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XTR111: 4-20mA conversion accuracy issue at high ambient temperature ( > +65C)

May 2, 2017, 8:20 am
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Part Number:XTR111

Hi Sir,

Attached SCH shows our 4-20mA conversion circuit  which is part of the circuit in our design. Basically we used design of TI evaluation board for XTR111.

The 4-20mA accuracy of this circuit meets our requirement when ambient temperature is between  -40C to +60C.

However, when temperature rises over +65C, the 4-20mA output current was out of our specification (< 2.5%) if Vin was below 2V.

The accuracy comparison can be found in the other attached file.

We measured the voltage of R226 (shown in attached SCH), this voltage only changed a little (less than 0.5%) compared with the voltage value at +22C.

It looks like that the current passing through B pole and E pole of Q8 significantly increased at +85C so that the 4-20mA output current accuracy was severely degraded. 

Because we used TI's evaluation design, does any one of TI engineers know this issue? Is there any recommendation to get it improved?(Please visit the site to view this file)(Please visit the site to view this file)(Please visit the site to view this file)

Thanks

William Chen

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LMP91200: LMP91200 reference design questions

May 2, 2017, 11:17 pm
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Part Number:LMP91200

Hi Team,

The customer would like to use LMP91200 to measure the PH of the polluted water.

For the E version datasheet, it removes the SPI function. 

He needs to the reference schematic for the PH design.  

Q1: Would you provide a reference schematic to measure the PH  for the E version datasheet?

Q2: For the E version datasheet, I think its content is very brief.

a). For the PH buffer, what are the voltage range for the GUARD1,INP, GUARD2, VOUT and VOCM pins?

b). For the VCM buffer,  what are the voltage range for the VREF, VCM and VCMHI pins?

c), For the PGA, is the GAIN 5V/V? Is this value 5V/V constant?

Best Wishes,
Mickey Zhang
Asia Customer Support Center
Texas Instruments

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INA326: Understanding the benefits of the current mirror system

May 3, 2017, 11:52 am
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Part Number:INA326

I'm currently designing an amplifier circuit for a photodiode. The photodiode uses a trans impedance amplifier initially but, to keep the bandwidth up, this has fairly low gain. In order to boost the signal later on I've decided to use an instrumentation amplifier.

In choosing one of these I've been looking for low noise, high stability and low thermal drift. I came across the INA326 previously and thought to apply it here: it has some very clever current mirroring going on which removes the need for internal trimmed resistors. However, in comparing it with e.g. the INA103, I found that it underperforms on most all figures of merit.

If that's true then fine, I can use the INA103 instead, but I think I must be misunderstanding the INA326's strengths. Surely the added internal complexity of the current mirroring circuitry must have been done for a good reason, but so far as I can see all it achieved was to limit the bandwidth by 4 orders of magnitude, which makes me think I must be missing something.

So my question is, other than the past-the-rail output, what advantages does the INA326 have over more conventional instrumentation amplifiers (particularly in unity / low gain systems)?

Thanks in advance!

Charles

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PGA308EVM: How does the PGA308EVM be configured for three-wire mode

May 4, 2017, 3:02 am
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Part Number:PGA308EVM

Hi,

I want to configure PGA308EVM for three-wire mode,  so I set JUMP1 to Vout to 1W, JUMP7 to one to Vout. JUMP8(in the USB DAQ Platform ) to SPD_UP.

But it doesn't work. The software show "One Wire Time Out".

Thanks.

Best regards.

Ricardo Li

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Differential signalling to single ended adc

May 4, 2017, 4:34 am
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differential receiver signal of anlog front end to single ended adc

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XTR110: Datasheet information.

May 4, 2017, 8:11 am
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Part Number:XTR110

The data sheet for XTR110 has a FIGURE 10. 0A to 10A Output Voltage-to-Current Converter.

1) Shouldn't pin 10 be to Com? That pin is not shown.

2) if I want my input to be 0 to +5V, Pin 10 would go to Com and I would reverse pins 4 and 5? Thanks.

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OPA4197: question regarding absolute maximum input voltage and current rating.

May 4, 2017, 11:17 am
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Part Number:OPA4197

Absolute maximum ratings for OPA4171 and OPA4197 specify signal inputs should stay below V+ +0.5V. Can this be exceeded as long as the current is much lower than the signal input pin current rating of 10mA?

Here is my application schematic. This board measures 0-10V inputs, which can be as high as 30V under fault conditions. 100k limits the fault current into the non-inverting input of the OPA4197 to worst case of 300uA.

I have pads for schottky diodes on the PCB to clamp the non-inverting amplfier, but I'd like to not populate them if they aren't needed because their leakage current and will add error to the ADC reading.

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XTR115: XTR115 phase shift between voltage and current occurs during convertion

May 5, 2017, 2:23 am
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Part Number:XTR115

dear all i would like to have some help on the component XTR115

in fact i use the recommended digram specified in the datasheet.

however i converting analog voltage sine into analog current.

i have to use it until 13kHz frequency, when the frequency increse i have two phenomenas

- ouput current is shifted a lot

-the current amplitude decrease alot as well .

does anybody please knows how to make it more stable, in amplitude and in phase ?

here is my setup  and the printscreen is at 10kHz frequency

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Op-amp selection for switching current measurement

May 5, 2017, 5:34 am
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Hi All,

I am building a 800W pushpull converter operating at 40kHz - 65kHz switching frequency with primary current going till max 100A. Converter input voltage on primary side can vary from 30-42V. See the circuit shown in figure below.

I want to implement peak current mode control for this converter. So, I used a shunt resistor of 1mOhm to sense the primary switching current. Shunt can be placed in two positions (1 - high side of battery or 2 - low side of battery). 

In order to amplify the CS1-CS2 signal I used TLV271 op-amp (in case of low side sensing) but it is not able to reproduce the switching current signal. I need your help in finding the right op-amp for my application.

Thanks in advance!

Best Regards,

Kashyap Gundlapalli

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TINA/Spice/AMC1200-Q1: AMC1200 shunt connexion

May 5, 2017, 8:41 am
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Part Number:AMC1200-Q1

Tool/software:TINA-TI or Spice Models

Hello,

I'm currently designing current sense measuring in H bridge and I have a question about GND1 connexion: in typical application, shunt resistor is connected to GND1 but there is no explanation about this. I made SPICE simulation and its working fine. It is mandatory to connect shunt resistor to GND1 ?

Regards

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LMP91000: how to mesuare nano ampere current from chemical sensor

May 5, 2017, 11:59 am
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Part Number:LMP91000

I had dissolved oxygen sensor purchased from manufacturer NENGSHI, polarization voltage is:-650mv and current output are 0 to 120nA since I required an interface circuit for measuring the current from the sensor, Does LMP91000 is used for this purpose?

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INA128: Using INA128 as current sensing. Maximum input voltage regard to ground limitation.

May 6, 2017, 10:22 am
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Part Number:INA128

Hello.
I need build a current sensor for a Full bridge inverter output.
The nominal output voltage of the inverter is 127 Vrms.
At their output there will gonna be a LC filter.
The main characteristic of the circuit is that the current is low, in the order of 100 mA, at most.
The basic schematic is below.

As I have some INA128 available, I intend to use it to sensing the output inverter current through Rshunt.

So there are three questions I need to ask:

1) This is a good ideia, use INA128 to measure such low current without using a high value of Rshunt?

2) In datasheet, there are Common-Mode Voltage Range ((V-) + 2 and (V+) - 1.4 V) and Safe Input Voltage (±40 V). Since the max power supply is ±18 V, could we put ±40 V at input?

3) My main concern is about . Despite the maximum differential voltage on IN+ and IN- be low because the low current, the voltage at input pins regard to ground will be in the order of hundreds of volts. Can this IC withstand such a voltage level?

Thanks,

Henrique Luna (BR)

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OPA2336: Vout Swing to the Rail when Vin is 0V

May 8, 2017, 9:09 am
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Part Number:OPA2336

The data sheet shows that Vout cannot reach 0V even if Vin = 0V. The data sheet states that the minimum voltage swing from the rail is ~ 3mV. Do we have any information on this for large loads (1M or 5M)? Would there be much improvement? I did not see hardly any difference in Vout in a TINA simulation, but I wanted to check and see if we had any test information on 1M or 5M load.

Thanks for your help with this!

Richard Elmquist

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OPA388: SOT23-5

May 8, 2017, 9:13 am
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Part Number:OPA388

Hello.

How to order the SOT23-5 type of OPA388?

I cannot find it in TI or orher distributors as mouser, digikey or arrow.

This is S.Korea. And  I require 10 pcs to make a DAC prototype.

Thanks.

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OPA2604: single supply condition

May 8, 2017, 10:40 pm
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Part Number:OPA2604

Hi Team,

I believe OPA2604 is operable under single supply V+=45V, V-=0V (GND) condition.
Is my understanding correct?
I would like to confirm just in case.



Best Regards,
Yaita / Japan disty

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LMP91000EVM: Extracting data real-time for custom graphing

May 8, 2017, 2:28 pm
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Part Number:LMP91000EVM

Hi!

*** Note: I would like to request that this forum post be made private for confidentiality purposes.***

BACKGROUND:

I have the LMP91000EVM evaluation module and SPIO-4 controller boards. I'm currently running the software that was provided for the LMP91000 hardware.  

I'm able to see an expected current from the electrochemical sensors that I have hooked up to the LMP91000EVM board.  

ISSUE/PROBLEM:

- I would like to be able to customize the graph to be able to change the x-axis (from time = 0 to time = when I stop the run and save the data).  Currently the graph that's shown on the GUI shows a constantly changing x-axis.  

- Ultimately, I'd like to be able to extract the value of the current (nA) in real-time to be visualized in LabView or Matlab so that I can visualize and analyze the data in real-time.  

- There have been posts with interfacing an Arduino with the LMP91000EVM.  Is there a way that I can use the LMP91000EVM (electrode sensing) + SPIO-4 (data capture) + Arduino Uno (to obtain the current signal for a custom visualization through Matlab/LabView/Arduino IDE/Processing) --> if this is possible, how would I physically connect the Arduino to the LMP91000EVM or SPIO-4 board(s)?

- Ideally, if using an Arduino is an option, I'd like to be able to create a custom GUI in which I can place "text markers" in the output data (e.g. a "text marker" to indicate when the concentration of the solution that the electrochemical sensors are submerged in changes)

- If an Arduino is not an option, any way that we can visualize the data in a customizable graph would be very helpful; furthermore, if we can save an ongoing text file as the an experiment is run with the electrochemical sensors, that'd be helpful as well (e.g. having an on-going text file vs. one text file at the end of the run from the save feature on the TI GUI).

Due to the time-sensitivity and confidentiality of this project, if it would be possible to schedule a call/video chat with one of the engineers, that'd be greatly appreciated. Thanks!

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OPA340: offset voltage for R/C integral

April 28, 2017, 1:39 am
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Part Number:OPA340

Hello

I have a question regarding the offset voltage caused by the R/C integral.

I would like the measure a signal from the output from Rogowski Coil. I use a R/C integral after. R is 1000k ohm and C is 5.6nF. And I use a Non-invert input Op Amp circuit to amplify the signal. I use 1.5V as the middle voltage. But I found the offset in the output of the R/C is 1.51V. Additional 80mV appears. When I reduce the resistor value. The offset reduced. Who can tell me how the offset occurs and how to reduce it?

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

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INA333: Terminate thermal pad on INA333 WSON package

May 10, 2017, 8:34 am
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Part Number:INA333

Hey all,

The datasheet for the INA333 is not clear on the termination of the thermal pad on the WSON package. Can/should the thermal pad be tied to the IC ground? is the termination for the pad discussed in any TI documentation?

thanks,

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OPA4140: OPA4140 IB specific over from -40C~85C

May 10, 2017, 9:31 pm
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Part Number:OPA4140

Hi Team,

I'm selecting a low IB(<200pA through -40c~85C), low offset(<200uV) support up to 30V supply amplifier. It seems OPAx140 is a choice, but I can't find the Ib curve across -40C~85C as some other datasheet showed(Below curve are from OPA2277), can you help provide the curve or give me some data to show this, thanks a !

Best regards,

Sulyn Zhang

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LMH6518: What's the cause of the offset drift in LMH6518

May 11, 2017, 2:33 am
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Part Number:LMH6518

Hi team,

  My customer has adopted LMH6518 in their end product. After running in the market for 5 months, one of the product was reperted abnormal behavior. Customerr found that LMH6518 has a huge offset change (up to 80mV)， while it's supposed to be much lower. It happens only after long time operation. 

  Customer is wondering what might be the cause for such a big offset drift (permanent drift)? It's related to heat or degradation? Thanks ahead for relying.

Reagrds,

Patrick

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