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AAT3119 Datasheet(PDF) 11 Page - Advanced Analogic Technologies |
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AAT3119 Datasheet(HTML) 11 Page - Advanced Analogic Technologies |
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11 / 16 page  AAT3119 High Efficiency 2X Charge Pump 3119.2005.08.1.1 11 In the operating state, the AAT3119 typically con- sumes 2mA of quiescent operating current. The enable pin (EN) is an active high input. When pulled low, the AAT3119 is shut down, the quies- cent current drops to less than 1µA, and the output is disconnected from the input. Charge Pump Efficiency The core of the AAT3119 is a regulated output volt- age doubling charge pump. The efficiency (η) for an ideal voltage doubling charge pump can typical- ly be expressed as the output power divided by the input power: In addition, with an ideal voltage doubling charge pump, the output current may be expressed as half the input current. The expression to define the ideal efficiency (η) can be rewritten as: -or- For a charge pump with an output of 5.0 volts and a nominal input of 3.0 volts, the theoretical efficien- cy is 83.3%. Due to internal switching losses and IC quiescent current consumption, the actual effi- ciency can be measured at approximately 82%. Efficiency will decrease as the level of VIN approaches that of the regulated VOUT. Refer to the device typical characteristics curves for expect- ed actual efficiency based on either input voltage or load current. Capacitor Selection Careful selection of the three external capacitors (CIN, CFLY, and COUT) is important because they will affect turn-on time, output ripple, efficiency, and load transient response. Optimum performance will be obtained when low equivalent series resistance (ESR) ceramic capacitors are used. In general, low ESR may be defined as less than 100mΩ. A value of 1µF for all three capacitors is a good starting point when designing with the AAT3119. This not only provides for a very small printed circuit board area, but cost is further reduced by the minimized bill of materials. Input Capacitor A 1µF multilayer ceramic chip capacitor is suggest- ed for the input. This capacitor should be connect- ed between the IN pin and ground. 1µF should be suitable for most applications. Even though the AAT3119 switching ripple and noise are very low, back-injected line noise may be further reduced by increasing the value of CIN. Other types of capaci- tors may be used for CIN at the cost of compro- mised circuit performance. Output Capacitor The output capacitor (COUT) should be connected between the OUT pin and ground. A 1µF ceramic capacitor is also suggested in this position. Switching noise and ripple seen on the charge pump output increases with load current. Typically 1µF is sufficient for minimizing output ripple seen by the load circuit. If the load current in an appli- cation is low, or if higher levels of switching ripple can be tolerated, COUT can be reduced as low as 0.33µF. If application circuits with greater load cur- rent demands require lower switching ripple ampli- tudes, COUT may be increased to values above 1µF. Capacitor types other than ceramic capaci- tors can be used for COUT. However, capacitors comprised of materials other than ceramic will typ- ically have a greater value of ESR, resulting in increased output switching ripple. η(%) = 100 V OUT 2V IN ⎛⎞ ⎝⎠ η = P OUT = V OUT × IOUT = VOUT P IN V IN × 2IOUT 2V IN η = P OUT P IN |
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