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university:courses:electronics:electronics-lab-window-comp-tmp01 [07 Mar 2018 12:20] – add hardware setup and procedure Antoniu Miclausuniversity:courses:electronics:electronics-lab-window-comp-tmp01 [07 Mar 2018 13:14] – Antoniu Miclaus
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 ===== Window Comparator ===== ===== Window Comparator =====
 +
 ==== Background ==== ==== Background ====
  
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  On the plot the "windows" can be noticed when the input voltage is between the upper and the lower voltage references.  On the plot the "windows" can be noticed when the input voltage is between the upper and the lower voltage references.
 +
 +===== Temperature Control =====
 +
 +==== Background ====
 +
 +An example of a window comparator application is a simple temperature controller circuit (Figure 2). The temperature sensor, TMP01, has the dual comparator configuration of figure 1 built in. By choosing the proper values for R<sub>1</sub>, R<sub>2</sub> and R<sub>3</sub> the circuit monitors if the temperature holds in the required range (25 ± ~10 °C).
 +
 +The TMP01 is a linear voltage-output temperature sensor, with a window comparator that can be programmed by the user to activate one of two open-collector outputs when a predetermined temperature set point voltage has been exceeded. A low drift voltage reference is available for set point programming. By connecting the two open collector outputs together as a single wire OR output we can obtain a signal which is at a logic high when the ambient temperature is within the target window.
 +
 +<WRAP centeralign>{{:university:courses:electronics:tmp01_window_comp-sch.png|}}</WRAP>
 +
 +<WRAP centeralign> Figure 4 Temperature sensor window comparator </WRAP>
 +
 +==== Programming TMP01 ====
 +
 +In the basic fixed set point application utilizing a simple resistor ladder voltage divider, the desired temperature set points are programmed in the following sequence:
 +
 +1. Select the desired hysteresis temperature.
 +
 +2. Calculate the hysteresis current I<sub>VREF</sub>.
 +
 +3. Select the desired set point temperatures.
 +
 +4. Calculate the individual resistor divider ladder values needed to develop the desired comparator set point voltages at SET HIGH and SET LOW.
 +
 +The hysteresis current is readily calculated. For example, for 2 degrees of hysteresis, I<sub>VREF</sub> = 17 μA. Next, the set point voltages, V<sub>SETHIGH</sub> and V<sub>SETLOW</sub>, are determined using the VPTAT scale factor of 5 mV/K = 5 mV/(°C + 273.15), which is 1.49 V for 25°C. Then, calculate the divider resistors, based on those set points. The equations used to calculate the resistors are:
 +
 +V<sub>SETHIGH</sub> = (T<sub>SETHIGH</sub>+ 273.15) (5 mV/°C)
 +
 +V<sub>SETLOW</sub> = (T<sub>SETLOW</sub> + 273.15) (5 mV/°C)
 +
 +R<sub>1</sub> (in kΩ) = (V<sub>VREF</sub>−V<sub>SETHIGH</sub>)/I<sub>VREF</sub>= (2.5 V −V<sub>SETHIGH</sub>)/I<sub>VREF</sub>
 +
 +R<sub>2</sub> (in kΩ) = (V<sub>SETHIGH</sub>−V<sub>SETLOW</sub>)/I<sub>VREF</sub>
 +
 +R<sub>3</sub> (in kΩ) = V<sub>SETLOW</sub>/I<sub>VREF</sub>
 +
 +The total R<sub>1<sub> + R<sub>2</sub> + R<sub>3</sub> is equal to the load resistance needed to draw the desired hysteresis current from the reference, or I<sub>VREF</sub>.
 +
 +I<sub>VREF</sub> = 2.5/( R<sub>1</sub> + R<sub>2</sub> + R<sub>3</sub>)
  
university/courses/electronics/electronics-lab-window-comp-tmp01.txt · Last modified: 03 Jan 2021 22:21 by Robin Getz

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