LT1765EFE-3.3

LT1765/LT1765-1.8/LT1765-2.5/ LT1765-3.3/LT1765-5 Monolithic 3A, 1.25MHz Step-Down Switching Regulator FEATURES DESCRIPTION n The LT®1765 is a 1.25MHz monolithic buck switching regulator. A high efficiency 3A, 0.09Ω switch is included on the die together with all the control circuitry required to construct a high frequency, current mode switching regulator. Current mode control provides fast transient response and excellent loop stability. n n n n n n n n n n 3A Switch in a Thermally Enhanced 16-Lead TSSOP or 8-Lead SO Package Constant 1.25MHz Switching Frequency Wide Operating Voltage Range: 3V to 25V High Efficiency 0.09Ω Switch 1.2V Feedback Reference Voltage Uses Low Profile Surface Mount Components Low Shutdown Current: 15μA Synchronizable to 2MHz Current Mode Loop Control Constant Maximum Switch Current Rating at All Duty Cycles* Available in 8-Lead SO and 16-Lead Thermally Enhanced TSSOP Packages New design techniques achieve high efficiency at high switching frequencies over a wide operating voltage range. A low dropout internal regulator maintains consistent performance over a wide range of inputs from 24V systems to Li-Ion batteries. An operating supply current of 1mA improves efficiency, especially at lower output currents. Shutdown reduces quiescent current to 15μA. Maximum switch current remains constant at all duty cycles. Synchronization allows an external logic level signal to increase the internal oscillator into the range of 1.6MHz to 2MHz. APPLICATIONS n n n n n DSL Modems Portable Computers Regulated Wall Adapters Battery-Powered Systems Distributed Power Full cycle-by-cycle current control and thermal shutdown are provided. High frequency operation allows the reduction of input and output filtering components and permits the use of chip inductors. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. *Patent Pending TYPICAL APPLICATION 5V to 3.3V Step-Down Converter Efficiency vs Load Current 90 CMDSH-3 VIN = 10V VOUT = 5V 0.18μF 1.5μH BOOST VIN VSW LT1765-3.3 OFF ON SHDN SYNC OUTPUT 3.3V 2.5A FB GND VC 2.2nF UPS120 4.7μF CERAMIC 1765 TA01 EFFICIENCY (%) 85 INPUT 5V 2.2μF CERAMIC 80 75 70 0 1.0 1.5 0.5 SWITCH CURRENT (A) 2.0 1765 • TAO1a 1765fd 1 LT1765/LT1765-1.8/LT1765-2.5/ LT1765-3.3/LT1765-5 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage ........................................................... 25V BOOST Pin Above SW ............................................. 20V Max BOOST Pin Voltage ............................................35V SHDN Pin ................................................................. 25V FB Pin Current......................................................... 1mA SYNC Pin Current ................................................... 1mA Operating Junction Temperature Range (Note 2)................................................. –40°C to 125°C Storage Temperature Range ................. –65°C to 150°C Lead Temperature (Soldering, 10 sec) ................ 300°C PIN CONFIGURATION TOP VIEW GND 1 16 GND BOOST 2 15 NC VIN 3 14 SYNC VIN 4 13 VC SW 5 SW 6 11 SHDN NC 7 10 NC GND 8 9 17 TOP VIEW BOOST 1 12 FB 8 SYNC VIN 2 7 VC SW 3 6 FB GND 4 5 SHDN S8 PACKAGE 8-LEAD PLASTIC SO GND TJMAX = 125°C, θJA = 90°C/W, θJC(PIN 4) = 30°C/W GROUND PIN CONNECTED TO LARGE COPPER AREA FE PACKAGE 16-LEAD PLASTIC TSSOP θJA = 45°C/W, θJC(PAD) = 10°C/W EXPOSED PAD (PIN 17) SOLDERED TO LARGE COPPER PLANE ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1765EFE#PBF LT1765EFE#TRPBF 1765EFE 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-1.8#PBF LT1765EFE-1.8#TRPBF 1765EFE-1.8 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-2.5#PBF LT1765EFE-2.5#TRPBF 1765EFE-2.5 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-3.3#PBF LT1765EFE-3.3#TRPBF 1765EFE-3.3 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-5#PBF LT1765EFE-5#TRPBF 1765EFE-5 16-Lead Plastic TSSOP –40°C to 125°C LT1765ES8#PBF LT1765ES8#TRPBF 1765 8-Lead Plastic SO –40°C to 125°C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1765EFE LT1765EFE#TR 1765EFE 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-1.8 LT1765EFE-1.8#TR 1765EFE-1.8 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-2.5 LT1765EFE-2.5#TR 1765EFE-2.5 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-3.3 LT1765EFE-3.3#TR 1765EFE-3.3 16-Lead Plastic TSSOP –40°C to 125°C LT1765EFE-5 LT1765EFE-5#TR 1765EFE-5 16-Lead Plastic TSSOP –40°C to 125°C LT1765ES8 LT1765ES8#TR 1765 8-Lead Plastic SO –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 1765fd 2 LT1765/LT1765-1.8/LT1765-2.5/ LT1765-3.3/LT1765-5 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 15V, VC = 0.8V, Boost = VIN + 5V, SHDN, SYNC and switch open unless otherwise noted. PARAMETER CONDITIONS Maximum Switch Current Limit 3.3V < VIN < 25V l Switch On Voltage Drop I = 3A l VIN Undervoltage Lockout (Note 3) l Oscillator Frequency MIN TYP MAX 3 4 6 1.1 1.25 1.6 MHz 270 430 mV 2.6 2.73 V 1 1.3 mA 15 35 55 μA μA 1.2 1.218 1.224 V V 2.47 l VIN Supply Current Shutdown Supply Current VSHDN = 0V, VIN = 25V, VSW = 0V Feedback Voltage 3V < VIN < 25V, 0.4V < VC < 0.9V (Note 3) l LT1765 (Adj) l 1.182 1.176 UNITS A LT1765-1.8 l 1.764 1.8 1.836 V LT1765-2.5 l 2.45 2.5 2.55 V LT1765-3.3 l 3.234 3.3 3.366 V LT1765-5 l 4.9 FB Input Current LT1765 (Adj) l FB Input Resistance LT1765-1.8 LT1765-2.5 LT1765-3.3 LT1765-5 l l l l FB Error Amp Voltage Gain 0.4V < VC < 0.9V 5 5.1 V –0.25 –0.5 μA 10.5 14.7 19 29 15 21 27.5 42 21 30 39 60 kΩ kΩ kΩ kΩ 150 350 FB Error Amp Transconductance ΔIVC = ±10μA l 500 850 1300 μMho VC Pin Source Current VFB = VNOM – 17% l 80 120 160 μA VC Pin Sink Current VFB = VNOM + 17% l 70 110 180 μA VC Pin to Switch Current Transconductance VC Pin Minimum Switching Threshold 5 Duty Cycle = 0% A/V 0.4 VC Pin 3A ISW Threshold 0.9 V 90 % % Maximum Switch Duty Cycle VC = 1.2V, ISW = 800mA, VIN = 6V Minimum Boost Voltage Above Switch ISW = 3A l 1.8 2.7 V Boost Current ISW = 1A (Note 4) ISW = 3A (Note 4) l l 20 70 30 140 mA mA l 85 80 V SHDN Threshold Voltage l 1.27 1.33 1.40 V SHDN Threshold Current Hysteresis l 4 7 10 μA l –7 –10 –13 μA 1.5 2.2 V SHDN Input Current (Shutting Down) SHDN = 60mV Above Threshold SYNC Threshold Voltage SYNC Input Frequency SYNC Pin Resistance 1.6 ISYNC = 1mA Note 1: 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 2: The LT1765E is guaranteed to meet performance specifications from 0°C to 125°C. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. 2 20 MHz kΩ Note 3: Minimum input voltage is defined as the voltage where the internal regulator enters lockout. Actual minimum input voltage to maintain a regulated output will depend on output voltage and load current. See Applications Information. Note 4: Current flows into the BOOST pin only during the on period of the switch cycle. 1765fd 3 LT1765/LT1765-1.8/LT1765-2.5/ LT1765-3.3/LT1765-5 TYPICAL PERFORMANCE CHARACTERISTICS FB vs Temperature (Adj) Switch On Voltage Drop 1.220 350 1.215 300 SWITCH VOLTAGE (mV) FB VOLTAGE (V) 1.210 1.205 1.200 1.195 1.190 TA = 125°C 250 200 TA = –40°C 150 TA = 25°C 100 50 1.185 1.180 –50 0 –25 0 25 50 75 100 2 1 SWITCH CURRENT (A) 0 125 TEMPERATURE (°C) 3 1765 G02 1765 G01 SHDN Threshold vs Temperature Oscillator Frequency 1.40 1.50 1.45 1.38 SHDN THRESHOLD (V) FREQUENCY (MHz) 1.40 1.35 1.30 1.25 1.20 1.36 1.34 1.32 1.15 1.10 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 1.30 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 1765 G04 1765 G03 SHDN Supply Current vs VIN SHDN IP Current vs Temperature 7 7 SHDN = 0V SHDN = 0V 6 6 5 5 VIN CURRENT (μA) VIN CURRENT (μA) 125 4 3 2 4 3 2 1 1 0 0 0 5 10 15 VIN (V) 20 25 30 1765 G05 0 5 10 15 VIN (V) 20 25 30 1765 G05 1765fd 4 LT1765/LT1765-1.8/LT1765-2.5/ LT1765-3.3/LT1765-5 TYPICAL PERFORMANCE CHARACTERISTICS Minimum Input Voltage for 2.5V Out SHDN Supply Current 3.5 300 VIN = 15V 250 VIN CURRENT (μA) INPUT VOLTAGE (V) 3.3 3.1 2.9 2.7 200 150 100 50 2.5 0.001 0.1 0.01 LOAD CURRENT (A) 0 1 0 0.2 0.4 0.6 0.8 1 1.2 SHUTDOWN VOLTAGE (V) 1765 G07 1765 G08 Input Supply Current Current Limit Foldback 1200 SWITCH PEAK CURRENT (A) UNDERVOLTAGE LOCKOUT 600 400 4 40 3 30 SWITCH CURRENT 2 20 1 10 FB CURRENT 200 0 0 0 5 10 15 20 INPUT VOLTAGE (V) 25 30 0 0.2 0.4 0.6 0.8 FEEDBACK VOLTAGE (V) 0 1.2 1 1765 G10 1765 G09 Maximum Load Current, VOUT = 5V Maximum Load Current, VOUT = 2.5V 3.0 3.0 L = 4.7μH 2.8 L = 4.7μH OUTPUT CURRENT (A) OUTPUT CURRENT (A) FB INPUT CURRENT (μA) VIN CURRENT (μA) 1000 800 1.4 2.6 2.4 L = 2.2μH 2.8 L = 2.2μH 2.6 L = 1.5μH 2.4 2.2 L = 1.5μH 2.2 2.0 0 5 10 15 INPUT VOLTAGE (V) 20 25 1765 G11 0 5 10 15 INPUT VOLTAGE (V) 20 25 1765 G12 1765fd 5 LT1765/LT1765-1.8/LT1765-2.5/ LT1765-3.3/LT1765-5 PIN FUNCTIONS FB: The feedback pin is used to set output voltage using an external voltage divider (adjustable version) that generates 1.2V at the pin when connected to the desired output voltage. The fixed voltage 1.8V, 2.5V, 3.3V and 5V versions have the divider network included internally and the FB pin is connected directly to the output. If required, the current limit can be reduced during start up or short-circuit when the FB pin is below 0.5V (see the Current Limit Foldback graph in the Typical Performance Characteristics section). An impedance of less than 5kΩ on the adjustable version at the FB pin is needed for this feature to operate. BOOST: The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. VIN: This is the collector of the on-chip power NPN switch. This pin powers the internal circuitry and internal regulator. At NPN switch on and off, high di/dt edges occur on this pin. Keep the external bypass capacitor and catch diode close to this pin. All trace inductance on this path will create a voltage spike at switch off, adding to the VCE voltage across the internal NPN. Both VIN pins of the TSSOP package must be shorted together on the PC board. GND: The GND pin acts as the reference for the regulated output, so load regulation will suffer if the “ground” end of the load is not at the same voltage as the GND pin of the IC. This condition will occur when load current or other currents flow through metal paths between the GND pin and the load ground point. Keep the ground path short between the GND pin and the load and use a ground plane when possible. Keep the path between the input bypass and the GND pin short. The exposed GND pad and/or GND pins of the package are directly attached to the internal tab. These pins/pad should be attached to a large copper area to reduce thermal resistance. VSW: The switch pin is the emitter of the on-chip power NPN switch. This pin is driven up to the input pin voltage during switch on time. Inductor current drives the switch pin negative during switch off time. Negative voltage must be clamped with an external catch diode with a VBR