LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET KEY FEATURES DESCRIPTION The LX1918 MODE feature can either maximize efficiency or reduce EMI depending on the needs of the application. High efficiency (MODE = GND) is obtained by allowing the LX1918 to enter a PFM mode with discontinuous inductor current. Low EMI (MODE=VCC) is obtained by only operating in PWM mode even at no load. The LX1918 features include soft start, cycle-by-cycle switch current limit, hiccup short circuit current limiting and thermal shut down. The LX1918 comes in small 8 pin MLP package (fully RoHS compliant). Input range voltage 2.7 to 5.5V Maximum output current, 1.8A Internal or External Synchronization Output Voltage from VIN to 0.6V PFM or PWM mode under light load EMI support with force PWM mode Efficiency up to 95% No external Schottky diode Thermal shutdown Cycle by cycle switch current limit UVLO Short circuit protection 8 pin MLP WWW . Microsemi .C OM The Microsemi LX1918 is a step down buck regulator with a synchronous rectifier. All MOSFET switches and compensation components are built in. The synchronous rectification eliminates the need of an external Schottky diode and maximizes efficiency (>95%) for a high step-down ratio and a low output voltage. The input supply voltage range is from 2.7V to 5.5V with a maximum output current of 1.8A. The LX1918 is a current mode PWM with optional PFM under light loads. The LX1918 can switch with a 1MHz free running internal oscillator or be synchronized with an external oscillator ranging from 500KHz to 1.25MHz; the high frequency allows for small size and low cost external components. The LX1918 output voltage is programmable with two resistors and can be tightly regulated down to 0.6V. APPLICATIONS IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com Lower power embedded applications WLAN power system Portable design with single cell Lion or 3 cells NiMH/NiCd Low power portable storage application PRODUCT HIGHLIGHT VIN VCC PWR VOUT @ 1.8 A SW MODE LX1918 ON OFF E/S FB PGND SGND LX1918 PACKAGE ORDER INFO TA (°C) LD Plastic MLP 8-Pin 3x3mm RoHS Compliant / Pb-free -40 to 85 LX1918CLD Note: Available in Tape & Reel. Append the letters “TR” to the part number.(i.e. LX1918CLD-TR) Copyright © 2004 Rev. 1.1, 2005-07-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET ABSOLUTE MAXIMUM RATINGS PACKAGE PIN OUT 1 8 E/S FB 2 7 3 6 4 5 MODE SGND VCC PGND PWR SW LD PACKAGE (Top View) 1918 xxxx MSC Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal. THERMAL DATA LD WWW . Microsemi .C OM Supply Input Voltage (PWR, VCC)..................................................-0.3V to 6.5V Supply Input Transient Voltage (PWR, VCC).................................................10V Input Voltage (E/S, FB,MODE) ......................................... -0.3V to (VCC + 0.3V) Maximum Switch Voltage (SW)....................................... -0.3V to (VPWR + 0.3V) SW Peak Current (Internally Limited)............................................................3.6A Operating Ambient Temperature Range ........................................-40°C to +85°C Operating Junction Temperature Range.......................................-40°C to +125°C Maximum Operating Junction Temperature ................................................ 150°C Storage Temperature Range...........................................................-65°C to 150°C Peak Package Solder Reflow Temp. (40 second max. exposure) ... 260°C (+0, -5) LD PACKAGE MARKINGS Plastic MLP 3mm X 3mm 8-Pin “xxxx” Denote Date Code and Lot Identification THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 35 – 50°C/W RoHS / Pb-free 100% Matte Tin Lead Finish Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. The variation in overall thermal resistance, ΘJA, is directly affected by heatsink area available on the PCB. FUNCTIONAL PIN DESCRIPTION PIN Name 1 FB 2 SGND 3 PGND 4 SW 5 PWR 6 VCC MODE 8 E/S Copyright © 2004 Rev. 1.1, 2005-07-05 Signal Ground – Low current signal ground reference for IC; also attaches to bottom pad. Connect to common ground reference. Ground – High current ground; connects to common ground reference. MOSFET Switch (Drain) Connects for inductor. Power Input – Connect a decoupled voltage source between 2.7V and 5.5V. Reference power supply for IC. Light Load Mode Select - Ground for Highest efficiency mode or pull high for Lowest EMI mode during light load operation. Enable and External Synchronization – Pull high to enable operation with internal oscillator. Apply an external oscillator signal to synchronize the PWM switch frequency. Apply logic low to cause IC to enter Shutdown mode. Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 PACKAGE DATA 7 Description Feedback Pin - This pin is regulated to the internal reference voltage. LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET ELECTRICAL CHARACTERISTICS Parameter ` Symbol Test Conditions Min ≤ 85°C3 except LX1918 Typ Max Units ENTIRE REGULATOR Input Voltage3 Efficiency1 Quiescent Current • Active • Shutdown Line Regulation1 Load Regulation1 Feedback Voltage FB Input Current Internal Oscillator frequency E/S Pin Bias Current E/S Logic High Input E/S Logic Low Input SYNC Capture Range SYNC Minimum Pulse Width MODE Bias Current MODE Logic High VPWR, VCC η VOUT = 1.8V, IOUT = 200mA MODE Logic Low V MODE(LO) SW Pin Current Limit Thermal Shutdown Threshold1 Under Voltage Lockout Notes 1. 2. 3. ICC VFB IFB FOSC 2.7 VE/S = 3.6V; VFB = 1.0V; T = 25°C VE/S = GND VIN = 2.7 to 5.5V IOUT = 10mA to 1.5A VFB = 0.5V to 0.7V VE/S = 3.6V; VMODE= 3.6V VE/S = GND VE/S(HI) VE/S(LO) 6.0 V % 500 1.0 µA 92 0.588 -50 0.75 350 0.5 1 1 0.600 1.00 0.1 0.612 50 1.25 1.0 1.6 VMODE= 3.6V High or Low; VMODE= 3.6V VE/S = GND: VMODE= VIN VMODE(HI) 0.4 1250 500 100 1.0 2.0 0.9 x VIN Peak Current 2.0 130 VUVLO 2.7 140 0.1 x VIN 3.6 150 2.7 % % V nA MHz µA WWW . Microsemi .C OM Unless otherwise specified, the following specifications apply over the operating ambient temperature2 -40°C ≤ TA where otherwise noted and the following test conditions: VIN = 3.7V; VE/S = 3.7V; VMODE = GND V kHz ns µA V A °C V Guaranteed by design, but not tested. Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature. Functionality over the -40°C to +85°C operating temperature range is assured by design, characterization, and correlation. ELECTRICALS Copyright © 2004 Rev. 1.1, 2005-07-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET SIMPLIFIED BLOCK DIAGRAM WWW . Microsemi .C OM PWR VCC 2.7A UVLO AND ENABLE LOGIC Soft Start Ramp and Cur Limit Clamp 0mA Current Limit + + - Current Sense Slope Compensation VREF OR ADJ + FB - gm Error Amp Compensation FET Drivers SW Cur Limit Turn on Blanking S Q Thermal Overload - Q + R Synchronous FET Driver LOGIC Reverse Current Detect PGND CLOCK LOGIC E/S CCO <1 MHZ LIMITER SGND MODE Figure 1 – Simplified Block Diagram ELECTRICALS Copyright © 2004 Rev. 1.1, 2005-07-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET APPLICATION CIRCUITS 4.7µF LX1918 PWR 40.2 0.1µF L1 1.8V @ 1.5A SW 3.3µH VCC 47µF LX1918FB E/S MODE PGND ON OFF 20K R1 10K R2 WWW . Microsemi .C OM VIN = 2.7 to 5.5V SGND Figure 2 – Typical Application: Highest Light Load Efficiency Mode During Light Load With Internal 1MHz PWM Frequency VIN = 2.7 to 5.5V 4.7µF LX1918 PWR 40.2 0.1µF L1 1.5V @ 1.5A SW 3.3µH VCC LX1918FB 47µF E/S MODE PGND 15k R1 10k R2 SGND 500kHz APPLICATIONS Figure 3 – Typical Application: PWM Low EMI Mode Operation During Light Load With External 500kHz Synchronization Copyright © 2004 Rev. 1.1, 2005-07-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET THEORY OF OPERATION If MODE pin is LOW, discontinuous current is selected. The PWM frequency slows down as the load decreases and this reduces switching losses. In this mode, the NMOS switch turns off to prevent negative current flow and allows the inductor current to reduce to zero (which is known as discontinuous conduction mode). Comparing the efficiency of the two modes of operation under light loading, when IOUT = 25mA, LX1918 efficiency is 80% (MODE=GND) and 68% (MODE=VCC). Switching frequency The E/S pin has dual function. If E/S pin pulls HIGH, the 1MHz internal oscillator is enabled. If E/S pin is held LOW, the LX1918 will enter Shut Down mode. Designers can apply an external oscillator signal, 500 KHz to 1.25MHz, to E/S pin to synchronize the switching frequency to a system clock. When applying external oscillator signal, the MODE pin must pull up to VCC activating the forced PWM mode. High Efficiency Operation: PFM, PWM, and EMI force PWM modes WWW . Microsemi .C OM LX1918 is synchronous step down converter with input voltage range from 2.7V to 5.5V; and outputs ranging from 0.6V to 80% of VIN. The LX1918 can deliver a maximum output current up to 1.8A. The LX1918 has two selectable operating modes for light loads: high efficiency PFM (MODE=GND) or low noise forced PWM (MODE=VCC). Under heavy load, LX1918 always operates in PWM mode and switches at fixed internal 1MHz frequency or can be synchronized with an external oscillator clock with a frequency ranging from 500 KHz to 1.25MHz. Under heavy load (IOUT>500mA), LX1918 always operates in PWM mode, with an efficiency up to 92%. Protection: LX1918 provides thermal shutdown, UVLO, and current limit protection: The LX1918 has two selectable operating modes for light loads: high efficiency PFM (MODE=GND) or low noise forced PWM(MODE=VCC). Only one mode can be active at any time. Under light load operation, defined as IOUT <300mA, if the MODE pin = VCC, the continuous inductor current mode is selected. This forces fixed frequency PWM and synchronous rectification regardless of loading. The inductor ripple current and duty cycle remain the same, the synchronous rectifier allows the inductor current to go positive or negative preventing system from going into discontinuous conduction and preventing possible EMI associated with inductor ringing. Thermal shutdown: if the die temperature reaches 150ºC. UVLO: an under voltage lock out, LX1918 will shut down when VIN < 2.7V. Current limiting protection: o Switch current limit: The PMOS switch is limited to a peak current of 2.7A. The PMOS “switch on” cycle is terminated when the switch current limit is reached. o Soft start: Upon start up, the switch current is limited to a gradual rise of 0 to 2.7A in 100us. The synchronous rectifier remains off during soft start preventing reverse load current. o Hiccup mode: If the PMOS switch is current limited when it attempts to turns on (indicating an output short circuit) , the converter will enter a partial soft start cycle mode to prevent a runaway output current. APPLICATIONS Copyright © 2004 Rev. 1.1, 2005-07-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET Load Regulation (%) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% REGULATION 5V TO 3.3V η - low emi η - hi eff 1 10 100 1000 0.4% 0.3% 0.2% 0.1% 0.0% -0.1% -0.2% -0.3% -0.4% -0.5% -0.6% 10000 reg-low emi reg - hi eff 0 500 Output Current (mA) 1000 1500 Output Current (mA) EFFICIENCY 3.3V TO 1.8V REGULATION 3.3V TO 1.8V 100.0% 0.6% 90.0% reg-low emi reg - hi eff 0.4% Regulation (%) 80.0% 70.0% Efficiency WWW . Microsemi .C OM Efficiency EFFICIENCY 5V TO 3.3V 60.0% η - low emi η - hi eff 50.0% 40.0% 30.0% 0.2% 0.0% -0.2% -0.4% 20.0% -0.6% 10.0% -0.8% 0.0% 1 10 100 1000 0 10000 500 1000 1500 Output Current (in mA) Output Current (in mA) LINE REGULATION (1.8V OUT) OUTPUT CURRENT VS. DUTY CYCLE Iout max DC Load vs Duty Cycle 1.9 High n (100mA) Low EMI (100mA) High n (600mA) Low EMI (600mA) 1.8 Iout DC, Amps 0.5% 0.0% -0.5% 1.7 1.6 CHARTS Variation from ideal 1.0% 1.5 1.4 1.3 -1.0% 2.7 3.2 3.7 4.2 4.7 5.2 Copyright © 2004 Rev. 1.1, 2005-07-05 0% 25% 50% 75% 100% Duty Cycle Input Voltage Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1918 ® TM 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET PACKAGE DIMENSIONS WWW . Microsemi .C OM LD 8 Pin Plastic MLP Dual Exposed Pad L D E2 E D2 b top bottom A3 Dim A A1 A3 b D D2 e E E2 L MILLIMETERS MIN MAX 0.80 1.00 0 0.05 0.20 REF 0.25 0.30 3.00 BSC 1.60 2.50 0.65 BSC 3.00 BSC 1.35 1.75 0.30 0.50 INCHES MIN MAX 0.0315 0.0394 0 0.0019 0.0079 REF 0.010 0.0118 0.1181 BSC 0.0630 0.0984 0.0260 BSC 0.1181 BSC 0.0531 0.0689 0.0071 0.0197 A side e Note: 1. Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006”) on any side. Lead dimension shall not include solder coverage. A1 MECHANICALS Copyright © 2004 Rev. 1.1, 2005-07-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8 LX1918 TM ® 1.8A Step-Down Synchronous Converter P RODUCTION D ATA S HEET NOTES WWW . Microsemi .C OM NOTES PRODUCTION DATA – Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time. Copyright © 2004 Rev. 1.1, 2005-07-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 9