* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download DN74 - Techniques for Deriving 3.3V from 5V Supplies
Control system wikipedia , lookup
Electrical ballast wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Stray voltage wikipedia , lookup
Solar micro-inverter wikipedia , lookup
Signal-flow graph wikipedia , lookup
Three-phase electric power wikipedia , lookup
Power inverter wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Electrical substation wikipedia , lookup
Voltage optimisation wikipedia , lookup
Integrating ADC wikipedia , lookup
Mains electricity wikipedia , lookup
Current source wikipedia , lookup
Schmitt trigger wikipedia , lookup
Alternating current wikipedia , lookup
Distribution management system wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Two-port network wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Power electronics wikipedia , lookup
Opto-isolator wikipedia , lookup
Current mirror wikipedia , lookup
Network analysis (electrical circuits) wikipedia , lookup
Voltage regulator wikipedia , lookup
advertisement Techniques for Deriving 3.3V from 5V Supplies – Design Note 74 Mitchell Lee Microprocessor chip sets and logic families that operate from 3.3V supplies are gaining acceptance in both desktop and portable computers. Computing rates, and in most cases, energy consumed by these circuits show a strong improvement over 5V technology. The main power supply in most systems is still 5V, necessitating a local 5V to 3.3V regulator. Linear regulators are viable solutions at lower (IO ≤ 1A) currents, but they must have a low dropout voltage in order to maintain regulation with a worst case input of only 4.5V. 5 4.5V TO 5.5V IN 1 OUT 3.3V OUT 700mA + LT1129-3.3 4 SHUTDOWN 2 SENSE GND 3.3µF SOLID TANTALUM DN74 • F01 3 Figure 1. Low Dropout Regulator Delivers 3.3V from 5V Logic Supply Figure 1 shows a circuit that converts a 4.5V minimum input to 3.3V with an output tolerance of only 3% (100mV). The LT1129-3.3 can handle up to 700mA in surface mount configurations, and includes both 16µA shutdown and 50µA standby currents for system sleep modes. Unlike other linear regulators, the LT1129-3.3 combines both low dropout and low voltage operation. Small input and output capacitors facilitate compact, surface mount designs. For the LT1129-3.3, dissipation amounts to a little under 1.5W at full output current. The 5-lead surface mount DD package handles this without the aid of a heat sink, provided the device is mounted over at least 2500mm2 of ground or power supply plane. Efficiency is around 62%. Dissipation in linear regulators becomes prohibitive at higher current levels where they are supplanted by high efficiency switching regulators. A 2A, 5V to 3.3V switching regulator is shown in Figure 2. This synchronous buck converter is implemented with an LTC1148-3.3 converter. The LTC1148 uses both Burst ModeTM operation and continuous, constant off-time control to regulate the output Burst ModeTM is a trademark of Linear Technology Corporation 4.5V TO 5.5V INPUT + C1 1µF + C2 100nF 3 VIN 10 SHUTDOWN P DRIVE 1 Q1 Si9430DY L1 50µH LT1148-3.3 6 ITH R1 1k SENSE + 8 SENSE – 7 R2 0.05Ω 3.3V 2A C6 10nF + 4 C4 3.3nF X7R C3 22µF × 3 25V C5 470pF NPO CT N DRIVE SGND PGND 11 12 14 Q2 Si9410DY D1 MBRS140T3 C7 220µF × 2 10V DN74 • F02 Figure 2. 94% Efficiency Synchronous Buck Regulator Pumps Out 2A at 3.3V from 5V Logic Supply 09/93/74 www.BDTIC.com/Linear voltage, and maintain high efficiency across a wide range Table 2 summarizes the practical current range of a number of output loading conditions. Efficiency as a function of of switching regulators for 5V to 3.3V applications, along with their typical efficiencies. output current is plotted in Figure 3. A 5V to 3.3V converter circuit collection is presented in Application Note 55, covering the entire range of currents listed in Tables 1 and 2. 100 VIN = 5V EFFICIENCY (%) 90 Table 1. Linear Regulators for 5V to 3.3V Conversion 80 LOAD CURRENT 70 60 50 1mA 10mA 100mA DEVICE LT1121-3.3 Shutdown, Small Capacitors 700mA LT1129-3.3 Shutdown, Small Capacitors 800mA LT1117-3.3 SOT-223 1.5A LT1086 DD Package 3A to 7.5A LT1083 LT1084 LT1085 High Current, Low Quiescent Current at High Loads 1A 2A OUTPUT CURRENT DN74 • F03 FEATURES 150mA 2 × LT1087 10A Parallel, Kelvin Sensed Figure 3. LTC1148-3.3: Measured Efficiency Table 2. Switching Regulators for 5V to 3.3V Conversion All of the components used in the Figure 2 switching regulator are surface mount types, including the inductor and shunt resistor, which are traditionally associated with through hole assembly techniques. LOAD CURRENT Depending on the application, a variety of linear and switching regulator circuits are available for output currents ranging from 150mA to 20A. Choices in linear regulators are summarized in Table 1. There are some cases, such as in minicomputers and workstations, where higher dissipations may be an acceptable compromise against the circuit complexity and cost of a switching regulator, hence the >1A entries. Heat sinks are required. DEVICE EFFICIENCY FEATURES 200mA to 400mA LTC1174-3.3 90% Internal P-Channel Switch, 1µA Shutdown 0.5A to 2A LTC1147-3.3 92% 8-Pin SO, High Efficiency Converter 1A to 5A LTC1148-3.3 94% Ultra-High Efficiency Synchronous Converter 5A to 20A LT1158 91% Ultra-High Current Synchronous Converter For literature on our Voltage Regulators, call (800) 637-5545. For applications help, call (408) 432-1900, Ext. 361 Linear Technology Corporation LT/GP 0993 190K 1630 McCarthy Blvd., Milpitas, CA 95035-7487 www.BDTIC.com/Linear (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977 LINEAR TECHNOLOGY CORPORATION 1993