OPA320: Effect of signal source internal resistance on voltage follower - opa320

February 11, 2019, 11:41 pm

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Part Number:OPA320

In my design, I used opa320 in two places, voltage detection and current detection.

Current detection

A and B are almost equal.

Voltage detection

The resistance is temporarily selected to 5% accuracy，VA=4.14049V，VB=4.17855V，ΔV=38.06mV

Then, I tried the following

A and B become almost equal.

What is the difference between the two inputs?

The input impedance，because the output impedance of the amplifier is very small.

So，my guess is that the input impedance of the source is the cause.

Then, I tried to lower the input impedance: R31=10K,R32=1K,R34=1K. The voltage is reduced by taking into account the power consumption of the resistance.VCC_MAIN=24V.

The results are as follows: VA=1.97123V，VB=1.97141V，ΔV=0.18mV.  It's improved a lot.

The input impedance of the voltage follower is infinite, will the 1M resistance affect it so much?

In addition, the magnification tends to be 1 but not greater than 1.The signal source internal resistance will share a part of the voltage, why is the output of the voltage follower larger than the input?

Thanks for your help !

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LMV393: Operation outside the Input Common-mode Voltage Range

February 11, 2019, 11:47 pm

≫ Next: OPA2197: Voltage monitor

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Part Number:LMV393

Dear Specialists,

My customer is considering LMV393 and has a question.

I would be grateful if you could advise.

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Could you please see attached file（competitor's application note).

According to the application note, 

Even if it exceeds the common mode input voltage range only on one side of the input, it is described that it will output correctly as a comparator.

Does this also apply to TI's LMV393?

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I appreciate your great help in advance.

Best regards,

Shinichi

(Please visit the site to view this file)

OPA2197: Voltage monitor

February 11, 2019, 11:48 pm

≫ Next: INA219: small resistor causes calibration register value over 32768

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Part Number:OPA2197

Dear Team,

If my customer wants to monitor Vout voltage, do you have suitable reference design and use which part number?

They want to monitor Vout rail, if Vout is higher or lower the circuit need to send a signal to the MCU.

BR

Kevin

INA219: small resistor causes calibration register value over 32768

February 12, 2019, 1:52 am

≫ Next: INA219: ina219 transient spec

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Part Number:INA219

Hi expert,

My customer use INA219 at their server application and condition is shown below.

• maximum current = 10A.
• Rshunt=2mohm.
• Vshunt_max=20mV.
• current LSB = 305*10^6.
• calibration register = 67108.

67108 is over 32768 so we cannot fill in calibration register. Do we have resistor limitation which causes calibration register value over 32768? Thanks a lot!!

Best regards,

Ann Lien

INA219: ina219 transient spec

February 12, 2019, 2:42 am

≫ Next: INA210-Q1: REF pin connection

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Part Number:INA219

Hi expert,

My customer is wondering Common mode voltage transient tolerance for INA219. Do we have transient spec for common mode voltage for INA219? (like 32V tolerance in 20ns) Thanks a lot!!

Best regards,

Ann Lien

INA210-Q1: REF pin connection

February 12, 2019, 2:47 am

≫ Next: AMC1301-Q1: How to connect two parallel sense resistors.

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Part Number:INA210-Q1

Hello,

Our customer is asking how to connect REF pin in case INA210-Q1 is used as positive half wave current on the rails.

Do you recommend to connect REF pin to GND in this case ?

In my understanding, REF pin bias voltage depends on the current measurement range. REF pin should be connected to GND if the customer needs to measure large current accurately. He should connect to a certain voltage if he needs to measure small current accurately. Because INA210-Q1 guarantees the +/-0.02% Gain error in VSENSE=-5mV to 5mA range.

Best regards,

AMC1301-Q1: How to connect two parallel sense resistors.

February 12, 2019, 7:21 am

≫ Next: LM2907-N: Component selection confusing in the datasheet

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Part Number:AMC1301-Q1

Due to high current, the application will use two equal sense resistors. I need to measure both resistor voltages as the current split might be 49%/51% (or similar)

Using just one LMC1301, what would be the correct way to sum (average) the two nearly equal sense resistor voltages?

LM2907-N: Component selection confusing in the datasheet

February 12, 2019, 8:26 am

≫ Next: Buffer amp for 50 ohm line

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Part Number:LM2907-N

Hello,

I'm looking to design a circuit using the LM2907 to measure the frequency of a motor.  We are designing a  safety cutoff if the motor RPMs reach 50,000, anything from 0-45,000RPMs is deemed safe.

The maximum frequency will be less than 900Hz, so we should be fine to use this component.

I'd like to run the IC off of a 3.3V supply, but I can't seem to find if that's ok in the datasheet.  If not, I could run it off of 24V, but the hall signal that I'm using for the frequency input will be a square wave from 0-3.3V at roughly a 30% duty cycle, so it seemed to make sense to run the supply off that voltage too (if possible)

That leaves the selection of R1, C1, and C2.  I'm not sure what these should be set to at all.  I want to have 3V on the output at 50,000RPM, so I can trigger the motor to safely shut off.

If you can help me with the component selection I would appreciate it.  I'd also like to get confirmation that my supply voltage will be ok.

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Buffer amp for 50 ohm line

February 12, 2019, 10:20 am

≫ Next: OPA128: What is the Theta JC?

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I am building an electrometer type circuit, probably using an LMC6001. However, I want the output to drive 50 cable and the LMC6001 does not have enough output current. I have been searching for various op amps that can act as a driver for 50 ohms such as BUF634, LMH6672, and OPA633. A 5 volt signal into 50 ohms is 100mA so I need at least 100mA output current for the buffer. I don't need a lot of bandwidth and some of those amps are more oriented towards high bandwidth. Right now, the BUF634 is my main choice but I am open to other suggestions. I could not find much in the General Op Amp section. The BUF634 was sort of hidden away in a different section. I think the only important parameter for this output amp is the current. I don't need a hug multi-amp power op amp. Just maybe 200 mA.

OPA128: What is the Theta JC?

February 12, 2019, 10:24 am

≫ Next: LMH6654: I_off on inputs

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Part Number:OPA128

What is the Theta JC of part OPA128?  The datasheet indicates 200 C/W for Theta JA only.  To be more specific, I am only concerned with OPA128SM.

LMH6654: I_off on inputs

February 12, 2019, 12:55 pm

≫ Next: INA226-Q1: Does this part use a flipped-chip die?

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Part Number:LMH6654

Hi,

When the LMH6654 is off (no voltage on V, V-), how much leakage/ off current can be observed on the input pins (IN+/-) when a  1V -3.2V is applied? - the part is configured as unity gain buffer.

 Are there protection diodes on the IN  & IN- pins?

Thank you!

Regards,

Alberto

INA226-Q1: Does this part use a flipped-chip die?

February 12, 2019, 1:19 pm

≫ Next: LMH5401-SP: FDA Single-ended to Differential Circuit Design Calculator

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Part Number:INA226-Q1

Does this component use a flip-chip package?  Is there any SEE data available for this part? 

LMH5401-SP: FDA Single-ended to Differential Circuit Design Calculator

February 12, 2019, 1:24 pm

≫ Next: INA190: Need ultralibrarian file for INA190

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Part Number:LMH5401-SP

An excel calculator is provided to help designers solve circuit components around the LMH5401-SP fully differential amplifier (FDA).  The calculator is customized to the LMH5401-SP as the formulas take into account the internal 25 ohm feedback resistance integrated on the IC.

Users should enter the values highlighted in yellow which are (1)  Target Voltage Gain (2) Source Impedance and (3) Target Feedback Resistance.

The green highlighted values are the calculated values.

(Please visit the site to view this file)

INA190: Need ultralibrarian file for INA190

February 12, 2019, 6:22 pm

≫ Next: INA181: Internal bias network

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Part Number:INA190

Hello,

I'd like to request TI add the ultralibrarian footprint file for the INA190.  I can't find it here:

https://webench.ti.com/cad/

INA181: Internal bias network

February 12, 2019, 10:55 pm

≫ Next: THS4140: Gain accuracy

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Part Number:INA181

Hello,

Our customer use the INA181.

The customer have a question about the internal bias circuit shown in Figure 48.

What is the internal bias network? Is it a circuit like an attenuator for high common mode voltage?

Best Regards,

Naoki Aoyama

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THS4140: Gain accuracy

February 13, 2019, 3:52 am

≫ Next: INA821: Temperature Drift Coefficient

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Part Number:THS4140

Hi,

While simulating with TINA circuit with THS4140 for gain = 10, we see that result is not as expected and furthermore, the values of the positive and negative terminals not symmetric.

Rf and Rg are as recommended by datasheet.

As shown in diagram, for the 1V input, the gain is 9.97 instead of 10, and output differential terminals are 50 and 20 mV off (and not symmetrical).

Assumption was that we should be able to see gain = 10, as per recommendations, and symmetrical differential output, in the simulation.

Is the problem in the simulation environment or does it reflect "accurate" device behavior? (can we rely on simulation results in this case?)

Thanks,

Arie

INA821: Temperature Drift Coefficient

February 13, 2019, 4:37 am

≫ Next: LM5056A: AEC-Q100

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Part Number:INA821

Hi,

in our application with INA821, G=10, sensing a thermocouple, we have measured a drift:

• INA821 CH1: 12 ppm/K
• INA821 CH2: 10.8 ppm/K

as per data-sheet (section 8.3.1.1) it specifies min gain drifft of 5 ppm/K, and the rest of contribution is due to external resistor relative to internal resistors.

Can we assume that in a lot of INA821 the gain drift will always be, for the same operation of INA821 at G=10:

1. positive (same direction)
2. of similar values (assuming the use of 5 ppm/K external gain resistor)

BR Uros

LM5056A: AEC-Q100

February 13, 2019, 4:50 am

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Part Number:LM5056A

Dear Team,

If my customer wants to measure current and voltage with the I2C interface. It seems the LM5056A is the most suitable part here.

But it is not AEC-Q100 device. The customer will need the device can support voltage up to 80V.

Or you have road map can share with me related to AEC-Q100.

The customer mentioned, Linear Tech will release a device with AEC-Q100 soon.

Please kindly help on win the socket here.

BR

Kevin

question about a circuit

February 13, 2019, 5:43 am

≫ Next: Comparator for restoring 27MHz clock from sine signal.

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Part Number: LT1167

I have quesion please, I am trying to build a Load cell circuit. I have to use LT1167 to amplify the volt but my question is what should I use after the LT1167? any opa and why please?

the load cell is s type, 200kg

Comparator for restoring 27MHz clock from sine signal.

February 13, 2019, 6:33 am

≫ Next: OPA4388: When is OPA4388 in TSSOP14 available?

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Hello,

I'm looking for comparator that allowes me to restore 27MHz clock from sinusoidal waveform ( min. 100mVpp ). I'm struggling with finding one because it's low power solution, so maximum quiescent current suppose to be around 1mA, and minimum supply voltage around 2V7 / 3V0. Are you familiar with any solution that meets the requirements? Thank you for any help.

Best regards,

Adam Pelc