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lm2940/lm2940c 1a low dropout regulator general description the lm2940/lm2940c positive voltage regulator features the ability to source 1a of output current with a dropout volt- age of typically 0.5v and a maximum of 1v over the entire temperature range. furthermore, a quiescent current reduc- tion circuit has been included which reduces the ground cur- rent when the differential between the input voltage and the output voltage exceeds approximately 3v. the quiescent current with 1a of output current and an input-output differ- ential of 5v is therefore only 30 ma. higher quiescent cur- rents only exist when the regulator is in the dropout mode (v in ?v out 3v). designed also for vehicular applications, the lm2940/ lm2940c and all regulated circuitry are protected from re- verse battery installations or 2-battery jumps. during line transients, such as load dump when the input voltage can momentarily exceed the specified maximum operating volt- age, the regulator will automatically shut down to protect both the internal circuits and the load. the lm2940/ lm2940c cannot be harmed by temporary mirror-image in- sertion. familiar regulator features such as short circuit and thermal overload protection are also provided. features n dropout voltage typically 0.5v @ i o = 1a n output current in excess of 1a n output voltage trimmed before assembly n reverse battery protection n internal short circuit current limit n mirror image insertion protection n p + product enhancement tested typical application ordering information temperature range output voltage package 5.0 8.0 9.0 10 12 15 0c t a 125c lm2940ct-5.0 lm2940ct-9.0 lm2940ct-12 lm2940ct-15 to-220 lm2940cs-5.0 lm2940cs-9.0 lm2940cs-12 lm2940cs-15 to-263 ?40c t a 125c lm2940t-5.0 lm2940t-8.0 lm2940t-9.0 lm2940t-10 lm2940t-12 to-220 lm2940s-5.0 lm2940s-8.0 lm2940s-9.0 lm2940s-10 lm2940s-12 to-263 ?40c t a 85c lm2940imp-5.0 lm2940imp-8.0 lm2940imp-9.0 lm2940imp-10 lm2940imp-12 lm2940imp-15 sot-223 sot-223 package marking l53b l54b l0eb l55b l56b l70b the physical size of the sot-223 is too small to contain the full device part number. the package markings indicated are what will appear on the actual de vice. temperature range output voltage package 5.0 8.0 12 15 ?55c t a 125c lm2940j-5.0/883 5962-8958701ea lm2940j-8.0/883 5962-9088301qea lm2940j-12/883 5962-9088401qea lm2940j-15/883 5962-9088501qea j16a lm2940wg5.0/883 5962-8958701xa wg16a for information on military temperature range products, please go to the mil/aero web site at http://www.national.com/appinfo/milaero/index.ht ml. ds008822-3 * required if regulator is located far from power supply filter. ** c out must be at least 22 f to maintain stability. may be increased without bound to maintain regulation during transients. locate as close as possible to the regulator. this capacitor must be rated over the same operating temperature range as the regulator and the esr is critical; see curve. june 1999 lm2940/lm2940c 1a low dropout regulator ? 1999 national semiconductor corporation ds008822 www.national.com
connection diagrams (to-220) plastic package ds008822-2 front view order number lm2940ct-5.0, lm2940ct-9.0, lm2940ct-12, lm2940ct-15, lm2940t-5.0, lm2940t-8.0, lm2940t-9.0, lm2940t-10 or lm2940t-12 see ns package number to3b 3-lead sot-223 ds008822-42 front view order part number lm2940imp-5.0, lm2940imp-8.0, lm2940imp-9.0, lm2940imp-10, lm2940imp-12 or lm2940imp-15 see ns package number ma04a 16-lead dual-in-line package (j) ds008822-43 top view order number lm2940j-5.0/883 (5962-8958701ea), lm2940j-8.0/883 (5962-9088301qea), lm2940j-12/883 (5962-9088401qea), lm2940j-15/883 (5962-9088501qea) see ns package number j16a 16-lead ceramic surface-mount package (wg) ds008822-44 top view order number lm2940wg5.0/883 (5962-8958701xa) see ns package number wg16a (to-263) surface-mount package ds008822-11 top view ds008822-12 side view order number lm2940cs-5.0, lm2940cs-9.0, lm2940cs-12, lm2940cs-15, lm2940s-5.0, lm2940s-8.0, lm2940s-9.0, lm2940s-10 or lm2940s-12 see ns package number ts3b www.national.com 2
absolute maximum ratings (note 1) if military/aerospace specified devices are required, please contact the national semiconductor sales office/ distributors for availability and specifications. lm2940s, t, mp 100 ms 60v lm2940cs, t 1 ms 45v internal power dissipation (note 2) internally limited maximum junction temperature 150c storage temperature range ?65c t j +150c lead temperature, time for wave soldering to-220 (t) package 260c, 10s to-263 (s) package 260c, 4s sot-223 (mp) package 260c, 4s esd susceptibility (note 3) 2 kv operating conditions (note 1) input voltage 26v temperature range lm2940t, lm2940s ?40c t a 125c lm2940ct, lm2940cs 0c t a 125c lm2940imp ?40c t a 85c lm2940j, lm2940wg ?55c t a 125c electrical characteristics v in = v o + 5v, i o = 1a, c o = 22 f, unless otherwise specified. boldface limits apply over the entire operating tempera- ture range of the indicated device. all other specifications apply for t a = t j = 25c. output voltage (v o )5v 8v units lm2940 lm2940/883 lm2940 lm2940/883 parameter conditions typ limit limit typ limit limit (note 4) (note 5) (note 4) (note 5) 6.25v v in 26v 9.4v v in 26v output voltage 5 ma i o 1a 5.00 4.85/ 4.75 4.85/ 4.75 8.00 7.76/ 7.60 7.76/ 7.60 v min 5.15/ 5.25 5.15/ 5.25 8.24/ 8.40 8.24/ 8.40 v max line regulation v o +2v v in 26v, 20 50 40/ 50 20 80 50/ 80 mv max i o = 5ma load regulation 50 ma i o 1a lm2940, lm2940/883 35 50/ 80 50/ 100 55 80/ 130 80/ 130 mv max lm2940c 35 50 55 80 output 100 madc and impedance 20 marms, 35 1000/ 1000 55 1000/ 1000 m w f o = 120 hz quiescent v o +2v v in 26v, current i o = 5ma lm2940, lm2940/883 10 15/ 20 15/ 20 10 15/ 20 15/ 20 ma max lm2940c 10 15 v in = v o + 5v, 30 45/ 60 50/ 60 30 45/ 60 50/ 60 ma max i o = 1a output noise 10 hz ? 100 khz, 150 700/ 700 240 1000/ 1000 v rms voltage i o = 5ma ripple rejection f o = 120 hz, 1 v rms , i o = 100 ma lm2940 72 60/ 54 66 54/ 48 db min lm2940c 72 60 66 54 f o = 1khz,1v rms , 60/ 50 54/ 48 db min i o = 5ma long term 20 32 mv/ stability 1000 hr dropout voltage i o = 1a 0.5 0.8/ 1.0 0.7/ 1.0 0.5 0.8/ 1.0 0.7/ 1.0 v max i o = 100 ma 110 150/ 200 150/ 200 110 150/ 200 150/ 200 mv max short circuit current (note 6) 1.9 1.6 1.5/ 1.3 1.9 1.6 1.6/ 1.3 a min www.national.com 3
electrical characteristics (continued) v in = v o + 5v, i o = 1a, c o = 22 f, unless otherwise specified. boldface limits apply over the entire operating tempera- ture range of the indicated device. all other specifications apply for t a = t j = 25c. output voltage (v o )5v 8v units lm2940 lm2940/883 lm2940 lm2940/883 parameter conditions typ limit limit typ limit limit (note 4) (note 5) (note 4) (note 5) maximum line r o = 100 w v min transient lm2940, t 100 ms 75 60/ 60 75 60/ 60 lm2940/883, t 20 ms 40/ 40 40/ 40 lm2940c, t 1ms5545 5545 reverse polarity r o = 100 w dc input voltage lm2940, lm2940/883 ?30 ?15/ ?15 ?15/ ?15 ?30 ?15/ ?15 ?15/ ?15 v min lm2940c ?30 ?15 ?30 ?15 reverse polarity r o = 100 w transient input lm2940, t 100 ms ?75 ?50/ ?50 ?75 ?50/ ?50 v min voltage lm2940/883, t 20 ms ?45/ ?45 ?45/ ?45 lm2940c, t 1 ms ?55 ?45/ ?45 electrical characteristics v in = v o + 5v, i o = 1a, c o = 22 f, unless otherwise specified. boldface limits apply over the entire operating tempera- ture range of the indicated device. all other specifications apply for t a = t j = 25c. output voltage (v o ) 9v 10v units parameter conditions typ lm2940 typ lm2940 limit limit (note 4) (note 4) 10.5v v in 26v 11.5v v in 26v output voltage 5 ma i o 1a 9.00 8.73/ 8.55 10.00 9.70/ 9.50 v min 9.27/ 9.45 10.30/ 10.50 v max line regulation v o +2v v in 26v, 20 90 20 100 mv max i o = 5ma load regulation 50 ma i o 1a lm2940 60 90/ 150 65 100/ 165 mv max lm2940c 60 90 output impedance 100 madc and 20 marms, 60 65 m w f o = 120 hz quiescent v o +2v v in < 26v, current i o = 5ma lm2940 10 15/ 20 10 15/ 20 ma max lm2940c 10 15 v in = v o + 5v, i o = 1a 30 45/ 60 30 45/ 60 ma max output noise 10 hz ? 100 khz, 270 300 v rms voltage i o = 5ma ripple rejection f o = 120 hz, 1 v rms , i o = 100 ma lm2940 64 52/ 46 63 51/ 45 db min lm2940c 64 52 long term stability 34 36 mv/ 1000 hr dropout voltage i o = 1a 0.5 0.8/ 1.0 0.5 0.8/ 1.0 v max i o = 100 ma 110 150/ 200 110 150/ 200 mv max www.national.com 4
electrical characteristics (continued) v in = v o + 5v, i o = 1a, c o = 22 f, unless otherwise specified. boldface limits apply over the entire operating tempera- ture range of the indicated device. all other specifications apply for t a = t j = 25c. output voltage (v o ) 9v 10v units parameter conditions typ lm2940 typ lm2940 limit limit (note 4) (note 4) short circuit (note 6) 1.9 1.6 1.9 1.6 a min current maximum line r o = 100 w transient t 100 ms lm2940 75 60/ 60 75 60/ 60 v min lm2940c 55 45 reverse polarity r o = 100 w dc input voltage lm2940 ?30 ?15/ ?15 ?30 ?15/ ?15 v min lm2940c ?30 ?15 reverse polarity r o = 100 w transient input t 100 ms voltage lm2940 ?75 ?50/ ?50 ?75 ?50/ ?50 v min lm2940c ?55 ?45/ ?45 electrical characteristics v in = v o + 5v, i o = 1a, c o = 22 f, unless otherwise specified. boldface limits apply over the entire operating tempera- ture range of the indicated device. all other specifications apply for t a = t j = 25c. output voltage (v o ) 12v 15v units lm2940 lm2940/833 lm2940 lm2940/833 parameter conditions typ limit limit typ limit limit (note 4) (note 5) (note 4) (note 5) 13.6v v in 26v 16.75v v in 26v output voltage 5 ma i o 1a 12.00 11.64/ 11.40 11.64/ 11.40 15.00 14.55/ 14.25 14.55/ 14.25 v min 12.36/ 12.60 12.36/ 12.60 15.45/ 15.75 15.45/ 15.75 v max line regulation v o +2v v in 26v, 20 120 75/ 120 20 150 95/ 150 mv max i o = 5ma load regulation 50 ma i o 1a lm2940, lm2940/883 55 120/ 200 120/ 190 150/ 240 mv max lm2940c 55 120 70 150 output 100 madc and impedance 20 marms, 80 1000/ 1000 100 1000/ 1000 m w f o = 120 hz quiescent current v o +2v v in 26v, i o = 5ma lm2940, lm2940/883 10 15/ 20 15/ 20 15/ 20 ma max lm2940c 10 15 10 15 v in = v o + 5v, i o = 1a 30 45/ 60 50/ 60 30 45/ 60 50/ 60 ma max output noise 10 hz ? 100 khz, 360 1000/ 1000 450 1000/ 1000 v rms voltage i o = 5ma ripple rejection f o = 120 hz, 1 v rms , i o = 100 ma lm2940 66 54/ 48 db min lm2940c 66 54 64 52 f o = 1khz,1v rms , 52/ 46 48/ 42 db min i o = 5ma www.national.com 5
electrical characteristics (continued) v in = v o + 5v, i o = 1a, c o = 22 f, unless otherwise specified. boldface limits apply over the entire operating tempera- ture range of the indicated device. all other specifications apply for t a = t j = 25c. output voltage (v o ) 12v 15v units lm2940 lm2940/833 lm2940 lm2940/833 parameter conditions typ limit limit typ limit limit (note 4) (note 5) (note 4) (note 5) long term 48 60 mv/ stability 1000 hr dropout voltage i o = 1a 0.5 0.8/ 1.0 0.7/ 1.0 0.5 0.8/ 1.0 0.7/ 1.0 v max i o = 100 ma 110 150/ 200 150/ 200 110 150/ 200 150/ 200 mv max short circuit (note 6) 1.9 1.6 1.6/ 1.3 1.9 1.6 1.6/ 1.3 a min current maximum line r o = 100 w transient lm2940, t 100 ms 75 60/ 60 lm2940/883, t 20 ms 40/ 40 40/ 40 v min lm2940c, t 1ms5545 5545 reverse polarity r o = 100 w dc input lm2940, lm2940/883 ?30 ?15/ ?15 ?15/ ?15 ?15/ ?15 v min voltage lm2940c ?30 ?15 ?30 ?15 reverse polarity r o = 100 w transient input lm2940, t 100 ms ?75 ?50/ ?50 voltage lm2940/883, t 20 ms ?45/ ?45 ?45/ ?45 v min lm2940c, t 1 ms ?55 ?45/ ?45 ?55 ?45/ ?45 note 1: absolute maximum ratings are limits beyond which damage to the device may occur. operating conditions are conditions under which the device function s but the specifications might not be guaranteed. for guaranteed specifications and test conditions see the electrical characteristics. note 2: the maximum allowable power dissipation is a function of the maximum junction temperature, t j , the junction-to-ambient thermal resistance, q j?a , and the ambient temperature, t a . exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. the value of q j?a (for devices in still air with no heatsink) is 60c/w for the to-220 package, 80c/w for the to-263 package, and 174c/w for the sot-223 package. the effective value of q j?a can be reduced by using a heatsink (see application hints for specific information on heatsinking). the values of q j?a and q j?c for the k02a package are 39c/w and 4c/w respectively. note 3: esd rating is based on the human body model, 100 pf discharged through 1.5 k w . note 4: all limits are guaranteed at t a = t j = 25c only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type). all limits at t a = t j = 25c are 100 % production tested. all limits at temperature extremes are guaranteed via correlation using standard statistical quality control methods. note 5: all limits are guaranteed at t a = t j = 25c only (standard typeface) or over the entire operating temperature range of the indicated device (boldface type). all limits are 100 % production tested and are used to calculate outgoing quality levels. note 6: output current will decrease with increasing temperature but will not drop below 1a at the maximum specified temperature. typical performance characteristics dropout voltage ds008822-13 dropout voltage vs temperature ds008822-14 output voltage vs temperature ds008822-15 www.national.com 6
typical performance characteristics (continued) quiescent current vs temperature ds008822-16 quiescent current ds008822-17 quiescent current ds008822-18 line transient response ds008822-19 load transient response ds008822-20 ripple rejection ds008822-21 low voltage behavior ds008822-25 low voltage behavior ds008822-26 low voltage behavior ds008822-27 low voltage behavior ds008822-28 low voltage behavior ds008822-29 low voltage behavior ds008822-30 www.national.com 7
typical performance characteristics (continued) output at voltage extremes ds008822-31 output at voltage extremes ds008822-32 output at voltage extremes ds008822-33 output at voltage extremes ds008822-34 output at voltage extremes ds008822-35 output at voltage extremes ds008822-36 output capacitor esr ds008822-6 peak output current ds008822-8 www.national.com 8
typical performance characteristics (continued) output impedance ds008822-22 maximum power dissipation (to-220) ds008822-23 maximum power dissipation (to-3) ds008822-24 maximum power dissipation (to-263) see (note 2) ds008822-10 www.national.com 9
equivalent schematic diagram application hints external capacitors the output capacitor is critical to maintaining regulator stabil- ity, and must meet the required conditions for both esr (equivalent series resistance) and minimum amount of ca- pacitance. minimum capacitance: the minimum output capacitance required to maintain stabil- ity is 22 f (this value may be increased without limit). larger values of output capacitance will give improved tran- sient 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 essen- tial that the output capacitor meet these requirements, or oscillations can result. it is important to note that for most capacitors, esr is speci- fied 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 tem- perature operation. solid tantalum capacitors have a more stable esr over tem- perature, but are more expensive than aluminum electrolyt- ics. a cost-effective approach sometimes used is to parallel ds008822-1 output capacitor esr ds008822-6 figure 1. esr limits www.national.com 10
application hints (continued) 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 par- allel of the two individual values. the aflattero esr of the tan- talum 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 junc- tion temperature must be within the range specified under absolute maximum ratings. to determine if a heatsink is required, the power dissipated by the regulator, p d , must be calculated. 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: the next parameter which must be calculated is the maxi- mum allowable temperature rise, t r (max). this is calcu- lated by using the formula: t r (max) = t j (max) ? t a (max) where: t j (max) is the maximum allowable junction tem- perature, which is 125c for commercial grade parts. t a (max) is the maximum ambient temperature which will be encountered in the applica- tion. using the calculated values for t r (max) and p d , the maxi- mum allowable value for the junction-to-ambient thermal re- sistance, q (j?a) , can now be found: q (j?a) = t r (max)/p d important: if the maximum allowable value for q (j?a) is found to be 3 53c/w for the to-220 package, 3 80c/w for the to-263 package, or 3 174c/w for the sot-223 pack- age, no heatsink is needed since the package alone will dis- sipate enough heat to satisfy these requirements. if the calculated value for q (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 se- cured to a copper plane on a pc board. if a copper plane is to be used, the values of q (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, q (h?a) , must first be calculated: q (h?a) = q (j?a) ? q (c?h) ? q (j?c) where: q (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 q (j?c) for this calculation. q (c?h) is defined as the thermal resistance be- tween the case and the surface of the heat- sink. the value of q (c?h) will vary from about 1.5c/w to about 2.5c/w (depend- ing on method of attachment, insulator, etc.). if the exact value is unknown, 2c/w should be assumed for q (c?h) . when a value for q (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. q (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 (aso) and sot-223 (ampo) 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 q (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. 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 q (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 q (j?a) is 35c/w and the maxi- mum junction temperature is 125c). ds008822-37 i in = i l i g p d = (v in ?v out )i l +(v in )i g figure 2. power dissipation diagram ds008822-38 figure 3. q (j?a) vs copper (1 ounce) area for the to-263 package www.national.com 11
application hints (continued) figure 5 and figure 6 show the information for the sot-223 package. figure 6 assumes a q (j?a) of 74c/w for 1 ounce copper and 51c/w for 2 ounce copper and a maximum junction temperature of 125c. ds008822-39 figure 4. maximum power dissipation vs t amb for the to-263 package ds008822-40 figure 5. q (j?a) vs copper (2 ounce) area for the sot-223 package ds008822-41 figure 6. maximum power dissipation vs t amb for the sot-223 package www.national.com 12
physical dimensions inches (millimeters) unless otherwise noted 3-lead sot-223 package order part number lm2940imp-5.0 lm2940imp-8.0 lm2940imp-9.0 lm2940imp-10 lm2940imp-12 lm2940imp-15 ns package number ma04a www.national.com 13
physical dimensions inches (millimeters) unless otherwise noted (continued) 16 lead dual-in-line package (j) order number lm2940j-5.0/883 (5962-8958701ea), lm2940j-8.0/883 (5962-9088301qea), lm2940j-12/883 (5962-9088401qea), lm2940j-15/883 (5962-9088501qea) see ns package number j16a www.national.com 14
physical dimensions inches (millimeters) unless otherwise noted (continued) 16 lead surface mount package (wg) order number lm2940wg5.0/883 (5962-8958701xa) see ns package number wg16a www.national.com 15
physical dimensions inches (millimeters) unless otherwise noted (continued) 3-lead to-220 plastic package (t) order number lm2940t-5.0, lm2940t-8.0, lm2940t-9.0, lm2940t-10, lm2940t-12, lm2940ct-5.0, lm2940ct-12 or lm2940ct-15 ns package number to3b www.national.com 16
physical dimensions inches (millimeters) unless otherwise noted (continued) 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. as used herein: 1. life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. a critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. national semiconductor corporation americas tel: 1-800-272-9959 fax: 1-800-737-7018 email: support@nsc.com national semiconductor europe fax: +49 (0) 1 80-530 85 86 email: europe.support@nsc.com deutsch tel: +49 (0) 1 80-530 85 85 english tel: +49 (0) 1 80-532 78 32 fran?ais tel: +49 (0) 1 80-532 93 58 italiano tel: +49 (0) 1 80-534 16 80 national semiconductor asia pacific customer response group tel: 65-2544466 fax: 65-2504466 email: sea.support@nsc.com national semiconductor japan ltd. tel: 81-3-5639-7560 fax: 81-3-5639-7507 www.national.com 3-lead to-263 surface mount package (mp) order number lm2940s-5.0, lm2940s-8.0, lm2940s-9.0, lm2940s-10, lm2940s-12, lm2940cs-5.0, lm2940cs-12 or lm2940cs-15 ns package number ts3b lm2940/lm2940c 1a low dropout regulator national does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and national reserves the righ t at any time without notice to change said circuitry and specifications.

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