/etc... Amplifiers & Other Linear Forum - Recent Threads

OP AMP Differentiate 1 mV

nikhil vv — Sat, 15 Jun 2013 06:33:20 GMT

Dear Sir,

I am trying to find difference between two voltage sources using op amp. My application goal differentiate the voltage and give to ADC controller and it says what is the difference between two voltage.

I read using op amp as differentiators we can do it. but i need to get difference even it is 2 mV.

I am planning to use single supply for OP-Amp like LM324.

can i get such accurate result using op amp??

Or what else method will be good for this kind of application...

i am not good in op amp design kindly suggest a good design.

regards,

Nikhil

LM397 absolute maximum spec for Vout?

Roman Manka1 — Mon, 10 Jun 2013 17:34:46 GMT

looks like the spec sheet does not have this important information, It's open drain and I would expect it to be higher then Vs. Can someone confirm what it is ?

ISO122 Supply voltages

nilesh khupase — Wed, 26 Dec 2012 13:05:35 GMT

Can I use ISO122 with +Vs = 15V and -Vs = 0V/GND, for both sides input and Output. And if we can then is it possible to have Input voltage range upto 12.5V with these supplies?

Current shunt monitor DIP package

Gehan Manuel — Sat, 15 Jun 2013 10:11:36 GMT

Hi,

Does TI have any current shunt monitor that is in a DIP package. I searched in the parametric search but could not find any.

Regards

ISO122JP problem

Hiam Lib — Wed, 12 Jun 2013 20:28:34 GMT

I am trying to use ISO122JP with supply of Vs1 = +/- 15V and Vs2 = +/- 15V . Input signal range from 0 to 10V . Problem the big output error . For 8V input signal I am getting 13 V output . ????????????

LMV641

Vladimir Naumenkov — Tue, 11 Jun 2013 20:42:02 GMT

Please, report, will be this circuit work?

Whether the output signal of LMV641 is 500 mV ?

Please, see file attacment 11.06.2013.docx

TIA

Vladimir Naumenkov

www.agat.by

LMV358 Upgrade

Rustin Schroeder — Mon, 10 Jun 2013 18:26:31 GMT

I am looking for a new dual OpAmp to provide better performance than the LMV358 that we have been using. Here are the requirements:

Industrial temp range
Standard SO-8 package / pinout to match LMV358
Gain Bandwidth product > 1MHz
Power supply range 3.0 to 5.5V
Rail-to-Rail input and output (within 100mV at 2k load)
Input Offset < 51uV

In general, it needs to be low power, low noise and low drift, but I do not have hard specs on these as they are tradeoffs. The price target is $0.50 per dual amplifier in volume (50k per year).

LMC7111 same pinout replacement?

Paul Perlic — Thu, 06 Jun 2013 15:56:01 GMT

Hi,

I have a design with a LMC7111BIM5NOPB but need to replace it with a same pin-out part with a higher GBW. After some seaching of other op-amps, it seems the pinout of the LMC7111 is unique (the power inputs are reversed). Does TI have any other op-amps with the same pinout?

Thanks,

Paul

INA226 slave address

hisakichi kobayashi — Mon, 03 Jun 2013 06:22:29 GMT

Hi all

There is a question.

Although it is at a customer, my customer using five INA226 in one PCB.
My custmer have connected A0 pin and A1 pin with "00", "01", "10", "11", "SDA,SCL" at a slave address setup in INA226.
My customer has a phenomenon in which the slave address of "SDA,SCL" is not recognized.(adr=1001011)

Although there are 16 kinds of slave addresses in INA226,
For example, are SCL and SDA connected to A0 pin and A1 pin, and is there any case where a slave address is not set?
Is there any corrective strategy?

Best Regards.

Hisa Kobayashi

INA168 input voltage range (measure inputs from 0 to 2,7v)

Iv��n mart��nez — Wed, 05 Jun 2013 10:39:58 GMT

INA168 specified supply and input voltage range is from 2.7V to 60V (see below), I need to measure from 0 to 2,7v, is it possible?

Input impedance of OPA360

Jaden Ghylin102047 — Wed, 05 Jun 2013 17:26:15 GMT

What isthe input impedance of OPA360 and also LMH730216 ?

Regards,

-Jaden

15kV ESD Op-Amp?

Audi McAvoy — Tue, 04 Jun 2013 14:28:52 GMT

I need to clean up a 5V TTL input signal with a Schmitt trigger device/circuit. The Schmitt trigger device/circuit needs to withstand 1kV for several seconds. I am unaware of any conventional logic family that can take this kind of punishment, so a 74x14 device seems an unlikely solution.

I am aware that some other companies offer input isolation devices that are marketed as "Schmitt trigger," but a close inspection of the datasheet (an a conversation with their FAE) shows that this is just barely a true statement (and not true enough for our needs).

I'm considering an op-amp based Schmitt trigger circuit. Does TI have anything that might fill this need?

OPA454 E/D logic connection

Arthur Elsenaar — Fri, 31 May 2013 12:39:24 GMT

I want to use the OPA454 to amplify a 3.3V varying amplitude pulse train to 50V. The pulses are 50us wide and repeat at 1ms. I chose the OPA454 because of its high voltage operation and relatively low Iq. In my described application the duty cycle of the pulses is rather high, so I want to make use of the shutdown capability of the opamp to significantly reduce Iq. (Device is battery operated.)

From the datasheet it is not entirely clear to me how to interface 3.3V control logic to the E/D and E/D Com pins. If someone can enlighten me on how to do this properly without frying my uC with 50V.. would be greatly appreciated!

Current Limiting in 4-20mA loop

Muhammad Rehan — Tue, 30 Apr 2013 11:31:15 GMT

Greetings,

I am using a two wire 4-20mA current loop. Now I want to limit the input current to 2mA forcefully if any fault occurs in the system so that I could check if my supervisory circuitry is working fine or not.

Please suggest me any circuitry or IC.

Regards,

Muhammad Rehan.

How to stabilize OPA551/OPA551 with capacitive load?

Alex Fang — Thu, 23 May 2013 05:19:38 GMT

Hello all:

I'm new in the OP amp system design. And I read many TI application note but still confused.

I have some OP amp stabilize issues in my design. I use DAC and OP amp in my system. And OP amp with a 22uF ceramic cap.

I use this op amp as non-inverting amplifier. And the schematic as attached pic. I found that Vout is oscillate and the current consume by OPA552 was very high(abt. 150mA).

I know that I can use OPA552 as Gain<5. Does this issues being solved if I change my op to OPA551? Or how do I stabilize this circuit? Thanks!

OPA445 : Offset trim pin

Gilles Malela — Thu, 30 May 2013 09:15:10 GMT

Hello ,

I want to use the OPA445 amplifier. There is two offset trim pin in order to null offset voltage. I would like to know if it may be floated or connected to GND.

Thank you for you reading.

Gilles Malela

Student from France

LMH6629 Evaluation Board - strange output signal

Guglielmo Sirna — Mon, 27 May 2013 14:25:00 GMT

Hi, I having trouble with two LMH6629 Eval boards.

Both units show either no output signal (for small input signal ~100mVpp, 10MHz) or a clipped waveform (for input signal ~1Vpp, 10MHz) .

I have set R10=0ohm and use single +5V supply.

I am using the standard non-inverting input. The current consumption is ~11mA;

The input and output impedance is ~50ohm;

The SW1A (PD) behaves as expected, powering down the device.

Here is the DC level I have measured with teh device powered ON and Idd~111mA

pin 1, PDZ: 5V

pin2, FB: 0.3V

pin 3, IN- : 0.02V

pin 4 , IN+ : 0V

pin 5, V- : 0V

pin 6, COMP: 5V

pin 7, OUT: 0.3V

pin 8, V+: 5V

Any idea what is going on?

guglielmo

problem with common ground

akhilesh sati — Mon, 27 May 2013 19:54:29 GMT

i am using op-amp TLV071 and operating it with a battery of 3V. in order to see the output of the op-amp on the oscilloscope, the GND terminal of the oscilloscope is connected with the GND terminal of the 3v battery. My confusion is that, the GND is a reference voltage for any circuit and the GND of the oscilloscope is derived from 220V/50Hz,rms voltage.

1. so is it necessary that the GND of the oscilloscope and the GND of the Battery will be at the same potential.

2.In circuit many time we connect the GND of two different power sources for making their GND common & then measure all the voltages with respect to this GND. At that point of time how one ensures that all the power supplies have same GND voltage.

regards

akhilesh sati

XTR 117

Purushottam Pawar — Fri, 24 May 2013 10:57:14 GMT

Hi,

I have assembled the circuit of XTR 117 on breadboard as provided on pspice.

Input voltage of 0-5 V is provided through variable power supply.(Positive terminal of supply connected to IN terminal via 33K resistor and negative terminal of supply connected to IRET.)

Supply voltage is 20V, load resistor of 100 E and BC 547 transistor is used and results are as mentioned below.

Voltage at pin no. 2- 0.15 V to 0.5 V (for 0 to 5 V input)

Voltage at pin no.3- 0V

Voltage across load resistor(100 E)-0.06 V (constant for entire input range)

Voltage at base terminal of transistor- 3.8 V (constant for entire input range)

Voltage at VREG terminal- 5.24 V (constant for entire input range)

Kindly check and suggest.

Thanks,

paddy

OPA551 common mode levels and noise predictions

Bjarke G�� — Mon, 27 May 2013 10:18:08 GMT

HI,

I have a design were I am using the OPA551 as an integrator. Positive supply is at 60V and the negative is at 0V.

The inputs are at +2.5V from the negative supply, which is at the low end of the permitted input range.

My concerns are:

1. Does this low input common mode level degrade input noise levels?

2. Can de device sustain low noise levels over temperatures?

bjarke

relaxtion oscillator

shared account — Sun, 26 May 2013 10:51:01 GMT

i need a equation that calculate a frequency of relaxation oscillator with op amp single supply

like this one

LM139 Output Failure Mode

Nonis — Wed, 22 May 2013 18:45:17 GMT

Hi,

I'm using a LM139 comparator, with a pull-up resistor and a MOSFET on output, to control a relay. But this relay also is controled by a pulse provided from a microprocessor. So I need to know, on a failure what will happen with the LM139 output. Will be low or high? In failure mode, has any diference if I use histeresys or not?

Thanks.

Isolating 4..20 mA lines

Stefano Infante — Mon, 20 May 2013 10:50:46 GMT

Hi all!

I have to ask you some help on how to isolate 4..20 mA lines... but let me first explain my situation.

I am designing a data logger, which will have 16 4..20 mA input channels. The sensors are static ones, so I don't need high speeds, and the resolution should be 12 bit. The board has to power all sensors, so I will surely have an available isolated power line.

For those reasons, in order for the data logger not to be too expensive, I would like to use an MCU with 16 12-bit analog inputs. This means, in general, I have to convert 4..20 mA inputs to a 0.66..3.3 V signal, using a 165 ohm conversion resistor (or similar).

Given that, my problem is now how to isolate the sensors' signals. I will surely put the conversion resistor at the very beginning of the signal chain, so I have to establish how to amplify and isolate the signals. Isolated amplifiers are not an option, as the total cost is too high (8 euros or more for ISO124, times 16 amplifiers on the board).

Then I found the article on EDN by Mike Score here: http://www.edn.com/design/analog/4402736/3/Inexpensive-analog-isolation-using-a-digital-isolator.

It seems to be an excellent solution for me, as the Class-D amplifier used is very cheap, and I can use multiple isolators (such as ISO7240) to save money and board space.

But now the problem moves on some considerations, and here comes my request for help:

is the resolution of such a solution compatible with my 12-bit needs? (I think I can use a 4th or even 6th order LPF after the isolators, if this helps)
in the article Mike suggests the use of a comparator after the digital isolator in order to "eliminate any error due to any peak-to-peak voltage difference from supply mismatch": this point is not so clear to me, can you please explain?
is there any multiple channel Class-D amplifier I could use instead of TPA2006D1, in order to save further space (and possibly cost)?
given that I have to put the 4..20 mA conversion resistor just befor the amplifier, how can I dimension the input stage (Rconversion and Ri)? Can I treat the resistors as they were separate circuits?
is there any more advice you can give me?

Thanks in advance for your help.

Stefano Infante

Comparator LMV7219

Vladimir Naumenkov — Thu, 23 May 2013 13:52:21 GMT

Comparator needed as a zero-crossing detector.

In the beginning was the circuit 1. Comparator never switched.

Then I did the circuit 2. Comparator works, at the 3 input of the comparator is Um = 50mV. Watched broadband oscilloscope.

The generator should have the load 10 kohm±20%. Otherwise, not required frequency stability is guaranteed! The output signal (sine wave) is symmetric with respect to zero (the output is connected through a capacitor, which is inside the generator). The signal amplitude of generator is 0.5 V.

Question: How do I estimate the value of the generator load ?

TIA

Vladimir Naumenkov www.agat.by

(Please visit the site to view this file)

Inqury regarding LMV358 Output Voltage vs.Output Sink Current

Atsushi Okui — Mon, 20 May 2013 08:51:58 GMT

Hello, all

Now we are considering to use LMV358 for the replacement from AZV358.

Then would like to know the characteristic on Output Voltage vs.Output Sink Current of this device.

On the datasheet page 8 of AZV358, I could find "Figure 14. Output Voltage vs.Output Sink Current".

(the datasheet is downloadable on the website below)

http://www.bcdsemi.com/Upload/Product%20Doc/Datasheet/AZV358%20D1.3%20100309.pdf

However, I could not find same characteristic on the datasheet of LMV358.

The key point of this inquiry is whether LMV358 could output 25mA sink current in case of VCC=2.7V.

Please let us clarify whether this is achievable for this device.

We thank you in advance for your information.

Best regards,