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| LX1911 TM (R) 1.5A, 1.1MHZ PWM Step-Down Regulator PRODUCTION DATA SHEET DESCRIPTION KEY FEATURES Internal Reference 800mv 2% Accuracy (Line and Temp.) 4.0V to 6.0V Input Range Internal Soft Start Adj. Output From 0.8V to VIN Output Current (I >1.5A) Quiescent Current < 550A, typical @ 23C 1.1MHz PWM Frequency Micro Lead-frame, Thin MO229, 6-Pin Package APPLICATIONS/BENEFITS Portable Microprocessor Core Voltage Supplies 5V to 3V The LX1911 operates as a Current Mode PWM Buck regulator that switches to PFM mode with light loads. The entire regulator function is implemented with minimal external components. The LX1911 responds quickly to dynamic load changes using a high bandwidth error amplifier and internal compensation. Tight output voltage regulation is maintained with the compensated 800mV, 2% reference (line and temp regulation). With two external resistors the output voltage is easily programmed, from 800mV to 90% of VIN. The regulator is capable of providing an output load current of 1.5A and has no minimum load current requirement for stable operation. Current limit is cycle-by-cycle to protect the switch. Power conversion efficiency is maximized with a low regulator IQ and PFM mode of operation. The LX1911 operational range covers 4.0V to 6.0V, features include power on delay; soft start to limit inrush currents; and thermal shutdown during fault conditions. The 6-pin package is a small, RoHS compliant / Pb-free, MO-229 with excellent power dissipation capacity. WWW .Microsemi .C OM IMPORTANT: For the most current data, consult MICROSEMI's website: http://www.microsemi.com PRODUCT HIGHLIGHT EFFICIENCY vs IOUT (VIN=5V) 100% 4.0 to 6V 4 6 Top VO=3.375V Lower VO=1.25V 90% 80% 3.3H 1.2V @ 1.5A C 25K 20F 10 C = 680p 50K Ground Range Tie-in 1 VINPOWER 5 N.C. 3 VINANALOG 4.7F 2 SW 70% 60% 50% 40% 30% 1 10 100 mA GND FB LX1911 1000 10000 Figure 1 - LX1911 Circuit Topology and Typical Efficiency Performance PACKAGE ORDER INFO TA (C) 0 to 70 Input Voltage 4.5V - 5.5V Output Voltage Range Adjustable LX1911 LX1911 LD Plastic MO-229 6 Pin 3mm LX1911CLD RoHS Compliant / Pb-free Part Markings For Tape & Reel, append the letters "TR" to the part number. (i.e. LX1911CLD-TR) Copyright (c) 2004 Rev. 1.1, 2006-05-15 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1911 TM (R) 1.5A, 1.1MHZ PWM Step-Down Regulator PRODUCTION DATA SHEET ABSOLUTE MAXIMUM RATINGS Input Voltage (IN) ..............................................................................................................-0.3V to 7.0V SW to GND.............................................................................................................-0.3V to (VIN + 0.3V) VFB to GND..........................................................................................................................-0.3V to +2V SW Peak Current (Internally Limited) ....................................................................................... 1800mA Operating Temperature Range.......................................................................................-40C to +125C Storage Temperature Range, TA...................................................................................... -65C to 150C Maximum Junction Temperature.................................................................................................... 150C RoHS / Pb-free Package Peak Solder Reflow Temperature (40 seconds maximum exposure) .......................................................................................260C (+0,-5) 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. PACKAGE PIN OUT WWW .Microsemi .C OM FB GND SW 1 2 3 6 5 4 N.C. VIN ANALOG VIN PWR LD PACKAGE (Top View) Note: Heatsink pad on bottom should be connected to ground or left floating. N.C. - No Connect RoHS / Pb-free 100% Matte Tin Lead Finish THERMAL DATA LD Plastic Micro Lead 6-Pin 25-40C/W THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. PCB Layout Dependent FUNCTIONAL PIN DESCRIPTION NAME VIN ANALOG VIN PWR FB GND SW DESCRIPTION Unregulated supply voltage input, ranging from +4V to 6.0V for internal analog control circuitry. Unregulated supply voltage input (+4V to 6.0V), high current path, connects to PMOS Source of PWM switch. Feedback input for setting programming output voltage. Circuit ground providing bias for IC operation and high frequency gate drive bias, can be connected to heatsink terminal. Inductor and commutation diode connection point. Connects to internal PMOSFET source. ELECTRICAL CHARACTERISTICS Specifications apply over junction temperature of: 0oC < TJ < 125oC for VIN = 5V (except where otherwise noted). Typical values are at TA=23C. Parameter Operating Range Feed Back Threshold FB Input Current Error Amplifier Quiescent Operating Current Soft Start, Vout Slew Rate P-Channel Switch ON Resistance Maximum Duty Cycle SW Leakage Current P-Channel Current Limit PWM Frequency PFM Mode Region Feed Back PSRR Closed Loop Load Regulation Thermal Shutdown Copyright (c) 2004 Rev. 1.1, 2006-05-15 Symbol VIN VFBT IFB BW IQ (Pin 5) Vo RDS(ON) D ILEAK ILIM FOP-PWM Io Load Reg TSD Test Conditions Functional operation guaranteed by design 4.0V < VIN < 6.0V VFB = 0.81V Closed Loop VFB > 0.825V, Rload Switch Pin < 1K ohms Initial Power On or after Short Circuit ISW = 1.0A ISW = 1.0A (assured by design, not ATE tested) VFB = 0.825V Peak Current at Switch Pin (not dc current) PWM Mode PFM Mode 1hz < Frequency Vin < 10Khz VO = 1.2V, 50mA < IO < 1.2A, ckt figure 1 (assured by design, not ATE tested) Min 4.5 784 Typ 800 40 100 500 21 0.25 Max 5.5 816 75 850 50 0.5 5 1400 Units V mV nA Khz A V/mS ELECTRICALS ELECTRICALS 80 1.6 700 100 0.01 1.9 1020 250 -40 0.85 % A A KHz mA dB %VO C 135 150 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1911 TM (R) 1.5A, 1.1MHZ PWM Step-Down Regulator PRODUCTION DATA SHEET SIMPLIFIED BLOCK DIAGRAM WWW .Microsemi .C OM VIN CL Clock and Ramp PWM S R SW EA BG Ref 800mV GND FB Figure 2 - LX1911 Block Diagram VOUT COUT Inductor Diode COUT COUT VIN RS LX1911 VIN ANALOG GND FB APPLICATIONS APPLICATIONS CS VIN PWR SW N.C. Rf CIN COUT Rf GROUND Figure 3 - PCB Layout Considerations Copyright (c) 2004 Rev. 1.1, 2006-05-15 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1911 TM (R) 1.5A, 1.1MHZ PWM Step-Down Regulator PRODUCTION DATA SHEET APPLICATION NOTE FUNCTIONAL DESCRIPTION The LX1911 is a Current Mode PWM regulator with internal compensation. The internal PMOS high side switch is protected with current limit on a pulse by pulse basis and with thermal shutdown. Thermal shutdown is activated with a junction temperature of 160C (typical) and has 20C of hysteresis. The regulator has an internal Power On Reset delay of 50-100s to ensure all circuitry is operating before enabling the Switch output. Soft Start is activated upon initial power-on, or following recovery from either thermal shutdown or short circuit. The Soft start control block generates a voltage ramp that clamps the error amplifier non-inverting reference voltage. As this clamp voltage rises, the duty cycle is gradually increased, thus limiting the peak inrush currents. PWM / PFM mode of operation is determined by the load current condition. The PFM mode increases system efficiency by reducing the switching frequency thus switching losses. During light loading, IOUT < 200mA typically, PFM mode becomes active, the switching frequency begins to decrease, the frequency change occurs over a continuous range, decreasing further as IOUT decreases. OUTPUT VOLTAGE PROGRAMMING Resistors R1 and R2 program the output voltage. The value of R2 (lower resistor of divider) should be less than 10K. The value of R1 can be determined using the following equation, note VREF is also referred to as VFBT. V R1 = R2 OUT - 1 V REF INDUCTOR SELECTION, CONT. The internal compensation of the LX1911 design was optimized for a 3.3H inductor but will operate with an inductor value in the range of 2.2H and 22H for a majority of applications. The benefit of a larger inductor value can increase efficiency at the lower output currents and reduces output voltage ripple, thus output capacitance related to ripple filtering. Smaller inductors typically provide smaller package size (critical in many portable applications) at the expense of increasing output ripple current. Regardless of inductor value, selecting a device manufactured with a ferrite-core produces lower losses at higher switching frequencies and thus better overall performance. Larger inductors may lead to diminished Step-Load response. CAPACITOR SELECTION To minimize ripple voltage, output capacitors with a low series resistance (ESR) are recommended. Multi-layer ceramic capacitors with X5R or X7R dielectric make an effective choice because they feature small size, very low ESR, a temperature stable dielectric, and can be connected in parallel to increase capacitance. Typical output capacitance values of 10 to 30F has proven effective. Other low ESR capacitors such as solid tantalum, specialty polymer, or organic semiconductor, make effective choices provided that the capacitor is properly rated for the output voltage and ripple current. Finally, choose an input capacitor of sufficient size to effectively decouple the input voltage source impedance (e.g., CIN > 4.7F). LAYOUT CONSIDERATIONS The high peak currents and switching frequencies present in DC/DC converter applications require careful attention to device layout for optimal performance. Basic design rules include: (1) maintaining wide traces for power components (e.g., width > 50mils); (2) place CIN, COUT, the Schottky diode, and the inductor close to the LX1911; (3) minimizing trace capacitance by reducing the etch area connecting the SW pin to the inductor; and (4) minimizing the etch length to the FB pin to reduce noise coupling into this high impedance sense input. Other considerations include placing a 0.1uF capacitor between the LX1911 VOUT pin and GND pin to reduce high frequency noise and decoupling the VIN pin using a 0.1F capacitor. The LX1911 Switch has fast switching speeds which may generate noise spikes when a high capacitance Schottky diode is selected for the catch diode. A simple snubber circuit, as shown in Figure 1, R=10 ohms and C=680pF has proven effective to reduce the spike voltage generated at the Switch Pin / Diode connection. WWW .Microsemi .C OM DIODE SELECTION A Schottky diode is required for switching speed and low forward voltage. Efficiency is determined mostly by the diode's forward voltage. The diode conducts 1-D%, for VOUT = 1.2V this becomes 76% in a 5V system. INDUCTOR SELECTION Selecting the appropriate inductor type and value ensures optimal performance of the converter circuit for the intended application. A primary consideration requires the selection of an inductor that will not saturate at the peak current level. EMI, output voltage ripple, and overall circuit efficiency affect inductor choice. The inductor that works best depends upon the application's requirements and some experimentation with actual devices in-circuit is typically necessary to make the most effective choice. Copyright (c) 2004 Rev. 1.1, 2006-05-15 APPLICATIONS APPLICATIONS Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 LX1911 TM (R) 1.5A, 1.1MHZ PWM Step-Down Regulator PRODUCTION DATA SHEET CHARACTERISTIC CURVES WWW .Microsemi .C OM CH2:VOUT CH1:SWITCH Figure 4- Step Load Response 250ma-1.2A 3.3H, 40F Blue: Vout 50mV/div AC; Green: ISTEP 200ma/div Figure 5 - Switching Waveforms: PFM Mode Regulated VOUT vs Temperature (Iout=10ma) 0.8% 0.6% 0.4% 0.2% 0.0% -0.2% -0.4% -0.6% -0.8% -25 Figure 6 - Power On and Soft Start For IOUT 10mA to 1amp CH1:VIN CH2:VOUT 0 25 50 75 100 125 150 GRAPHS GRAPHS TEMPERATURE, C Figure 7- Vout Temperature Stability Copyright (c) 2004 Rev. 1.1, 2006-05-15 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1911 TM (R) 1.5A, 1.1MHZ PWM Step-Down Regulator PRODUCTION DATA SHEET PACKAGE DIMENSIONS LD 6 Pin Plastic 3 x 3 x .9 mm D L1 WWW .Microsemi .C OM D2 Pin 1 ID E L E2 K b A or A1 or Pin 1 ID e Dim A A1 K e L b D2 E2 D E L1 Note: MILLIMETERS MIN MAX 0.80 1.00 0.00 0.05 0.20 MIN 0.95 BSC 0.30 0.50 0.30 0.45 1.90 2.40 1.15 1.65 3.00 BSC 3.00 BSC 0.00 0.15 INCHES MIN MAX 0.031 0.039 0.000 0.002 0.008 MIN 0.037 BSC 0.012 0.02 0.012 0.018 0.75 0.094 0.045 0.065 0.118 BSC 0.118 BSC 0.000 0.006 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. LD 6 Pin Plastic 3 x 3 x .9 mm D L1 D2 Pin 1 ID E L E2 K b A or A1 or Pin 1 ID e Dim A A1 K e L b D2 E2 D E L1 Note: MILLIMETERS MIN MAX 0.80 1.00 0.00 0.05 0.20 MIN 0.95 BSC 0.30 0.50 0.30 0.45 1.90 2.40 1.15 1.65 3.00 BSC 3.00 BSC 0.00 0.15 INCHES MIN MAX 0.031 0.039 0.000 0.002 0.008 MIN 0.037 BSC 0.012 0.02 0.012 0.018 0.75 0.094 0.045 0.065 0.118 BSC 0.118 BSC 0.000 0.006 M MECHANICALS 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. Copyright (c) 2004 Rev. 1.1, 2006-05-15 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1911 TM (R) 1.5A, 1.1MHZ PWM Step-Down Regulator PRODUCTION DATA SHEET NOTES WWW .Microsemi .C OM 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. NOTES NO T E S Copyright (c) 2004 Rev. 1.1, 2006-05-15 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 |
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