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LM2937 500 mA Low Dropout Regulator
December 1997
LM2937 500 mA Low Dropout Regulator
General Description
The LM2937 is a positive voltage regulator capable of supplying up to 500 mA of load current. The use of a PNP power transistor provides a low dropout voltage characteristic. With a load current of 500 mA the minimum input to output voltage differential required for the output to remain in regulation is typically 0.5V (1V guaranteed maximum over the full operating temperature range). Special circuitry has been incorporated to minimize the quiescent current to typically only 10 mA with a full 500 mA load current when the input to output voltage differential is greater than 3V. The LM2937 requires an output bypass capacitor for stability. As with most low dropout regulators, the ESR of this capacitor remains a critical design parameter, but the LM2937 includes special compensation circuitry that relaxes ESR requirements. The LM2937 is stable for all ESR below 3. This allows the use of low ESR chip capacitors. Ideally suited for automotive applications, the LM2937 will protect itself and any load circuitry from reverse battery connections, two-battery jumps and up to +60V/-50V load dump transients. Familiar regulator features such as short circuit and thermal shutdown protection are also built in.
Features
n Fully specified for operation over -40C to +125C n Output current in excess of 500 mA n Output trimmed for 5% tolerance under all operating conditions n Typical dropout voltage of 0.5V at full rated load current n Wide output capacitor ESR range, up to 3 n Internal short circuit and thermal overload protection n Reverse battery protection n 60V input transient protection n Mirror image insertion protection
Connection Diagram and Ordering Information
TO-220 Plastic Package SOT-223 Plastic Package
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Front View Order Number LM2937ET-5.0, LM2937ET-8.0, LM2937ET-10, LM2937ET-12 or LM2937ET-15 See NS Package Number T03B
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Front View Order Number LM2937IMP-5.0, LM2937IMP-8.0, LM2937IMP-10, LM2937IMP-12 or LM2937IMP-15 See NS Package Number MA04A
TO-263 Surface-Mount Package
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Side View
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Top View Order Number LM2937ES-5.0, LM2937ES-8.0, LM2937ES-10, LM2937ES-12 or LM2937ES-15 See NS Package Number TS3B
(c) 1999 National Semiconductor Corporation
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Connection Diagram and Ordering Information
Temperature Range -40C TA 125C -40C TA 85C SOT-223 Package Markings Output Voltage 5.0 LM2937ES-5.0 LM2937ET-5.0 LM2937IMP-5.0 L71B 8.0 LM2937ES-8.0 LM2937ET-8.0 LM2937IMP-8.0 L72B 10 LM2937ES-10 LM2937ET-10 LM2937IMP-10 L73B
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NSC 12 15 LM2937ES-15 LM2937ET-15 LM2937IMP-15 L75B Package Drawing TS3B T03B MA04A TO-263 TO-220 SOT-223 Package
LM2937ES-12 LM2937ET-12 LM2937IMP-12 L74B
The small physical size of the SOT-223 package does not allow sufficient space to provide the complete device part number. The actual devices will be labeled with the package markings shown.
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Voltage Continuous Transient (t 100 ms) Internal Power Dissipation (Note 2) Maximum Junction Temperature Storage Temperature Range TO-220 (10 seconds) TO-263 (10 seconds) 26V 60V Internally Limited 150C -65C to +150C 260C 230C
SOT-223 (Vapor Phase, 60 seconds) SOT-223 (Infared, 15 seconds) ESD Susceptibility (Note 3)
215C 220C 2 kV
Operating Conditions (Note 1)
Temperature Range (Note 2) Junction Temperature (TJ) LM2937ET, LM2937ES LM2937IMP Maximum Input Voltage 125C -40C TA 125C -40C TA 85C 26V
Electrical Characteristics
VIN = VNOM + 5V, (Note 4) IOUTmax = 500 mA for the TO-220 and TO-263 packages, IOUTmax = 400mA for the SOT-223 package, COUT = 10 F unless otherwise indicated. Boldface limits apply over the entire operating temperature range of the indicated device., all other specifications are for TA = TJ = 25C. Output Voltage (VOUT) Parameter Output Voltage Conditions 5 mA IOUT IOUTmax 5.00 Typ 5V Limit 4.85 4.75 5.15 5.25 Line Regulation Load Regulation Quiescent Current (VOUT + 2V) VIN 26V, IOUT = 5 mA 5 mA IOUT IOUTmax (VOUT + 2V) VIN 26V, IOUT = 5 mA VIN = (VOUT + 5V), IOUT = IOUTmax Output Noise Voltage Long Term Stability Dropout Voltage Short-Circuit Current Peak Line Transient Voltage Maximum Operational Input Voltage Reverse DC Input Voltage Reverse Transient Input Voltage tr < 1 ms, RL = 100 -75 -50 -75 -50 -75 -50 V(Min) VOUT -0.6V, RL = 100 -30 -15 -30 -15 -30 -15 V(Min) 26 26 26 V(Min) tf < 100 ms, RL = 100 10 Hz-100 kHz IOUT = 5 mA 1000 Hrs. IOUT = IOUTmax IOUT = 50 mA 15 5 2 10 150 20 0.5 110 1.0 75 1.0 250 0.6 60 50 50 10 20 24 8 2 10 240 32 0.5 110 1.0 75 1.0 250 0.6 60 8.00 Typ 8V Limit 7.76 7.60 8.24 8.40 80 80 10 20 30 10 2 10 300 40 0.5 110 1.0 75 1.0 250 0.6 60 10.00 Typ 10V Limit 9.70 9.50 10.30 10.50 100 100 10 20 V(Min) V(Min) V(Max) V(Max) mV(Max) mV(Max) mA(Max) mA(Max) Vrms mV V(Max) mV(Max) A(Min) V(Min) Units
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Electrical Characteristics
VIN = VNOM + 5V, (Note 4) IOUTmax = 500 mA for the TO-220 and TO-263 packages, IOUTmax = 400mA for the SOT-223 package, COUT = 10 F unless otherwise indicated. Boldface limits apply over the entire operating temperature range of the indicted device., all other specifications are for TA = TJ = 25C. Output Voltage (VOUT) Parameter Output Voltage Conditions 5 mA IOUT IOUTmax 12.00 Typ 12V Limit 11.64 11.40 12.36 12.60 Line Regulation Load Regulation Quiescent Current (VOUT + 2V) VIN 26V, IOUT = 5 mA 5 mA IOUT IOUTmax (VOUT + 2V) VIN 26V, IOUT = 5 mA VIN = (VOUT + 5V), IOUT = IOUTmax Output Noise Voltage Long Term Stability Dropout Voltage Short-Circuit Current Peak Line Transient Voltage Maximum Operational Input Voltage Reverse DC Input Voltage Reverse Transient Input Voltage
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device outside of its rated Operating Conditions. Note 2: The maximum allowable power dissipation at any ambient temperature is PMAX = (125 - TA)/JA, where 125 is the maximum junction temperature for operation, TA is the ambient temperature, and JA is the junction-to-ambient thermal resistance. If this dissipation is exceeded, the die temperature will rise above 125C and the electrical specifications do not apply. If the die temperature rises above 150C, the LM2937 will go into thermal shutdown. For the LM2937, the junction-to-ambient thermal resistance JA is 65C/W, for the TO-220 package, 73C/W for the TO-263 package, and 174C/W for the SOT-223 package. When used with a heatsink, JA is the sum of the LM2937 junction-to-case thermal resistance JC of 3C/W and the heatsink case-to-ambient thermal resistance. If the TO-263 or SOT-223 packages are used, the thermal resistance can be reduced by increasing the P.C. board copper area thermally connected to the package (see Application Hints for more information on heatsinking). Note 3: ESD rating is based on the human body model, 100 pF discharged through 1.5 k. Note 4: Typicals are at TJ = 25C and represent the most likely parametric norm.
15V Typ 15.00 Limit 14.55 14.25 15.45 15.75 45 15 2 10 450 56 1.0 250 0.6 60 26 0.5 110 1.0 75 1.0 250 0.6 60 26 -30 -75 -15 -50 150 150 10 20
Units V (Min) V(Min) V(Max) V(Max) mV(Max) mV(Max) mA(Max) mA(Max) Vrms mV V(Max) mV(Max) A(Min) V(Min) V(Min) V(Min) V(Min)
36 12 2 10 360 44 0.5 110 1.0 75
120 120 10 20
10 Hz-100 kHz, IOUT = 5 mA 1000 Hrs. IOUT = IOUTmax IOUT = 50 mA tf < 100 ms, RL = 100
VOUT -0.6V, RL = 100 tr < 1 ms, RL = 100
-30 -75
-15 -50
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Typical Performance Characteristics
Dropout Voltage vs Output Current Dropout Voltage vs Temperature Output Voltage vs Temperature
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Quiescent Current vs Temperature
Quiescent Current vs Input Voltage
Quiescent Current vs Output Current
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Line Transient Response
Load Transient Response
Ripple Rejection
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Output Impedance
Maximum Power Dissipation (TO-220)
Maximum Power Dissipation (TO-263) (Note 2)
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Typical Performance Characteristics
Low Voltage Behavior
(Continued) Low Voltage Behavior
Low Voltage Behavior
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Output at Voltage Extremes
Output at Voltage Extremes
Output Capacitor ESR
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Peak Output Current
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Typical Application
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* Required if the regulator is located more than 3 inches from the power supply filter capacitors. ** Required for stability. Cout must be at least 10 F (over the full expected operating temperature range) and located as close as possible to the regulator. The equivalent series resistance, ESR, of this capacitor may be as high as 3.
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Application Hints
EXTERNAL CAPACITORS The output capacitor is critical to maintaining regulator stability, and must meet the required conditions for both ESR (Equivalent Series Resistance) and minimum amount of capacitance. MINIMUM CAPACITANCE: The minimum output capacitance required to maintain stability is 10 F (this value may be increased without limit). Larger values of output capacitance will give improved transient response. ESR LIMITS: The ESR of the output capacitor will cause loop instability if it is too high or too low. The acceptable range of ESR plotted versus load current is shown in the graph below. It is essential that the output capacitor meet these requirements, or oscillations can result. Output Capacitor ESR
The figure below shows the voltages and currents which are present in the circuit, as well as the formula for calculating the power dissipated in the regulator:
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IIN = IL / IG PD = (VIN - VOUT) IL + (VIN) IG
FIGURE 2. Power Dissipation Diagram The next parameter which must be calculated is the maximum allowable temperature rise, TR (max). This is calculated by using the formula: TR (max) = TJ(max) - TA (max) where: TJ (max) is the maximum allowable junction temperature, which is 125C for commercial grade parts. TA (max) is the maximum ambient temperature which will be encountered in the application. Using the calculated values for TR(max) and PD, the maximum allowable value for the junction-to-ambient thermal resistance, (J-A), can now be found: (J-A) = TR (max)/PD IMPORTANT: If the maximum allowable value for (J-A) is found to be 53C/W for the TO-220 package, 80C/W for the TO-263 package, or 174C/W for the SOT-223 package, no heatsink is needed since the package alone will dissipate enough heat to satisfy these requirements. If the calculated value for (J-A)falls below these limits, a heatsink is required. HEATSINKING TO-220 PACKAGE PARTS The TO-220 can be attached to a typical heatsink, or secured to a copper plane on a PC board. If a copper plane is to be used, the values of (J-A) will be the same as shown in the next section for the TO-263. If a manufactured heatsink is to be selected, the value of heatsink-to-ambient thermal resistance, (H-A), must first be calculated: (H-A) = (J-A) - (C-H) - (J-C) is defined as the thermal resistance from the junction to the surface of the case. A value of 3C/W can be assumed for (J-C) for this calculation. is defined as the thermal resistance be(C-H) tween the case and the surface of the heatsink. The value of (C-H) will vary from about 1.5C/W to about 2.5C/W (depending on method of attachment, insulator, etc.). If the exact value is unknown, 2C/W should be assumed for (C-H). When a value for (H-A) is found using the equation shown, a heatsink must be selected that has a value that is less than or equal to this number. Where: (J-C)
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FIGURE 1. ESR Limits It is important to note that for most capacitors, ESR is specified only at room temperature. However, the designer must ensure that the ESR will stay inside the limits shown over the entire operating temperature range for the design. For aluminum electrolytic capacitors, ESR will increase by about 30X as the temperature is reduced from 25C to -40C. This type of capacitor is not well-suited for low temperature operation. Solid tantalum capacitors have a more stable ESR over temperature, but are more expensive than aluminum electrolytics. A cost-effective approach sometimes used is to parallel an aluminum electrolytic with a solid Tantalum, with the total capacitance split about 75/25% with the Aluminum being the larger value. If two capacitors are paralleled, the effective ESR is the parallel of the two individual values. The "flatter" ESR of the Tantalum will keep the effective ESR from rising as quickly at low temperatures. HEATSINKING A heatsink may be required depending on the maximum power dissipation and maximum ambient temperature of the application. Under all possible operating conditions, the junction temperature must be within the range specified under Absolute Maximum Ratings. To determine if a heatsink is required, the power dissipated by the regulator, PD, must be calculated.
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Application Hints
(Continued)
(H-A) is specified numerically by the heatsink manufacturer in the catalog, or shown in a curve that plots temperature rise vs power dissipation for the heatsink. HEATSINKING TO-263 AND SOT-223 PACKAGE PARTS Both the TO-263 ("S") and SOT-223 ("MP") packages use a copper plane on the PCB and the PCB itself as a heatsink. To optimize the heat sinking ability of the plane and PCB, solder the tab of the package to the plane.
Figure 3 shows for the TO-263 the measured values of (J-A) for different copper area sizes using a typical PCB with 1 ounce copper and no solder mask over the copper area used for heatsinking.
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FIGURE 5. (J-A) vs Copper (2 ounce) Area for the SOT-223 Package
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FIGURE 3. (J-A) vs Copper (1 ounce) Area for the TO-263 Package As shown in the figure, increasing the copper area beyond 1 square inch produces very little improvement. It should also be observed that the minimum value of (J-A) for the TO-263 package mounted to a PCB is 32C/W. As a design aid, Figure 4 shows the maximum allowable power dissipation compared to ambient temperature for the TO-263 device (assuming (J-A) is 35C/W and the maximum junction temperature is 125C).
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FIGURE 6. Maximum Power Dissipation vs TAMB for the SOT-223 Package SOT-223 SOLDERING RECOMMENDATIONS It is not recommended to use hand soldering or wave soldering to attach the small SOT-223 package to a printed circuit board. The excessive temperatures involved may cause package cracking. Either vapor phase or infrared reflow techniques are preferred soldering attachment methods for the SOT-223 package.
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FIGURE 4. Maximum Power Dissipation vs TAMB for the TO-263 Package
Figure 5 and Figure 6 show the information for the SOT-223 package. Figure 6 assumes a (J-A) of 74C/W for 1 ounce copper and 51C/W for 2 ounce copper and a maximum junction temperature of 125C.
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Physical Dimensions
inches (millimeters) unless otherwise noted
Plastic Package Order Number LM2937ET-5.0, LM2937ET-8.0, LM2937ET-10, LM2937ET-12, or LM2937ET-15 NS Package Number T03B
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Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
TO-263 3-Lead Plastic Surface Mount Package Order Number LM2937ES-5.0, LM2937ES-8.0, LM2937ES-10, LM2937ES-12 or LM2937ES-15 NS Package Number TS3B
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LM2937 500 mA Low Dropout Regulator
Physical Dimensions
inches (millimeters) unless otherwise noted (Continued)
SOT-223 3-Lead Plastic Surface Mount Package Order Number LM2937IMP-5.0, LM2937IMP-8.0, LM2937IMP-10, LM2937IMP-12 or LM2937IMP-15 NS Package Number MA04A
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