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AME7739 Datasheet(PDF) 6 Page - Analog Microelectronics |
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AME7739 Datasheet(HTML) 6 Page - Analog Microelectronics |
6 / 11 page AME, Inc. 6 REV. A.02 Step-Up / Step-Down 60mA Regulated Charge Pump AME7739 n Detailed Description The AME7739 regulated charge pump provides a regulated input voltages ranging from less than the output to greater than the input. This is accomplshed by automatic mode switch- ing within the device. n Short Circuit and Thermal Protection The AME7739 has a thermal protection and shutdown cir- cuit that continuously monitors the IC junction temperature. If the thermal protection circuit senses the die temperature exceeding approximately 160OC, the thermal shutdown will disable the charge pump switching cycle operation, The ther- mal limit system has 20OC of system hysteresis before the charge pump can reset. Once the over current event is re- moved 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 out- put short circuit condition persists. This will allow the AME7739 to operate indefinitely a short circuit condition with- out damage to the device. n Shutdown Mode A control pin EN 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 ca- pacitors generally have a higher Effective Series Resistance (ESR) and may contribute to higher output voltage ripple. Leaded capacitors also increase ripple due to the higher in- ductance of the package itself. To achieve best operation with low input voltage and high load current, the input and pump capacitors (C IN, CPUMP respectively) should also be surface- mount ceramic types. In all cases, X7R dielectric is recom- mended. 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: 5.5V , 5V Version (V IN<= VOUT) Efficiency (%) = V OUT / 2VIN . 100% Others 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 ca- pacitor (C IN and COUT, respectively) can be used. To minimize output voltage ripple, increase the output capacitor, C OUT, to 10 µF or larger. |
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