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MIC4420BN Datasheet(PDF) 7 Page - MIC GROUP RECTIFIERS |
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MIC4420BN Datasheet(HTML) 7 Page - MIC GROUP RECTIFIERS |
7 / 12 page July 2005 7 M9999-072205 MIC4420/4429 Micrel, Inc. Applications Information Supply Bypassing Charging and discharging large capacitive loads quickly requires large currents. For example, charging a 2500pF load to 18V in 25ns requires a 1.8 A current from the device power supply. The MIC4420/4429 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. To guarantee low supply impedance over a wide frequency range, a parallel capacitor combination is recommended for supply bypassing. Low inductance ceramic disk capacitors with short lead lengths (< 0.5 inch) should be used. A 1µF low ESR film capacitor in parallel with two 0.1 µF low ESR ceramic capacitors, (such asAVX RAM GUARD®), provides adequate bypassing. Connect one ceramic capacitor di- rectly between pins 1 and 4. Connect the second ceramic capacitor directly between pins 8 and 5. Grounding The high current capability of the MIC4420/4429 demands careful PC board layout for best performance Since the MIC4429 is an inverting driver, any ground lead impedance will appear as negative feedback which can degrade switch- ing speed. Feedback is especially noticeable with slow-rise time inputs. The MIC4429 input structure includes 300mV of hysteresis to ensure clean transitions and freedom from oscillation, but attention to layout is still recommended. Figure 3 shows the feedback effect in detail.As the MIC4429 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 MIC4429 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 MIC4429 GND pins will ensure full logic drive to the input and ensure fast output switching. Both of the MIC4429 GND pins should, however, still be connected to power ground. Figure 3. Self-Contained Voltage Doubler MIC4429 1µF 50V MKS2 UNITED CHEMCON SXE 0.1µF WIMA MKS2 1 8 6, 7 5 4 0.1µF 50V 5.6 kΩ 560 Ω +15 220 µF 50V BYV 10 (x 2) 35 µF 50V (x2) 1N4448 2 + + + |
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