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TC1273 Datenblatt(PDF) 6 Page - Microchip Technology |
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TC1273 Datenblatt(HTML) 6 Page - Microchip Technology |
6 / 12 page TC1272/TC1273/TC1274 DS21382B-page 6 2003 Microchip Technology Inc. 4.2 VCC Transient Rejection The TC1272/TC1273/TC1274 provides accurate VCC monitoring and reset timing during power-up, power- down and brownout/sag conditions, and rejects negative-going transients (glitches) on the power supply line. Figure 4-5 shows the maximum transient duration vs. maximum negative excursion (overdrive) for glitch rejection. Any combination of duration and overdrive that lays under the curve will not generate a reset signal. Combinations above the curve are detected as a brownout or power-down condition. Transient immunity can be improved by adding a capacitor in close proximity to the VCC pin of the TC1272/TC1273/TC1274. 4.3 RESET Signal Integrity During Power-Down The TC1272 RESET output is valid to VCC = 1.2V. Below this voltage the output becomes an "open circuit" and does not sink current. This means CMOS logic inputs to the µP will be floating at an undeter- mined voltage. Most digital systems are completely shut down well above this voltage. However, in situa- tions where RESET must be maintained valid to VCC = 0V, a pull-down resistor must be connected from RESET to ground to discharge stray capacitances and hold the output low (Figure 4-6). This resistor value, though not critical, should be chosen such that it does not appreciably load RESET under normal operation (100 k Ω will be suitable for most applications). Simi- larly, a pull-up resistor to VCC is required for the TC1274 to ensure a valid high RESET for VCC below 1.8V. FIGURE 4-5: Maximum Transient Duration vs. Overdrive For Glitch Rejection At +25°C. FIGURE 4-6: Ensuring Reset Valid To Vcc =0V. RESET COMPARATOR OVERDRIVE, [VCCTP-VCC] (mV) 500 300 200 400 100 0 1 10 100 1000 TA = +25°C VTH Duration Overdrive VCC TC1272/3/4 TC1272 VCC VCC R1 100 k Ω RESET GND |
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Ähnliche Beschreibung - TC1273 |
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