Low-Ripple 250mA Switched Capacitor Step-Down DC/DC Converter

www.DataSheet4U.com LM2771 Low-Ripple 250mA Switched Capacitor Step-Down DC/DC Converter March 2006 LM2771 Low-Ripple 250mA Switched Capacitor Step-Down DC/DC Converter General Description The LM2771 is a switched capacitor step-down regulator that produces a 1.5V output without the use of an inductor. It is capable of supplying loads up to 250mA. The LM2771 operates with an input voltage from 2.7V to 5.5V, and requires only 3 low-cost ceramic capacitors. The LM2771 uses a regulated 0.5x charge pump to give power conversion efficiencies nearly twice as high as an LDO. Pre-regulated 1.1MHz fixed-frequency switching results in very low ripple and noise on both the input and the output. When output currents are low ( < 30mA typ.), the part automatically switches to a low-ripple PFM regulation mode to maintain high efficiency over the entire load range. At input voltages below 3.5V (Typ), the charge pump goes into pass mode, with efficiencies similar to an LDO. The LM2771 is available in National’s 10-pad Leadless Leadframe No-Pullback Package (LLP-10). Features n n n n n n n n n n n n Low-Noise Fixed Frequency Operation 1.5V Output Voltage Li-Ion (3.6V) to 1.5V with 81% Efficiency 1.7% Output Voltage Accuracy Very Low Output Ripple: 8mV @ 250mA Output Currents up to 250mA 2.7V to 5.5V Input Range Shutdown Disconnects Load from VIN 1.1MHz Switching Frequency No Inductors…Small Solution Size Current Limit and Thermal Protection LLP-10 Package (3mm x 3mm x 0.8mm) Applications n DSP, Memory, and Microprocessor Power Supplies n Mobile Phones and Pagers n Portable Electronic Devices Typical Application Circuit LM2771 Efficiency vs. Low-Dropout Linear Regulator (LDO) Efficiency 20183801 20183813 © 2006 National Semiconductor Corporation DS201838 www.national.com LM2771 Connection Diagram and Package Mark Information 10-Pin Non-Pullback Leadless Frame Package (LLP-10) National Semiconductor Package Number SDA10A 20183802 Pin Descriptions Pin # 1 2 3 4 5 6 7 8 9 10 Name VIN GND VOUT NC NC C1C1+ NC GND EN Ground Output Voltage No Connect No Connect Flying Capacitor 1: Negative Terminal Flying Capacitor 1: Positive Terminal No Connect Ground Enable Pin Logic Input. Applying a logic HIGH voltage signal enables the part. A logic LOW voltage signal places the the device in shutdown. Description Input Voltage: Recommended VIN operating range 3.0V to 5.5V. Order Information Output Voltages 1.5V 1.5V Order Number LM2771SD LM2771SDX Package Mark ID XXXXX = CZC2CX YYYYY = L2771 XXXXX = CZC2CX YYYYY = L2771 Package SDA10A Non-Pullback LLP Supplied as: 1000 Units, Tape and Reel 4500 Units, Tape and Reel www.national.com 2 LM2771 Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN Pin Voltage EN Pin Voltage Continuous Power Dissipation (Note 3) Junction Temperature (TJ-MAX) Storage Temperature Range Maximum Lead Temperature (Note 4) ESD Rating (Note 5) Human Body Model: Machine Model -0.3V to 6.0V -0.3V to (VIN+0.3V) w/ 6.0V max Internally Limited 150 C -65oC to +150o C 265oC o Operating Ratings Input Voltage Range (Notes 1, 2) 2.7V to 5.5V 0mA to 250mA -30˚C to +110˚C -30˚C to +85˚C Recommended Load Current Range Junction Temperature (TJ) Range Ambient Temperature (TA) Range (Note 6) Thermal Properties Junction-to-Ambient Thermal Resistance (θJA), LLP10 Package (Note 7) 55˚C/W 2.0kV 200V (Notes 2, 8) o Electrical Characteristics Limits in standard typeface are for TJ = 25 C. Limits in boldface type apply over the full operating junction temperature range (-30˚C ≤ TJ ≤ +110˚C) . Unless otherwise noted, specifications apply to the LM2771 Typical Application Circuit (pg. 1) with: VIN = 3.6V; V(EN) = 1.8V, CIN = C1 = 1.0µF, COUT = 4.7µF. (Note 9) Symbol VOUT Parameter 1.5V Output Voltage Regulation Condition 3.0V ≤ VIN ≤ 5.5V 0mA ≤ IOUT ≤ 200mA 3.0V ≤ VIN ≤ 5.5V IOUT = 150mA 3.0V < VIN ≤ 5.5V, 0mA ≤ IOUT ≤ 250mA VOUT/IOUT VOUT/VIN E IQ VR VR–PFM ISD FSW ROL ICL Output Load Regulation Output Line Regulation Power Efficiency Quiescent Supply Current Fixed Frequency Output Ripple PFM–Mode Output Ripple Shutdown Current Switching Frequency Open–Loop Output Resistance Output Current Limit IOUT = 200mA IOUT = 0mA (Note 10) 40mA ≤ IOUT ≤ 250mA IOUT < 40mA V(EN) = 0V 3.2V ≤ VIN ≤ 5.5V IOUT = 200mA (Note 11) VIN = 5.5V 0V ≤ VOUT ≤ 0.2V (Note 12) 3.0V ≤ VIN ≤ 5.5V 3.0V ≤ VIN ≤ 5.5V V(EN) = 1.8V (Note 13) Logic Input = 0V 0 0.95 5 0.1 0.80 VOUT = 1.5V 0mA ≤ IOUT ≤ 250mA Min 1.455 (−3%) 1.475 (−1.7%) 1.445 (−3.7%) Typ 1.5 1.5 1.5 0.17 0.1 81 45 8 12 0.1 1.1 1.0 500 0.5 1.40 50 Max 1.545 (+3%) 1.525 (+1.7%) 1.545 (+3%) mV/mA %/V % µA mV mV µA MHz Ω mA Units V tON VIL VIH IIH IIL Turn-on Time Logic-low Input Voltage Logic-high Input Voltage Logic-high Input Current Logic-low Input Current 150 0.5 VIN µs V V µA µA Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: All voltages are with respect to the potential at the GND pins. Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150oC (typ.) and disengages at TJ=140oC (typ.). 3 www.national.com LM2771 Electrical Characteristics (Notes 2, 8) (Continued) Note 4: For detailed information on soldering requirements and recommendations, please refer to National Semiconductor’s Application Note 1187 (AN-1187): Leadless Leadframe Package (LLP). Note 5: The Human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly into each pin. MIL-STD-883 3015.7 Note 6: Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 110oC), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA x PD-MAX). Note 7: Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues. Note 8: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. Note 9: CIN, COUT, C1: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics. Note 10: VOUT is set to 1.6V during this test. Note 11: Open loop output resistance can be used to predict output voltage when, under low VIN and high IOUT conditions, VOUT falls out of regulation. VOUT = VIN/2 − (ROL x IOUT) Note 12: Maximum input current is equal to half the maximum output current for buck-mode switched capacitor converters. Note 13: There is a 350kΩ pull-down resistor connected internally between the EN pin and GND. Block Diagram 20183803 www.national.com 4 LM2771 Typical Performance Characteristics Unless otherwise specified: VIN = 3.6V, CIN = C1 = 1.0µF, COUT = 4.7µF, TA = 25oC. Capacitors are low-ESR multi-layer ceramic capacitors (MLCC’s). Output Voltage vs. Input Voltage Output Voltage vs. Output Current 20183812 20183814 Efficiency vs. Input Voltage Efficiency vs. Output Current 20183813 20183826 Input Voltage Ripple, Load=6Ω(250mA) Output Voltage Ripple, Load=6Ω(250mA) 20183815 20183821 CH1: VIN, CIN = 1µF; Scale: 50mV/Div, AC Coupled CH2: VIN, CIN = 10µF; Scale: 50mV/Div, AC Coupled Time scale: 200ns/Div CH2: VOUT, COUT = 4.7µF; Scale: 20mV/Div, AC Coupled Time scale: 200ns/Div 5 www.national.com LM2771 Typical Performance Characteristics Unless otherwise specified: VIN = 3.6V, CIN = C1 = 1.0µF, COUT = 4.7µF, TA = 25oC. Capacitors are low-ESR multi-layer ceramic capacitors (MLCC’s). (Continued) Load Step, 15mA to 200mA Load Step, 200mA to 15mA 20183823 20183824 CH2: VOUT; Scale: 20mV/Div, AC Coupled CH4: IOUT; Scale: 200mA/Div Time scale: 20µs/Div CH2: VOUT; Scale: 20mV/Div, AC Coupled CH4: IOUT; Scale: 200mA/Div Time scale: 10µs/Div Line Step, 3.6V to 4.5V with Load=7.5Ω(200mA) Oscillator Frequency vs. Input Voltage 20183822 CH1: VIN; Scale: 1V/Div, AC Coupled CH2: VOUT; Scale: 20mV/Div, AC Coupled Time scale: 40µs/Div 20183825 Startup and Shutdown Behavior, Load=6Ω(250mA) 20183816 CH1: VEN; Scale: 2V/Div, DC Coupled CH2: VOUT; Scale: 500mV/Div, DC Coupled Time scale: 100µs/Div www.national.com 6 LM2771 Operation Description OVERVIEW The LM2771 is a switched capacitor converter that produces a regulated, low voltage output. The core of the part is a highly efficient charge pump that utilizes fixed frequency pre-regulation and Pulse Frequency Modulation to minimize ripple and power losses over wide input voltage and output current ranges. A description of the principal operational characteristics of the LM2771 is detailed in the Circuit Description, and Efficiency Performance sections. These sections refer to details in the Block Diagram. CIRCUIT DESCRIPTION The core of the LM2771 is a two-phase charge pump controlled by an internally generated non-overlapping clock. The charge pump operates by using an external flying capacitor, C1, to transfer charge from the input to the output. At input voltages below 3.5V (typ.) the LM2771 operates in a "pass mode", with the input current being equal to the load current. At input voltages above 3.5V (typ.) the part utilizes a gain of 1⁄2, resulting in an input current equa