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MCP1318 bảng dữ liệu(PDF) 29 Page - Microchip Technology |
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MCP1318 bảng dữ liệu(HTML) 29 Page - Microchip Technology |
29 / 44 page © 2005 Microchip Technology Inc. DS21985A-page 29 MCP131X/2X 4.3 Negative Going VDD Transients The minimum pulse width (time) required to cause a Reset may be an important criteria in the implementa- tion of a Power-on Reset (POR) circuit. This time is referred to as transient duration. The MCP131X/2X devices are designed to reject a level of negative-going transients (glitches) on the power supply line. Transient duration is the amount of time needed for these supervisory devices to respond to a drop in VDD. The transient duration time (tTRAN) is dependant on the magnitude of VTRIP – VDD (overdrive). Any combination of duration and overdrive that lies under the dura- tion/overdrive curve will not generate a Reset signal. Generally speaking, the transient duration time decreases with and increases in the VTRIP – VDD volt- age. Combinations of duration and overdrive that lies above the duration/overdrive curve are detected as a brown-out or power-down condition. Figure 4-16 shows a typical transient duration vs. Reset comparator overdrive, for which the MCP131X/2X will not generate a Reset pulse. It shows that the farther below the trip point the transient pulse goes, the duration of the pulse required to cause a Reset gets shorter. Figure 4-16 shows the transient response characteristics for the MCP131X/2X. Transient immunity can be improved by adding a bypass capacitor (typically 0.1 μF) as close as possible to the VDD pin of the MCP131X/2X device. FIGURE 4-16: Example of Typical Transient Duration Waveform. 4.4 Manual Reset Input The Manual Reset input pin (MR) allows the Reset pins (RST/RST) to be manually forced to their active states. The MR pin has circuitry to filter noise pulses that may be present on the pin. Figure 4-17 shows a block dia- gram for using the MCP131X/2X with a push button switch. To minimize the required external components, the MR input has an internal pull-up resistor. A mechanical push button or active logic signal can drive the MR input. Once MR has been low for a time, tMRD (the Manual Reset delay time), the Reset output pins are forced active. The Reset output pins will remain in their active states for the Reset delay timer time out period (t R ST) Figure 4-18 shows a waveform for the Manual Reset switch input and the Reset pins output. FIGURE 4-17: Push Button Reset and Watchdog Timer. FIGURE 4-18: MR Input – Push Button. 4.4.1 NOISE FILTER The noise filter filters out noise spikes (glitches) on the Manual Reset pin (MR). Noise spikes less than 100 ns (typical) are filtered. Time (μs) 0V 5V VTRIP(MIN) - VDD tTRANS VTRIP(MAX) VTRIP(MIN) (Overdrive) (Duration) VDD MR VSS RST WDI I/O MCLR +5V MCP13XX PICmicro® MCU RST VIL tMR RST tMRD VIH tRST MR The MR input typically ignores input pulses of 100 ns. |
Số phần tương tự - MCP1318 |
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Mô tả tương tự - MCP1318 |
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