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LMP7721: Gamma radiation sensor

October 5, 2018, 11:16 am
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Part Number:LMP7721

Hi all, 

I am modifying the circuit for a gamma radiation sensor used in our radio-synthesizer. Original design is attached. (Please visit the site to view this file) As part of modification for noise and stability, I have decided to add a guard ring as recommended in the datasheet and LMP7721 multi-function evaluation board user's guide. In one part the datasheet states: "A cover or shield connected to the guard should protect the circuitry above (or below) the PC board". And in another part it says: "The guard trace should not be relied upon as the only method of shielding. A ground plane or shield should surround and protect the guard from large external leakages and noise, as the guard trace has the potential to couple noise back into the input".

As you can see on the schematic, there is a grounded shield that covers the whole circuit, and there is a second grounded shield that covers the PD which is mounted on the back of the board. Now the question is that;

1- Should I connect the main shield to the guard rind or shall I leave it connected to GND just the way it is?

2- Shall I connect the shield for PD to the guard ring or GND?

Thanks

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OPA333: OPA333 input-referred voltage noise variance with temperature

October 5, 2018, 11:24 am
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Part Number:OPA333

From one of my customers:

"Is there any information available for how the OPA333 input-referred voltage noise varies with temperature? I am interested mainly in the frequency range of 1 to 100Hz. I’ve seen some indications with the OPA333 that there can be noise maxima at certain temperatures in the 20C to 50C range. The amplitude and frequency of these maxima vary from part to part. I suspect the OPA333 vs other parts of the circuit since I can swap the OP333 between circuits and the noise signature vs temperature follows the OPA333."

An additional question to the customer question: Should we be looking at a different amplifier, and if so, which would you recommend?

Thanks

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LMH5401: LMH5401 for transimpedance amplifier

October 5, 2018, 12:34 pm
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Part Number:LMH5401

Hello,

I am interested in using this LMH5401  device as a transimpedance amplifier for passing signals DC to 900MHz, and a differential output for a control circuit. I would like to use it with an optical input. I would like to purchase an evaluation board to test out the circuit design with.  I read the questions in the  online TI community on using this device and the recommendation to use the OPA856. I am interested in modifying the eval board that would allow easy application of a photodiode and that has the required bandwidth and output. The application of the photodiode to maintain a low capacitance to the chip would be essential for the control to get working.

Are there any other eval board recommendations or other transimpedance amplifiers with eval boards that have photodiode inputs I should look at also?

thank you for your help with this.  

Bryan 

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TIPD164: About TIPD164 Module

October 6, 2018, 2:29 am
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Part Number:TIPD164

Hello,

I planing to use TIPD164 Analog Input Module for Industrial Outputs and Temperature Sensors  module.

But I realized your module is obsolete. I want to know why your module is obsolete. If the card have a trouble then can you inform me about that.

Best regards.  

Analog Input Module for Industrial Outputs and Temperature Sensors 

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OPA615: OPA615 FAST PEAK DETECTOR PROBLEM

October 7, 2018, 11:24 am
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Part Number:OPA615

Hi,


I would like to build fast peak detector. It should be analog circiut.

I decided to try with OPA615 and BUF602 IC.

The signal to measure: PPM, 4MHz, 10ns pulse amplitude from 10 mV to 5V. The very short pulse time is problem in this design.

I don't need ultra fast and precision detector. Error around few % and reaction time in ms is acceptable to me.

I think that OTA and fast comparator in OPA615 is good solution.

I built the circuit from datasheet on two sided PCB with good rules of design (all SMD, well grounded capacitors etc.)

In first version I used DB3X314 diodes (1ns, 300nA reverse current, 1pf) and 22pF capacitors.

Iq of OPA615=13mA

Supply +/-5V.

Hold control pin not conected.

Below my results with 10ns pulses with 250ns repetition:

BLUE - INPUT SIGNAL

MAGENTA - POSITIVE OUTPUT SIGNAL FROM DETECTOR

-100mVpp

-300mVpp

-500mV

-1Vpp

-1Vpp but 1MHz and 500ns pulse to compare

THEN I CHANGED CAPACITORS TO 1nF

I CHANGED DIODES TO BAS16 AND 22pf CAP

I CHANGED CAPACITORS TO 1nF (BAS16 diodes)

1) What my detector lowers amplitude - capacitor is not charged to peak value?

2)It is possible to built 10ns peak detector with OPA615?

3)How i can built analog fast peak detector for 10ns pulses if OPA615 is not suitable? Wchich IC (OPAMP/COMPARATOR) i must use?

I need to detect low amplitude pulses - from 10mV.

I conluded that:

-capacitor value is important - small cap. is fast charged and too fast discharged.

-diodes has parasitic capacity and forward current which discharge my detector capacitor.

- I had different results witch different diodes

- detector for pulses above 100ns  works good.

Where is the problem? Damage OTA? Diode? Capacitor? Bad design? OPA too slow?

Other solutions:

www.edn.com/.../High-speed-peak-detector-uses-ECL-comparator

sound.whsites.net/.../an014.htm

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LOG114: Unexpected behavior of LOG114 output

October 7, 2018, 1:52 pm
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Part Number:LOG114

Hallo,

I have a weird problem with the LOG114 log amplifier, which is the part of an experimental power supply for monitoring current consumption of low-power devices.

I include the relevant schematic part and the layout too.

Information to the schematic:

  • The supply current of the DUT (powered by the circuit) is intended to flow from the P3 banana jack to GND (common ground plane designated with the triangle like ground symbol). The current is divided by R10 and R12, so approximately the hundredth of the current is expected to flow through the LOG114I1 input to GND.
  • VCC is +5V, VEE is –5V, supplied by 78L05 and 79L05 linear regulators.
  • The Vcom is from a DAC buffered by U7.
  • The "ARAM" reference label is connected to a single-ended ADC input (R9 and D3 protects the ADC from incidental negative voltages).

After the first power-up the Vlogout output of LOG114 was expected to be a negative voltage (to GND) with no current flowing in P3 (Vcom was set to 0V), but it was cca. +0.10V (to GND). This output voltage seemed to rise slowly until it reached cca. +0.3V. I tried multiple things:

  • Tied P3 to GND. No change in the output.
  • Connected P3 to a current source of a few tens of milliamperes. The output would be more positive, so something is working :)
  • Resoldered the LOG114 many times. After soldering (but the circuit is still hot) the Vlogout pin went to near –5V, but during cool-down it was suddenly risen up to cca. –0.2V, and from this it was slowly increased to the original value.
  • Cleaned the flux residues, no change.
  • Connected the A4 and A5 internal op amps to a more fixed state (non-inverting input to GND, inverting input soldered to output), no change.

Then I replaced the IC with a new one. With this new chip the Vlogout voltage was changed to a stable +0.4V, no slow increment or decrement. The output still responded to test current input, but no change to anything else (the 0.4V seemed to be stable even at higher temperatures, in contrast with the previous chip).

Then I soldered back the former IC, but I experienced the same effects listed above.

Do you have any idea what may be wrong in this circuit? May the chips damaged during soldering? (We use 270-300°C hot air, 60/40 leaded no-clean flux solder wire and Chipquik SMD291 for QFN chips.)  Or some currents flowing in the ground plane may affect the measurement so seriously?

Thank you in advance for help.

Gábor

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INA333: Thermal pad connection of WSON package (INA333)

October 7, 2018, 8:26 pm
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Part Number:INA333

Hi team,

I'm using the INA333 WSON package in a low-power sensor application with a single rail supply.

Should the thermal pad be tied to ground or left unconnected? I didn't find any specific information for the INA333

Thanks for your time. 

Best,
Sunaal

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INA225: Step response waveform

October 7, 2018, 9:53 pm
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Part Number:INA225

Hi team,

Do you have any zooming waveform to show the step response like below one? The time scale < 5us per div will be better.

Thank you.

Regards,

Allen

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RCV420: RCV420 4-20mA to 5-0V Conversion

October 7, 2018, 10:09 pm
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Part Number:RCV420

I need to convert 4-20 mA to 0-5V.

I refer to the datasheet (FIGURE 12. 4-20mA to 5-0V Conversion)

I would like to ask about the connection of the circuit.
1.PIN3-floating?
2. Is PIN4-connected to ground or -VDD?
3. Can the PIN14 output be connected to a 20k resistor to ground?

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OPA564: paralleled operation in TINA

October 7, 2018, 10:46 pm
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Part Number:OPA564

Hello,

Ive been working with the OPA564 for a few weeks now and I've gotten my circuit working nicely with a single OPA564. I'm looking to expand the current capabilities, and was looking to try and parallel a second OPA564 into my existing simulation model. While this "new" version does simulate in TINA, I am aware there are nightmares that probably come with this in 'reality' (e2e.ti.com/.../paralleling-op-amps-is-it-possible)

In the end, the desired goal would be to have two OPA564's on a board sharing the current load and have the output of the final boards be parallel-able as well. Stacking boards for flexible current configurations

Again, simulations *seem* to work, but I'm sure there's gotchas somewhere. 

Sim attached.

(Please visit the site to view this file)

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THS3217: ths3217

October 7, 2018, 11:04 pm
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Part Number:THS3217

Need a very fast differential amp such as THS3217.

I need to model my circuit & simulate its transient and  ac response.

What  model TINA-TI will correspond to THS3217 chip?

You can suggest any other opamp similar to THS3217 that has a TINA-TI model...It does not have to be 800 Meg. Even 1 MHz  will do. As long as it can act on the input difference  & amplify. I need to remove the 2.5V common mode from a sensor. Output will be bipolar as a result. But has to be fast. INA series wont do.

thnx

robin

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OPA4330: About oscillation problem

October 8, 2018, 12:53 am
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Part Number:OPA4330

OPA4330 is used below circuit, but occur oscillation.

If there any reason and modification point, please let me know.

【Additional information】

・Output side is connecting ADS1274 input side.

   C60 is GRM32ER71H106KA12 (Murata) and C62 is GRM155B31H104KE14 (Murata)

・When C60 remove and left open, frequency and oscillation was be large.

Best regards,

Satoshi

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THS4551: DC Non-linearity issue

October 8, 2018, 2:02 am
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Part Number:THS4551

Hello Team,

we are building a 500 kHz low pass active filter for driving an ADS127L01 according to THS4551& ADS127L01 datasheets.

After the pcb has been routed and assembled, the DC linearity measurement of circuit has been performed. The results of measurement was quite surprising for us, because the measured nonlinearity is in range of 20ppm for -1V to +1V of output voltage of THS4551 powered by 3.3V High PSRR and low noise LDO.

As Rg and Rf resistors the LT5400-4 was used, other resistors are 0.1%, 10ppm/C. All capacitors excluding bypassing ones (X7R) are NPO. We use 4 layer stack up for pcb and we strictly meet all criteria recommended in THS4551& ADS127L01 datasheets for pcb layout, IC bypassing, fully symmetrical routing etc.

Our measurement setup includes: Fluke 5720A Calibrator (calibrated approx. two months ago) used as a signal source, Wavetek 1281 (calibrated approx. month ago) used as voltage meter. The whole circuit was powered from 6V lead acid battery. All measurement cables, power cables and pcb itself was properly shielded to reject environment influence. 

If schematic is needed, we could send it offline.

Do you have any ideas what could be the issue? Is it some characteristics feature of the FDA due to its internal structure or might it be some natural behavior of FDA itself? 

Thanks for your help,
TI Customer

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ONET8521T: ONET8521T

October 8, 2018, 2:34 am
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Part Number:ONET8521T

We are planning to work in an application using the ONET8521T. The input currents to the TIA will be around 90-100 uA, and it is very important to have the TIA working in its linear region since the signal should not experience any distortion. Looking at the datasheet, Fig.3, we understand that for this range of currents we are in the linear range so it should work. But we have doubts about the AGC performance. We understand from page 6 in the datasheet, that this AGC only operates if the input signal current exceeds a certain value. So we require if you can confirm us that the AGC will not operate for this range of input currents of our application. Thank you.

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LM293: I want ROHS of all Ti components

October 8, 2018, 4:18 am
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Part Number:LM293

Hi ,

In our design we are using so many TI components(IC's).

I want ROHS compliances of all it's components, where we will get this information

Thanks,

siva

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ONET8521T: Purchasing problem

October 8, 2018, 5:19 am
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Part Number:ONET8521T

Dear

I was working with this component but now I cannot find a provider, please could you help me with some information about where and when can I get the ONET8521T?

regards

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RCV420: RCV420 for 4 to 20mA RS233 application

October 8, 2018, 5:36 am
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Part Number:RCV420

Hi Sir,

Our customer SPEC want to Design RS232 type 4 to 20mA receiver & transmitter, Similar as below,
Do you have TI solution suggest for me? What's the TI solution Benefits?

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THS7002: PRE AMP used as a "diferential" LPF

October 8, 2018, 7:07 am
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Part Number:THS7002

Hi!

Can the "PRE AMP" of the THS7002 be used as an "LPF subtracter"? Such as represented in the diagram.

The inputs "Vin +" and "Vin -" would have a DC value (of the order of 4 Vdc) that is wanted to cancel, but keep (and amplify x4) the difference between "Vin +" and "Vin -".

Thank you. Regards!

Aldo.

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THS4541: ths4541

October 8, 2018, 8:03 am
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INA240: INA240

October 8, 2018, 8:23 am
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Part Number:INA240

Hi All

If a circuit using INA240 is powered by a battery can it then be used as an isolated current measurement device without regards to its common mode input voltage range?

Regards

ik

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