LP2985AITPX-1.8 Schematic ( PDF Datasheet ) - National Semiconductor

Teilenummer	LP2985AITPX-1.8
Beschreibung	Micropower 150 mA Low-Noise Low-Dropout Regulator in SOT-23 and micro SMD packages for Applications
Hersteller	National Semiconductor
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Gesamt 17 Seiten May 2004 LP2985LV Micropower 150 mA Low-Noise Low-Dropout Regulator in SOT-23 and micro SMD packages for Applications with Output Voltages ≤ 2.3V Designed for Use with Very Low ESR Output Capacitors General Description The LP2985LV is a 150 mA, fixed-output voltage regulator designed to providehigh performance and low noise in ap- plications requiring output voltages < 2.3V. Using an optimized VIP™ (Vertically Integrated PNP) pro- cess, the LP2985LV delivers unequalled performance in all specifications critical to battery-powered designs: Ground Pin Current: Typically 825 µA @ 150 mA load, and 75 µA @ 1 mA load. Enhanced Stability: The LP2985LV is stable with output capacitor ESR as low as 5 mΩ, which allows the use of ceramic capacitors on the output. Sleep Mode: Less than 1 µA quiescent current when ON/ OFF pin is pulled low. Smallest Possible Size: micro SMD package uses absolute minimum board space. Precision Output: 1% tolerance output voltages available (A grade). Low Noise: By adding a 10 nF bypass capacitor, output noise can be reduced to 30 µV (typical). Features n Guaranteed 150 mA output current n Smallest possible size (micro SMD) n Requires minimum external components n Stable with low-ESR output capacitor n <1 µA quiescent current when shut down n Low ground pin current at all loads n Output voltage accuracy 1% (A Grade) n High peak current capability n Wide supply voltage range (16V max) n Low ZOUT: 0.3Ω typical (10 Hz to 1 MHz) n Overtemperature/overcurrent protection n −40˚C to +125˚C junction temperature range n Custom voltages available Applications n Cellular Phone n Palmtop/Laptop Computer n Personal Digital Assistant (PDA) n Camcorder, Personal Stereo, Camera Block Diagram VIP™ is a trademark of National Semiconductor Corporation. © 2004 National Semiconductor Corporation DS101295 10129501 www.national.com Typical Performance Characteristics Unless otherwise specified: CIN = 1µF, COUT = 4.7µF, VIN = VOUT(NOM) +1, VOUT = 1.8V, TA = 25˚C, ON/OFF pin is tied to VIN VOUT vs Temperature Short-Circuit Current Short-Circuit Current 10129507 10129516 Short-Circuit Current vs Output Voltage 10129517 Ripple Rejection COUT = 4.7µF, Bypass = 10nF 10129518 Ripple Rejection COUT = 4.7µF, No Bypass www.national.com 10129525 6 10129526 6 Page Application Hints (Continued) One disadvantage of ceramic capacitors is that their capaci- tance can vary with temperature. Most large value ceramic capacitors (≥ 2.2 µF) are manufactured with the Z5U or Y5V temperature characteristic, which results in the capacitance dropping by more than 50% as the temperature goes from 25˚C to 85˚C. This could cause problems if a 2.2 µF capacitor were used on the output since it will drop down to approximately 1 µF at high ambient temperatures (which could cause the LP2985LV to oscillate). If Z5U or Y5V capacitors are used on the output, a minimum capacitance value of 4.7 µF must be observed. A better choice for temperature coefficient in ceramic capaci- tors is X7R, which holds the capacitance within ±15%. Un- fortunately, the larger values of capacitance are not offered by all manufacturers in the X7R dielectric. Tantalum Tantalum capacitors are less desirable than ceramics for use as output capacitors because they are more expensive when comparing equivalent capacitance and voltage ratings in the 1 µF to 4.7 µF range. Another important consideration is that Tantalum capacitors have higher ESR values than equivalent size ceramics. This means that while it may be possible to find a Tantalum capacitor with an ESR value within the stable range, it would have to be larger in capacitance (which means bigger and more costly) than a ceramic capacitor with the same ESR value. It should also be noted that the ESR of a typical Tantalum will increase about 2:1 as the temperature goes from 25˚C down to −40˚C, so some guard band must be allowed. On/off Input Operation The LP2985LV is shut off by driving the ON/OFF input low, and turned on by pulling it high. If this feature is not to be used, the ON/OFF input should be tied to VIN to keep the regulator output on at all times. To assure proper operation, the signal source used to drive the ON/OFF input must be able to swing above and below the specified turn-on/turn-off voltage thresholds listed in the Electrical Characteristics section under VON/OFF. To prevent mis-operation, the turn-on (and turn-off) voltage signals ap- plied to the ON/OFF input must have a slew rate which is ≥ 40 mV/µs. Caution: the regulator output voltage can not be guaranteed if a slow-moving AC (or DC) signal is applied that is in the range between the specified turn-on and turn-off voltages listed under the electrical specification VON/OFF (see Electri- cal Characteristics). REVERSE INPUT-OUTPUT VOLTAGE The PNP power transistor used as the pass element in the LP2985LV has an inherent diode connected between the regulator output and input. During normal operation (where the input voltage is higher than the output) this diode is reverse-biased. However, if the output is pulled above the input, this diode will turn ON and current will flow into the regulator output. In such cases, a parasitic SCR can latch which will allow a high current to flow into VIN (and out the ground pin), which can damage the part. In any application where the output may be pulled above the input, an external Schottky diode must be connected from VIN to VOUT (cathode on VIN, anode on VOUT), to limit the reverse voltage across the LP2985LV to 0.3V (see Absolute Maximum Ratings). MICRO SMD MOUNTING The micro SMD package requires specific mounting tech- niques which are detailed in National Semiconductor Appli- cation Note # 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 the 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. MICRO SMD LIGHT SENSITIVITY Exposing the micro SMD device to direct sunlight will cause misoperation of the device. Light sources such as Halogen lamps can also affect electrical performance if brought near to the device. The wavelenghts which have the most detrimental effect are reds and infra-reds, which means that the fluorescent light- ing used inside most buildings has very little effect on per- formance. A micro SMD test board was brought to within 1 cm of a fluorescent desk lamp and the effect on the regu- lated output voltage was negligible, showing a deviation of less than 0.1% from nominal. www.national.com 12 12 Page
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Besondere Datenblatt

Teilenummer	Beschreibung	Hersteller
LP2985AITPX-1.8	Micropower 150 mA Low-Noise Low-Dropout Regulator in SOT-23 and micro SMD packages for Applications	National Semiconductor
LP2985AITPX-1.8	Micropower 150 mA Low-Noise Low-Dropout Regulator in SOT-23 and micro SMD packages for Applications	National Semiconductor

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