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® APPLICATION NOTE TSM101 USED IN A VOLTAGE SUPERVISOR by S. LAFFONT This technical note shows how to use the TSM101 · the positive input (V5) of the second operator integrated circuit to realize a voltage supervisor. (pin 5) is lower than 1.24V. An example of realization is given. A resistor network (R1, R2, R3) is used to bias theinput of the two operators, when the input voltageis out of the limits, the output (pin 6) is close to zero. 1 - TSM101 PRESENTATION This signal can be used directly to power an opto- The TSM101 integrated circuit incorporates a high coupler. stability series band gap voltage reference, two In our application, we have added a transistor (Q1). ORed operational amplifiers and a current source(Figure 1). This transistor is driven via a Zener diode (D1).This circuit has two advantages : Figure 1 : TSM101 Schematic Diagram 1 - this Zener diode avoids problems encoun-tered with many voltage supervisors : when thesupply voltage is lower than the operating volt-age of those circuits, the behavior is erratic.The minimum operating voltage of the TSM101 is5V. With a 4.7V Zener diode, the transistor Q1 willnever be saturated if the supply voltage is lower 1 Vref 8 than 5V whatever the output of the TSM101. 2 7 2 - the optocoupler is ON only if the input voltageis inside the specified range. 3 6 3 - CALCULATION OF THE ELEMENTS 4 5 Let assume :· Vmin. = minimum threshold voltage· Vmax. = maximum threshold voltage· VCC = nominal voltage We have the following equations : 2 - PRINCIPLE OF OPERATION AND (Vmin. x (R1+R2)) SCHEMATIC DIAGRAM V5 = = V R ref The two operational amplifiers are used as compa- (V rators. max. x R1) V7 = = Vref R The first operator has its + input wired to the internal1.24V reference and the second one its - input Vre x Rf) R1 = wired to 1.24V. Vmax.

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