LP2992IM5X-2.5 Schematic - National Semiconductor

LP2992IM5X-2.5 Schematic ( PDF Datasheet ) - National Semiconductor

Teilenummer	LP2992IM5X-2.5
Beschreibung	Micropower 250 mA Low-Noise Ultra Low-Dropout Regulator in SOT-23 and LLP Packages Designed for Use with Very Low ESR Output Capacitors
Hersteller	National Semiconductor
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Gesamt 15 Seiten June 2002 LP2992 Micropower 250 mA Low-Noise Ultra Low-Dropout Regulator in SOT-23 and LLP Packages Designed for Use with Very Low ESR Output Capacitors General Description The LP2992 is a 250 mA, fixed-output voltage regulator designed to provide ultra low-dropout and low noise in bat- tery powered applications. Using an optimized VIP™ (Vertically Integrated PNP) pro- cess, the LP2992 delivers unequalled performance in all specifications critical to battery-powered designs: Dropout Voltage: Typically 450 mV @ 250 mA load, and 5 mV @ 1 mA load. Ground Pin Current: Typically 1500 µA @ 250 mA load, and 75 µA @ 1 mA load. Enhanced Stability: The LP2992 is stable with output ca- pacitor 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: SOT-23 and LLP packages use 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). Multiple voltage options, from 1.5V to 5.0V, are available as standard products. Consult factory for custom voltages. Features n Ultra low dropout voltage n Guaranteed 250 mA output current n Smallest possible size (SOT-23, LLP package) 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. © 2002 National Semiconductor Corporation DS200294 20029401 www.national.com Typical Performance Characteristics Unless otherwise specified: CIN = 1µF, COUT = 4.7µF, VIN = VOUT(NOM) +1, TA = 25˚C, ON/OFF pin is tied to VIN. VOUT vs Temperature Short-Circuit Current Short-Circuit Current 20029408 20029409 Short Circuit Current vs Output Voltage 20029410 Ripple Rejection Ripple Rejection 20029411 20029413 www.national.com 6 20029414 6 Page Application Hints EXTERNAL CAPACITORS Like any low-dropout regulator, the LP2992 requires external capacitors for regulator stability. These capacitors must be correctly selected for good performance. Input Capacitor An input capacitor whose capacitance is ≥ 1 µF is required between the LP2992 input and ground (the amount of ca- pacitance may be increased without limit). This capacitor must be located a distance of not more than 1 cm from the input pin and returned to a clean analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input. Important: Tantalum capacitors can suffer catastrophic fail- ure due to surge current when connected to a low-impedance source of power (like a battery or very large capacitor). If a Tantalum capacitor is used at the input, it must be guaranteed by the manufacturer to have a surge current rating sufficient for the application. There are no requirements for ESR on the input capacitor, but tolerance and temperature coefficient must be consid- ered when selecting the capacitor to ensure the capacitance will be ≥ 1 µF over the entire operating temperature range. Output Capacitor: The LP2992 is designed specifically to work with ceramic output capacitors, utilizing circuitry which allows the regula- tor to be stable across the entire range of output current with an output capacitor whose ESR is as low as 5 mΩ. It may also be possible to use Tantalum or film capacitors at the output, but these are not as attractive for reasons of size and cost (see next section Capacitor Characteristics). The output capacitor must meet the requirement for mini- mum amount of capacitance and also have an ESR (equiva- lent series resistance) value which is within the stable range. Curves are provided which show the stable ESR range as a function of load current (see ESR graph below). 20029407 Important: The output capacitor must maintain its ESR within the stable region over the full operating temperature range of the application to assure stability. The LP2992 requires a minimum of 4.7 µF on the output (output capacitor size can be increased without limit). It is important to remember that capacitor tolerance and variation with temperature must be taken into consideration when selecting an output capacitor so that the minimum required amount of output capacitance is provided over the full operating temperature range. It should be noted that ceramic capacitors can exhibit large changes in capacitance with temperature (see next section, Capacitor Characteris- tics). The output capacitor must be located not more than 1 cm from the output pin and returned to a clean analog ground. Noise Bypass Capacitor: Connecting a 10 nF capacitor to the Bypass pin significantly reduces noise on the regulator output. It should be noted that the capacitor is connected directly to a high-impedance cir- cuit in the bandgap reference. Because this circuit has only a few microamperes flowing in it, any significant loading on this node will cause a change in the regulated output voltage. For this reason, DC leakage current through the noise bypass capacitor must never ex- ceed 100 nA, and should be kept as low as possible for best output voltage accuracy. The types of capacitors best suited for the noise bypass capacitor are ceramic and film. High-quality ceramic capaci- tors with either NPO or COG dielectric typically have very low leakage. 10 nF polypropolene and polycarbonate film capacitors are available in small surface-mount packages and typically have extremely low leakage current. CAPACITOR CHARACTERISTICS The LP2992 was designed to work with ceramic capacitors on the output to take advantage of the benefits they offer: for capacitance values in the 2.2 µF to 10 µF range, ceramics are the least expensive and also have the lowest ESR values (which makes them best for eliminating high-frequency noise). The ESR of a typical 4.7 µF ceramic capacitor is in the range of 5 mΩ to 10 mΩ, which easily meets the ESR limits required for stability by the LP2992. 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 4.7 µF capacitor were used on the output since it will drop down to approximately 2.3 µF at high ambient temperatures (which could cause the LP2992 to oscillate). If Z5U or Y5V capacitors are used on the output, a minimum capacitance value of 10 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. www.national.com 12 12 Page
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Teilenummer	Beschreibung	Hersteller
LP2992IM5X-2.5	Micropower 250 mA Low-Noise Ultra Low-Dropout Regulator in SOT-23 and LLP Packages Designed for Use with Very Low ESR Output Capacitors	National Semiconductor
LP2992IM5X-2.5	Micropower 250 mA Low-Noise Ultra Low-Dropout Regulator in SOT-23 and LLP Packages Designed for Use with Very Low ESR Output Capacitors	National Semiconductor

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