LT1083/LT1084/LT A, 5A, 3A Low Dropout Positive Adjustable Regulators DESCRIPTION FEATURES APPLICATIONS TYPICAL APPLICATION

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1 LT8/LT8/LT85 7.5A, 5A, A Low Dropout Positive Adjustable Regulators FEATURES n -Terminal Adjustable n Output Current of A, 5A or 7.5A n Operates Down to V Dropout n Guaranteed Dropout Voltage at Multiple Current Levels n Line Regulation:.5% n Load Regulation:.% n % Thermal Limit Functional Test n Fixed Versions Available n Available in -Lead Plastic TO-, TO-P and DD Packages APPLICATIONS n High Effi ciency Linear Regulators n Post Regulators for Switching Supplies n Constant Current Regulators n Battery Chargers DEVICE PUT CURRENT* LT8 7.5A LT8 5.A LT85.A *For a.5a low dropout regulator see the LT8 data sheet. DESCRIPTION The LT 8 series of positive adjustable regulators are designed to provide 7.5A, 5A and A with higher efficiency than currently available devices. All internal circuitry is designed to operate down to V input-to-output differential and the dropout voltage is fully specified as a function of load current. Dropout is guaranteed at a maximum of.5v at maximum output current, decreasing at lower load currents. On-chip trimming adjusts the reference voltage to %. Current limit is also trimmed, minimizing the stress on both the regulator and power source circuitry under overload conditions. The LT8/LT8/LT85 devices are pin compatible with older -terminal regulators. A μf output capacitor is required on these new devices. However, this is included in most regulator designs. Unlike PNP regulators, where up to % of the output current is wasted as quiescent current, the LT8 quiescent current flows into the load, increasing efficiency., LT, LTM and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Dropout Voltage vs Output Current.5V μf *REQUIRED FOR STABILITY 5V, 7.5A Regulator LT8 Ω % 5Ω % 5V AT 7.5A μf* TANTALUM 8//5 TA PUT/PUT VOLTAGE DIFFERENTIAL (V) PUT CURRENT I FULL LOAD 8//5 TA 85fg

2 LT8/LT8/LT85 ABSOLUTE MAXIMUM RATGS Power Dissipation...Internally Limited Input-to-Output Voltage Differential C-Grades...V I-Grades...V M-Grades (OBSOLETE)...5V Operating Junction Temperature Range (Note 9) C-Grades: Control Section... C to 5 C Power Transistor... C to 5 C I-Grades: Control Section... C to 5 C Power Transistor... C to 5 C P CONFIGURATION (Note ) M-Grades: (OBSOLETE) Control Section C to 5 C Power Transistor C to C Storage Temperature Range... 5 C to 5 C Lead Temperature (Soldering, sec)... C PRECONDITIONG % thermal shutdown functional test. FRONT VIEW TAB IS PUT FRONT VIEW TAB IS PUT V V T PACKAGE -LEAD PLASTIC TO- θ JA = 5 C/W P PACKAGE -LEAD PLASTIC TO-P θ JA = 5 C/W BOTTOM VIEW CASE IS PUT TAB IS PUT FRONT VIEW V K PACKAGE -LEAD TO- METAL CAN θ JA = 5 C/W OBSOLETE PACKAGE M PACKAGE -LEAD PLASTIC DD θ JA = C/W* *WITH PACKAGE SOLDERED TO.5 COPPER AREA OVER BACKSIDE GROUND PLANE OR TERNAL POWER PLANE. θ JA CAN VARY FROM C/W TO > C/W DEPENDG ON MOUNTG TECHNIQUE 85fg

3 LT8/LT8/LT85 ORDER FORMATION LEAD FREE FISH TAPE AND REEL PART MARKG* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8CP#PBF LT8CP#TRPBF LT8CP -Lead Plastic TO-P Control: C to 5 C Power: C to 5 C LT8CP#PBF LT8CP#TRPBF LT8CP -Lead Plastic TO-P Control: C to 5 C Power: C to 5 C LT8CT#PBF LT8CT#TRPBF LT8CT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT8IT#PBF LT8IT#TRPBF LT8IT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT85CT#PBF LT85CT#TRPBF LT85CT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT85IT#PBF LT85IT#TRPBF LT85IT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT85CM#PBF LT85CM#TRPBF LT85CM -Lead Plastic DD Control: C to 5 C Power: C to 5 C LT85IM#PBF LT85IM#TRPBF LT85IM -Lead Plastic DD Control: C to 5 C Power: C to 5 C LEAD BASED FISH TAPE AND REEL PART MARKG* PACKAGE DESCRIPTION TEMPERATURE RANGE LT8CP LT8CP#TR LT8CP -Lead Plastic TO-P Control: C to 5 C Power: C to 5 C LT8CP LT8CP#TR LT8CP -Lead Plastic TO-P Control: C to 5 C Power: C to 5 C LT8CT LT8CT#TR LT8CT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT8IT LT8IT#TR LT8IT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT85CT LT85CT#TR LT85CT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT85IT LT85IT#TR LT85IT -Lead Plastic TO- Control: C to 5 C Power: C to 5 C LT85CM LT85CM#TR LT85CM -Lead Plastic DD Control: C to 5 C Power: C to 5 C LT85IM LT85IM#TR LT85IM -Lead Plastic DD Control: C to 5 C Power: C to 5 C LT8CK LT8CK#TR LT8CK -Lead TO- Metal Can Control: C to 5 C Power: C to 5 C LT8MK LT8MK#TR LT8MK -Lead TO- Metal Can Control: 55 C to 5 C Power: 55 C to C LT8CK LT8CK#TR LT8CK -Lead TO- Metal Can Control: C to 5 C Power: C to 5 C LT8MK LT8MK#TR LT8MK -Lead TO- Metal Can Control: 55 C to 5 C Power: 55 C to C LT85CK LT85CK#TR LT85CK -Lead TO- Metal Can Control: C to 5 C Power: C to 5 C LT85MK LT85MK#TR LT85MK -Lead TO- Metal Can Control: 55 C to 5 C Power: 55 C to C OBSOLETE PACKAGE Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: For more information on tape and reel specifi cations, go to: 85fg

4 LT8/LT8/LT85 ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at T A = 5 C. PARAMETER CONDITIONS M TYP MAX UNITS Reference Voltage I = ma, T J = 5 C, ( V ) = V ma I I FULL_LOAD.8.5. V.5V ( V ) 5V (Notes,, 7) l V Line Regulation I LOAD = ma,.5v ( V ) 5V, T J = 5 C (Notes, ).5. % l.5. % M-Grade: 5V ( V ) 5V (Notes, ) l.5.5 % C-, I-Grades: 5V ( V ) V (Notes, ) l.5.5 % Load Regulation ( V ) = V, ma I I FULL_LOAD, T J = 5 C.. % (Notes,,, ) l.. % Dropout Voltage ΔV REF = %, I = I FULL_LOAD (Notes 5,, 8) l..5 V Current Limit LT8 LT8 LT85 ( V ) = 5V ( V ) = 5V ( V ) = 5V ( V ) = 5V ( V ) = 5V ( V ) = 5V Minimum Load Current ( V ) = 5V l 5 ma Thermal Regulation LT8 LT8 LT85 Ripple Rejection T A = 5 C, ms Pulse f = Hz, C = 5μF, C = 5μF Tantalum I = I FULL_LOAD, ( V ) = V (Notes, 7, 8) l l l l l l A A A A A A %/W %/W %/W l 75 db Adjust Pin Current T J = 5 C 55 μa l μa Adjust Pin Current Change ma I I FULL_LOAD,.5V ( V ) 5V (Note ) l. 5 μa Temperature Stability l.5 % Long-Term Stability T A = 5 C, Hrs. % RMS Output Noise (% of V ) T A = 5 C, Hz = f khz. % 85fg

5 LT8/LT8/LT85 ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at T A = 5 C. PARAMETER CONDITIONS M TYP MAX UNITS Thermal Resistance Junction-to-Case LT8 LT8 LT85 Control Circuitry/Power Transistor K Package P Package K Package P Package T Package K Package M, T Package./..5/..75/..5/..5/.7.9/..7/. C/W C/W C/W C/W C/W C/W C/W Note : Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note : See thermal regulation specifi cations for changes in output voltage due to heating effects. Load and line regulation are measured at a constant junction temperature by low duty cycle pulse testing. Note : Line and load regulation are guaranteed up to the maximum power dissipation (W for the LT8, 5W for the LT8 (K, P), W for the LT8 (T) and W for the LT85). 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 voltage range. Note : I FULL_LOAD is defined in the current limit curves. The I FULL_LOAD curve is defi ned as the minimum value of current limit as a function of input-to-output voltage. Note that the W power dissipation for the LT8 (5W for the LT8 (K, P), W for the LT8 (T), W for the LT85) is only achievable over a limited range of input-to-output voltage. Note 5: Dropout voltage is specifi ed over the full output current range of the device. Test points and limits are shown on the Dropout Voltage curve. Note : For LT8 I FULL_LOAD is 5A for 55 C T J < C and 7.5A for T J C. Note 7:.7V ( V ) 5V for LT8 at 55 C T J C. Note 8: Dropout is.7v maximum for LT8 at 55 C T J C. Note 9: The LT8/LT8/LT85 regulators are tested and specified under pulse load conditions such that T J T A. The C-grade LT8/ LT8/LT85 are % tested at 5 C.The I-grade LT8/LT85 are guaranteed over the full C to 5 C operating ambient temperature range. 85fg 5

6 LT8/LT8/LT85 TYPICAL PERFORMANCE CHARACTERISTICS MIMUM PUT/PUT DIFFERENTIAL (V) LT8 Dropout Voltage DICATES GUARANTEED TEST POT C T J 5 C C T J 5 C T J = 5 C T J = 5 C T J = 55 C PUT CURRENT (A) SHORT-CIRCUIT CURRENT (A) 8 LT8 Short-Circut Current 55 C I FULL LOAD GUARANTEED 5 C 5 C PUT/PUT DIFFERENTIAL (V) PUT VOLTAGE DEVIATION (%) LT8 Load Regulation ΔI = 7.5A TEMPERATURE ( C) LT8//5 G LT8//5 G LT8//5 G MIMUN PUT/PUT DIFFERENTIAL (V) LT8 Dropout Voltage DICATES GUARANTEED TEST POT C T J 5 C T J = 5 C 55 C T J 5 C T J = 5 C PUT CURRENT (A) T J = 55 C 5 SHORT-CIRCUIT CURRENT (A) LT8 Short-Circut Current I FULL LOAD GUARANTEED 5 C 5 C 55 C PUT/PUT DIFFERENTIAL (V) PUT VOLTAGE DEVIATION (%) LT8 Load Regulation ΔI = 5A TEMPERATURE ( C) LT8//5 G LT8//5 G5 LT8//5 G MIMUM PUT/PUT DIFFERENTIAL (V) LT85 Dropout Voltage DICATES GUARANTEED TEST POT C T J 5 C T J = 5 C 55 C T J 5 C T J = 5 C T J = 55 C PUT CURRENT (A) SHORT-CIRCUIT CURRENT (A) 5 LT85 Short-Circuit Current 55 C I FULL LOAD GUARANTEED 5 C 5 C PUT/PUT DIFFERENTIAL (V) PUT VOLTAGE DEVIATION (%) LT85 Load Regulation ΔI = A TEMPERATURE ( C) LT8//5 G7 LT8//5 G8 LT8//5 G9 85fg

7 TYPICAL PERFORMANCE CHARACTERISTICS LT8/LT8/LT85 MIMUM OPERATG CURRENT (ma) Minimum Operating Current Temperature Stability Adjust Pin Current T J = 5 C T J = 5 C T J = 55 C PUT/PUT DIFFERENTIAL (V) REFERENCE VOLTAGE (V) TEMPERATURE ( C) UST P CURRENT (μa) TEMPERATURE ( C) RIPPLE REJECTION (db) RIPPLE REJECTION (db) V RIPPLE V P-P ( V ) V DROP LT8//5 G V RIPPLE.5V P-P ( V ) V C = μf AT FREQUENCIES < Hz C = 5μF AT FREQUENCIES > Hz I = 7A k k k FREQUENCY (Hz) LT8 Ripple Rejection LT8 Ripple Rejection V RIPPLE V P-P ( V ) V DROP 8//5 G V RIPPLE.5V P-P ( V ) V C = μf AT FREQUENCIES < Hz C = 5μF AT FREQUENCIES > Hz I = 5A k k k FREQUENCY (Hz) 8//5 G RIPPLE REJECTION (db) RIPPLE REJECTION (db) LT8 Ripple Rejection vs Current f R = khz V RIPPLE.5V P-P V = 5V C = 5μF C = 5μF LT8//5 G f R = Hz V RIPPLE V P-P PUT CURRENT (A) LT8 Ripple Rejection vs Current f R = khz V RIPPLE.5V P-P V = 5V C = 5μF C = 5μF 8//5 G f R = Hz V RIPPLE V P-P 5 PUT CURRENT (A) 8//5 G7 POWER (W) POWER (W) LT8//5 G LT8MK 5 LT8CP LT8CK CASE TEMPERATURE ( C) * AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE 5 LT8 Maximum Power Dissipation* LT8 Maximum Power Dissipation* LT8CT LT8CK LT8MK LT8CP LT8//5 G CASE TEMPERATURE ( C) * AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE LT8//5 G8 85fg 7

8 LT8/LT8/LT85 TYPICAL PERFORMANCE CHARACTERISTICS RIPPLE REJECTION (db) LT85 Ripple Rejection V RIPPLE V P-P ( V ) V DROP V RIPPLE.5V P-P ( V ) V C = μf AT FREQUENCIES < Hz C = 5μF AT FREQUENCIES > Hz I = A k k k FREQUENCY (Hz) 8//5 G9 RIPPLE REJECTION (db) LT85 Ripple Rejection vs Current f R = Hz V RIPPLE V P-P f R = khz V RIPPLE.5V P-P V = 5V C = 5μF C = 5μF PUT CURRENT (A) 8//5 G POWER (W) 5 LT85 Maximum Power Dissipation* LT85MK LT85CK LT85CT CASE TEMPERATURE ( C) * AS LIMITED BY MAXIMUM JUNCTION TEMPERATURE LT8//5 G PUT VOLTAGE DEVIATION (V) LOAD CURRENT (A) LT8 Load Transient Response C = 5 TIME (μs) C = μf C = μf C = μf TANTALUM V =V =V PRELOAD=mA PUT VOLTAGE DEVIATION (V) LOAD CURRENT (A) LT8 Load Transient Response C = C = μf C = μf TANTALUM 5 TIME (μs) C = μf V =V =V PRELOAD=mA PUT VOLTAGE DEVIATION (V) LOAD CURRENT (A) LT85 Load Transient Response C = C = μf C = μf TANTALUM 5 TIME (μs) C = μf V =V =V PRELOAD=mA 8//5 G 8//5 G 8//5 G PUT VOLTAGE DEVIATION (mv) PUT DEVIATION (V) LT8 Line Transient Response C = C = μf V = V I =.A C = μf TANTALUM C = μf TANTALUM PUT VOLTAGE DEVIATION (mv) PUT DEVIATION (V) LT8 Line Transient Response C = C = μf V = V I =.A C = μf TANTALUM C = μf TANTALUM PUT VOLTAGE DEVIATION (mv) PUT DEVIATION (V) LT85 Line Transient Response C = C = μf V = V I =.A C = μf TANTALUM C = μf TANTALUM TIME (μs) TIME (μs) TIME (μs) 8//5 G5 8//5 G 8//5 G7 8 85fg

9 LT8/LT8/LT85 BLOCK DIAGRAM THERMAL LIMIT V 8//5 BD V APPLICATIONS FORMATION The LT8 family of -terminal adjustable regulators is easy to use and has all the protection features that are expected in high performance voltage regulators. They are short-circuit protected, and have safe area protection as well as thermal shutdown to turn off the regulator should the junction temperature exceed about 5 C. These regulators are pin compatible with older -terminal adjustable devices, offer lower dropout voltage and more precise reference tolerance. Further, the reference stability with temperature is improved over older types of regulators. The only circuit difference between using the LT8 family and older regulators is that this new family requires an output capacitor for stability. Stability The circuit design used in the LT8 family requires the use of an output capacitor as part of the device frequency compensation. For all operating conditions, the addition of a 5μF aluminium electrolytic or a μf solid tantalum on the output will ensure stability. Normally, capacitors much smaller than this can be used with the LT8. Many different types of capacitors with widely varying characteristics are available. These capacitors differ in capacitor tolerance (sometimes ranging up to ±%), equivalent series resistance, and capacitance temperature coefficient. The 5μF or μf values given will ensure stability. When the adjustment terminal is bypassed to improve the ripple rejection, the requirement for an output capacitor increases. The value of μf tantalum or 5μF aluminum covers all cases of bypassing the adjustment terminal. Without bypassing the adjustment terminal, smaller capacitors can be used with equally good results and the table below shows approximately what size capacitors are needed to ensure stability. Recommended Capacitor Values PUT PUT USTMENT μf μf μf Tantalum, 5μF Aluminum μf Tantalum, 5μF Aluminum None μf 85fg 9

10 LT8/LT8/LT85 APPLICATIONS FORMATION Normally, capacitor values on the order of μf are used in the output of many regulators to ensure good transient response with heavy load current changes. Output capacitance can be increased without limit and larger values of output capacitor further improve stability and transient response of the LT8 regulators. Another possible stability problem that can occur in monolithic IC regulators is current limit oscillations. These can occur because, in current limit, the safe area protection exhibits a negative impedance. The safe area protection decreases the current limit as the input-to-output voltage increases. That is the equivalent of having a negative resistance since increasing voltage causes current to decrease. Negative resistance during current limit is not unique to the LT8 series and has been present on all power IC regulators. The value of the negative resistance is a function of how fast the current limit is folded back as input-to-output voltage increases. This negative resistance can react with capacitors or inductors on the input to cause oscillation during current limiting. Depending on the value of series resistance, the overall circuitry may end up unstable. Since this is a system problem, it is not necessarily easy to solve; however, it does not cause any problems with the IC regulator and can usually be ignored. Protection Diodes In normal operation, the LT8 family does not need any protection diodes. Older adjustable regulators required protection diodes between the adjustment pin and the output and from the output to the input to prevent overstressing the die. The internal current paths on the LT8 adjustment pin are limited by internal resistors. Therefore, even with capacitors on the adjustment pin, no protection diode is needed to ensure device safety under short-circuit conditions. Diodes between input and output are usually not needed. The internal diode between the input and the output pins of the LT8 family can handle microsecond surge currents of 5A to A. Even with large output capacitances, it is very difficult to get those values of surge currents in normal operations. Only with a high value of output capacitors, such as μf to 5μF and with the input pin instantaneously shorted to ground, can damage occur. A crowbar circuit at the input of the LT8 can generate those kinds of currents, and a diode from output to input is then recommended. Normal power supply cycling or even plugging and unplugging in the system will not generate current large enough to do any damage. The adjustment pin can be driven on a transient basis ±5V, with respect to the output without any device degradation. Of course, as with any IC regulator, exceeding the maximum input to output voltage differential causes the internal transistors to break down and none of the protection circuitry is functional. D N (OPTIONAL) LT8 C μf R R V C 5μF 8//5 F Overload Recovery Like any of the IC power regulators, the LT8 has safe area protection. The safe area protection decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a safe operating region for all values of input-to-output voltage. The LT8 protection is designed to provide some output current at all values of input-to-output voltage up to the device breakdown. When power is first turned on, as the input voltage rises, the output follows the input, allowing the regulator to start up into very heavy loads. During the start-up, as the input voltage is rising, the input-to-output voltage differential remains small, allowing the regulator to supply large output currents. With high input voltage, a problem can occur wherein removal of an output short will not allow the output voltage to recover. Older regulators, such as the 78 series, also exhibited this phenomenon, so it is not unique to the LT8. 85fg

11 APPLICATIONS FORMATION The problem occurs with a heavy output load when the input voltage is high and the output voltage is low, such as immediately after removal of a short. The load line for such a load may intersect the output current curve at two points. If this happens, there are two stable output operating points for the regulator. With this double intersection, the power supply may need to be cycled down to zero and brought up again to make the output recover. LT8/LT8/LT85 I 5μA LT8 V =V REF R ( R ) I R V REF R R Figure. Basic Adjustable Regulator V 8//5 F Ripple Rejection The typical curves for ripple rejection reflect values for a bypassed adjustment pin. This curve will be true for all values of output voltage. For proper bypassing and ripple rejection approaching the values shown, the impedance of the adjust pin capacitor at the ripple frequency should be less than the value of R, (normally Ω to Ω). The size of the required adjust pin capacitor is a function of the input ripple frequency. At Hz the adjust pin capacitor should be 5μF if R = Ω. At khz only.μf is needed. For circuits without an adjust pin bypass capacitor, the ripple rejection will be a function of output voltage. The output ripple will increase directly as a ratio of the output voltage to the reference voltage (V /V REF ). For example, with the output voltage equal to 5V and no adjust pin capacitor, the output ripple will be higher by the ratio of 5V/.5V or four times larger. Ripple rejection will be degraded by db from the value shown on the typical curve. Output Voltage The LT8 develops a.5v reference voltage between the output and the adjust terminal (see Figure ). By placing a resistor R between these two terminals, a constant current is caused to flow through R and down through R to set the overall output voltage. Normally this current is the specified minimum load current of ma. Because I is very small and constant when compared with the current through R, it represents a small error and can usually be ignored. Load Regulation Because the LT8 is a -terminal device, it is not possible to provide true remote load sensing. Load regulation will be limited by the resistance of the wire connecting the regulator to the load. The data sheet specification for load regulation is measured at the bottom of the package. Negative side sensing is a true Kelvin connection, with the bottom of the output divider returned to the negative side of the load. Although it may not be immediately obvious, best load regulation is obtained when the top of the resistor divider R is connected directly to the case not to the load. This is illustrated in Figure. If R were connected to the load, the effective resistance between the regulator and the load would be: R P R R, RP Parasitic Line R = Resistance LT8 *CONNECT R TO CASE CONNECT R TO LOAD R P PARASITIC LE RESISTANCE R* R* 8//5 F Figure. Connections for Best Load Regulation R L 85fg

12 LT8/LT8/LT85 APPLICATIONS FORMATION Connected as shown, R P is not multiplied by the divider ratio. R P is about.ω per foot using -gauge wire. This translates to mv/ft at A load current, so it is important to keep the positive lead between regulator and load as short as possible and use large wire or PC board traces. Thermal Considerations The LT8 series of regulators have internal power and thermal limiting circuitry designed to protect the device under overload conditions. For continuous normal load conditions however, maximum junction temperature ratings must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. This includes junction-to-case, caseto-heat sink interface, and heat sink resistance itself. New thermal resistance specifications have been developed to more accurately reflect device temperature and ensure safe operating temperatures. The data section for these new regulators provides a separate thermal resistance and maximum junction temperature for both the Control Section and the Power Transistor. Previous regulators, with a single junction-to-case thermal resistance specification, used an average of the two values provided here and therefore could allow excessive junction temperatures under certain conditions of ambient temperature and heat sink resistance. To avoid this possibility, calculations should be made for both sections to ensure that both thermal limits are met. Junction-to-case thermal resistance is specified from the IC junction to the bottom of the case directly below the die. This is the lowest resistance path for heat flow. Proper mounting is required to ensure the best possible thermal flow from this area of the package to the heat sink. Thermal compound at the case-to-heat sink interface is strongly recommended. If the case of the device must be electrically isolated, a thermally conductive spacer can be used, as long as its added contribution to thermal resistance is considered. Note that the case of all devices in this series is electrically connected to the output. For example, using an LT8CK (TO-, Commercial) and assuming: (Max Continuous) = 9V, V = 5V, I = A, T A = 75 C, θ HEAT SK = C/W, θ CASE-TO-HEAT SK =. C/W for K package with thermal compound. Power dissipation under these conditions is equal to: P D = ( V )(I ) = W Junction temperature will be equal to: T J = T A P D (θ HEAT SK θ CASE-TO-HEAT SK θ JC ) For the Control Section: T J = 75 C W ( C/W. C/W. C/W) = 8 C 8 C < 5 C = T JMAX (Control Section Commercial Range) For the Power Transistor: T J = 75 C W ( C/W. C/W. C/W) = C C < 5 C = T JMAX (Power Transistor Commercial Range) In both cases the junction temperature is below the maximum rating for the respective sections, ensuring reliable operation. 85fg

13 TYPICAL APPLICATION 7.5A Variable Regulator LT8/LT8/LT85 VAC T TRIAD F-9U 5V 5V CB Ω Ω T L mh N C 5,μF LT8 LT-. 75Ω*.5k V TO 5V OA TO 7.5A μf N CB N μf 5Ω N9 k* k PUT UST LT-. 8k k N8 5k 8 LT 5V 7 k.μf NC k* pf k*.7k 5V 7 5V 8 LT *% FILM RESISTOR L: DALE TO-5 TYPE T: STANCOR Z- GENERAL PURPOSE REGULATOR WITH SCR PREREGULATOR TO LOWER POWER DISSIPATION. AB.7V DIFFERENTIAL IS MATAED ACROSS THE LT8 DEPENDENT OF PUT VOLTAGE AND LOAD CURRENT N9 k 5K 5V 8 LMA 7 5V 5V μf k* LT8//5 TA5 85fg

14 LT8/LT8/LT85 TYPICAL APPLICATION Paralleling Regulators LT8.5Ω FEET #8 WIRE* ( ) V =.5V R R I = A TO 5A LT8 R Ω *THE #8 WIRE ACTS AS BALLAST RESISTANCE SURG CURRENT SHARG BETWEEN BOTH DEVICES R LT8//5 TA Improving Ripple Rejection μf LT8 R Ω % R 5Ω % C 5μF* V 5V 5μF *C IMPROVES RIPPLE REJECTION. X C SHOULD BE < R AT RIPPLE FREQUENCY 8//5 TA Remote Sensing μf LT8 Ω 5Ω 5Ω μf R P (MAX DROP mv) 7 pf LMA 8 5μF k R L V 5V RETURN 5Ω RETURN 8//5 TA7 85fg

15 TYPICAL APPLICATION LT8/LT8/LT85 High Effi ciency Regulator with Switching Preregulator 8V k mh MR,μF 7Ω LT8 Ω V 8V N9 k k M N8 k LT k 8V 8//5 TA N9.V to 5V Adjustable Regulator C* μf LT8 R k R 9.9Ω V C μf *NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS ( ) V =.5V R R 8//5 TA8 5V Regulator with Shutdown* TTL μf k LT8 N9 k Ω % 5Ω % V 5V μf *PUT SHUTS DOWN TO.V 8//5 TA9 85fg 5

16 LT8/LT8/LT85 PACKAGE DESCRIPTION K Package -Lead TO- Metal Can (Reference LTC DWG # 5-8-)..5 ( ) (9. 9.9)..5 (.5.9).. ( ) (9.9.) (. 7.5).5. (.8.9) DIA, PLCS..8 (.7.9).8. (.95.9).5.5 (.8.5).7.77 (.7.9) OBSOLETE PACKAGE.9.5 (.5.95) R.7.77 (..9) R K (TO-) 8 M Package -Lead Plastic DD Pak (Reference LTC DWG # 5-8-).5 (.5). (.5). (.5) TYP.9.5 (9.9.5) (.9.57).5.55 (..97). (.5).8 (.8)..7 ( ).59 (.99)..8. (... ). (7.).75 (.95) BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SK RECOMMENDED SOLDER PAD LAY.... ( ).5 (.7). (.5) BSC.8.. (..58) RECOMMENDED SOLDER PAD LAY FOR THICKER SOLDER PASTE APPLICATIONS (..9).5 ±. (.7 ±.5) NOTE:. DIMENSIONS CH/(MILLIMETER). DRAWG NOT TO SCALE M (DD) 85fg

17 PACKAGE DESCRIPTION P Package -Lead Plastic TO-P (Similar to TO-7) (Reference LTC DWG # 5-8-5) LT8/LT8/LT85.5 (.).5 (8.55).75 (.985)..O (5.75.) MOUNTG HOLE.5.5 (.9.8) DIA (.75 5.)..8 (.5.).58 (.7).7 (7.78).8.87 (.8.).58.OO (.7 5.).7.OO (. 5.8) EJECTOR P MARKS.5.5 (.7.8) DIA.98 (.89). (.9).78.8 (9.8.).7 (.) MAX 7 BOTTOM VIEW OF TO-P HATCHED AREA IS SOLDER PLATED COPPER HEAT SK..5 (.7.).7.8 (.88.).5 (5.) BSC.. (.87.).87. (..59).. (.5.) P 8 T Package -Lead Plastic TO- (Reference LTC DWG # 5-8-).9.5 (9.9.5).7.55 (.7.97) DIA.5.8 (.9.57).5.55 (..97)..7 ( )..5 (.8.7)..7 ( ).57. ( ).98.7 ( ).5.57 (.8.78).8.5 (5.57.). (.5) BSC.8.8 (.7.95).5 (.7) TYP.. (..58).95.5 (..9) T (TO-) 8 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 85fg 7

18 LT8/LT8/LT85 TYPICAL APPLICATIONS Automatic Light Control LT8 μf.k μf 8//5 TA Protected High Current Lamp Driver V 5A LT8 5V TTL OR CMOS 8//5 TA k RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT8.5A Low Dropout Regulator Fixed.85V,.V,.V, 5V and V Output LT7 8mA Low Dropout Regulator Fixed.85V,.V, 5V or Adjustable Output LT58/LT585/LT587 7A/.A/A Fast Response Low Dropout Regulators For High Performance Microprocessors LT58 7A Very Low Dropout Linear Regulator.5V Dropout at 7A, Fixed.5V and Adjustable LT58 A Very Low Dropout Linear Regulator.V Dropout at A, Fixed.5V and Adjustable LT High Power Step-Down Switching Regulator 5V to.v at A, >9% Effi ciency LT575 UltraFast Transient Response LDO Controller External MOSFET Pass Element LT57 UltraFast Transient Response LDO Controller External PNP Pass Element UltraFast is a trademark of Linear Technology Corporation. 8 LT 9 REV G PRTED USA Linear Technology Corporation McCarthy Blvd., Milpitas, CA (8) -9 FAX: (8) LEAR TECHNOLOGY CORPORATION 99 85fg