I'm using the ina 220 to monitor the current and bus voltage, I am reading data via i2c every 2mS interval. The current readings are close to my expectations . But the bus voltage value at few instances reads zero. Is it because of the data read sampling frequency? or it could be because of some other factors?

the below is the reading of bus voltage for a period of 400mS.

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OPA615: Supply rail and Bias problem

March 19, 2019, 3:27 am

≫ Next: OPA547: About the variation of the current limit

≪ Previous: INA220: Bus voltage reading showing zero at few instances of time.

Part Number:OPA615

I am using the OPA615 as a high speed integrator as per Fig 47 in the data sheet. I have simulated it in Altium and all looks OK. There is something wrong on my board however. When I power up, the -5V line gets dragged down and my chip starts to overheat. I have resolved this by adding a resistor (1Meg) from the base (pin 2) to ground. This appears to work and stops the -5V being dragged down but I am not clear why this is necessary and why it is not shown or mentioned in the DS. The downside of course is that my hold capacitor is discharging quite rapidly.

Any thoughts?

Ian

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OPA547: About the variation of the current limit

March 19, 2019, 5:55 am

≫ Next: LMC6492: Thermal Resistance

≪ Previous: OPA615: Supply rail and Bias problem

Part Number:OPA547

Hello team,

My customer is designing the current limit value of OPA547 with 56.33mA.
*Please see the attached file.

(Please visit the site to view this file)

　Please let me ask you two questions about the variation of
the current limit value.

Q1) Could you please inform me of the variation of the current limit value
        including the temperature influence?

Q2) Could you please inform me of the variation of internal resistance,
       the internal reference and the gain to estimate the variation of current limit
        value when changing the external resistance value,if possible?

Sincerely,
Tsuyoshi Tokumoto

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LMC6492: Thermal Resistance

March 19, 2019, 8:13 am

≫ Next: THS4509: 4th stage butterworth LPF distortion

≪ Previous: OPA547: About the variation of the current limit

Part Number:LMC6492

Regarding part number: LMC6492BEM/NOPB

I need the thermal resistance of the package. Specifically I need the theta JC (junction to case) or the theta JB (junction to board) thermal resistance.

Thanks

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THS4509: 4th stage butterworth LPF distortion

March 19, 2019, 9:20 am

≫ Next: INA199: Asking or the INA199 schematic review

≪ Previous: LMC6492: Thermal Resistance

Part Number:THS4509

Hello,

I'm struggling with the distortion generated by an active filter using a THS4509 and a THS4541.

The (AC coupled) low pass filter has a gain of 17dB and a cutoff frequency of 33MHz. The output of this filter is used to drive an ADS4128 12 bit 200MSPS ADC.

The input of the filter is single ended terminated at 50 Ohm and the output is differential.

Both stages are amplifiers with RLC LPF outputs in order to lower GBW requirements.

I am using TinaTI to simulate the circuit.

My problem is that I get a very very low harmonic distortion (in nV) at 10MHz (within the band pass) which is good, but a lot higher distortion at 5MHz (in tens of µV) for example (within the band pass too), which does not makes sense to me. Is this expected? How can I remedy to such variations due to the input frequency?

The PCB is already manufactured. I have a source able to generate a good 10MHz sine, and I was able to obtain the graph below. However, I don't have any other clean source, so I can't measure 5MHz for exemple in real life, I have to rely on TinaTI.

The TINA TI simulation file is attached.(Please visit the site to view this file)

Thanks in advance for your help!

Victor

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INA199: Asking or the INA199 schematic review

March 19, 2019, 9:49 am

≫ Next: LM293A: Common mode input voltage understanding

≪ Previous: THS4509: 4th stage butterworth LPF distortion

Part Number:INA199

Hi Team,
customer is evaluating INA199.
Would you please review the schematic and provide your comment?

The trigger voltage will be designed as 1.65V for 33mA as below calculation.

txn.box.com/.../71ikwey1ngjhn2gmfq96grhngs6xffuy

BR,
SHH

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LM293A: Common mode input voltage understanding

March 19, 2019, 10:54 am

≫ Next: INA240: INA240A2 stuck at ground with Vcm = 0

≪ Previous: INA199: Asking or the INA199 schematic review

Part Number:LM293A

Dear all：

For the LM293, the input voltage should be less than 3.5V at room temperature, and 3V over temperature. We recommend the 3V limit.——This is the specification.

The "common mode input voltage" should be less than 3V, is it consistent with our understanding that the voltage between IN- and IN+ of the comparator and the supply negative (GND) of the comparator should be less than 3V?Or is it something else?

for example：

The following is the description of the specification：

But here's how it works：

(1) IN the first stage, the voltage adjustment of U5A IN+ to GND is 4.5v, and the voltage adjustment of IN- to GND is 4V, and the output is 5V, (correct)
IN the first stage, the voltage adjustment of U5A IN+ to GND is 4.5v, and the voltage adjustment of in-gnd is 5V, and the output is 0V, (correct) which is inconsistent with the specification description

(2) voltage adjustment of U5A IN IN the first stage to GND is 4.5v, and voltage adjustment of IN+ to GND is 5V, and output is 0V, (error)
IN the first stage, the voltage adjustment of U5A IN to GND is 4.5v, and the voltage adjustment of IN+ to GND is 0V, and the output is 0V, (correct) which is consistent with the description IN the specification

So am I wrong about the definition of the common mode input voltage?

Thank you！

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INA240: INA240A2 stuck at ground with Vcm = 0

March 19, 2019, 11:37 am

≫ Next: THS4631: About how to obtain a scaled-down signal of op amp's output

≪ Previous: LM293A: Common mode input voltage understanding

Part Number:INA240

I have designed a board with many INA240A2 for current sensing. Some, but not all of the parts will power up with the output ground. The output should be at 1.024V due to a 2.048V offset applied to REF1, and REF2 grounded.The power supply is regulated to 5.1V. The inputs are across a 0.02 ohm sense resistor and held strongly at ground at startup. If I increase the common mode voltage to 1V, then the output goes to the expected 1.024V. Taking Vcm back to zero, the INA240 output returns to 0. According to my reading of the datasheet, the part should be functioning properly with Vcm from -4V to +80V. The individual chips are all marked I240A2 and 86KG4. What is going on ?

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THS4631: About how to obtain a scaled-down signal of op amp's output

March 19, 2019, 6:26 pm

≫ Next: MC3303: ESD rating

≪ Previous: INA240: INA240A2 stuck at ground with Vcm = 0

Part Number:THS4631

Dear TI expert,

I use THS4631 to integrate a signal as fig1. And the actual PCB is as fig2. Due to power supplies, Vo will be saturated to about +18V. Since I want to compare the output with a reference by a high-speed comparator that is powered by +3.3V, I need to scale down the Vo to Vos, that is, 1/6 of Vo.

Currently, I use a regular slide rheostat as Rt1 in fig2, but Vos waveform is not good and deviates from theoretical waveforms obviously. In fig3, yellow is Vos, blue is Vo and Vo is intended to be halved . However, they don’t meet the proportional relationship.

Can you please tell me how to obtain a scaled down signal that follows Vo well and as precise as possible?

fig1

fig2

fig3

Best Regards

Yatao

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MC3303: ESD rating

March 19, 2019, 9:23 pm

≫ Next: LM293A: Schematic problem

≪ Previous: THS4631: About how to obtain a scaled-down signal of op amp's output

Hi Team,

My customer need the information to get the device approval in their system, but cannot find ESD rating of MC3303DR in datasheet. Could team help to provide it?

Thanks a lot.

Vincent Chen

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LM293A: Schematic problem

March 19, 2019, 11:07 pm

≫ Next: Searching suitable quadruple op amp as buffer for ADC

≪ Previous: MC3303: ESD rating

Part Number:LM293A

Hi all:

Have a reply:"The first stage, U5A, is at the biggest risk. Both the input and reference voltage exceed the limit and has the possibility of an incorrect output."

However, IN my actual test, the voltage of U5A IN+ to GND IN the first stage is about 3.9v, and the voltage of IN- to GND is about 1~ 4.5v. My test results are all normal

So, is it ok to assume that I designed this circuit?

Or my input and reference voltage are over 3V, there are hidden dangers, how to improve?I've made thousands of them

Thank you!

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