LM2991 Negative Low Dropout Adjustable Regulator General Description Features The LM2991 is a low dropout adjustable negative regulator with a output voltage range between -3V to -24V. 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 (VOUT - VIN 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. The LM2991 is available in 5-lead TO-220 and TO-263 packages and is rated for operation over the automotive temperature range of -40C to +125C. Mil-Aero versions are also available. n Output voltage adjustable from -3V to -24V, typically -2V to -25V n Output current in excess of 1A n Dropout voltage typically 0.6V at 1A load n Low quiescent current n Internal short circuit current limit n Internal thermal shutdown with hysteresis n TTL, CMOS compatible ON/OFF switch n Functional complement to the LM2941 series Applications n Post switcher regulator n Local, on-card, regulation n Battery operated equipment Typical Application DS011260-1 VOUT = 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. (c) 2000 National Semiconductor Corporation DS011260 www.national.com LM2991 Negative Low Dropout Adjustable Regulator September 2000 LM2991 Connection Diagrams and Ordering Information 5-Lead TO-220 Straight Leads 5-Lead TO-220 Bent, Staggered Leads DS011260-9 DS011260-2 Front View Order Number LM2991T See NS Package Number T05A Front View Order Number LM2991T Flow LB03 See NS Package Number T05D TO263 5-Lead Surface-Mount Package DS011260-11 Top View DS011260-12 Side View Order Number LM2991S See NS Package Number TS5B 16-Lead Ceramic Dual-in-Line Package 16-Lead Ceramic Surface-Mount Package DS011260-29 DS011260-30 Top View Order Number LM2991J-QMLV 5962-9650501VEA Order Number LM2991J-QML 5962-9650501QEA See NS Package Number J16A www.national.com Top View Order Number LM2991WG-QML 5962-9650501QXA See NS Package Number WG16A 2 Storage Temperature Range Lead Temperature (Soldering, 10 sec.) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Voltage ESD Susceptibility (Note 2) Power Dissipation (Note 3) Junction Temperature (TJmax) -65C to +150C 230C Operating Ratings (Note 1) -26V to +0.3V 2 kV Internally limited 125C Junction Temperature Range (TJ) Maximum Input Voltage (Operational) -40C to +125C -26V Electrical Characteristics VIN = -10V, VO = -3V, IO = 1A, CO = 47 F, R1 = 2.7k, TJ = 25C, unless otherwise specified. Boldface limits apply over the entire operating junction temperature range. Parameter Conditions Typical Min Max Units -1.234 -1.186 V -1.27 -1.15 V -3 V 0.04 %/V (Note 4) Reference Voltage 5 mA IO 1A -1.210 5 mA IO 1A, VO - 1V VIN -26V Output Voltage -2 Range VIN = -26V Line Regulation IO = 5 mA, VO - 1V VIN -26V 0.004 Load Regulation 50 mA IO 1A 0.04 0.4 % Dropout Voltage IO = 0.1A, VO 100 mV 0.1 0.2 V IO = 1A, VO 100 mV 0.6 -25 -24 V 0.3 0.8 V 1 Quiescent Current IO 1A 0.7 5 mA Dropout Quiescent VIN = VO, IO 1A 16 50 mA Current Ripple Rejection Vripple = 1 Vrms, f ripple = 1 kHz, 60 50 dB IO = 5 mA Output Noise 10 Hz - 100 kHz, IO = 5 mA 200 450 V ON /OFF Input (VOUT: ON) 1.2 0.8 V A Voltage (VOUT: OFF) 1.3 ON /OFF Input VON/OFF = 0.8V (VOUT: ON) 0.1 10 Current VON/OFF = 2.4V (VOUT: OFF) 40 100 Output Leakage VIN = -26V, VON/OFF = 2.4V 60 250 Current VOUT = 0V Current Limit VOUT = 0V 2 2.4 1.5 A A Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the deivce is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: Human body model, 100 pF discharged through a 1.5 k resistor. Note 3: The maximum power dissipation is a function of TJmax, JA and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJmax - TA)/JA. If this dissipation is exceeded, the die temperature will rise above 125C and the LM2991 will go into thermal shutdown. For the LM2991, the junction-to-ambient thermal resistance is 53C/W for the TO-220, 73C/W for the TO-263, and junction-to-case thermal resistance is 3C. If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package. Using 0.5 square inches of copper area, JA is 50C/W; with 1 square inch of copper area, JA is 37C/W; and with 1.6 or more square inches of copper area, JA is 32C/W. Note 4: Typicals are at TJ = 25C and represent the most likely parametric norm. 3 www.national.com LM2991 Absolute Maximum Ratings (Note 1) LM2991 Typical Performance Characteristics Dropout Voltage Normalized Output Voltage DS011260-13 Output Noise Voltage Load Transient Response DS011260-19 DS011260-18 Maximum Output Current DS011260-20 Output Impedance 4 DS011260-21 ON /OFF Control Voltage DS011260-23 DS011260-22 www.national.com Maximum Output Current DS011260-17 DS011260-16 Ripple Rejection DS011260-15 DS011260-14 Quiescent Current Line Transient Response Output Voltage DS011260-24 (Continued) Low Voltage Behavior Adjust Pin Current LM2991 Typical Performance Characteristics Maximum Power Dissipation (TO-220) DS011260-26 DS011260-25 DS011260-27 Maximum Power Dissipation (TO-263) (See Note 3) DS011260-28 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 25 from ambient to assure the amount of capacitance is sufficient. 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. These capacitors should be avoided if possible, and kept as far 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. INPUT CAPACITOR: An input capacitor is reqiuired if the regulator is located more than 6 from the input power supply filter capacitor (or if no other input capaciotr 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. 5 www.national.com LM2991 Application Hints The output voltage of the LM2991 is set externally by a resistor divider using the following equation: (Continued) VOUT = VREF x (1 + R2/R1) - (IADJ x R2) Output Capacitor ESR Range 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%. 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 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 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. DS011260-5 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 Typical Applications Fully Isolated Post-Switcher Regulator DS011260-6 www.national.com 6 LM2991 Typical Applications (Continued) Adjustable Current Sink DS011260-10 7 www.national.com DS011260-8 LM2991 Equivalent Schematic www.national.com 8 LM2991 Physical Dimensions inches (millimeters) unless otherwise noted 5-Lead T0-220, Straight Leads (T) Order Number LM2991T NS Package Number T05A 5-Lead T0-220, Bent, Staggered Leads (T) Order Number LM2991T Flow LBO3 NS Package Number T05D 9 www.national.com LM2991 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) TO-263 5-Lead Plastic Surface Mount Package Ordering Number LM2991S NS Package Number TS5B www.national.com 10 LM2991 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 16-Lead Ceramic Dual-in-Line Package Order Number LM2991J-QMLV 5962-9650501VEA Order Number LM2991J-QML 5962-9650501QEA NS Package Number J16A 11 www.national.com LM2991 Negative Low Dropout Adjustable Regulator Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 16-Lead Ceramic Surface-Mount Package Order Number LM2991WG-QML 5962-9650501QXA NS Package Number WG16A LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. 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