LX1911 1.5A, 1.1MHZ PWM Step-Down Regulator ® TM P RODUCTION D ATA S HEET KEY FEATURES DESCRIPTION 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. 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 < 550μA, typical @ 23°C 1.1MHz PWM Frequency Micro Lead-frame, Thin MO229, 6-Pin Package WWW . Microsemi .C OM 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. APPLICATIONS/BENEFITS Portable Microprocessor Core Voltage Supplies 5V to 3V IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com PRODUCT HIGHLIGHT EFFICIENCY vs IOUT (VIN=5V) Top VO=3.375V Lower VO=1.25V 100% 90% 4.0 to 6V 4 N.C. VINANALOG SW 5 4.7µF 80% 6 VINPOWER 3.3µH 3 1.2V @ 1.5A C 2 1 GND FB 20µF 10 LX1911 50K Ground Range Tie-in C = 680p 70% 25K 60% 50% 40% 30% 1 10 100 1000 10000 mA Figure 1 – LX1911 Circuit Topology and Typical Efficiency Performance TA (°C) 0 to 70 Input Voltage 4.5V – 5.5V Output Voltage Range LD Adjustable LX1911 PACKAGE ORDER INFO Plastic MO-229 6 Pin 3mm² RoHS Compliant / Pb-free LX1911CLD Part Markings For Tape & Reel, append the letters “TR” to the part number. (i.e. LX1911CLD-TR) Copyright © 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 1.5A, 1.1MHZ PWM Step-Down Regulator ® TM P RODUCTION D ATA S HEET ABSOLUTE MAXIMUM RATINGS PACKAGE PIN OUT FB 1 6 N.C. GND 2 5 VIN ANALOG SW 3 4 VIN PWR LD PACKAGE (Top View) 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. Note: Heatsink pad on bottom should be connected to ground or left floating. N.C. – No Connect THERMAL DATA WWW . Microsemi .C OM 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.......................................................................................-40°C to +125°C Storage Temperature Range, TA...................................................................................... -65°C to 150°C Maximum Junction Temperature.................................................................................................... 150°C RoHS / Pb-free Package Peak Solder Reflow Temperature (40 seconds maximum exposure) .......................................................................................260°C (+0,-5) RoHS / Pb-free 100% Matte Tin Lead Finish LD Plastic Micro Lead 6-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 25-40°C/W† 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. † PCB Layout Dependent FUNCTIONAL PIN DESCRIPTION NAME VIN ANALOG VIN PWR FB 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. GND Circuit ground providing bias for IC operation and high frequency gate drive bias, can be connected to heatsink terminal. SW 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=23°C. Parameter ` Symbol Operating Range VIN Feed Back Threshold Test Conditions Min Functional operation guaranteed by design 4.5 4.0V < VIN < 6.0V 784 Typ Max Units 5.5 V mV 800 816 FB Input Current IFB VFB = 0.81V 40 75 Error Amplifier BW Closed Loop 100 VFB > 0.825V, Rload Switch Pin < 1K ohms 500 850 µA Initial Power On or after Short Circuit 21 50 V/mS 0.25 0.5 VFBT Quiescent Operating Current P-Channel Switch ON Resistance IQ (Pin 5) Vo RDS(ON) ISW = 1.0A D SW Leakage Current ILEAK VFB = 0.825V P-Channel Current Limit ILIM Peak Current at Switch Pin (not dc current) 1.6 1.9 FOP-PWM PWM Mode 700 1020 Io PFM Mode 250 1hz < Frequency Vin < 10Khz -40 dB VO = 1.2V, 50mA < IO < 1.2A, ckt figure 1 0.85 %VO 150 °C PWM Frequency PFM Mode Region Feed Back PSRR Closed Loop Load Regulation Thermal Shutdown Copyright © 2004 Rev. 1.1, 2006-05-15 Load Reg TSD ISW = 1.0A (assured by design, not ATE tested) (assured by design, not ATE tested) 80 100 Ω Maximum Duty Cycle 0.01 135 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 % 5 µA 1400 KHz A mA Page 2 ELECTRICALS Soft Start, Vout Slew Rate nA Khz LX1911 1.5A, 1.1MHZ PWM Step-Down Regulator ® TM P RODUCTION D ATA S HEET 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 ANALOG GND N.C. FB CS SW COUT Rf VIN PWR APPLICATIONS CIN RS LX1911 VIN Rf GROUND Figure 3 – PCB Layout Considerations Copyright © 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 1.5A, 1.1MHZ PWM Step-Down Regulator P RODUCTION D ATA S HEET APPLICATION NOTE OUTPUT VOLTAGE PROGRAMMING Resistors R1 and R2 program the output voltage. The value of R2 (lower resistor of divider) should be less than 10KΩ. The value of R1 can be determined using the following equation, note VREF is also referred to as VFBT. ⎡⎛ V ⎞ ⎤ R1 = R2⎢⎜⎜ OUT ⎟⎟ − 1⎥ ⎢⎣⎝ VREF ⎠ ⎥⎦ 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. Copyright © 2004 Rev. 1.1, 2006-05-15 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 30µF 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 > 4.7µF). 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 0.1µF 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. Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 APPLICATIONS 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. INDUCTOR SELECTION, CONT. The internal compensation of the LX1911 design was optimized for a 3.3µH inductor but will operate with an inductor value in the range of 2.2µH and 22µH 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. WWW . Microsemi .C OM 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 160°C (typical) and has 20°C of hysteresis. The regulator has an internal Power On Reset delay of 50-100µs 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. LX1911 ® TM 1.5A, 1.1MHZ PWM Step-Down Regulator P RODUCTION D ATA S HEET CHARACTERISTIC CURVES WWW . Microsemi .C OM CH2:VOUT CH1:SWITCH Figure 4– Step Load Response 250ma-1.2A 3.3µH, 40µF 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% CH1:VIN CH2:VOUT 0 25 50 75 100 125 150 TEMPERATURE, °C Figure 7– Vout Temperature Stability Copyright © 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 GRAPHS -25 Figure 6 – Power On and Soft Start For IOUT 10mA to 1amp LX1911 1.5A, 1.1MHZ PWM Step-Down Regulator ® TM P RODUCTION D ATA S HEET PACKAGE DIMENSIONS 6 Pin Plastic 3 x 3 x .9 mm D L1 D2 Pin 1 ID E E2 L K e b A or Dim A A1 K e L b D2 E2 D E L1 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 WWW . Microsemi .C OM LD or A1 Note: Pin 1 ID 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 E2 L K e b A 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 or Pin 1 ID 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. Copyright © 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 MECHANICALS or A1 Dim A A1 K e L b D2 E2 D E L1 LX1911 TM ® 1.5A, 1.1MHZ PWM Step-Down Regulator P RODUCTION D ATA S HEET 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. NO T E S Copyright © 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