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university:courses:electronics:electronics-lab-window-comp-tmp01 [07 Mar 2018 12:20]
Antoniu Miclaus add hardware setup and procedure
university:courses:electronics:electronics-lab-window-comp-tmp01 [07 Mar 2018 12:36]
Antoniu Miclaus add tmp01 background and programming
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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