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AAT3119 Datasheet(PDF) 12 Page - Advanced Analogic Technologies |
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AAT3119 Datasheet(HTML) 12 Page - Advanced Analogic Technologies |
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12 / 18 page  AAT3119 High Efficiency 2X Charge Pump 12 3119.2007.02.1.2 Flying Capacitor Due to the switching operation of the voltage dou- bling circuit topology, current flow through the flying capacitor is bi-directional. The flying capacitor selected must be a non-polarized type. A 1μF low ESR ceramic capacitor is ideal for this application. Capacitor Characteristics Ceramic composition capacitors are highly recom- mended over all other types of capacitors for use with the AAT3119. Ceramic capacitors offer many advan- tages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lowest cost, has a smaller PCB footprint, and is non-polarized. Low ESR ceramic capacitors help maximize charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Equivalent Series Resistance: ESR is an impor- tant characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capaci- tor that is determined by the leads, internal con- nections, size or area, material composition, and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors. Ceramic Capacitor Materials: Ceramic capacitors less than 0.1μF are typically made from NPO or C0G materials. NPO and C0G materials typically have tight tolerance and are stable over tempera- ture. Large capacitor values are typically com- posed of X7R, X5R, Z5U, or Y5V dielectric materi- als. Large ceramic capacitors, typically greater than 2.2μF, are often available in low-cost Y5V and Z5U dielectrics, but large capacitors are not required in most AAT3119 applications. Capacitor area is another contributor to ESR. Capacitors that are physically large will have a lower ESR when compared to an equivalent material smaller capac- itor. These larger devices can improve circuit tran- sient response when compared to an equal value capacitor in a smaller package size. Applications Information White LED Backlight Driver LED Selection: In applications where the AAT3119 is utilized as a white LED backlight driver, LEDs with forward voltages up to 5.0V may be used. The AAT3119 is available in two regulated output volt- age versions: 4.5V and 5.0V. The output voltage option selected will determine the maximum LED forward voltage that can be driven. The trade-off for the lower 4.5V output voltage version is the device’s ability to supply greater output current. Refer to the "Output Voltage vs. Output Current" curves in the Typical Characteristics section of this datasheet to determine the best AAT3119 output voltage option based on the requirements of a given application. LED Ballast Resistors: To set the maximum brightness of white LEDs connected in parallel from a voltage source supply, a ballast resistor connect- ed between each LED cathode and ground is required. Refer to the application schematic in Figure 1. The maximum brightness is determined by the forward current (IF) through the respective LED for a given forward voltage (VF). The typical forward voltage of a specific LED is usually stated in the typical characteristics of the given LED manu- facturer's datasheet. The correct ballast resistor value can be determined by the following equation: Where: RB = Ballast resistor value in ohms ( Ω) VOUT = Regulated charge pump output voltage VF = LED forward voltage at the desired forward current IF = Desired LED forward current R B = (V OUT - VF) I F |
Similar Part No. - AAT3119_07 |
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Similar Description - AAT3119_07 |
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