Hello,
While this is the expected behavior of the XTR300, we do not specify the behavior in the product datasheet. To our knowledge there is no way to reduce the overshoot effects at light loads.
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Forum Post: RE: Inquiry regarding suggested minimum load impedance on XTR300
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Forum Post: RE: LMP7721 Evaluation board Transimpedance config.
Hi Ishara,
The feedback resistor pads were a compromise. You can get up to 550G in 1206. To put the pads for a 2512 resistor would have added too much surface area. The majority of the resistors used would be 1206 or smaller - and you can stretch 0402's onto 1206 pads...but the 2512 just would have been too big. You can't please everybody...:^(
You can mount the large 1T resistors on their side...it also reduces the stray capacitance to the board...tricky, but possible. Not great for production, but good for prototyping (and easier to remove). Solder one end down (an intentional "tombstone") and solder a thin wire from the other terminal to the other pad. Ideally the wire should be on the low impedance (output) side.
Or you could get two of the 549G resistors and tombstone them together...it also reduces the series capacitance by half....IF you can get them...Ultra-high resistance values are not a high volume item and distributors generally don't stock them. You may have to go directly to the manufacturer and ask for "samples".
Sorry... I do not have any 'spare' boards here...I sent them all to the warehouse. Just tack the cap across the top of the resistor (if possible, use a 1206 cap - larger body will reduce leakage).
Regards,
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Forum Post: RE: LM6084 opamp stability with very high source resistor
Hi Bill,
It should be stable.
Where it could go unstable (oscillate) is during reset when the switch is closed. With the switch closed, the op-amp is a pure follower (output connected to -IN) and it will see the 10pF as an additional output capacitive load (in addition to any existing output C load). Followers are the most unstable configuration, and the most sensitive to capacitive load. 10pF extra could push it over the edge.
Place at least 100 ohms in series with the switch to keep the amplifier from driving the 10pF directly back through the switch. Simple integrator schematics tend to omit this important resistor.
See Ron Mancini's article:
http://www.edn.com/design/analog/4333099/The-nuances-of-op-amp-integrators
Regards,
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Forum Post: RE: 4136 Quad OP-AMP Replacement with TL075 or TL075CN? What does "CN" mean?
Hi Tony,
C: Comercial Temperature Range (0 to 70oC)
N is the package naming. It shows the package in the dataseet.
The TL075 is actually the same device as the TL074, but with different pinouts.
If you are looking for drop-in device, then the RC4136 (I assume you meant RC4136) will be your choice.
Thanks,
Ying
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Forum Post: RE: TLV2374 Absolute Maximum question for VDD and Vout
Hi, Ken
As you said, I wanted to know the ABS spec to protect OPAMP.
If you have, Would you share a application note for protecting OPAMP?
Thanks for the great support
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Forum Post: RE: High precision differential amplifier 50 kHz
Markus,
The "Differential input capacitance" spec is typically 12pF. Op-amps with lower cap spec should be helpful. Lowering the resistor values will also help.
As another thought; is the output also pure sine wave? Amplifier non-linearity (distortion) could affect results.
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Forum Post: RE: XTR111 IS pin voltage
Hello,
Unfortunately this result is not correct. If the supply voltage is at 12V and the IS pin is at 6.3V it means that current is flowing out of the IS pin and causing a voltage drop across the internal current sensing circuitry. Could you put an ammeter in series with the IS pin to measure the current flow?
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Forum Post: RE: PGA117 Shutdown Mode: Safe Apply Voltage to Inputs?
Hello Edmond,
There is no problem with applying voltage to the PGA117 inputs while in shutdown mode with power applied. However, if you remove the power supply AVDD, you could possibly damage the device if you do not remove the input as well.
If you look at the Absolute Maximum Ratings table (copied below), you can see that the maximum input ratings are given relative to GND and AVDD. Ensure that you stay within these ratings to avoid damage to the IC.
Best regards,
Ian Williams
Linear Applications Engineer
Precision Analog - Op Amps
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Forum Post: RE: ISO124 Gain error
Hello cafain,
Unfortunately we only have a typical specification for that parameter.
Best regards,
Jose
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Forum Post: RE: TLV2374 Absolute Maximum question for VDD and Vout
You could put a simple diode in series with the power supply pins. Cathode to the VDD pin and Anode to the offending reverse battery.
Under normal operation the op-amp will see a diode drop, so be prepared for the loss across the diode. Maybe a Schottky for a lower drop, maybe the body diode of a FET (higher expense),
-Ken
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Forum Post: Single Supply OPA350 Rail toRail Operation
Hello,
I am designing power electronics converter in which I will measure the DC capacitor voltage. As an isolated voltage sensor, I will use ACPL-C87X from Avago. This IC needs a post amplifier to combine its differential output into single ended signal with a difference amplifier. The IC suggest usage of OPA327 but I will use OPA350 because I assume it is superior.
The point is I want to use single supply for cost reasons.
When I search the net, I found that some people shift the referance point to Vdd/2 to resemble the structure with split supply case in which references previosly were at GND potential. Furthermore, inputs of the amplifier are AC coupled by caps.
Considering my both inputs to the difference amplifier is positive and their difference is never negative and so output voltage, do I need such things? I am measuring DC cap voltage which is unipolar (DC and 50Hz swing - maybe 10 or 20 percent at worse). I think I dont need such extra precaution. I believe what I just need to is to connect GND to negative supply pin of opamp.
The suggested application schematic can viewed in Figure 19 of the ACPL-C87X datasheet and input signal variation (Vout+ and Vout-) of the amplifier is shown in Figure 13 at the same document.
Also, I wonder the offset voltage and other undesired effects when I design the circuit as I described.
Lastly, I will use the opamp output signal to feed the ADC of F28377D of TI. So how should I feed this signal to the DSP? An RC filter? What values?
Thank you!
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Forum Post: RE: High precision differential amplifier 50 kHz
Markus,
First, make sure your measuring equipment has flat response. Use a high-quality sine or square wave generator as a signal source. Don't forget to calibrate your scope probe.
Second, input a square wave into your circuit. Does the output ring? If so, the input capacitance of the op amp may be giving an underdamped response and frequency peaking. You can try two things to fix this: reduce the R values, or add a small C across the feedback resistor. If the input C is the problem, you may see unacceptable unit-to-unit variations. The best way to solve this is probably to reduce the R values.
Another thing that can cause problems is poor power supply bypassing.
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Forum Post: RE: ISO124 Gain error
Hello Jose,
I understand.
Thank you,
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Forum Post: ICL7652P Chopper Stabilized OPAmp: C Return
Hi all,
I would like to use the ICL7652P (8-pin device) for the first stage of an analouge integrator.
From the datasheet you see the functional block diagram and there you are told to connect the capacitors CXA and CXB to VDD- or C Return.
For my given PCB I connected them to C Return and this results in utter malfunction.
According to the block diagram I should expect a low impedance connection between C Return and VDD- but this is not true.
So next step was to short C Return and VDD- on the board and now the circuit works but with very bad performance concerning noise.
Is there a typo in the datasheet or do I miss here anything?
Thanks and best regards,
Gerald
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Forum Post: RE: Inquiry regarding suggested minimum load impedance on XTR300
Hello,
This disagrees with the data I provided a few posts ago where the output overshoot is within a standard range once the output load is roughly 30 Ohms. We took data using the XTR300 EVM with the default components. This includes a 15Ohm series resistor and 10nF capacitor to GND on the output terminal. What type of output loading circuitry is your customer using?
You can see the schematic for the XTR300EVM in the User's Guide: http://www.ti.com/lit/ug/sbou034a/sbou034a.pdf
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Forum Post: RE: TLV2374 Absolute Maximum question for VDD and Vout
Hello Jake,
1. How much negative voltage VDD pin can endure?
Intergrated circuits in general are not intended to be subjected to reversed supplies. Most integrated circuit structures have a substrate diode, or something equivalent to a substrate diode, that exists between the VDD and GND pins. This diode is normally reverse biased when the circuit is powered normally, but will become forward biased when the supplies are reversed. Once the forward bias increases beyond about a half a volt the diode conducts higher and higher current as the voltage across the diode is increased. If the voltage becomes too high the diode will conduct so much current that the integrated circuit is damaged. The diode isn't characterized for this type operation and one should avoid it.
2. What about negative input on VDD with respect to the GND. How much negative voltage can TLV2374 endure on Vout pin?
The TLV2374 inputs and output have ESD steering diodes connected from each of them, to each supply. They are reverse biased in normal operation. If you attempt to drive these pins below GND, they will become forward biased and draw higher and higher current as the forward bias is increased. Again, this is something you should avoid. The data sheet limits the voltage to 200 mV beyond the supply rail voltages.
Regards, Thomas
PA - Linear Applications Engineering
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Forum Post: RE: pH measurement with TI's INA116
Hello Marko,
Can you please give us the part number of your pH electrode(s) so we can look at the data sheet(s)?
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Forum Post: RE: TLC2652 layout instruction
Generally a ground plane is a good thing, but you have to be a little careful. Here's perhaps a starting point:
First, make sure you decouple both power supplies with a ceramic cap (one supply if you are operating single supply). 0.01uF to 0.1uF usually works. I also tend to put a large tantalum cap in parallel with the ceramic (10uF to 100uF depending on what I am doing). The ground connection on the decoupling cap should be as short as possible (multiple vias to ground is always nice) and the ceramic cap should be as close to the power pin as possible. The tantalum can be a little further away. Wide traces keep inductance down (inductance is what you are trying to reduce with a ground plane)
Second, I often remove the ground plane from under the inverting input node to reduce capacitance. For the TLC2652 this might not be as important (lower GBW) but it is a good habit. The stray capacitance on this node can introduce a zero in the noise gain (aka a pole in the loop gain AvB) and reduce the phase margin of the amplifier. Whether this is an issue depends on your circuit. Test with a square wave input and look at the overshoot and ringing.
When laying out the circuit, keep the inverting node as small as possible. It's OK for the output node traces to be longer since the output impedance is low, but also don't route the output node near the inputs as it can capacitively couple and create an unwanted feedback path (and likely an oscillator).
Also, remember Bob Pease's advice...always put a small capacitor across the feedback resistor unless you can prove you don't need it. Often a few pF is sufficient.
Hope that helps!
Tim
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Forum Post: INA117KU ratings
Hello,
I am using INA117KU to sense a current going to my DC motor on the high side. The max. voltage across the motor is +/-36vdc (travels in both directions). The sense resistor is 0.1 Ohm. I have no other resistors in line with the input pins of INA117. I have experienced failures of INA117 on three occasions. One of the things to mention is that I am powering INA117 with +/-12Vdc. I do know that the specs on CM will not be +/-200V and it will decrease but not sure by how much. I am wondering if the inputs could be protected somehow. I have seen some samples with isolated pre-op amps but that I can’t do due to the space requirement.
Any ideas?
Thanks
Peter V.
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Forum Post: RE: Single Supply OPA350 Rail to Rail Operation
I think you can do it as you suggest, fully single ended. As long as the instantaneous current through the sense resistor is always greater than zero. When the inputs to the differential amplifier are zero, Vout will try to go to the same voltage as GND2 (in Figure 19 of the Avago data sheet). Since the opamp only goes to a few 10s of mV above, that would be an error. But as long as the current always flow one way through R2, it should work. You could try it in TINA-TI and see for yourself.
I can't answer about the ADC.
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