Input 4/20mA / 0/10V

Hello Fabrice,

We've worked on other designs similar to this one and the overall design method is valid.  Consider putting your design into TINA-TI SPICE to test the behavior and adjust the gain / scaling if required.  Also, we created a similar design that you may find interesting:  TIPD195 - 3-Terminal PLC Input reference design.   

Hi Collin,

Thank you for your diagram. I'll look it, and ask you if I have some questions.

Best regards,

Fabrice

Hi Collin,

I just look your design, it's very interesting but I think some points will be very difficult for us.

On my module, there will be 8 channels, INA188 has only one channel, so I will need 8 INA188, but is there another reference which can has more channels (2 or 4) ?

Moreover, in this design, INA188 is supplied with + or - 15V, is it compulsory to do that, because the output voltage is between 0.2 and 4.8V, so is it possible to supply it between 0 and 3V3 ? Then, my µc accepts voltage up to 3V3, so I think I need to recalculate resistors to adap the output voltage and also the power supply.

For example, I can put Vref at 1.66V and output voltage can be between 0.2 and 3.1V, do you think it's possible ? Because I'm trying to simulate it with TINA-TI, but 1,66V is for 0V and not for 5V. So, it means that my input will be between 0 and 10V.

Thank you in advance,

Best regards,

Fabrice Péden

Hello Fabrice,

The INA188 will not work with a +3.3V supply.  Consider using the INA333.  You can modify the TINA files associated with TIPD195 to use the INA333 and the different voltage scaling ratios that you determined using the equations from the design guide.

Hello Collin,

Thank you for this information.

I'm trying to do that. To simulate the INA333, I have just to modify the value of resistor of INA188 (150k instead of 20k and 50k instead of 25k) ? Or I need to modify another thing ?

Thank you in advance,

Regards,

Fabrice Péden

Attach your simulation file and we'll take a look. Depending on your configuration the input common-mode voltage vs. output voltage may limit the output voltage swing when operating on a 0/+3.3V supply. We'll take a look once we see the circuit.

Hello Collin,

Thank you for your help, I'm also discovering TINA-TI software ;-)

I have found INA333 in the library, but can I use the same formula than in the TIPD195 document ?

Regards,

Fabrice Péden

TIPD195_functional_with_INA333.TSC

Hello Collin,

I'have try to recalculate values of resistors.

R1 = 100k

R2 = ((R1*Vd)/(Vin-Vd)) = ((100k * 400mV)/(10 - 400mV)) = 4.167k

G = ((Vout - Vref)/(Vd)) = (3.1 - 1.67)/(400mV)) = 3.575

GINA333 = 100k/(3.575-1) = 39k

But with these values, I haven't the wished curbe. For me, I'd like to have : Input : 0V --> 0.24V & 10V --> 3.1V

Regards,

Fabrice

8664.TIPD195_functional_with_INA333.TSC

Hello,

Looks like you're getting closer.  Could you share an image of the circuit results you're getting as well as the desired results?  It was a little unclear in your last message. 

For example: 

Input = 0-10V

Output = ?

Input = 0-20mA

Output = ?

Hello Collin,

Sorry for my unclear message. Please, find below :

- My design

- result for 0/10v

- result for 4/20mA

Regards,

Fabrice Péden

Hello Collin,

Have you take a loot at my design ? What do you think about it ?

Thank you in advance,

Regards,

Fabrice Péden

Hi Fabrice,

I looked over the circuit and it looks to be performing as desired.  Were there any changes or modifications you need to make to the circuit operation?  The 0-10V and 0-20mA signals produce an output voltage of roughly 3V to 60-80mV. 

Hello Collin,

Thank you very much for your help.

Regards,

Fabrice Péden

Hi Collin,

I have mounted this diagram in real.

Voltages seems to be good everywhere (Vin, Vdiff, Vref) according to the waveforms except for Vout. I must have an outpu voltage which comes from 3V to 0.2V. When I measured, for 0V in input, I have effectively 3V, but for 10V in output, I have 3.4V (I think the AOP is in saturation).

I don't understand what I have these values. It's like my "+" and "-" were inverted, but I've checked everything is good. I tried to make this design two times, on both cards, it's the same.

If you can help me.

Thank you,

Regards,

Fabrice Péden

Hi Fabrice,

It does sound like the "+" and "-" inputs may be switched. If you input 0.5V, what is the output voltage? If it is greater than 3V (approximately 3.14V) then I believe the "+" and "-" inputs of the INA333 have been switched.

If inputting 0.5V does not increase the output voltage above 3V, please provide us with a table of measurement results of the output voltage for an input voltage of 0.5, 1V, 1.5V, 2V, etc.

-Tim Claycomb

Hi Tim,

I have swichted the both inputs. Now, it's working perfectly. But, it's not in agreement with the design, so I don't understand everything. I'll check once again to be sure that I did the good design.

Thanks

Regards,

Fabrice

Hi Tim,

I understand what happened.

The design of INA333 in Tina-TI and in the datasheet are different.

Tina-TI : 

Where Pin 2 is V+ and Pin 3 is V-

and datasheet :

where Pin 2 is V- and Pin 3 is V+.

There is a mistake in one of them (I supposed that it's in the Tina-TI).

Regards,

Fabrice Péden

Hi Fabrice,

The pin out shown in the datasheet is correct. Thank you for making us aware of the mistake with the Tina-TI model.

-Tim Claycomb

hello Tim,

I have the same electronics circuit, but i have some problem to undestand the result.

If i look your result => Vin = 10V => Vdiff = 2.16V => Vout = 0V

But if i try to calculate with Vin = 10V and Vdiff = 2.16V i found Vout = -1.5V (Vref =3V, Rg = 90.9Kohm, R1 = 100Kohm, R2 = 27.4Kohm and R3 = 107ohm)

can you help to undestand my mistakes ?

Thank you in advance

Best Regards

Malo

Hi Malo,

Could you please share a copy of your schematic? I know it is similar to above but it sounds like you have changed a few things.

Hi Zak,

my schematic is exactly the same and the measures on my electronic card are goods.

But i don't understand your formula (i want to write the formula in my SW). When i try to calculate i don't find the good result => my curve is more sloping.

I think one parameter is forgotten, but which one ?

Best regards

Malo Hénaff

Malo,

I'm not sure what you are referring to. Do you mean you do not see a gain of 2.1 (1 + 100k/RG)? I will need more information about the issue you are seeing to assist you.

Hi Zak,

Sorry, i have some diffficulty to explain my problem

Exactly, i see a gain of 2.1. So, if i calculate with G = 2.1 =>

Vout = ((V+) - (V-))*G + Vref

Incase of Vin= 10V => V+ = 0V and V- = 2.15V => Vdiff = 2.15V

Vout = (0 - 2.15)*2.1 + 3 = -1.5V

if i look your curve with Vin = 10V, the result is 0V => i don't undestand why my result is different

The blue curve it's texas instrument result, and red curve it's my result when i try to calculate.

So i don't undestand the theoretical calculation. Can you explain me the theoretical calculation ?

Best Regards,

Malo