LM2991QML LM2991QML Negative Low Dropout Adjustable Regulator Literature Number: SNVS392A LM2991QML Negative Low Dropout Adjustable Regulator General Description Features The LM2991 is a low dropout adjustable negative regulator with a output voltage range between -2V to -25V. The LM2991 provides up to 1A of load current and features a On /Off pin for remote shutdown capability. The LM2991 uses new circuit design techniques to provide a low dropout voltage, low quiescent current and low temperature coefficient precision reference. The dropout voltage at 1A load current is typically 0.6V and a guaranteed worst-case maximum of 1V over the entire operating temperature range. The quiescent current is typically 1 mA with a 1A load current and an input-output voltage differential greater than 3V. A unique circuit design of the internal bias supply limits the quiescent current to only 9 mA (typical) when the regulator is in the dropout mode (VO - VI 3V). The LM2991 is short-circuit proof, and thermal shutdown includes hysteresis to enhance the reliability of the device when inadvertently overloaded for extended periods. Output voltage adjustable from -2V to -25V Output current in excess of 1A Dropout voltage typically 0.6V at 1A load Low quiescent current Internal short circuit current limit Internal thermal shutdown with hysteresis TTL, CMOS compatible ON/OFF switch Functional complement to the LM2941 series Applications Post switcher regulator Local, on-card, regulation Battery operated equipment Ordering Information NS Part Number SMD Part Number LM2991GW-QML 5962-9650502QXA NS Package Number WG16A Package Description 16LD Ceramic SOIC Connection Diagrams 16-Lead Ceramic Surface-Mount Package 20158730 Top View See NS Package Number WG16A (c) 2011 National Semiconductor Corporation 201587 www.national.com LM2991QML Negative Low Dropout Adjustable Regulator October 5, 2011 20158708 LM2991QML Equivalent Schematic www.national.com 2 LM2991QML Absolute Maximum Ratings (Note 1) Input Voltage Power Dissipation (Note 2) Junction Temperature (TJmax) Storage Temperature Range -26V to +0.3V Internally limited 150C -65C TA +150C Thermal Resistance JA Ceramic SOIC (Still Air @ 0.5C/W) "GW" Ceramic SOIC (500LF/Min Air flow @ 0.5C/W) "GW" 130C/W 80C/W JC Ceramic SOIC "GW" Package Weight "GW" Lead Temperature (Soldering, 10 sec.) ESD Susceptibility (Note 4) 6C/W 410mg 260C 1,500V Recommended Operating Conditions (Note 1) -55C TA +125C -26V Operating Temperature Range (TA) Maximum Input Voltage (Operational) Quality Conformance Inspection Mil-Std-883, Method 5005 - Group A Subgroup Description Temp C 1 Static tests at +25 2 Static tests at +125 3 Static tests at -55 4 Dynamic tests at +25 5 Dynamic tests at +125 6 Dynamic tests at -55 7 Functional tests at +25 8A Functional tests at +125 8B Functional tests at -55 9 Switching tests at +25 10 Switching tests at +125 11 Switching tests at -55 12 Settling time at +25 13 Settling time at +125 14 Settling time at -55 3 www.national.com LM2991QML LM2991 Electrical Characteristics DC Parameters The following conditions apply, unless otherwise specified. DC: VI = -10V, VO = -3V, IO = 1A, CO = 47F, RL = 2.7K Symbol VRef Parameter Reference Voltage Conditions Notes Min Max Units Subgroups 5mA IO 1A -1.23 -1.18 4 6 V 1 5mA IO 1A, -1.27 -1.15 V 2, 3 -3.0 V 1 VO - 1V VI -26V VO Output Voltage Range VI = -26V -24 V 1 -25 V 2, 3 VRLine Line Regulation IO = 5mA, VO - 1V VI -26V -26 +26 mV 1, 2, 3 VRLoad Load Regulation 50mA IO 1A -12 +12 mV 1 -15 +15 mV 2, 3 VDO Dropout Voltage 0.2 V 1 0.3 V 2, 3 0.8 V 1 1.0 V 2, 3 IO = 0.1A, VO 100mV IO = 1A, VO 100mV IQ VON Quiescent Current IO 1A 5.0 mA 1, 2, 3 Dropout Quiescent Current VI = VO, IO 1A 50 mA 1, 2, 3 Output Noise 10Hz - 100KHz, IO = 5mA 450 V 1 500 V 2, 3 0.6 V 1, 2, 3 V 1, 2, 3 ON/OFF Input Voltage VO : ON VO : OFF ON/OFF Input Current 2.4 VON/OFF = 0.6V (VO : ON) 10 A 1 25 A 2, 3 100 A 1 150 A 2, 3 250 A 1 300 A 2, 3 1.5 2.5 A 1 1.0 4.0 A 2, 3 Min Max Units Subgroups dB 1 VON/OFF = 2.4V (VO : OFF) IL Output Leakage Current ILimit Current Limit VI = -26V, VON/OFF = 2.4V, VO = 0V VO = 0V AC Parameters The following conditions apply, unless otherwise specified. AC: VI = -10V, VO = -3V, IO = 1A, CO = 47F, RL = 2.7K Symbol RR Parameter Ripple Rejection www.national.com Conditions VRipple = 1VRMS, FRipple = 1KHz, IO = 5mA 4 Notes 50 LM2991QML DC Drift Parameters The following conditions apply, unless otherwise specified. DC: VI = -10V, VO = -3V, IO = 1A, CO = 47F, RL = 2.7K Deltas not required on B-Level product. Deltas required for S-Level product ONLY. Symbol VRef Parameter Reference Voltage Conditions 5mA IO 1A Notes Min Max Units Subgroups 20 mV 1 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test conditions. Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (maximum junction temperature), JA (package junction to ambient thermal resistance), and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PDmax = (TJmax - TA)/ JA or the number given in the Absolute Maximum Ratings, whichever is lower. Note 3: The package material for these devices allows much improved heat transfer over our standard ceramic packages. In order to take full advantage of this improved heat transfer, heat sinking must be provided between the package base (directly beneath the die), and either metal traces on, or thermal vias through, the printed circuit board. Without this additional heat sinking, device power dissipation must be calculated using JA, rather than JC, thermal resistance. It must not be assumed that the device leads will provide substantial heat transfer out the package, since the thermal resistance of the leadframe material is very poor, relative to the material of the package base. The stated JC thermal resistance is for the package material only, and does not account for the additional thermal resistance between the package base and the printed circuit board. The user must determine the value of the additional thermal resistance and must combine this with the stated value for the package, to calculate the total allowed power dissipation for the device. The user must determine the value of the additional thermal resistance and must combine this with the stated value for the package, to calculate the total allowed power dissipation for the device. Note 4: Human body model, 1.5 k in series with 100 pF. 5 www.national.com LM2991QML Typical Performance Characteristics Dropout Voltage Normalized Output Voltage 20158713 20158714 Output Voltage Output Noise Voltage 20158715 20158716 Quiescent Current Maximum Output Current 20158717 www.national.com 20158718 6 LM2991QML Line Transient Response Load Transient Response 20158719 20158720 Maximum Output Current Ripple Rejection 20158722 20158721 Output Impedance ON /OFF Control Voltage 20158723 20158724 7 www.national.com LM2991QML Adjust Pin Current Low Voltage Behavior 20158726 20158725 These capacitors should be avoided if possible, and kept as far away from the LDO output as is practical. Application Hints EXTERNAL CAPACITORS Like any low-dropout regulator, external capacitors are reqired to stabilize the control loop. These capacitors must be correctly selected for proper performance. Output Capacitor ESR Range INPUT CAPACITOR An input capacitor is required if the regulator is located more than 6" from the input power supply filter capacitor (or if no other input capacitor is present). A solid Tantalum or ceramic capacitor whose value is at least 1 F is recommended, but an aluminum electrolytic ( 10 F) may be used. However, aluminum electrolytics should not be used in applications where the ambient temperature can drop below 0C because their internal impedance increases significantly at cold temperatures. OUTPUT CAPACITOR The output capacitor must meet the ESR limits shown in the graph, which means it must have an ESR between about 25 m and 10. A solid Tantalum (value 1 F) is the best choice for the output capacitor. An aluminum electrolytic ( 10 F) may be used if the ESR is in the stable range. It should be noted that the ESR of a typical aluminum electrolytic will increase by as much as 50X as the temperature is reduced from 25C down to -40C, while a Tantalum will exhibit an ESR increase of about 2X over the same range. For this and other reasons, aluminum electrolytics should not be used in applications where low operating temperatures occur. The lower stable ESR limit of 25 m means that ceramic capacitors can not be used directly on the output of an LDO. A ceramic ( 2.2 F) can be used on the output if some external resistance is placed in series with it (1 recommended). Dielectric types X7R or X5R must be used if the temperature range of the application varies more than 25C from ambient to assure the amount of capacitance is sufficient. 20158705 MINIMUM LOAD A minimum load current of 500 A is required for proper operation. The external resistor divider can provide the minimum load, with the resistor from the adjust pin to ground set to 2.4 k. SETTING THE OUTPUT VOLTAGE The output voltage of the LM2991 is set externally by a resistor divider using the following equation: VOUT = VREF x (1 + R2/R1) - (IADJ x R2) where VREF = -1.21V. The output voltage can be programmed within the range of -3V to -24V, typically an even greater range of -2V to -25V. The adjust pin current is about 60 nA, causing a slight error in the output voltage. However, using resistors lower than 100 k makes the adjust pin current negligible. For example, neglecting the adjust pin current, and setting R2 to 100 k and VOUT to -5V, results in an output voltage error of only 0.16%. CERAMIC BYPASS CAPACITORS Many designers place distributed ceramic capacitors whose value is in the range of 1000 pF to 0.1 F at the power input pins of the IC's across a circuit board. These can cause reduced phase margin or oscillations in LDO regulators. The advent of multi-layer boards with dedicated power and ground planes has removed the trace inductance that (previously) provided the necessary "decoupling" to shield the output of the LDO from the effects of bypass capacitors. www.national.com ON/OFF PIN The LM2991 regulator can be turned off by applying a TTL or CMOS level high signal to the ON/OFF pin (see Adjustable Current Sink Application). FORCING THE OUTPUT POSITIVE Due to an internal clamp circuit, the LM2991 can withstand positive voltages on its output. If the voltage source pulling 8 of the source. However, if the transients have a duration of over 1 mS, the output should be clamped with a Schottky diode to ground. Typical Applications 20158701 VO = VRef (1 + R2/R1) *Required if the regulator is located further than 6 inches from the power supply filter capacitors. A 1 F solid tantalum or a 10 F aluminum electrolytic capacitor is recommended. **Required for stability. Must be at least a 10 F aluminum electrolytic or a 1 F solid tantalum to maintain stability. May be increased without bound to maintain regulation during transients. Locate the capacitor as close as possible to the regulator. The equivalent series resistance (ESR) is critical, and should be less than 10 over the same operating temperature range as the regulator. Fully Isolated Post-Switcher Regulator 20158706 9 www.national.com LM2991QML the output positive is DC, the current must be limited to 1.5A. A current over 1.5A fed back into the LM2991 could damage the device. The LM2991 output can also withstand fast positive voltage transients up to 26V, without any current limiting LM2991QML Adjustable Current Sink 20158710 www.national.com 10 Released Revision Section Changes 03/10/06 A New Release, Corporate format 1 MDS data sheet converted into one Corp. data sheet format. MNLM2991-X Rev 1A1 will be archived. 05-Oct-2011 B Ordering Information, Absolute Maximum Ratings Added new 'GW' NSID and --02 SMD part number. Added Theta JA & Theta JC as well as the weight for the 'GW' device. LM2991QML Rev A will be archived. 11 www.national.com LM2991QML Revision History LM2991QML Physical Dimensions inches (millimeters) unless otherwise noted 16-Lead Ceramic Surface-Mount Package NS Package Number WG16A www.national.com 12 LM2991QML Notes 13 www.national.com LM2991QML Negative Low Dropout Adjustable Regulator Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH(R) 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 References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise(R) Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagicTM www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise(R) Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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