin 4 of the INA826 is allways connected to 30V. Pin 1 varies between 28 and 30 V. That means the maximum output voltage is 2 V. 

Now the Problem: The INA826 gets allways damaged. I cant explain why. I tried other Instrumentation Amplifiers from other companies at the same conditions and it worked fine. Also I tried the INA828 and it gets damaged too. As soon as voltage is turned on, the INA826 blows. I damaged allmost 10 devices. 

Is something wrong with the wiring of the INA826?

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INA129: CMRR problem with a buffer on VIN+

December 28, 2017, 11:34 pm
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Part Number:INA129

Customer's circuit is as bellow and they care the CMRR most.

The test input is VCM=10V@10Hz, VDIFF=100uV@10Hz.

While input from INS+ and INS-, CMRR>119dB;    but from IN+ and IN-, CMRR<80dB.

Customer's requirement is how to make CMRR>110dB while input from IN+ & IN-.

Thank you and happy new year!

Marc

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looking for TI's Logarithmic Amplifier device

December 31, 2017, 5:18 am
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Hello Team,

My customer is looking for Logarithmic Amplifier for his application with the following spec:

Input range 1uV to 100mV

Approximate Output Range 0 to 5V

 

General Schematics:

Please advise relevant part from TI that could fit for this application?

Thanks a lot.

Kind Regards,

Shai

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LMC6001: Why -IN is short-circuit with GND? How I broken it?

January 1, 2018, 3:17 am
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Part Number:LMC6001

I am designing a signal amplification circuit using LMC6001BIN.

the schematic is like this:

Before I test this current I test my LMC6001, It is ok. And I also check my circuit map and it is just like this schematic.When I power it on, I find the temperature is so high. And it is not work as what I want. So I test it and I find Pin2(-IN) is short-current with Pin4(GND). And I get signal voltage is about 8.5V .And I remove this chip and test it. And yes it is broken.

（Ip[current] on D1 is 0.7uA at most by the way.）

But I don't know why but I am sure I am wrong. So help me, Thanks? If the amplification ratio what I design is too high.

(I am a chinese so my english is not so good, I translate it to Chinese. Thanks)

我使用上面的电路去做一个光电二极管的放大电路。因为我的输入电流至多0.7uA,所以我设计这个电路端的电压等于Ip*R3*(1+R2/R1)

但是在我上电之后（尚没有给予光线照射），发现输出信号一直是8.5V左右，然后我察觉到芯片温度很高，所以我断电取下芯片测试发现LMC6001的pin2和pin4短路。

我个人觉得一定是我使用这个芯片没有注意哪些参数导致的。是不是我的放大倍数太大了？

而且我检查了电路确认电路和原理图是一致的。

请您给与帮助，谢谢。

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LMC6001: LMC6001 is broken, but I don't know why?

January 1, 2018, 11:04 pm
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Part Number:LMC6001

I am design a signal amplifier circuit. But I don't know why my LMC6001 is broken. And here is the basic schamatic.

I am afriad if I give a such large amplification.  Cause my signal Ip is really small, it is 0.6uA max. (Ip is the current of D1 and D1 is a photodiode)

 When I powen on my circuit just for a while. I find LMC6001 is really hot, and I don't get a right output. When I power off and take LMC6001 off and test it. I find Pin2(-IN) and Pin4(GND) is short-circuit.

Please help me. Thanks.

By the why, the chip is LMC6001BIN。

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LM331: The selection for the voltage-to-Frequency Converter

January 1, 2018, 11:33 pm
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Part Number:LM331

Hi team,

The customer needs to select a voltage-to-Frequency converter. His requirements are as below:

1. The power supply is 12V.

2. Convert 0~10KHZ to 0~10V.

The customer would like to verify if LM2917-N or LM331 can meet his requirements. If they cannot meet the customer's

requirements, would you recommend a suitable device and send me a TINA circuit? I think the customer needs to use

the double power supply to achieve his application, is my understand correct?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

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LMC6482: How to Terminate the Inverting Terminal of Unused Voltage follower with single supply -Opamp LMC6482

January 2, 2018, 2:10 am
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Part Number:LMC6482

Hi,

 

 I am using LMC6482 op-amp in a Voltage follower configuration (with inverting terminal connected to output ). What will be the voltage at the output when Non inverting terminal is pulled down with 10K resistor. I am using 3.3V single supply .

I have interfaced the output of this op amp LMC6482 to the input of ADC (Processors Internal ADC)

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AMC1100: AMC1100

January 2, 2018, 9:17 am
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Part Number:AMC1100

Hello,

 I want to sense 3 Ph voltage and also display that voltage on LCD.I am go through the data sheet of AMC1100 but I have doubt so I am post this question.Can I go ahead with this  IC or an other option for this.Also I have to check Phase sequence of 3 Ph corect or not. Please give suggestion.

Thank You

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LOG114: What ADC is suggested to digitize the signal from the LOG114

January 2, 2018, 10:02 am
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Part Number:LOG114

Hello,

I'm struggling to wrap my head around which ADC to use for the digitization of the photodiode signal that comes from the LOG114. I presume that I'll need a very high resolution ADC to get resolution across the entire 8 decades of amplifier range, but I'm not sure which architecture and resolution to choose. The implementation is used to measure scattered light from smooth surfaces and spectral reflectance of relatively high intensity - thus the need for 8 decades of range. Please provide a suggestion and a EVM that I could attach to the LOG114 EVM would be great.

Thank you,

Patrick

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TINA/Spice: 2nA to 100mA Constant Current Source - design suggestions ?

January 2, 2018, 12:16 am
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Tool/software:TINA-TI or Spice Models

You may find my design. I used 4 parallel op-amp for higher current supply.  There is no problem with TINA simulations. 

my plan is changing current range with relays. Resistor values may change to compensate current range. I'm also planning to measure applied current to compensate leakages. 

Paralleling 4 op-amps will reduce noise or not? 

Is this possible to get %1 accuracy? 

Any suggestion to improve my design? 

How will opa209 output leakage current affect my precision?

Also, I want to use triax connector for current output(R_LOAD). How can I drive inner shield of triax(Guard)?

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LMH6642MF

January 3, 2018, 5:41 pm
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Support Path: /Product/Development and troubleshooting/Find key information on a device/

Hello,

Our customer received the parts,but they found there are 13 kinds of STC code.And they contanct with TI taiwan.TI taiwan replys that the parts which are 1510 DCcode noly have 5 kinds of STC code.Can you help me check the STC code is correct or false ?

Secondly, they have some question about the marking.They said the part received without pin 1 dot and without orientation dot.

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