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AAT3242ITP-QQ-T1 Datasheet(PDF) 10 Page - Advanced Analogic Technologies |
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AAT3242ITP-QQ-T1 Datasheet(HTML) 10 Page - Advanced Analogic Technologies |
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10 / 15 page  AAT3242 300mA/150mA Dual CMOS LDO Linear Regulator PowerLinearTM PRODUCT DATASHEET 10 3242.2008.08.1.11 www .analogictech.com lator output operation, ceramic capacitors are recom- mended for CIN due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources such as batteries in porta- ble devices. Output Capacitor For proper load voltage regulation and operational stabil- ity, a capacitor is required between pins VOUT and GND. The COUT capacitor connection to the LDO regulator ground pin should be made as direct as practically pos- sible for maximum device performance. The AAT3242 has been specifically designed to function with very low ESR ceramic capacitors. For best performance, ceramic capacitors are recommended. Typical output capacitor values for maximum output cur- rent conditions range from 1μF to 10μF. Applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteris- tics of the AAT3242 should use 2.2μF or greater for COUT. If desired, COUT may be increased without limit. In low output current applications where output load is less than 10mA, the minimum value for COUT can be as low as 0.47μF. Capacitor Characteristics Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT3242. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counter- parts. A ceramic capacitor typically has very low ESR, is lower cost, has a smaller PCB footprint, and is non- polarized. Line and load transient response of the LDO regulator is improved by using low ESR ceramic capaci- tors. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage. Equivalent Series Resistance ESR is a very important characteristic to consider when selecting a capacitor. ESR is the internal series resistance associated with a capacitor that includes lead resistance, internal connections, size and area, material composi- tion, and ambient temperature. Typically, capacitor ESR is measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or alumi- num electrolytic capacitors. Ceramic Capacitor Materials Ceramic capacitors less than 0.1μF are typically made from NPO or C0G materials. NPO and C0G materials gen- erally have tight tolerance and are very stable over tem- perature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials. These two material types are not recommended for use with LDO regulators since the capacitor tolerance can vary more than ±50% over the operating temperature range of the device. A 2.2μF Y5V capacitor could be reduced to 1μF over temperature; this could cause problems for circuit operation. X7R and X5R dielectrics are much more desir- able. The temperature tolerance of X7R dielectric is bet- ter than ±15%. Capacitor area is another contributor to ESR. Capacitors which are physically large in size will have a lower ESR when compared to a smaller sized capacitor of an equivalent material and capacitance value. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size. Consult capacitor vendor datasheets carefully when selecting capacitors for LDO regulators. POK Output The AAT3242 features integrated Power OK comparators which can be used as an error flag. The POK open drain output goes low when output voltage is 6% (typ) below its nominal regulation voltage. Additionally, any time one of the regulators is in shutdown, the respective POK out- put is pulled low. Connect a pull-up resistor from POKA to OUTA, and POKB to OUTB. Enable Function The AAT3242 features an LDO regulator enable/disable function. Each LDO has its own dedicated enable pin. These pins (EN) are active high and are compatible with CMOS logic. To assure the LDO regulators will switch on, ENA/B must be greater than 1.6V. The LDO regulators will shut down when the voltage on the ENA/B pins falls below 0.6V. In shutdown, the AAT3242 will consume less than 1.0μA of current. If the enable function is not needed in a specific application, it may be tied to VIN to keep the LDO regulator in a continuously on state. When the LDO regulators are in shutdown mode, an internal 20Ω resistor is connected between VOUT and GND. This is intended to discharge COUT when the LDO regulators are disabled. The internal 20Ω has no adverse effects on device turn-on time. |
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