LT1767EMS8-5

LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 Monolithic 1.5A, 1.25MHz Step-Down Switching Regulators U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 1.5A Switch in a Small MSOP Package Constant 1.25MHz Switching Frequency High Power Exposed Pad (MS8E) Package Wide Operating Voltage Range: 3V to 25V High Efficiency 0.22Ω Switch 1.2V Feedback Reference Voltage Fixed Output Voltages of 1.8V, 2.5V, 3.3V, 5V 2% Overall Output Tolerance Uses Low Profile Surface Mount Components Low Shutdown Current: 6µA Synchronizable to 2MHz Current Mode Loop Control Constant Maximum Switch Current Rating at All Duty Cycles* U APPLICATIO S ■ ■ ■ ■ ■ DSL Modems Portable Computers Wall Adapters Battery-Powered Systems Distributed Power The LT®1767 is a 1.25MHz monolithic buck switching regulator. A high efficiency 1.5A, 0.22Ω switch is included on the die together with all the control circuitry required to complete a high frequency, current mode switching regulator. Current mode control provides fast transient response and excellent loop stability. New design techniques achieve high efficiency at high switching frequencies over a wide operating range. A low dropout internal regulator maintains consistent performance over a wide range of inputs from 24V systems to LiIon batteries. An operating supply current of 1mA improves efficiency, especially at lower output currents. Shutdown reduces quiescent current to 6µA. Maximum switch current remains constant at all duty cycles. Synchronization allows an external logic level signal to increase the internal oscillator from 1.4MHz to 2MHz. The LT1767 is available in an 8-pin MSOP fused leadframe package and a low thermal resistance exposed pad package. Full cycle-by-cycle short-circuit protection and thermal shutdown are provided. High frequency operation allows the reduction of input and output filtering components and permits the use of chip inductors. , LTC and LT are registered trademarks of Linear Technology Corporation. *Patent Pending U TYPICAL APPLICATIO Efficiency vs Load Current 95 12V to 3.3V Step-Down Converter D2 CMDSH-3 C3 2.2µF CERAMIC L1 5µH BOOST VIN 12V VIN OPEN OR HIGH = ON VSW LT1767-3.3 SHDN SYNC OUTPUT 3.3V 1.2A* EFFICIENCY (%) C2 0.1µF VIN = 10V VOUT = 5V 90 85 VIN = 5V VOUT = 3.3V 80 FB GND VC CC 1.5nF D1 UPS120 C1 10µF CERAMIC RC 4.7k *MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING. 75 70 0 1767 TA01 0.2 0.4 0.6 0.8 1 LOAD CURRENT (A) 1.2 1.4 1767 TA01a sn1767 1767fas 1 LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 W W U W ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage .......................................................... 25V BOOST Pin Above SW ............................................ 20V Max BOOST Pin Voltage .......................................... 35V SHDN Pin ............................................................... 25V FB Pin Voltage .......................................................... 6V FB Pin Current ....................................................... 1mA SYNC Pin Current .................................................. 1mA Operating Junction Temperature Range (Note 2) LT1767E .......................................... – 40°C to 125°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C U W U PACKAGE/ORDER INFORMATION ORDER PART NUMBER ORDER PART NUMBER TOP VIEW BOOST VIN SW GND 1 2 3 4 8 7 6 5 SYNC VC FB SHDN MS8 PACKAGE 8-LEAD PLASTIC MSOP LT1767EMS8 LT1767EMS8-1.8 LT1767EMS8-2.5 LT1767EMS8-3.3 LT1767EMS8-5 TJMAX = 125°C, θJA = 110°C/W MS8 PART MARKING GROUND PIN CONNECTED TO LARGE COPPER AREA LTLS LTWG LTWD LTWE LTWF MS8E PACKAGE 8-LEAD PLASTIC MSOP LT1767EMS8E LT1767EMS8E-1.8 LT1767EMS8E-2.5 LT1767EMS8E-3.3 LT1767EMS8E-5 TJMAX = 125°C, θJA = 40°C/W MS8E PART MARKING TOP VIEW BOOST VIN SW GND 1 2 3 4 8 7 6 5 SYNC VC FB SHDN EXPOSED GND PAD CONNECTED TO LARGE COPPER AREA ON PCB LTZG LTZH LTZJ LTZK LTZL Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● 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 CONDITION MIN TYP MAX Maximum Switch Current Limit TA = 0°C to 125°C TA = < 0°C 1.5 1.3 2 3 3 Oscillator Frequency 3.3V < VIN < 25V 1.1 1.1 1.25 1.4 1.5 MHz MHz 330 400 500 mV mV 2.6 2.73 V 1 1.3 mA 6 20 45 µA µA ● Switch On Voltage Drop ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C ● VIN Undervoltage Lockout (Note 3) ● VIN Supply Current VFB = VNOM + 17% ● Shutdown Supply Current VSHDN = 0V, VIN = 25V, VSW = 0V 2.47 ● Feedback Voltage FB Input Current 3V < VIN < 25V, 0.4V < VC < 0.9V (Note 3) LT1767 (Adj) LT1767 (Adj) UNITS A A 1.182 1.176 1.2 ● 1.218 1.224 V V LT1767-1.8 ● 1.764 1.8 1.836 V LT1767-2.5 ● 2.45 2.5 2.55 V LT1767-3.3 ● 3.234 3.3 3.366 V LT1767-5 ● 4.9 5 5.1 V – 0.25 – 0.5 ● µA sn1767 1767fas 2 LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 ELECTRICAL CHARACTERISTICS The ● 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 CONDITION FB Input Resistance LT1767-1.8 LT1767-2.5 LT1767-3.3 LT1767-5 MIN TYP MAX ● ● ● ● 10.5 14.7 19 29 15 21 27.5 42 21 30 39 60 UNITS kΩ kΩ kΩ kΩ Error Amp Voltage Gain 0.4V < VC < 0.9V 150 350 Error Amp Transconductance ∆IVC = ±10µA ● 500 850 1300 µMho VC Pin Source Current VFB = VNOM – 17% ● 80 120 160 µA VC Pin Sink Current VFB = VNOM + 17% ● 70 110 180 µA VC Pin to Switch Current Transconductance VC Pin Minimum Switching Threshold Duty Cycle = 0% VC Pin 1.5A ISW Threshold 85 80 2.5 A/V 0.35 V 0.9 V 90 % % Maximum Switch Duty Cycle VC = 1.2V, ISW = 400mA Minimum Boost Voltage Above Switch ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C ● 1.8 2.7 V Boost Current ISW = – 0.5A (Note 4) ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C (Note 4) ● ● 10 30 15 45 mA mA ● SHDN Threshold Voltage ● 1.27 1.33 1.40 V SHDN Input Current (Shutting Down) SHDN = 60mV Above Threshold ● –7 –10 –13 µA SHDN Threshold Current Hysteresis SHDN = 100mV Below Threshold ● 4 7 10 µA 1.5 2.2 SYNC Threshold Voltage SYNC Input Frequency 1.5 SYNC Pin Resistance ISYNC = 1mA V 2 MHz 20 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1767E 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. 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. U W TYPICAL PERFORMANCE CHARACTERISTICS FB vs Temperature (Adj) Switch On Voltage Drop 1.22 Oscillator Frequency 1.50 400 125°C 1.45 350 1.20 1.19 1.18 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 1767 G01 1.40 25°C 300 FREQUENCY (MHz) SWITCH VOLTAGE (mV) FB VOLTAGE (V) 1.21 250 –40°C 200 150 1.35 1.30 1.25 100 1.20 50 1.15 0 0 0.5 1 SWITCH CURRENT (A) 1.5 1767 G02 1.10 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 1767 G03 sn1767 1767fas 3 LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 U W TYPICAL PERFOR A CE CHARACTERISTICS SHDN Threshold vs Temperature SHDN Supply Current vs VIN 1.40 SHDN IP Current vs Temperature 7 –12 SHDN = 0V 6 –10 1.36 1.34 SHUTTING DOWN 5 SHDN INPUT (µA) VIN CURRENT (µA) SHDN THRESHOLD (V) 1.38 4 3 –8 –6 –4 2 1.32 –2 1 1.30 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 0 125 STARTING UP 0 5 10 15 VIN (V) 20 25 1767 G04 0 –50 30 –25 0 25 50 75 TEMPERATURE (°C) 100 1767 G06 1767 G05 Minimum Input Voltage for 2.5V Out SHDN Supply Current 3.5 125 Input Supply Current 1200 300 VIN = 15V 3.1 2.9 2.7 VIN CURRENT (µA) VIN CURRENT (µA) 200 150 100 0.1 0.01 LOAD CURRENT (A) 0 1 0.2 0 0.4 0.6 0.8 1 1.2 SHUTDOWN VOLTAGE (V) 1767 G07 400 0 1.4 0 5 10 15 20 INPUT VOLTAGE (V) 2.0 40 1.5 30 Maximum Load Current, VOUT = 2.5V 1.5 1.5 L = 4.7µH 0.5 10 FB CURRENT 0 0 0.2 0.4 0.6 0.8 FEEDBACK VOLTAGE (V) FB INPUT CURRENT (µA) 20 OUTPUT CURRENT (A) 1.3 SWITCH CURRENT 30 1767 G09 Maximum Load Current, VOUT = 5V 1.0 25 1767 G08 Current Limit Foldback SWITCH PEAK CURRENT (A) 600 200 50 2.5 0.001 MINIMUM INPUT VOLTAGE 800 L = 4.7µH OUTPUT CURRENT (A) INPUT VOLTAGE (V) 1000 250 3.3 1.1 0.9 L = 2.2µH 1.3 L = 2.2µH 1.1 L = 1.5µH 0.9 0.7 L = 1.5µH 1 0 1.2 1767 G10 0.5 0.7 0 5 10 15 INPUT VOLTAGE (V) 20 25 1767 G11 0 5 10 15 INPUT VOLTAGE (V) 20 25 1767 G12 sn1767 1767fas 4 LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5 U U U PIN FUNCTIONS FB: The feedback pin is used to set output voltage using an external voltage divider that generates 1.2V at the pin with 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 (adjustable part only) 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. Without this added voltage, the typical switch voltage loss would be about 1.5V. The additional boost voltage allows the switch to saturate and voltage loss approximates that of a 0.22Ω FET structure. 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 in this path will create a voltage spike at switch off, adding to the VCE voltage across the internal NPN. 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 GND pin of the MS8 package is directly attached to the internal tab. This pin should be attached to a large copper area to improve thermal resistance. The exposed pad of the MS8E package is also connected to GND. This should be soldered to a large copper area to improve its 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