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TL7700CPSR 数据表(PDF) 10 Page - Texas Instruments |
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TL7700CPSR 数据表(HTML) 10 Page - Texas Instruments |
10 / 15 page TL7700 SUPPLY VOLTAGE SUPERVISOR SLVS220C − JULY 1999 − REVISED NOVEMBER 2004 10 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 sense-voltage hysteresis setting If the sense voltage, Vs’, does not have hysteresis in it, and the voltage on the sensing line contains ripples, the resetting of TL7700 will be unstable. Hysteresis is added to the sense voltage to prevent such problems. As shown in Figure 20, the hysteresis, Vhys, is added, and the value is determined as: Vhys = Is × R1 Where: Is = 2.5 µA, typically at TA = 25°C At room temperature, Is has variations of 2.5 µA ± 0.5 µA. Therefore, in the circuit shown in Figure 19, Vhys has variations of ( ±0.5 × R1) µV. In circuit design, it is necessary to consider the voltage-dividing resistor tolerance and temperature coefficient in addition to variations in Vs and Vhys. tpo tpo RESET Vhys VCC 1.5 V T T Vs’ NOTE A: The sense voltage, Vs’, is different from the SENSE terminal input voltage, Vs. Vs normally is 500 mV for triggering. Figure 20. VCC-RESET Timing Chart output pulse-duration setting Constant-current charging starts on the timing capacitor when the sensing-line voltage reaches the TL7700 sense voltage. When the capacitor voltage exceeds the threshold level of the output drive comparator, RESET changes from a low to a high level. The output pulse duration is the time between the point when the sense-pin voltage exceeds the threshold level and the point when the RESET output changes from a low level to a high level. When the TL7700 is used for system power-on reset, the output pulse duration, tpo, must be set longer than the power rise time. The value of tpo is: tpo = Ct × 105 seconds Where: Ct is the timing capacitor in farads There is a limit on the device response speed. Even if Ct = 0, tpo is not 0, but approximately 5 µs to 10 µs. Therefore, when the TL7700 is used as a comparator with hysteresis, without connecting Ct, switching speeds (tr/tf, tpo/tpd, etc.) must be considered. |
类似零件编号 - TL7700CPSR |
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类似说明 - TL7700CPSR |
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