AT1084 5A Low Dropout Positive Voltage Regulator

Transcription

1 FEATURES DESCRIPTION Three-Terminal Adjustable or Fixed Output Output Current of 5A Low Dropout 1.3V at 5A Output Current Line Regulation: 0.04% Load Regulation: 0.2% Fast Transient Response OCP & OTP Protected APPLICATION High Efficiency Linear Regulators Post Regulators for Switching Supplies Constant Current Regulators Battery Chargers Battery Chargers The series of positive adjustable regulators are designed to provide 5A with higher efficiency than currently available devices. All internal circuitry is designed to operate down to 1.3V input-to-output differential and the dropout voltage is fully specified as a function of load current. Dropout is guaranteed at a maximum of 1.5V at maximum output current, decreasing at lower load currents. On-chip trimming adjusts the reference voltage to 1%. Current limit is also trimmed, minimizing the stress on both the regulator and power source circuitry under overload conditions. The devices are pin compatible with older three-terminal regulators. A 10µF output capacitor is required on these new devices. However, this is included in most regulator designs. Unlike PNP regulators, where up to 10% of the output current is wasted as quiescent current, the quiescent current flows into the load, increasing efficiency. ORDER INFORMATION PIN CONFIGURATIONS (TOP VIEW) IAT Circuit Type AT A TE R Shipping: R: Tape & Reel T: Tube Output Voltage: A:Adj, 1.5:1.5V 1.8:1.8V, 2.5:2.5V 3.3:3.3V, 5.0:5.0V TE: TO TH:TO TJ:TO

2 PIN DESCRIPTIONS Pin Name ADJ GND V OUT V IN Pin Description Feedback for setting the output voltage, connect external resistors network for adjustable output. Reference ground. V OUT =V REF (1+ R2 )+I ADJ R2 R1 The pin is the power output of the device. Input voltage. TYPICAL APPLICATION CIRCUITS 2

3 BLOCK DIAGRAM ABSOLUTE MAXIMUM RATING Parameter Symbol Range Unit Junction Temperature Range T J 0 to +125 C Storage Temperature Range T STG -65 to +150 C Lead Temperature (Soldering, 5 sec) T LEAD 260 C Power dissipation P T A =25 C (Note 2) PD Internally limited W TO-263-2L 3.5 Thermal Resistance Junction to Case TO-220 θ JC 3.5 TO C/ W ESD Rating (Human body mode) (Note 3) V ESD 2 kv 3

4 ELECTRICAL CHARACTERISTICS Electrical Characteristics at I LOAD= 0mA and T J = +25 C (unless otherwise noted) Parameter Device Symbol Test Conditions Min Typ Max Unit Reference Voltage (Note 1) ADJ V REF I LOAD =10mA,V IN = 5V mA I LOAD 5A, 2.75V V IN 10V* V V IN -V OUT =1.5V Variator from nominal V OUT Output Voltage (Note 1) All Fixed Versions V OUT V IN -V OUT =1.5V I LOAD = 0mA to 5A Variator from nominal % V OUT (Note 1)* Line Regulation (Note 1) All REG LINE I LOAD = 10mA, V OUT + 1.5V V IN 10V* % Load Regulation (Note 1) All REG LOAD V IN = V OUT + 1.5V 10mA I LOAD 5A* % Dropout Voltage (Note 1,3) Current Limit (Note 1) Minimum Load Current All V D I LOAD = 5A* V All I CL V IN =V OUT + 1.5V* A ADJ I L(min) V IN = 5V, V ADJ = 0V* ma All Fixed Ground Pin Current Versions Adjust Pin Current ADJ I ADJ Temperature All Coefficient I G T C V IN = V OUT + 1.5V 10mA I LOAD 5A* I LOAD =10mA, 2.75V V IN 10V* V IN = V OUT + 1.5V, I LOAD =10mA * ma µa %/ C Ripple Rejection (Note 2) All RR V IN = V OUT + 1.5V, I LOAD =5A* db The*dentes the specifications which apply over the full temperature range (see absolute maximum ratings, T J ) Note 1: Low duty pulse testing with kelvin connections required. Note 2: 120Hz input ripple (C ADJ for ADJ = 25µF, C OUT = 25 µf) Note 3: V OUT V REF = 1%. 4

5 TYPICAL OPERATING CHARACTERISTICS 5

6 APPLICATION INFORMATION series linear regulators provide fixed and adjustable output voltages at currents up to 5.0A. These regulators are protected against over-current conditions and include thermal shutdown protection. The has a composite PNP-NPN output transistor and require an output capacitor for stability. A detailed procedure for selecting this capacitor is as followed. Stability Considerations The output compensation capacitor helps to determine three main characteristics of a linear regulator's performance: start-up delay, load transient response, and loop stability. The capacitor value and type is based on cost, availability, size, and temperature constraints. A tantalum or aluminum electrolytic capacitor is preferred, as a film or ceramic capacitor with almost zero ESR can cause instability. An aluminum electrolytic capacitor is the least expensive type. But when the circuit operates at low temperatures, both the value and ESR of the capacitor will vary widely. For optimum performance over the full operating temperature range, a tantalum capacitor is the best. A 22µF tantalum capacitor will work fine in most applications. But with high current regulators, such as higher capacitance values will improve the transient response and stability. Most applications for involve large changes in load current, so the output capacitor must supply instantaneous load current. The ESR of the output capacitor causes an immediate drop in output voltage given by: V= I ESR In microprocessor applications an output capacitor network of several tantalum and ceramic capacitors in parallel is commonly used. This reduces overall ESR and minimizes the instantaneous output voltage drop under transient load conditions. The output capacitor network should be placed as close to the load as possible for the best results. Protection Diodes When large external capacitors are used with most linear regulator, it is wise to add protection diodes. If the input voltage of the regulator is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of capacitor, output voltage, and rate at which V IN drops. Figure 1 (a),(b) Protection Diode Scheme for Large Output Capacitors 6

7 APPLICATION INFORMATION(CONTINUED) In linear regulators, the discharge path is through a large junction, and protection diodes are normally not needed. However, if the regulator is used with large output capacitance values and the input voltage is instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown above in Figure 1. Output Voltage Sensing series is three terminal regulator, so they cannot provide true remote load sensing. Load regulation is lim-ited by the resistance of the conductors connecting the reg-ulator to the load. For best results, should be con-nected as shown in Figure 2. Requirements series precision linear regulators include thermal shutdown and current limit circuitry to protect the devices. However, high power regulators normally operate at high junction temperatures so it is important to calculate the power dissipation and junction temperatures accurately to be sure that you use and adequate heat sink. The case is connected to V OUT on. so electrical isola-tion may be required for some applications. Thermal com-pound should always be used with high current regulators like. The thermal characteristics of an IC depend on four factors: 1. Maximum Ambient Temperature T A ( C ) 2. Power Dissipation P D (Watts) 3. Maximum Junction Temperature T J ( C ) J 4. Thermal Resistance Junction to ambient R θja ( C /W) These relationship of these four factors is expressed by equation (1): T J =T A +P D R θja...(1) Figure 2 (a),(b) Conductor Parasitic Resistance Effects are Minimized by this Grounding Scheme For Fixed and Maximum ambient temperature and power dissipation are determined by the design while the maximum junc-tion temperature and thermal resistance depend on the manufacturer and the package type. The maximum power dissipation for a regulator is ex-pressed by equation (2): { VIN(max) VOUT(min) } IOUT(max) VIN(max) IQ P D(max) = +... (2) Adjustable Output Regulators 7

8 APPLICATION INFORMATION(CONTINUED) where: V IN(max) is the maximum input voltage, voltage, V OUT(min) is the minimum output voltage, I OUT(max) is the maximum output current, I Q is the maximum quiescent current at V OUT(max). A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC into the air. Each material in the heat flow path between the IC and the environment has a thermal resistance. Like series electrical resistances, these resistance are summed to determine R, the total thermal resistance between the junction and the air. This is expressed by equation (3): R θja =R θjc +R θcs +R θsa...(3) Where all of the following are in /W: R θjc is thermal resistance of junction to case. R θcs is thermal resistance of case to heat sink. R θsa is thermal resistance of heat sink to ambient air. The value for R θja is calculated using equation (3) and the result can be substituted in equation (1). The value for R is 3.5 C /W for a given package type based on an average die size. For a high current regulator such as TH, the majority of the heat is generated in the power transistor section. 8

9 PACKAGE OUTLINE DIMENSIONS TO-252 PACKAGE OUTLINE DIMENSIONS TO-263 PACKAGE OUTLINE DIMENSIONS 9

10 PACKAGE OUTLINE DIMENSIONS TO-220 PACKAGE OUTLINE DIMENSIONS Note : Information provided by IAT is believed to be accurate and reliable. However, we cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an IAT product; nor for any infringement of patents or other rights of third parties that may result from its use. We reserve the right to change the circuitry and specifications without notice. Life Support Policy: IAT does not authorize any IAT product for use in life support devices and/or systems. Life support devices or systems are devices or systems which, (I) are intended for surgical implant into the body or (II) 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. Typical numbers are at 25 C and represent the most likely norm. 10