April 23, 2009 LP2978 Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout Regulator Designed for Use with Very Low ESR Output Capacitors General Description Features The LP2978 is a 50 mA, fixed-output voltage regulator designed to provide ultra low-dropout and low noise in battery powered applications. Using an optimized VIP® (Vertically Integrated PNP) process, the LP2978 delivers unequalled performance in all specifications critical to battery-powered designs: Dropout Voltage: Typically 120 mV @ 50 mA load, and 7 mV @ 1 mA load. Ground Pin Current: Typically 350 µA @ 50 mA load, and 75 µA @ 1 mA load. Enhanced Stability: The LP2978 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: SOT-23 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). ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Ultra low dropout voltage Smallest possible size (SOT-23 Package) Requires minimum external components Stable with low-ESR output capacitor <1 µA quiescent current when shut down Low ground pin current at all loads Output voltage accuracy 1% (A Grade) High peak current capability Wide supply voltage range (16V max) Low ZOUT: 0.3Ω typical (10 Hz to 1 MHz) Overtemperature/overcurrent protection −40°C to +125°C junction temperature range Custom voltages available Applications ■ ■ ■ ■ Cellular Phone Palmtop/Laptop Computer Personal Digital Assistant (PDA) Camcorder, Personal Stereo, Camera Block Diagram 10093501 VIP® is a registered trademark of National Semiconductor Corporation. © 2009 National Semiconductor Corporation 100935 100935 Version 6 Revision 2 www.national.com Print Date/Time: 2009/04/23 16:08:18 LP2978 Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout Regulator OBSOLETE LP2978 Basic Application Circuit 10093502 *ON/OFF input must be actively terminated. Tie to VIN if this function is not to be used. **Minimum capacitance is shown to ensure stability (may be increased without limit). Ceramic capacitor required for output (see Application Hints). ***Reduces output noise (may be omitted if application is not noise critical). Use ceramic or film type with very low leakage current (see Application Hints). Connection Diagram 10093503 See NS Package Number MF05A Ordering Information TABLE 1. Package Marking and Ordering Information Output Voltage (V) Grade Order Information Package Marking 3.8 A LP2978AIM5X-3.8 LØLA 3000 Units on Tape and Reel 3.8 A LP2978AIM5-3.8 LØLA 1000 Units on Tape and Reel 3.8 STD LP2978IM5X-3.8 LØLB 3000 Units on Tape and Reel 3.8 STD LP2978IM5-3.8 LØLB 1000 Units on Tape and Reel www.national.com Supplied As: 2 100935 Version 6 Revision 2 Print Date/Time: 2009/04/23 16:08:18 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature Range Operating Junction Temperature Range Lead Temp. (Soldering, 5 sec.) ESD Rating (Note 2) −65°C to +150°C −40°C to +125°C 260°C 2 kV Internally Limited −0.3V to +16V 2.5V to +16V −0.3V to +16V −0.3V to +9V Short Circuit Protected −0.3V to +16V Input-Output Voltage (Survival, (Note 5)) Electrical Characteristics Limits in standard typeface are for TJ = 25°C. and limits in boldface type apply over the full operating temperature range. Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, CIN = 1 µF, COUT = 4.7 µF, VON/OFF = 2V. Symbol ΔVO Parameter Conditions Typ LP2978AI-X.X (Note 6) LP2978I-X.X (Note 6) Min Max Min Max Output Voltage Tolerance IL = 1 mA −1.0 1.0 −1.5 1.5 1 mA ≤ IL ≤ 50 mA −1.5 1.5 −2.5 2.5 2.5 −3.5 Output Voltage VO(NOM)+1V ≤ VIN ≤ 16V −2.5 0.007 Line Regulation VIN–VO Dropout Voltage (Note 7) IL = 0 1 IL = 1 mA IGND Ground Pin Current 7 VON/OFF ION/OFF en 0.014 0.032 0.032 3 3 5 5 10 10 15 15 60 40 60 90 90 IL = 50 mA 120 150 150 225 225 IL = 0 65 95 95 125 125 IL = 1 mA 75 110 110 170 170 220 220 400 400 600 600 120 %VNOM 3.5 0.014 IL = 10 mA IL = 10 mA Units IL = 50 mA 350 1000 1000 VON/OFF < 0.3V 0.01 0.8 0.8 VON/OFF < 0.15V 0.05 2 2 %/V mV µA ON/OFF Input Voltage (Note 8) High = O/P ON 1.4 Low = O/P OFF 0.55 0.15 0.15 ON/OFF Input Current VON/OFF = 0 0.01 −2 −2 VON/OFF = 5V 5 15 15 BW = 300 Hz to 50 kHz, COUT = 10 µF 30 µV 45 dB Output Noise Voltage (RMS) 1.6 1.6 V µA CBYPASS = 10 nF Ripple Rejection f = 1 kHz, CBYPASS = 10 nF COUT = 10 µF IO(SC) Short Circuit Current RL = 0 (Steady State) 400 mA IO(PK) Peak Output Current VOUT ≥ Vo(NOM) −5% 350 mA 3 100935 Version 6 Revision 2 Print Date/Time: 2009/04/23 16:08:18 www.national.com LP2978 Power Dissipation (Note 3) Input Supply Voltage (Survival) Input Supply Voltage (Operating) Shutdown Input Voltage (Survival) Output Voltage (Survival, (Note 4)) IOUT (Survival) Absolute Maximum Ratings (Note 1) LP2978 Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the device outside of its rated operating conditions. Note 2: The ESD rating of pins 3 and 4 is 1 kV. Note 3: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperture is calculated using: Where the value of θJ-A for the SOT-23 package is 220°C/W in a typical PC board mounting. Exceeding the maximum allowable dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Note 4: If used in a dual-supply system where the regulator load is returned to a negative supply, the LP2978 output must be diode-clamped to ground. Note 5: The output PNP structure contains a diode between the VIN to VOUT terminals that is normally reverse-biased. Reversing the polarity from VIN to VOUT will turn on this diode. Note 6: Limits are 100% production tested at 25°C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. The limits are used to calculate National's Average Outgoing Quality Level (AOQL). Note 7: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below the value measured with a 1V differential. Note 8: The ON/OFF input must be properly driven to prevent possible misoperation. For details, refer to Application Hints. www.national.com 4 100935 Version 6 Revision 2 Print Date/Time: 2009/04/23 16:08:18 EXTERNAL CAPACITORS Like any low-dropout regulator, the LP2978 requires external capacitors for regulator stability. These capacitors must be correctly selected for good performance. 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 circuit 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 exceed 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 capacitors 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. Input Capacitor An input capacitor whose capacitance is ≥ 1 µF is required between the LP2978 input and ground (the amount of capacitance 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 failure 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 considered when selecting the capacitor to ensure the capacitance will be ≥ 1 µF over the entire operating temperature range. CAPACITOR CHARACTERISTICS The LP2978 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 4.7 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 2.2 µF ceramic capacitor is in the range of 10 mΩ to 20 mΩ, which easily meets the ESR limits required for stability by the LP2978. One disadvantage of ceramic capacitors is that their capacitance 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 LP2978 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 capacitors is X7R, which holds the capacitance within ±15%. Unfortunately, the larger values of capacitance are not offered by all manufacturers in the X7R dielectric. Output Capacitor The LP2978 is designed specifically to work with ceramic output capacitors, utilizing circuitry which allows the regulator 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 minimum amount of capacitance and also have an ESR (equivalent 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). 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. 10093507 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 LP2978 requires a minimum of 2.2 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 5 100935 Version 6 Revision 2 Print Date/Time: 2009/04/23 16:08:18 www.national.com LP2978 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 Characteristics). The output capacitor must be located not more than 1 cm from the output pin and returned to a clean analog ground. Application Hints LP2978 ON/OFF INPUT OPERATION The LP2978 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 misoperation, the turn-on (and turn-off) voltage signals applied 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 Electrical Characteristics). www.national.com REVERSE INPUT-OUTPUT VOLTAGE The PNP power transistor used as the pass element in the LP2978 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 reversebiased. 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 LP2978 to 0.3V (see Absolute Maximum Ratings). 6 100935 Version 6 Revision 2 Print Date/Time: 2009/04/23 16:08:18 LP2978 Physical Dimensions inches (millimeters) unless otherwise noted 5-Lead Small Outline Package (M5) NS Package Number MF05A 7 100935 Version 6 Revision 2 Print Date/Time: 2009/04/23 16:08:18 www.national.com LP2978 Micropower SOT, 50 mA Low-Noise Ultra Low-Dropout Regulator Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH® Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage Reference www.national.com/vref Design Made Easy www.national.com/easy PowerWise® Solutions www.national.com/powerwise Solutions www.national.com/solutions Serial Digital Interface (SDI) www.national.com/sdi Mil/Aero www.national.com/milaero Temperature Sensors www.national.com/tempsensors SolarMagic™ www.national.com/solarmagic Wireless (PLL/VCO) www.national.com/wireless Analog University® www.national.com/AU THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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