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LP3999ITL-2.8NOPB Datasheet(PDF) 11 Page - National Semiconductor (TI) |
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LP3999ITL-2.8NOPB Datasheet(HTML) 11 Page - National Semiconductor (TI) |
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11 / 12 page  Application Hints (Continued) The types of capacitors best suited for the noise bypass capacitor are ceramic and film. High quality ceramic capaci- tors with NPO or COG dielectric typically have very low leakage. Polypropolene and polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low leakage current. Unlike many other LDO’s, the addition of a noise reduction capacitor does not effect the transient response of the de- vice. ENABLE OPERATION The LP3999 may be switched ON or OFF by a logic input at the ENABLE pin, V EN. A high voltage at this pin will turn the device on. When the enable pin is low, the regulator output is off and the device typically consumes 3 nA. If the application does not require the shutdown feature, the V EN pin should be tied to V IN to keep the regulator output permanently on. To ensure proper operation, the signal source used to drive the V EN input must be able to swing above and below the specified turn-on/off voltage thresholds listed in the Electrical Characteristics section under V IL and VIH. FAST TURN ON Fast turn-on is guaranteed by control circuitry within the reference block allowing a very fast ramp of the output voltage to reach the target voltage. There is no active turn-off on this device. Refer to LP3995 for a similar device with active turn-off. microSMD MOUNTING The micro SMD package requires specific mounting tech- niques which are detailed in National Semiconductor Appli- cation Note AN-1112. Referring to the section Surface Mount Technology (SMT) Assembly Considerations, it should be noted that the pad style which must be used with the 5 pin package is NSMD (non-solder mask defined) type. For best results during assembly, alignment ordinals on the PC board may be used to facilitate placement of the micro SMD device. microSMD LIGHT SENSITIVITY Exposing the micro SMD device to direct sunlight will cause incorrect operation of the device. Light sources such as halogen lamps can affect electrical performance if they are situated in proximity to the device. Light with wavelengths in the red and infra-red part of the spectrum have the most detrimental effect thus the fluores- cent lighting used inside most buildings has very little effect on performance. Tests carried out on a micro SMD test board showed a negligible effect on the regulated output voltage when brought within 1 cm of a fluorescent lamp. A deviation of less than 0.1% from nominal output voltage was observed. www.national.com 11 |
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