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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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MIC2753-RBM5 Fiches technique(PDF) 10 Page - Micrel Semiconductor |
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MIC2753-RBM5 Fiches technique(HTML) 10 Page - Micrel Semiconductor |
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10 / 12 page  MIC2753/2754 Micrel MIC2753/2754 10 June 1999 Microcontroller Manual Reset MIC2754 VCC HV MR RST VCC IN RST IN GND Fuse RPULL-DOWN 100k MCR708A SCR 2200pF 10k MIC94030 1k 22 Ω GND Figure 2a. MIC2754 Valid Reset Below 1.5V Microcontroller Manual Reset MIC2753 VCC HV MR RST VCC IN RST IN GND Fuse RPULL-UP 100k MCR708A SCR 2200pF 10k MIC94030 1k 22 Ω GND Figure 2b. MIC2753 Valid Reset Below 1.5V Microcontroller Manual Reset MIC2754 VCC HV MR RST VCC IN RST IN GND GND Fuse MCR708A SCR RSERIES 4.7k BUFFER /RST signal to other circuits 2200pF 10k MIC94030 1k 22 Ω Figure 3. MIC2754 With Processors Using Bidirectional Reset Inputs. Crowbar Applications The following MIC275x applications diagrams show an SCR crowbar circuit. The function of this circuit is to protect system components from damage caused by excessive supply volt- age, as might be generated by a runaway power supply. The low R DS(on) of the MIC94030 P-channel MOSFET (<1Ω at V GS = 4.5V) and the 22Ω resistor assure adequate gate current to trigger the SCR. The crowbar circuit is designed to be functional over all operating ranges of the MIC275x. Since the lowest upper- threshold voltage of the MIC275x family is only 3.08V, and since the SCR-gate forward voltage is about 1V, there is about 90mA of gate-drive current available: 2.08V ÷ 23Ω = 0.09A. The highest upper-threshold voltage is 5.38V, so available gate-drive current is about 190mA: 4.38V ÷ 23Ω = 0.190A. The maximum forward gate current of the SCR is 200mA. The SCR trigger characteristics and the gate-drive capability provide a workable solution for the power-supply voltage range in question. The 10k Ω resistor is the pull-up for the open-drain /HV output of the MIC275x, and the 2200pF capacitor avoids inadvertent premature triggering of the SCR, which might be caused by a very narrow spike on the /HV line. Similarly, the 1k Ω resistor from the SCR-gate to ground keeps the SCR-gate biased off. The fuse shown in the diagrams, which ultimately protects both the system components and the crowbar SCR, should be a fast-blow type. The SCR is rated at 4A(rms), but it can withstand a brief 25A surge. The crowbar circuit shown should, conservatively, be capable of blowing a 5A or 6A fuse. |
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