Estimated method of the CQ-3 series IC internal temperature

【Method】

Because the temperature properties of forward voltage of diodes have good linearity, we can use the diodes as a thermometer. A diode leads to GND terminal and TEST1 terminal in the CQ-3 series IC inside, as shown in Figure 1. When we energize a current between these terminals, we can estimate IC internal temperature from the forward voltage of time we let a diode have conduction.


 Figure 1. Estimated method of IC internal temperature

 

【The prior measurement of IC internal temperature】

To use a diode as a thermometer, we must measure the forward voltage of diode beforehand. Using measurement circuit of Figure 1, we measure the forward voltage of diode while changing environmental temperature. In addition, we don't have to apply the power supply voltage between VDD-GND of the current sensor. After having changed environmental temperature, please measure it after confiring that a value of the forward voltage of diode is stable.

 

As an example, we show temperature property of the forward voltage of diode that we measured in Figure 2.


 Figure 2. Temperature property example of the forward voltage of diode.

 

【About temperature estimate】

We estimate IC internal temperature using the correlation that we found in Figure 2 from a value of the forward voltage of diode.

 e.g.) In the case of Vf = 600mV, Tj = 40℃

※Please be careful because diode properties are not the same circumstances in all current sensors.

 

【Notice: About the voltage between the GND-TEST1 terminal when we apply VDD.】

When we apply VDD, the voltage between the GND-TEST1 terminal does not show the forward voltage of diode because an internal circuit operates, and estimate precision of the IC internal temperature using the correlation of Figure 2 turns worse. If you want to estimate IC internal temperature when you applied VDD, please turn off VDD only at the time of the measurement of the forward voltage of diode.


 Figure 3. Estimate method of the IC internal temperature in applying VDD.

 



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