LIN D O C #: 8585 LX8585-xx/8585A-xx 4 . 6 A LOW DR O P O U T P OSITIVE R E G U L AT O R S T H E I P N F I N I T E O W E R I O F P N N O VA T I O N DESCRIPTION The LX8585/85A Series ICs are low dropout three-terminal regulators with a minimum of 4.6A output current. Pentium® Processor and Power PCTM applications requiring fast transient response are ideally suited for this product family. The LX8585A is guaranteed to have < 1.2V at 4.6A, while the LX8585 are specified for 1.4V, making them ideal to provide well regulated outputs of 2.5V to 3.6V using a 5V input supply. Fixed versions are also available and specified in the Available Options table below. Current limit is trimmed above 4.6A to ensure adequate output current and con- trolled short-circuit current. On-chip thermal limiting provides protection against any possible overload that would create excessive junction temperatures. The LX8585/85A family is available in both through-hole and surface-mount versions of the industry standard 3-pin TO-220 / TO-263 power packages. The LX1431 Programmable Reference and LX8585A Series products offer precision output voltage and are ideal for use in VRE applications (see application below). For higher current applications, see the LX8584 data sheet. T HE A PPLICATION OF THE LX8585A & LX1431 IN A 75 & 166MHZ P54C P ROCESSORS U SING 5V C ACHE VIN VOUT VO 4.6A (See Table Below) 2 LX8585A 1kΩ ADJ 1kΩ 1 0.01µF 1 2 220µF 10V Low ESR from Sanyo COL V+ REF LX1431 0.1µF 50V SGND 21k 1% 1µF x 10 SMD JP1 FGND 5 VOUT 3.50 3.38 2.84kΩ 0.1% H E E T ■ THREE-TERMINAL ADJUSTABLE OR FIXED OUTPUT ■ GUARANTEED < 1.2V HEADROOM AT 4.6A (LX8585A) ■ GUARANTEED < 1.4V HEADROOM AT 4.6A (LX8585) ■ GUARANTEED < 1.3V HEADROOM AT 3A ■ OUTPUT CURRENT OF 4.6A MINIMUM p FAST TRANSIENT RESPONSE p 1% VOLTAGE REFERENCE INITIAL ACCURACY p OUTPUT SHORT CIRCUIT PROTECTION p BUILT-IN THERMAL SHUTDOWN ■ ■ ■ ■ ■ ■ ■ ■ PENTIUM PROCESSOR SUPPLIES POWER PC SUPPLIES MICROPROCESSOR SUPPLIES LOW VOLTAGE LOGIC SUPPLIES BATTERY POWERED CIRCUIT POST REGULATOR FOR SWITCHING SUPPLY CYRIX® 6x86TM SUPPLIES AMD-K5TM SUPPLIES A VA I L A B L E O P T I O N S 100µF x 6 10V AVX TYPE TPS 1k 0.1% 8 PLACE IN µP SOCKET CAVITY 2x 330µF, 6.3V Low ESR Oscon Type from Sanyo 250pF 3 S A P P L I C AT I O N S PRODUCT HIGHLIGHT 3 A T A K E Y F E AT U R E S IMPORTANT: For the most current data, consult LinFinity's web site: http://www.linfinity.com. 5V D R O D U C T I O N Part # µP Load PER PAR T # Output Voltage LX8585/85A-00 LX8585/85A-15 Adjustable 1.5V LX8585/85A-33 3.3V Other voltage options may be available — Please contact factory for details. 6 JP1 Short Open TYPICAL APPLICATION 120/166MHz, VRE, 5V Cache 75/90/100/133MHz, STND, 5V Cache Thick traces represent high current traces which must be low resistance / low inductance traces in order to achieve good transient response. PA C K A G E O R D E R I N F O R M AT I O N TO-220 T0-263 Dropout TA (°C) P Plastic DD Plastic Voltage 3-pin 3-pin 0 to 125 1.4V LX8585-xxCP LX8585-xxCDD 1.2V LX8585A-xxCP LX8585A-xxCDD Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX8585A-00CDDT) "xx" refers to output voltage, please see table above. Copyright © 1997 Rev. 2.2 12/97 LINFINITY MICROELECTRONICS INC. 11861 W ESTERN A VENUE, G ARDEN G ROVE, CA. 92841, 714-898-8121, F AX: 714-893-2570 1 PRODUCT DATABOOK 1996/1997 LX8585-xx/8585A-xx 4 . 6 A LOW D R O P O U T P OSITIVE R E G U L AT O R S P R O D U C T I O N A B S O L U T E M A X I M U M R AT I N G S D A T A S H E E T PACKAGE PIN OUTS (Note 1) Power Dissipation .................................................................................. Internally Limited Input Voltage ................................................................................................................ 10V Input to Output Voltage Differential ........................................................................... 10V Operating Junction Temperature Plastic (P, DD Package) ........................................................................................ 150°C Storage Temperature Range ...................................................................... -65°C to 150°C Lead Temperature (Soldering, 10 seconds) ............................................................. 300°C Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of the specified terminal. T H E R MAL DATA TAB IS VOUT 3 VIN VOUT ADJ / GND* 2 1 P PACKAGE (Top View) * Pin 1 is GND for fixed voltage versions. TAB IS V OUT P PACKAGE: THERMAL RESISTANCE-JUNCTION TO TAB, θJT 3.0°C/W THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ JA 60°C/W 3 VIN 2 VOUT 1 ADJ / GND* DD PACKAGE: THERMAL RESISTANCE-JUNCTION TO TAB, θJT 3.0°C/W THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ JA 60°C/W* Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. * θ JAcan be improved with package soldered to 0.5IN2 copper area over backside ground plane or internal power plane. θJAcan vary from 20ºC/W to > 40ºC/W depending on mounting technique. 2 DD PACKAGE (Top View) * Pin 1 is GND for fixed voltage versions. Copyright © 1997 Rev. 2.2 12/97 PRODUCT DATABOOK 1996/1997 LX8585-xx/8585A-xx 4 . 6 A LOW DR O P O U T P OSITIVE R E G U L AT O R S P R O D U C T I O N D A T A S H E E T ELECTRICAL CHARACTERISTICS (Unless otherwise specified, these specifications apply over the operating ambient temperatures for the LX8585-xxC/85A-xxC with 0°C ≤ TA ≤ 125°C; VIN - VOUT = 3V; IOUT = 4.6A. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.) LX8585-00 / 8585A-00 (Adjustable) Parameter Reference Voltage Symbol LX8585/85A Test Conditions VREF IOUT = 10mA, TA = 25°C 10mA ≤ IOUT ≤ 4.6A, 1.5V ≤ (VIN - VOUT), VIN ≤ 7V, P ≤ PMAX Line Regulation (Note 2) ∆VREF (V IN) IOUT = 10mA, 1.5V ≤ (VIN - VOUT ), VIN ≤ 7V ∆VREF (IOUT) VIN - V OUT = 3V, 10mA ≤ IOUT ≤ 4.6A Load Regulation (Note 2) Thermal Regulation ∆VOUT (Pwr) TA = 25°C, 20ms pulse Ripple Rejection (Note 3) VOUT = 3.3V, f =120Hz, COUT = 100µf Tantalum, VIN = 5V CADJ = 10µF, TA = 25°C, IOUT = 4.6A Adjust Pin Current I ADJ Adjust Pin Current Change ∆IADJ 10mA ≤ IOUT ≤ 4.6A, 1.5V ≤ (VIN - VOUT), VIN ≤ 7V Dropout Voltage LX8585 ∆V ∆VREF = 1%, IOUT = 4.6A ∆VREF = 1%, IOUT = 3A LX8585A ∆VREF = 1%, IOUT = 4.6A Minimum Load Current IOUT(MIN) VIN ≤ 7V Maximum Output Current (Note 4) I OUT(MAX) 1.4V ≤ (V IN - VOUT), VIN ≤ 7V Temperature Stability (Note 3) ∆VOUT(t) Long Term Stability (Note 3) ∆VOUT (t) TA = 125°C, 1000 hrs RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 125°C, 10Hz £ f £ 10kHz LX8585/85A-00 Min. Typ. Max. 1.238 1.225 60 4.6 Units 1.250 1.250 0.035 0.1 0.01 83 1.262 1.275 0.2 0.5 0.02 V V % % %/W dB 55 0.2 1.2 1.1 1.1 2 6 0.25 0.3 0.003 100 5 1.4 1.3 1.2 10 µA µA V V V mA A % % % 1 LX8585-15 / 8585A-15 (1.5V Fixed) Parameter Output Voltage (Note 4) Symbol VOUT Test Conditions VIN = 5V, IOUT = 0mA, TA = 25°C 4.75V ≤ V IN ≤ 10V, 0mA ≤ IOUT ≤ 7A, TA = 25°C, P ≤ PMAX Line Regulation (Note 2) ∆VOUT 4.75V ≤ V IN ≤ 7V (VIN ) 4.75V ≤ VIN ≤ 10V ∆VOUT (IOUT) VIN = 5V, 10mA ≤ IOUT ≤ IOUT (MAX) Load Regulation (Note 2) Thermal Regulation (Note 3) ∆VOUT (Pwr) TA = 25°C, 20ms pulse Ripple Rejection (Note 3) COUT = 100µF (Tantalum), IOUT = 4.6A, TA = 25°C Quiescent Current IQ 0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V Dropout Voltage LX8585-15 ∆V ∆VOUT = 1%, IOUT ≤ IOUT (MAX) , V IN - VOUT ≤ 7V ∆VOUT = 1%, IOUT ≤ 3A, VIN - VOUT ≤ 7V LX8585A-15 ∆VOUT = 1%, IOUT ≤ IOUT (MAX) , V IN - VOUT ≤ 7V Temperature Stability (Note 3) ∆VOUT (T) Long Term Stability (Note 3) ∆VOUT (t) TA = 125°C, 1000 hours RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz LX8585/85A-15 Min. Typ. Max. 1.485 1.470 65 1.50 1.50 1 1 2.5 0.01 83 4 1.2 1.1 1.1 0.25 0.3 0.003 1.515 1.530 3 5 7 0.02 10 1.4 1.3 1.2 1 Units V V mV mV mV %/W dB mA V V V % % % Note 2. Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered under the specification for thermal regulation. Note 3. These parameters, although guaranteed, are not tested in production. Note 4. IOUT (MAX) is measured under the condition that VOUT is forced below its nominal value by 100mV. Copyright © 1997 Rev. 2.2 12/97 3 PRODUCT DATABOOK 1996/1997 LX8585-xx/8585A-xx 4 . 6 A LOW D R O P O U T P OSITIVE R E G U L AT O R S P R O D U C T I O N D A T A S H E E T ELECTRICAL CHARACTERISTICS (Continued) LX8585-33 / 8585A-33 (3.3V Fixed) Parameter Output Voltage (Note 4) Symbol VIN = 5V, IOUT = 0mA, TA = 25°C 4.75V ≤ V IN ≤ 10V, 0mA ≤ IOUT ≤ 7A, TA = 25°C, P ≤ PMAX Line Regulation (Note 2) ∆VOUT 4.75V ≤ VIN ≤ 7V (VIN ) 4.75V ≤ VIN ≤ 10V ∆VOUT (IOUT) VIN = 5V, 10mA ≤ IOUT ≤ IOUT (MAX) Load Regulation (Note 2) Thermal Regulation (Note 3) ∆VOUT (Pwr) TA = 25°C, 20ms pulse Ripple Rejection (Note 3) COUT = 100µF (Tantalum), IOUT = 4.6A, TA = 25°C 0mA ≤ IOUT ≤ IOUT (MAX) , 4.75V ≤ VIN ≤ 10V Quiescent Current IQ Dropout Voltage LX8585-33 ∆V ∆VOUT = 1%, IOUT ≤ IOUT (MAX) , V IN - VOUT ≤ 7V ∆VOUT = 1%, IOUT ≤ 3A, VIN - VOUT ≤ 7V LX8585A-33 ∆VOUT = 1%, IOUT ≤ IOUT (MAX) , V IN - VOUT ≤ 7V Temperature Stability (Note 3) ∆VOUT (T) Long Term Stability (Note 3) ∆VOUT (t) TA = 125°C, 1000 hours RMS Output Noise (% of VOUT) (Note 3) VOUT (RMS) TA = 25°C, 10Hz ≤ f ≤ 10kHz 4 VOUT Test Conditions LX8585/85A-33 Min. Typ. Max. 3.267 3.235 65 3.3 3.3 1 2 5 0.01 83 4 1.2 1.1 1.1 0.25 0.3 0.003 3.333 3.365 6 10 15 0.02 10 1.4 1.3 1.2 1 Units V V mV mV mV %/W dB mA V V V % % % Copyright © 1997 Rev. 2.2 12/97 PRODUCT DATABOOK 1996/1997 LX8585-xx/8585A-xx 4 . 6 A LOW DR O P O U T P OSITIVE R E G U L AT O R S P R O D U C T I O N D A T A S H E E T A P P L I C AT I O N N O T E S The LX8585/85A Series ICs are easy to use Low-Dropout (LDO) voltage regulators. They have all of the standard self-protection features expected of a voltage regulator: short circuit protection, safe operating area protection and automatic thermal shutdown if the device temperature rises above approximately 165°C. Use of an output capacitor is REQUIRED with the LX8585/85A series. Please see the table below for recommended minimum capacitor values. These regulators offer a more tightly controlled reference voltage tolerance and superior reference stability when measured against the older pin-compatible regulator types that they replace. STABILITY The output capacitor is part of the regulator’s frequency compensation system. Many types of capacitors are available, with different capacitance value tolerances, capacitance temperature coefficients, and equivalent series impedances. For all operating conditions, connection of a 220µF aluminum electrolytic capacitor or a 47µF solid tantalum capacitor between the output terminal and ground will guarantee stable operation. If a bypass capacitor is connected between the output voltage adjust (ADJ) pin and ground, ripple rejection will be improved (please see the section entitled “RIPPLE REJECTION”). When ADJ pin bypassing is used, the required output capacitor value increases. Output capacitor values of 220µF (aluminum) or 47µF (tantalum) provide for all cases of bypassing the ADJ pin. If an ADJ pin bypass capacitor is not used, smaller output capacitor values are adequate. The table below shows recommended minimum capacitance values for stable operation. RECOMMENDED CAPACITOR VALUES INPUT OUTPUT ADJ 10µF 10µF 15µF Tantalum, 100µF Aluminum 47µF Tantalum, 220µF Aluminum None 15µF To ensure good transient response from the power supply system under rapidly changing current load conditions, designers generally use several output capacitors connected in parallel. Such an arrangement serves to minimize the effects of the parasitic resistance (ESR) and inductance (ESL) that are present in all capacitors. Costeffective solutions that sufficiently limit ESR and ESL effects generally result in total capacitance values in the range of hundreds to thousands of microfarads, which is more than adequate to meet regulator output capacitor specifications. Output capacitance values may be increased without limit. The circuit shown in Figure 1 can be used to observe the transient response characteristics of the regulator in a power system under changing loads. The effects of different capacitor types and values on transient response parameters, such as overshoot and undershoot, can be compared quickly in order to develop an optimum solution. Copyright © 1997 Rev. 2.2 12/97 Power Supply IN LX8585/85A OUT ADJ Minumum Load (Larger resistor) Full Load (Smaller resistor) RDSON << RL Star Ground 10ms 1 sec FIGURE 1 — DYNAMIC INPUT and OUTPUT TEST OVERLOAD RECOVERY Like almost all IC power regulators, the LX8585/85A regulators are equipped with Safe Operating Area (SOA) protection. The SOA circuit limits the regulator's maximum output current to progressively lower values as the input-to-output voltage difference increases. By limiting the maximum output current, the SOA circuit keeps the amount of power that is dissipated in the regulator itself within safe limits for all values of input-to-output voltage within the operating range of the regulator. The LX8585/85A SOA protection system is designed to be able to supply some output current for all values of input-to-output voltage, up to the device breakdown voltage. Under some conditions, a correctly operating SOA circuit may prevent a power supply system from returning to regulated operation after removal of an intermittent short circuit at the output of the regulator. This is a normal mode of operation which can be seen in most similar products, including older devices such as 7800 series regulators. It is most likely to occur when the power system input voltage is relatively high and the load impedance is relatively low. When the power system is started “cold”, both the input and output voltages are very close to zero. The output voltage closely follows the rising input voltage, and the input-to-output voltage difference is small. The SOA circuit therefore permits the regulator to supply large amounts of current as needed to develop the designed voltage level at the regulator output. Now consider the case where the regulator is supplying regulated voltage to a resistive load under steady state conditions. A moderate input-to-output voltage appears across the regulator but the voltage difference is small enough that the SOA circuitry allows sufficient current to flow through the regulator to develop the designed output voltage across the load resistance. If the output resistor is shortcircuited to ground, the input-to-output voltage difference across the regulator suddenly becomes larger by the amount of voltage that had appeared across the load resistor. The SOA circuit reads the increased input-to-output voltage, and cuts back the amount of current that it will permit the regulator to supply to its output terminal. When the short circuit across the output resistor is removed, all the regulator output current will again flow through the output resistor. The maximum current that the regulator can supply to the resistor will be limited by the SOA circuit, based on the large input-to-output voltage across the regulator at the time the short circuit is removed from the output. 5 PRODUCT DATABOOK 1996/1997 LX8585-xx/8585A-xx 4 . 6 A LOW D R O P O U T P OSITIVE R E G U L AT O R S P R O D U C T I O N D A T A S H E E T A P P L I C AT I O N N O T E S OVERLOAD RECOVERY (continued) If this limited current is not sufficient to develop the designed voltage across the output resistor, the voltage will stabilize at some lower value, and will never reach the designed value. Under these circumstances, it may be necessary to cycle the input voltage down to zero in order to make the regulator output voltage return to regulation. C = 1 / (6.28 * FR * R1) ≡ the value of the capacitor in Farads; select an equal or larger standard value. F R ≡ the ripple frequency in Hz R1 ≡ the value of resistor R1 in ohms where: C At a ripple frequency of 120Hz, with R1 = 100Ω: C = 1 / (6.28 * 120Hz * 100Ω) = 13.3µF The closest equal or larger standard value should be used, in this case, 15µF. When an ADJ pin bypass capacitor is used, output ripple amplitude will be essentially independent of the output voltage. If an ADJ pin bypass capacitor is not used, output ripple will be proportional to the ratio of the output voltage to the reference voltage: M = VOUT/VREF where: M VREF ≡ a multiplier for the ripple seen when the ADJ pin is optimally bypassed. = 1.25V. For example, if VOUT = 2.5V the output ripple will be: M = 2.5V/1.25V= 2 VOUT VREF VOUT = VREF 1 + R2 + IADJ R2 R1 R1 R2 FIGURE 2 — BASIC ADJUSTABLE REGULATOR LOAD REGULATION Because the LX8585/85A regulators are three-terminal devices, 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, (R1), is connected directly to the case of the regulator, not to the load. This is illustrated in Figure 3. If R1 were connected to the load, the effective resistance between the regulator and the load would be: RPeff = RP * R2+R1 R1 where: R P ≡ Actual parasitic line resistance. When the circuit is connected as shown in Figure 3, the parasitic resistance appears as its actual value, rather than the higher RPeff. VIN IN LX8585/85A OUT ADJ RP Parasitic Line Resistance Output ripple will be twice as bad as it would be if the ADJ pin were to be bypassed to ground with a properly selected capacitor. R1 OUTPUT VOLTAGE R2 The LX8585/85A ICs develop a 1.25V reference voltage between the output and the adjust terminal (See Figure 2). By placing a resistor, R1, between these two terminals, a constant current is caused to flow through R1 and down through R2 to set the overall output voltage. Normally this current is the specified minimum load current of 10mA. Because IADJ is very small and constant when compared with the current through R1, it represents a small error and can usually be ignored. 6 LX8585/85A OUT ADJ IADJ 50µA RIPPLE REJECTION Ripple rejection can be improved by connecting a capacitor between the ADJ pin and ground. The value of the capacitor should be chosen so that the impedance of the capacitor is equal in magnitude to the resistance of R1 at the ripple frequency. The capacitor value can be determined by using this equation: IN VIN Connect R1 to Case of Regulator RL Connect R2 to Load FIGURE 3 — CONNECTIONS FOR BEST LOAD REGULATION Copyright © 1997 Rev. 2.2 12/97 PRODUCT DATABOOK 1996/1997 LX8585-xx/8585A-xx 4 . 6 A LOW DR O P O U T P OSITIVE R E G U L AT O R S P R O D U C T I O N D A T A S H E E T A P P L I C AT I O N N O T E S LOAD REGULATION (continued) Even when the circuit is configured optimally, parasitic resistance can be a significant source of error. A 100 mil (2.54 mm) wide PC trace built from 1 oz. copper-clad circuit board material has a parasitic resistance of about 5 milliohms per inch of its length at room temperature. If a 3-terminal regulator used to supply 2.50 volts is connected by 2 inches of this trace to a load which draws 5 amps of current, a 50 millivolt drop will appear between the regulator and the load. Even when the regulator output voltage is precisely 2.50 volts, the load will only see 2.45 volts, which is a 2% error. It is important to keep the connection between the regulator output pin and the load as short as possible, and to use wide traces or heavy-gauge wire. The minimum specified output capacitance for the regulator should be located near the reglator package. If several capacitors are used in parallel to construct the power system output capacitance, any capacitors beyond the minimum needed to meet the specified requirements of the regulator should be located near the sections of the load that require rapidly-changing amounts of current. Placing capacitors near the sources of load transients will help ensure that power system transient response is not impaired by the effects of trace impedance. To maintain good load regulation, wide traces should be used on the input side of the regulator, especially between the input capacitors and the regulator. Input capacitor ESR must be small enough that the voltage at the input pin does not drop below VIN (MIN) during transients. 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. Example Given: VIN = 5V VOUT = 2.8V, IOUT = 5.0A Ambient Temp., TA = 50°C RθJT = 2.7°C/W for TO-220 300 ft/min airflow available Find: Proper Heat Sink to keep IC's junction temperature below 125°C.** Solution: The junction temperature is: TJ = PD (RθJT + RθCS + RθSA) + TA where: PD ≡ Dissipated power. RθJT ≡ Thermal resistance from the junction to the mounting tab of the package. RθCS ≡ Thermal resistance through the interface between the IC and the surface on which it is mounted. (1.0°C/W at 6 in-lbs mounting screw torque.) RθSA ≡ Thermal resistance from the mounting surface to ambient (thermal resistance of the heat sink). TS ≡ Heat sink temperature. TJ VIN (MIN) = VOUT + VDROPOUT (MAX) where: VIN (MIN) VOUT VDROPOUT (MAX) ≡ the lowest allowable instantaneous voltage at the input pin. ≡ the designed output voltage for the power supply system. ≡ the specified dropout voltage for the installed regulator. Rq JT Copyright © 1997 Rev. 2.2 12/97 TS Rq CS TA Rq SA First, find the maximum allowable thermal resistance of the heat sink: TJ - TA - (RθJT + RθCS ) RθSA = PD PD THERMAL CONSIDERATIONS The LX8585/85A regulators have internal power and thermal limiting circuitry designed to protect each 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, case to heat sink interface, and heat sink thermal resistance itself. Junction-to-case thermal resistance is specified from the IC junction to the back surface of the case directly opposite 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-toheat-sink interface is strongly recommended. If the case of the device must be electrically isolated, a thermally conductive spacer TC RθSA = (VIN(MAX) - VOUT) I OUT = (5.0V-2.8V) * 5.0A = 11.0W 125°C - 50°C = - (2.7°C/W + 1.0°C/W) (5.0V-2.8V) * 5.0A = 3.1°C/W Next, select a suitable heat sink. The selected heat sink must have RθSA ≤ 3.1°C/W. Thermalloy heatsink 6296B has RθSA = 3.0°C/W with 300ft/min air flow. Finally, verify that junction temperature remains within specification using the selected heat sink: TJ = 11W (2.7°C/W + 1.0°C/W + 3.0°C/W) + 50°C = 124°C ** Although the device can operate up to 150°C junction, it is recommended for long term reliability to keep the junction temperature below 125°C whenever possible. 7 PRODUCT DATABOOK 1996/1997 LX8585-xx/8585A-xx 4 . 6 A LOW D R O P O U T P OSITIVE R E G U L AT O R S P R O D U C T I O N D S A T A H E E T T Y P I C A L A P P L I C AT I O N S (Note A) VIN 10µF LX8585/85A OUT IN ADJ * C1 improves ripple rejection. XC should be » R1 at ripple frequency. 5V R1 121W 1% R2 365W 1% VOUT VIN IN (Note A) LX8585/85A OUT ADJ C1* 10µF 150µF VOUT** R1 121W R2 1k C1 10µF* C2 100µF * Needed if device is far from filter capacitors. ** VOUT = 1.25V 1 + R2 R1 FIGURE 4 — IMPROVING RIPPLE REJECTION VIN FIGURE 5 — 1.2V - 8V ADJUSTABLE REGULATOR IN (Note A) LX8585/85A OUT ADJ 5V 121W 1% 100µF 10µF 1k TTL Output 2N3904 1k 365W 1% FIGURE 6 — 5V REGULATOR WITH SHUTDOWN VIN 10µF Tantalum or 100µF Aluminum LX8585-33/85A-33 OUT IN GND 3.3V Min. 15µF Tantalum or 100µF Aluminum capacitor. May be increased without limit. ESR must be less than 50mW . FIGURE 7 — FIXED 3.3V OUTPUT REGULATOR Note A: V IN (MIN) = (Intended V OUT) + (VDROPOUT (MAX)) Pentium is a registered trademark of Intel Corporation. Cyrix is a registered trademark and 6x86 is a trademark of Cyrix Corporation. K5 is a trademark of AMD. Power PC is a trademark of International Business Machines Corporation. PRODUCTION DATA - Information contained in this document is proprietary to Lin Finity, and is current as of publication date. This document may not be modified in any way without the express written consent of LinFinity. Product processing does not necessarily include testing of all parameters. Linfinity reserves the right to change the configuration and performance of the product and to discontinue product at any time. 8 Copyright © 1997 Rev. 2.2 12/97