National Semiconductor LM1084 5A Low Dropout Positive Regulators handbook
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1. National Semiconductor LM1084 5A Low Dropout Positive Regulators General Description The LM1084 is a series of low dropout voltage positive regulators with a maximum dropout of 1 5V at 5A of load current It has the same pin out as National Semiconductor s industry standard LM317 The LM1084 is available in an adjustable version which can set the output voltage with only two external resistors It is also available in three fixed voltages 3 3V 5 0V and 12 0V The fixed versions intergrate the adjust resistors The LM1084 circuit includes a zener trimmed bandgap ref erence current limiting and thermal shutdown The LM1084 series is available in TO 220 and TO 263 pack ages Refer to the LM1085 for the 3A version and the LM1086 for the 1 5A version Connection Diagrams 10094636 Top View TO 263 INPUT OUTPUT ADJ GND fF 10094635 Top View Basic Functional Diagram Adjustable Version Input Output 1 24 Band gap Substrate Adjust 10094665 2002 National Semiconductor Corporation DS100946 August 2002 Features m Available in 3 3V 5 0V 12V and Adjustable Versions m Current Limiting and Thermal Protection m Output Current 5A m Industrial Temperature Range 40 C to 125 C m Line Regulation 0 015 typical Load Regulation 0 1 typical Applications m Post Regulator for Switching DC DC Conveter m High Efficiency Linear Regulators m Battery Charger Application Circu2. 0 25 50 75 100 125 TEMPERATURE 10094638 LM1084 ADJ Ripple Rejection vs Current RIPPLE REJECTION dB 100 90 80 70 60 50 40 fp 120 Hz 0 0 25 0 5 0 75 1 0 1 25 1 5 OUTPUT CURRENT 10094690 Short Circuit Current fe a e am 5 e me o 1 ET 2 0 5 10 15 20 25 30 INPUT OUTPUT DIFFERENTIAL V 10094671 LM1084 ADJ Ripple Rejection 100 30 3 0 5Vp p dB ta 2 70 p o 60 o 50 Vin 7 Your 3V 40 Vin Vout Ypropout H amp 3o ac 20 Capy 200 uF at Frequencies lt 60Hz 10 22 WF at Frequencies gt 60Hz lyr 1 5A o 977 10 100 1k 10k 100k FREQUENCY Hz 10094643 Temperature Stability 2 15 gt o 1 S 05 e g 0 E 0 5 a i 5 15 2 50 25 0 25 50 75 100 125 150 Temperature 9C 10094625 www national com t80 LINT LM1084 Adjust Pin Current OUTPUT VOLTAGE DEVIATION V INPUT DEVIATION V www national com 100 Adjust Pin Current 50 25 0 60 40 20 40 mo A Temperature 9C 25 50 75 100 125 150 10094626 LM1084 ADJ LineTransient Response Your 10 l 0 2 Cy 1 TANTALUM 10 uF TANTALUM 100 TIME ys 200 10094670 Typical Perfo
3. the internal diode between the output and input pins can withstand microsecond surge currents of 10A to 20A With an extremely large output capacitor 21000 uf and with input instantaneously shorted to ground the regulator could be damaged In this case an external diode is recom mended between the output and input pins to protect the regulator shown in Figure 5 1N4002 Optional 10094615 FIGURE 5 Regulator with Protection Diode Overload Recovery Overload recovery refers to regulator s ability to recover from a short circuited output A key factor in the recovery process is the current limiting used to protect the output from drawing too much power The current limiting circuit reduces the output current as the input to output differential increases Refer to short circuit curve in the curve section During normal start up the input to output differential is small since the output follows the input But if the output is shorted then the recovery involves a large input to output differential Sometimes during this condition the current lim iting circuit is slow in recovering If the limited current is too low to develop a voltage at the output the voltage will stabilize at a lower level Under these conditions it may be necessary to recycle the power of the regulator in order to get the smaller differential voltage and thus adequate start up conditions Refer to curve section for the short circuit current vs input diffe
4. to case thermal resistances for each of these sections while the maximum junction temperatures T for each section is listed in the Absolute Maximum section of the datasheet Tmax is 125 C for the control section while Tma iS 150 C for the output section max Should be calculated separately for each section as follows 8 4 max CONTROL SECTION 125 C Tamaw Po 04 max OUTPUT SECTION 150 C Tamaw Po The required heat sink is determined by calculating its re quired thermal resistance max max JA max 7 Och max Should also be calculated twice as follows 8 14 max Osa max CONTROL SECTION CON TROL SECTION 05 8 14 9 4 max OUTPUT SECTION OUTPUT SECTION If thermal compound is used can be estimated at 0 2 C W If the case is soldered to the heat sink then a can be estimated as 0 C W After max is calculated for each section choose the lower of the two max values to determine the appropri ate heat sink If PC board copper is going to be used as a heat sink then Figure 7 can be used to determine the appropriate area size of copper foil required PCB Heat Sink Thermal Resistance 9C W 0 2000 4000 6000 PCB Heat Sink Area mm 10094664 FIGURE 7 Heat sink thermal Resistance vs Area www national com t80 LINT LM1084 Typical Applicati
5. 6 60 7 11 14 61 0 085 0 390 0 410 1 y 2 16 9 91 10 41 0 028 0 038 0 425 E 0 71 0 97 10 80 E zl 0 330 0 350 1 ID 0 100 8 38 8 89 0 030 E ae R MAX TYP 050 MAX 0 76 TP 1 27 ZI pe 0 015 0 030 ETN Mr mere 0 38 0 76 Gata 0 035 10 41 042 0 175 0 183 0 89 1 07 4 45 4 65 A A LEAD POSITION OVERLAY E 004 0 10 oe ENJ TAPERED WES 0 048 0 052 SIDES 0 6 1 22 1 32 09 69 i 0 000 0 008 5 0 00 0 15 0 490 12 45 0 565 way 14 35 BACK VIEW TS38 REV C 3 Lead TO 263 NS Package Number TS3B www national com 12 Physical Dimensions inches millimeters unless otherwise noted Continued 0 240 0 260 0 330 0 350 6 10 6 60 8 38 8 89 0 100 0 120 g 0 149 0 153 2 54 3 05 3 78 3 89 us 228 279 0 400 5 005 29 2 0 190 0 210 10 16 1035 4 83 5 33 0 048 0 055 0 130 0 160 1 22 1 40 PIN 4 IB 3 30 4 06 TYP 1 005 1 035 0 027 0 037 25 53 26 29 0 69 0 94 TYP 79 rS en 0 525 0 555 0 015 0 38 7278 13 34 14 10 0 175 0 185 4 45 4 70 09 69 0 010 0 25 0 048 0 052 0 105 00 5 2 67 ys 1 22 1 32 SEATING PLANE TAPERED SIDES 1 TO3B REV L 3 Lead TO 220 NS Package Number LIFE SUPPORT POLICY NATIONAL S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES O
6. 65 2 7 C W Note 1 Absolute Maximum Ratings indicate limits beyond which damage to the device may occur Operating Ratings indicate conditions for which the device is intended to be functional but specific performance is not guaranteed For guaranteed specifications and the test conditions see the Electrical Characteristics Note 3 The maximum power dissipation is a function of Tymax and Ta The maximum allowable power dissipation at any ambient temperature is Ty maxj T AJ 0jA All numbers apply for packages soldered directly into a PC board Refer to Thermal Considerations in the Application Notes Note 7 IFULLLoap is defined in the current limit curves The IFuLLLoap Curve defines the current limit as a function of input to output voltage Note that 30W power dissipation for the LM1084 is only achievable over a limited range of input to output voltage Note 8 Load and line regulation are measured at constant junction temperature and are guaranteed up to the maximum power dissipation of 30W Power dissipation is determined by the input output differential and the output current Guaranteed maximum power dissipation will not be available over the full input output range Dropout Voltage V OUTPUT VOLTAGE DEVIATION Performance Characteristics Dropout Voltage Vin Vour 2 0 1 8 1 6 1 4 Output Current A 10094663 Load Regulation 0 20 40 25
7. R 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 2 critical component is any component of a life systems which a are intended for surgical implant support device or system whose failure to perform into the body or b support or sustain life and can be reasonably expected to cause the failure of whose failure to perform when properly used in the life support device or system or to affect its accordance with instructions for use provided in the safety or effectiveness labeling can be reasonably expected to result in a significant injury to the user National Semiconductor National Semiconductor National Semiconductor National Semiconductor Corporation Europe Asia Pacific Customer Japan Ltd Americas Fax 49 0 180 530 85 86 Response Group Tel 81 3 5639 7560 Email support nsc com Email europe support nsc com Tel 65 2544466 Fax 81 3 5639 7507 Deutsch Tel 49 0 69 9508 6208 Fax 65 2504466 English Tel 44 0 870 24 0 2171 Email ap support nsc com www national com Fran ais Tel 33 0 1 41 91 8790 National does not assume any responsibility for use of any circuitry described no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications sJoje nBag eAnisod 1nodouq VS p90LIWT
8. djustment terminal introduces an output error But since it is small 120uA max it becomes negligible when R1 is in the 100Q range For fixed voltage devices R1 and R2 are integrated inside the devices LM1084 ADJ ViN ViN Vour Vour ADJ 10 uF 10 uF lADJ Tantalum R2 Vout Veer 1 Rp laps R2 10094617 FIGURE 2 Basic Adjustable Regulator Stability Consideration Stability consideration primarily concern the phase response of the feedback loop In order for stable operation the loop must maintain negative feedback The LM1084 requires a certain amount series resistance with capacitive loads This series resistance introduces a zero within the loop to in crease phase margin and thus increase stability The equiva lent series resistance ESR of solid tantalum or aluminum electrolytic capacitors is used to provide the appropriate zero approximately 500 kHz The Aluminum electrolytic are less expensive than tantal ums but their ESR varies exponentially at cold tempera tures therefore requiring close examination when choosing the desired transient response over temperature Tantalums are a convenient choice because their ESR varies less than 2 1 over temperature The recommended load decoupling capacitance is a 10uF tantalum or a 50uF aluminum These values will assure stability for the majority of applications The adjustable versions allows an additional capacitor to be used at the ADJ pin to increase
9. for operation www national com Note 4 For testing purposes ESD was applied using human body model 1 5kQ in series with 100pF Note 5 Typical Values represent the most likely parametric norm Note 6 All limits are guaranteed by testing or statistical analysis Note 9 Dropout voltage is specified over the full output current range of the device Note 10 The minimum output current required to maintain regulation Note 2 Power dissipation is kept in a safe range by current limiting circuitry Refer to Overload Recovery in Application Notes Symbol Conditions ss Note 6 Units Current Limit LM1084 ADJ Vin Vout 5V A Vin Vout 25V A LM1084 3 3 Vin 8V A LM1084 5 0 Vin 10V A LM1084 12 Vin 17V A Minimum Load LM1084 ADJ Current Note 10 Vin Vout 25V mA Quiescent Current LM1084 3 3 Vin 18V LM1084 5 0 Vin 20V mA LM1084 12 Vin lt 25V mA Thermal Regulation T4 25 C 30ms Pulse N Ripple Rejection fRiepLe 120Hz Court 25pF Tantalum lour 5A LM1084 ADJ Capu 25pF Viy Vo 3V 60 75 dB LM1084 3 3 Vin 6 3V 60 72 dB LM1084 5 0 Vin 8V 60 68 dB LM1084 12 Vin 15V 54 60 dB Adjust Pin Current LM1084 55 120 pA Adjust Pin Current 10 lt lour lFuLL Loan 0 2 EN UA Change 1 5V lt Viy Vou1 lt 25V Temperature Long Term Stability of Vour Thermal Resistance 3 Lead TO 263 Control Section Output Section 0
10. g in Boldface type apply over the entire junc tion temperature range for operation ies Min Typ Max VREF Reference Voltage LM1084 ADJ lour 10mA Vin Vour V 10mA lt lour lt leui Loan 1 5V lt Vin Vout 25V V Note 7 Vour Output Voltage LM1084 3 3 Note 7 lout OMA 8V V 0 lout SlFuLL Loan 4 8V Vin lt 15 V LM1084 5 0 lout OMA Vin 8V V 0 lt lout IFuLL Loan 6 5V lt Vin lt 20V V LM1084 12 lour OMA 15V V 0 lout leui Loan 13 5V lt Vin 25V V AVour Line Regulation LM1084 ADJ 0 015 0 2 8 lour 10 1 5V lt Vin Vourt 15V a 0 035 0 2 LM1084 3 3 0 5 6 mV lout OMA 4 8V lt Vin lt 15V E 1 0 6 mV LM1084 5 0 0 5 10 mV lout OMA 6 5V lt Vin lt 20V 1 0 10 LM1084 12 1 0 25 mV our 0 13 5V lt Vin lt 25V NE 2 0 25 mV AVour Load Regulation LM1084 ADJ 0 1 0 3 Note 8 Vin V out 10mA lt lour lFuLL Loap 0 2 0 4 LM1084 3 3 3 15 mV LM1084 5 0 5 20 mV Vin 8V 0 lt lout lFuLL Loap EN 10 35 mV LM1084 12 12 36 mV Vin 15V 0 lout lFuLL Loap 24 72 mV Dropout Voltage LM1084 3 3 5 12 ADJ Note 9 AVrer 1 lout EN V www national com t80 LINT LM1084 Electrical Characteristics continued Typicals and limits appearing in normal type apply for T 25 Limits appearing in Boldface type apply over the entire junc tion temperature range
11. he adjust terminal can be bypassed to ground with a capacitor Capu The imped ance of the C p should be equal to or less than R1 at the desired ripple frequency This bypass capacitor prevents ripple from being amplified as the output voltage is in creased 1 2 lt Load Regulation The LM1084 regulates the voltage that appears between its output and ground pins or between its output and adjust pins In some cases line resistances can introduce errors to the voltage across the load To obtain the best load regula tion a few precautions are needed Figure 3 shows a typical application using a fixed output regulator Rt1 and Rt2 are the line resistances V is less www national com t80 LINT LM1084 APPLICATION NOTE continued than the by the sum of the voltage drops along the line resistances In this case the load regulation seen at the Would be degraded from the data sheet specification To improve this the load should be tied directly to the output terminal on the positive side and directly tied to the ground terminal on the negative side Vour RLoAD Vioap Your I Rt1 Rt2 10094618 FIGURE 3 Typical Application using Fixed Output Regulator When the adjustable regulator is used Figure 4 the best performance is obtained with the positive side of the resistor R1 tied directly to the output terminal of the regulator rather than nea
12. it Vour 10uF Tantalum NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS R2 ty 125 1 27 10094652 1 2V to 15V Adjustable Regulator www national com sioyeinbay P8OLINT LM1084 Ordering Information Package Temperature Range Part Number Transport Media NSC Drawing 3 lead TO 263 40 C to 125 C LM1084IS ADJ Rails LM10841SX ADJ Tape and Reel LM10841S 12 Rails TS3B LM10841SX 12 Tape and Reel LM1084IS 3 3 Rails 3 lead TO 220 40 C to 125 C T03B Simplified Schematic Thermal Limit O GND Fixed Output O ADJ Adjustable Output www national com 2 10094634 Absolute Maximum Ratings Note 1 Storage Temperature Range 65 C to 150 If Military Aerospace specified devices are required Lead Temperature 260 C to 10 sec please contact the National Semiconductor Sales Office ESD Tolerance Note 4 2000V Distributors for availability and specifications Maximum Input to Output Voltage Differential Operating Ratings Note 1 LM1084 ADJ 29V LM1084 12 18V Junction Temperature Range T Note 3 LM1084 3 3 27V Control Section 40 C to 125 C LM1084 5 0 25 Output Section 40 C to 150 C Power Dissipation Note 2 Internally Limited Junction Temperature T Note 3 150 C Electrical Characteristics Typicals and limits appearing in normal type apply for T 25 C Limits appearin
13. ons Viy 4 75V 3 3V at 5A 10 TANTALUM 10 uF TANTALUM MAY BE OMITTED IF INPUT SUPPLY IS WELL BYPASSED WITHIN 2 OF THE LM1085 10094667 5V to 3 3V 5A Regulator Vin 2 6 5 5V at 5A 10 uF TANTALUM REQUIRED FOR STABILITY 10094650 Adjustable 5V ViN Vout 10 uF Tantalum NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS R2 t E Vour 1 25V 1 aa 10094652 1 2V to 15V Adjustable Regulator 5V 100 uF 10094653 5V Regulator with Shutdown www national com 10 dv R2 Rg 1 77 10094654 Battery Charger SV to 10V OPTIONAL IMPROVES RIPPLE REJECTION 10094655 Adjustable Fixed Regulator gt 11 5 10 H T 10094656 Regulator with Reference TTL or CMOS 10094657 High Current Lamp Driver Protection Typical Applications continued 5 2V LINE Vin 5V BATTERY SELECT FOR CHARGE RATE qu uF 10094659 Battery Backup Regulated Supply FLOATING INPUT C1 IMPROVES RIPPLE REJECTION _ Xc SHOULD R1 AT RIPPLE FREQUENCY 10094660 Ripple Rejection Enhancement R p MAX DROP 300 mV Vout 5V RETURN RETURN 10094658 Remote Sensing 11 100 uF 10094661 Generating Negative Supply voltage www national com t80 LINT LM1084 Physical Dimensions inches millimeters unless otherwise noted 10 TYP 0 090 0 110 2 29 2 79 P 0 260 0 280 0 575
14. r the load This eliminates line drops from appearing effectively in series with the reference and degrading regu lation For example a 5V regulator with 0 05Q resistance between the regulator and load will have a load regulation due to line resistance of 0 050 x If R1 125Q is con nected near the load the effective line resistance will be 0 05Q 1 R2 R1 or in this case it is 4 times worse In addition the ground side of the resistor R2 can be returned near the ground of the load to provide remote ground sens ing and improve load regulation Vout Rt2 Vioap Vger R1 R2 R1 Rt 10094619 FIGURE 4 Best Load Regulation using Adjustable Output Regulator 3 0 Protection Diodes Under normal operation the LM1084 regulator does not need any protection diode With the adjustable device the internal resistance between the adjustment and output ter minals limits the current No diode is needed to divert the current around the regulator even with a capacitor on the adjustment terminal The adjust pin can take a transient signal of 25V with respect to the output voltage without damaging the device www national com When an output capacitor is connected to a regulator and the input is shorted the output capacitor will discharge into the output of the regulator The discharge current depends on the value of the capacitor the output voltage of the regulator and rate of decrease of Vn In the LM1084 regu lator
15. rential voltage Thermal Considerations ICs heats up when in operation and power consumption is one factor in how hot it gets The other factor is how well the heat is dissipated Heat dissipation is predictable by knowing the thermal resistance between the IC and ambient Thermal resistance has units of temperature per power C W The higher the thermal resistance the hotter the IC The LM1084 specifies the thermal resistance for each pack age as junction to case 0 In order to get the total resistance to ambient 0 4 two other thermal resistance must be added one for case to heat sink and one for heatsink to ambient 0 4 The junction temperature can be predicted as follows Ty Ta Pp Ona TA Pp APPLICATION NOTE continued Ty is junction temperature T4 is ambient temperature and Pp is the power consumption of the device Device power consumption is calculated as follows 10094616 li lL le Pp Vin Vour IL Vinla Figure 6 shows the voltages and currents which are present in the circuit FIGURE 6 Power Dissipation Diagram Once the devices power is determined the maximum allow able 0 4 max is calculated as Oja max Trmaxy Pp Tyma z Taimax Pp The LM1084 has different temperature specifications for two different sections of the IC the control section and the output section The Electrical Characteristics table shows the junc tion
16. ripple rejection If this is done the output capacitor should be increased to 22uF for tantal ums or to 150uF for aluminum Capacitors other than tantalum or aluminum can be used at the adjust pin and the input pin A 10uF capacitor is a reasonable value at the input See Ripple Rejection section regarding the value for the adjust pin capacitor It is desirable to have large output capacitance for applica tions that entail large changes in load current microproces sors for example The higher the capacitance the larger the available charge per demand It is also desirable to provide low ESR to reduce the change in output voltage AV Al x ESR It is common practice to use several tantalum and ceramic capacitors in parallel to reduce this change in the output voltage by reducing the overall ESR Output capacitance can be increased indefinitely to improve transient response and stability Ripple Rejection Ripple rejection is a function of the open loop gain within the feed back loop refer to Figure 1 and Figure 2 The LM1084 exhibits 75dB of ripple rejection typ When adjusted for voltages higher than Vgge the ripple rejection decreases as function of adjustment gain 1 R1 R2 or Vo Vgge There fore a 5V adjustment decreases ripple rejection by a factor of four 12dB Output ripple increases as adjustment voltage increases However the adjustable version allows this degradation of ripple rejection to be compensated T
17. rmance Characteristics continued LM1084 ADJ Load Transient Response OUTPUT VOLTAGE DEVIATION V LOAD CURRENT A POWER W 0 6 0 4 TIME ys 10094669 Maximum Power Dissipation 50 60 70 80 90 100110120130140 150 CASE TEMPERATURE 10094668 APPLICATION NOTE General Figure 1 shows a basic functional diagram for the LM1084 Adj excluding protection circuitry The topology is basically that of the LM317 except for the pass transistor Instead of a Darlingtion NPN with its two diode voltage drop the LM1084 uses a single NPN This results in a lower dropout voltage The structure of the pass transistor is also known as a quasi LDO The advantage a quasi LDO over a PNP LDO is its inherently lower quiescent current The LM1084 is guaranteed to provide a minimum dropout volt age 1 5V over temperature at full load Input 1 24 Band gap Substrate Adjust 10094665 FIGURE 1 Basic Functional Diagram for the LM1084 excluding Protection circuitry Output Voltage The LM1084 adjustable version develops at 1 25V reference voltage Vag between the output and the adjust terminal As shown in figure 2 this voltage is applied across resistor R1 to generate a constant current 11 This constant current then flows through R2 The resulting voltage drop across R2 adds to the reference voltage to sets the desired output voltage The current lapu from the a
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National Semiconductor LM1084 5A Low Dropout Positive Regulators handbook