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AME7720 Datasheet(PDF) 8 Page - Asahi Kasei Microsystems |
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AME7720 Datasheet(HTML) 8 Page - Asahi Kasei Microsystems |
8 / 16 page AME, Inc. 8 Step-Up/Step-Down 60mA Regulated Charge Pump AME7720 / 7721 n Detailed Description The AME7720 / 7721 regulated charge pump provides a regulated output voltages ranging from less than the output to greater than the output. This is accomplshed by auto- matic mode switching within the device. n Short Circuit and Thermal Protection The AME7720 / 7721 has a thermal protection and shut- down circuit that continuously monitors the IC junction tem- perature. If the thermal protection circuit senses the die temperature exceeding approximately 160OC, the thermal shutdown will disable the charge pump switching cycle op- eration, The thermal limit system has 20OC of system hys- teresis before the charge pump can reset. Once the over current event is removed from the output and the junction temperature drops below 140OC, the charge pump will the become active again. The thermal protection system will cycle on and off if an output short circuit condition persists. This will allow the AME7720 / 7721 to operate indefinitely a short circuit condition without damage to the device. n Shutdown Mode A control pin on the regulator can be used to place the device into an energy-saving shutdown mode. In this mode, the output is disconnected from the input as long as V IN is greater than or equal to minimum V IN and input quiescent current is reduced to 1 µA maximum. n Capacitor Selection For minimum output voltage ripple, the output capacitor C OUT should be a ceramic, surface-mount type. Tantalum capacitors generally have a higher Effective Series Resis- tance (ESR) and may contribute to higher output voltage ripple. Leaded capacitors also increase ripple due to the higher inductance of the package itself. To achieve best operation with low input voltage and high load current, the input and pump capacitors (C IN, CPUMP respecvively) should also be surface-mount ceramic types. In all cases, X7R or X5R dielectric are recommended. n Efficiency The efficiency of the charge pump regulator varies with the output voltage version, the applied input volt- age, the load current, and the internal operation mode of the device. The approximate efficiency is given by: 5V Version (V IN<= VOUT) Efficiency (%) = V OUT / 2V IN . 100 3.3V Version (V IN> VOUT) Efficiency (%) = V OUT / VIN . 100 n Layout Large ripple currents flow in the V IN and VOUT traces. To minimized both input and output ripple, keep the capacitors as close as possible to the regulator using short, direct circuit traces. The trace lengths from the input and output capaci- tors have been kept as short as possible. A star ground system has been implemented, with GND pin as the center of the star. No ground plane is provided in other layers, as this will provide capacitive coupling for noise spikes. With light loads or higher input voltage, a smaller 0.1 µF pump capacitor (C PUMP) and smaller 1µF input and output capacitor (C IN and COUT, respectively) can be used. To minimize output voltage ripple, increase the output capacitor, C OUT, to 10µF or larger. |
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Descripción similar - AME7720 |
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