Voltage scaling for Temperature

Thread Starter

SoundguyAL

Joined Nov 4, 2020
3
HI All,
I'm trying to figure out how to design the circuit to scale voltage from a TMP01 from Vptat to F.
I have made the circuit that is in the datasheet and it works but I want to learn more about opamp design.
Also, the circuit in the datasheet uses 2 opamps. I know it can be done with 1 using differential inputs.
I have reduced the equation and now I need to figure out to calculate R1, R2, R3, R4
On the TMP01 Vref = 2.5V.
The conversion for Vptat to 10mV/F is:
Vptat*3.6 - 4.6

So at room temperature, and as per the datasheet, 1.49*3.6 - 4.6 = .764 (76.4F)

Just to prove the eqn...
Boiling point = 1.86575
1.86575*3.6-4.6 = 2.1167 (212F)

and freezing
1.36575*3.6-4.6 = .3167 (32F)

circuit.PNG


The transfer function is:
Capture2.PNG

I need some tutelage on how to tackle finding the R values.
Do you just set 1 or more R values at say 100K and solve?

Whats the approach?
I really appreciate some knowledge here!
 

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Thread Starter

SoundguyAL

Joined Nov 4, 2020
3
Welcome to AAC, Saoundguy.

Isn't calculation of the divider resistors covered on page 9 of the datasheet or thereabouts?
Thanks jpanhalt!

No, those calculations are making the high and low temp set points for the comparator.
I'm trying to scale the output on pin 5.
 

Thread Starter

SoundguyAL

Joined Nov 4, 2020
3
I drew the opamp wrong.... Vref and Vptat are reversed.
And I didn't see how to edit the original post.

Here is the way it's supposed to be:

circuit.PNG
 

jpanhalt

Joined Jan 18, 2008
11,088
Are these the equations you need:

1604595239546.png

Source: National Semiconductor AN-31 (old). National Semi is currently owned by TI. I suspect the same or similar AN is on its site.
 
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