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MIC4421ACM Datasheet(PDF) 8 Page - MIC GROUP RECTIFIERS |
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MIC4421ACM Datasheet(HTML) 8 Page - MIC GROUP RECTIFIERS |
8 / 13 page Micrel, Inc. MIC4421A/4422A June 2007 8 M9999-062707 Application Information Supply Bypassing Charging and discharging large capacitive loads quickly requires large currents. For example, charging a 10,000pF load to 18V in 50ns requires 3.6A. The MIC4421A/4422A has double bonding on the supply pins, the ground pins and output pins. This reduces parasitic lead inductance. Low inductance enables large currents to be switched rapidly. It also reduces internal ringing that can cause voltage breakdown when the driver is operated at or near the maximum rated voltage. Internal ringing can also cause output oscillation due to feedback. This feedback is added to the input signal since it is referenced to the same ground. 1µF MIC4421A Drive Logic VS VS VS MIC4422A VS 1µF Ø1 Drive Signal Conduction Angle Control 0°C to 180°C Conduction Angle Control 180°C to 360°C Ø1 Ø2 Ø3 Phase 1 of 3 Phase Motor Driver Using MIC4421A/22A Figure 5. Direct Motor Drive To guarantee low supply impedance over a wide frequency range, a parallel capacitor combination is recommended for supply bypassing. Low inductance ceramic disk capacitor swith short lead lengths (< 0.5 inch) should be used. A 1µF low ESR film capacitor in parallel with two 0.1µF low ESR ceramic capacitors, (such as AVX RAM Guard ®), provides adequate bypassing. Connect one ceramic capacitor directly between pins 1 and 4. Connect the second ceramic capacitor directly between pins 8 and 5. Grounding The high current capability of the MIC4421A/4422A demands careful PC board layout for best performance. Since the MIC4421A is an inverting driver, any ground lead impedance will appear as negative feedback which can degrade switching speed. Feedback is especially noticeable with slow-rise time inputs. The MIC4421A input structure includes about 600mV of hysteresis to ensure clean transitions and freedom from oscillation, but attention to layout is still recommended. Figure 7 shows the feedback effect in detail. As the MIC4421A input begins to go positive, the output goes negative and several amperes of current flow in the ground lead. As little as 0.05Ω of PC trace resistance can produce hundreds of millivolts at the MIC4421A ground pins. If the driving logic is referenced to power ground, the effective logic input level is reduced and oscillation may result. To insure optimum performance, separate ground traces should be provided for the logic and power connections. Connecting the logic ground directly to the MIC4421A GND pins will ensure full logic drive to the input and ensure fast output switching. Both of the MIC4421A GND pins should, however, still be connected to power ground. MIC4422A VIN +15V 0.1µF 50V United Chemcon SXE 0.1µF WIMA MKS2 1µF WIMA MKS2 BYV 10 (x2) 100µF 50V 500µF 50V 1N4448 (x2) 30 29 28 27 26 25 mA Output Voltage vs. Load Current 0 50 100 150 200 250 300 350 Figure 6. Self Contained Voltage Doubler |
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