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 −40˚C to +125˚C. 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 µF solid tantalum or a 10 µF aluminum electrolytic capacitor is recommended. **Required for stability. Must be at least a 10 µF aluminum electrolytic or a 1 µF 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 10Ω over the same operating temperature range as the regulator. © 1999 National Semiconductor Corporation DS011260 www.national.com LM2991 Negative Low Dropout Adjustable Regulator May 1999 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 Absolute Maximum Ratings (Note 1) 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) −65˚C to +150˚C 230˚C Operating Ratings (Note 1) −26V to +0.3V 2 kV Internally limited 125˚C Junction Temperature Range (TJ) Maximum Input Voltage (Operational) −40˚C to +125˚C −26V Electrical Characteristics VIN = −10V, VO = −3V, IO = 1A, CO = 47 µF, R1 = 2.7k, TJ = 25˚C, 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 0.004 0.04 %/V 0.04 0.4 % 0.1 0.2 V (Note 4) Reference Voltage 5 mA ≤ IO ≤ 1A −1.210 5 mA ≤ IO ≤ 1A, VO − 1V ≥ VIN ≥ −26V Output Voltage Range Line Regulation Load Regulation Dropout Voltage −2 VIN = −26V IO = 5 mA, VO − 1V ≥ VIN ≥ −26V −25 50 mA ≤ IO ≤ 1A IO = 0.1A, ∆VO ≤ 100 mV −24 V 0.3 IO = 1A, ∆VO ≤ 100 mV 0.6 0.8 V 1 Quiescent Current Dropout Quiescent IO ≤ 1A VIN = VO, IO ≤ 1A 0.7 5 mA 16 50 mA Current Ripple Rejection Vripple = 1 Vrms, f IO = 5 mA Output Noise 10 Hz − 100 kHz, IO = 5 mA 200 450 µV ON /OFF Input (VOUT: ON) 1.2 0.8 V Voltage (VOUT: OFF) VON/OFF = 0.8V (VOUT: ON) VON/OFF = 2.4V (VOUT: OFF) VIN = −26V, VON/OFF = 2.4V 1.3 0.1 10 µA 40 100 60 250 ON /OFF Input Current Output Leakage Current Current Limit ripple = 1 kHz, 60 VOUT = 0V VOUT = 0V 2 50 dB 2.4 1.5 µA 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 kΩ resistor. Note 3: The maximum power dissipation is a function of TJmax, θJA and TA. The maximum allowable power dissipation at any ambient temperature is PD = (TJmax − TA)/θJA. If this dissipation is exceeded, the die temperature will rise above 125˚C and the LM2991 will go into thermal shutdown. For the LM2991, the junction-to-ambient thermal resistance is 53˚C/W for the TO-220, 73˚C/W for the TO-263, and junction-to-case thermal resistance is 3˚C. 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, θJA is 50˚C/W; with 1 square inch of copper area, θJA is 37˚C/W; and with 1.6 or more square inches of copper area, θJA is 32˚C/W. Note 4: Typicals are at TJ = 25˚C and represent the most likely parametric norm. 3 www.national.com 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 Typical Performance Characteristics Adjust Pin Current (Continued) Low Voltage Behavior Maximum Power Dissipation (TO-220) DS011260-26 DS011260-25 DS011260-27 Maximum Power Dissipation (TO-263) (See Note 3) DS011260-28 Application Hints Output Capacitor ESR Range EXTERNAL CAPACITORS The LM2991 regulator requires an output capacitor to maintain stability. The capacitor must be at least 10 µF aluminum electrolytic or 1 µF solid tantalum. The output capacitor’s ESR must be less than 10Ω, or the zero added to the regulator frequency response by the ESR could reduce the phase margin, creating oscillations. The shaded area in the Output Capacitor ESR graph indicates the recommended ESR range. An input capacitor, of at least 1 µF solid tantalum or 10 µF aluminum electrolytic, is also needed if the regulator is situated more than 6 inches from the input power supply filter. DS011260-5 MINIMUM LOAD A minimum load current of 500 µA 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 kΩ. 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 5 www.national.com Application Hints 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. (Continued) 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 kΩ makes the adjust pin current negligible. For example, neglecting the adjust pin current, and setting R2 to 100 kΩ 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). Typical Applications Fully Isolated Post-Switcher Regulator DS011260-6 Adjustable Current Sink DS011260-10 www.national.com 6 DS011260-8 Equivalent Schematic 7 www.national.com 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 www.national.com 8 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) TO-263 5-Lead Plastic Surface Mount Package Ordering Number LM2991S NS Package Number TS5B 9 www.national.com 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 www.national.com 10 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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