LX1910

LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET KEY FEATURES Internal Reference 1.17V ±2% Accuracy (Line and Temperature) 4V to 6.0V Input Range Adj. Output From 1.17V to VIN Output Current (IDC >850mA) Quiescent Current < 300µA 1MHz Operation Frequency MSOP 8-Pin APPLICATIONS/BENEFITS Portable Microprocessor Core Voltage Supplies 5V to 3V DESCRIPTION The LX1910 PWM buck regulator achieves very high efficiencies over a broad range of operating load conditions. The LX1910 implements a load-detection architecture and enters a power-saving PFM mode when driving small load currents ensuring optimal regulator efficiency over the entire output current range thus maximizing battery life. The PWM operating mode implements a fixed frequency of 1MHz (typ), the transconductance error amplifier has 12µA of drive with an output voltage swing rail to rail. Compensation is external for maximum user flexibility. The LX1910 does not require a minimum load current for stable operation. There is no Under Voltage Lockout for the input voltage, operational range includes 4V to 6V. The regulator is capable of providing an output dc load current of 850mA. The SHDN pin places the device in a sleep-mode drawing less than 1µA of quiescent current. The LX1910 comes in space-saving MSOP package allowing a complete application circuit to occupy a very small PCB area. These features make the LX1910 ideal for use in SmartPhones, PDAs, or other batteryoperated devices W WW . Microsemi . C OM IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com PRODUCT HIGHLIGHT LX1910 Efficiency @ Vout=1.5V 90% LX1910 VIN CIN 80% CONVERSION EFFICIENCY PVIN AVIN SHDN COMP RC CC L SW D CX R1 VOUT COUT 70% 60% 50% 40% 30% 20% 10% 0 100 200 300 400 500 600 700 OUTPUT CURRENT, mA FB PGND R2 AGND Figure 1 – LX1910 Circuit Topology and Typical Efficiency Performance PACKAGE ORDER INFO TJ(°C) 0 to 85 Input Voltage 4.5V – 6.0V Output Voltage Range 1.17V to VIN DU Plastic MSOP 8-PIN LX1910 LX1910 RoHS Compliant / Pb-free LX1910CDU Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1910-13016CDU-TR) Copyright © 2004 Rev. 1.1, 2005-02-25 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET PACKAGE PIN OUT ABSOLUTE MAXIMUM RATINGS Input Voltage (IN) or SHDN to GND .............................................................................-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) ....................................................................................... 1000mA 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 Peak Package Solder Reflow Temperature (40 seconds maximum exposure) ......................................................................................260°C (+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. PVIN AVIN SHDN COMP 1 2 3 4 8 7 6 5 SW PGND AGND FB W WW . Microsemi . C OM DU PACKAGE (Top View) RoHS / Pb-free 100% Matte Tin Lead Finish THERMAL DATA DU Plastic MSOP 8-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 206°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. FUNCTIONAL PIN DESCRIPTION NAME SW AGND FB DESCRIPTION Inductor and commutation diode connection point. Connects to internal MOSFET drain. Analog circuit ground providing bias for IC operation. Feedback input for setting adjustable output voltage Enable control input. Reduces quiescent current to 1µA. Pin 8, Output becomes high impedance. Unregulated supply voltage input connected to PMOS Source. Input range from +2.7V to 6.0V Frequency Compensation of the overall loop is effected by placing a series R/C combination between COMP pin and GND. Unregulated supply voltage input. Input range from +4V to 6.0V Power ground (return path for internal PMOS gate driver). SHDN PVIN COMP AVIN PGND PACKAGE DATA PACKAGE DATA Copyright © 2004 Rev. 1.1, 2005-02-25 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET ELECTRICAL CHARACTERISTICS Specifications apply over junction temperature of: 0oC < T < 85oC for VIN = 5V (except where otherwise noted). Typical values are at TA=25°C. W WW . Microsemi . C OM Parameter Operating Range Output Voltage Range Feed Back Threshold FB Input Current EA Drive Current (COMP Pin) Symbol VIN VOUT VFBT IFB ISOURCE ISINK Test Conditions Functional operation guaranteed by design Closed loop operating range 4V < VIN < 6V VFB = 1.2V VFB -125mV of Overdrive, VCOMP = 2.5V VFB +125mV of Overdrive, VCOMP = 2.5V VOL, Sinking 10µA VOH, Sourcing 10µA Pin 2 Supply Current VSHDN = 0V, SW Pin open VSHDN = 0V, SW grounded SHDN = GND or SHDN = 5V Device Off Device On ISW = 0.5A ISW = 0.5A (assured by design, not ATE tested) Min 3.5 VFB 1.146 Typ Max 6.0 0.95*VIN Units V V V nA µA µA mV V 1.170 300 1.193 500 10 10 16 16 95 4.86 250 400 1 2 5 100 0.2*VIN EA Output Swing (COMP Pin) Quiescent Operating Current Sleep (Shutdown Mode) Current Shutdown Input Bias Current Shutdown Voltage Threshold P-Channel Switch ON Resistance Maximum Duty Cycle SW Leakage Current P-Channel Current Limit Frequency Closed Loop Load Regulation Thermal Shutdown VEA OUT IQ IQVINSD IQVINSD ISD_IB VSD RDS(ON) D ILEAK ILIM FOP Load Reg TSD µA µA µA nA V V -100 0.8*VIN 0.53 80 900 0.80 100 1 950 1.07 0.35 125 150 5 1.2 0.5 0.8 Ω % µA mA MHz % VO °C VO = 1.5V, 5mA < IO < 700mA, ckt figure 3 E ELECTRICALS Copyright © 2004 Rev. 1.1, 2005-02-25 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET SIMPLIFIED BLOCK DIAGRAM AVIN PVIN W WW . Microsemi . C OM Ramp comparator + avin SW Logic + bg PWM FB Skip Mode Shutdown COMP Thermal Sense AGND Figure 2 – LX1910 Block Diagram LX1910 5.0V PVIN AVIN 4.7µF 4.7µH SHDN COMP 30KΩ 3300pF AGND Figure 3 – Circuit for 1.5V Output Voltage Copyright © 2004 Rev. 1.1, 2005-02-25 Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 agnd OSC pgnd ilimit SHDN LX1910 PGND SW 3300pF D 14KΩ 10µF 51KΩ 1.5V FB PGND BLOCK DIAGRAM Microsemi Page 4 LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET APPLICATION NOTE FUNCTIONAL DESCRIPTION The LX1910 implements a PFM / PWM architecture that improves power management efficiency across the output load range. OUTPUT VOLTAGE PROGRAMMING Resistors R1 and R2 program the output voltage. An optional capacitor CX may be inserted across R1 to improve the transient response (see Figure 1). The value of R2 should be less than 100KΩ. 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 ⎠ ⎥ ⎣ ⎦ 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 capacitance values of 4.7 to 30µF have 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 LX1910; (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 LX1910 VOUT pin and GND pin to reduce high frequency noise and decoupling the VIN pin using a 0.1µF capacitor. W WW . Microsemi . C OM DESIGN EXAMPLE: Let R2 equal 50K and the required VOUT equal to 3.0V. R1 = 50K ⎢⎜ ⎜ ⎡⎛ 3V ⎞ ⎤ ⎟ − 1⎥ ⎟ ⎢⎝ 1.17 ⎠ ⎥ ⎣ ⎦ = 78KΩ DIODE SELECTION A Schottky diode is recommended for use with the LX1910 because it provides fast switching and superior reverse recovery performance. The Microsemi UPS5817 (20V @ 1A) makes an effective choice for most applications. INDUCTOR SELECTION Selecting the appropriate inductor type and value ensures optimal performance of the converter circuit for the intended application. This selection process requires the designer to make trade-offs between circuit performance and cost. A primary consideration requires the selection of an inductor that will not saturate at the peak current level. Other considerations that affect inductor choice include EMI, output voltage ripple, and overall circuit efficiency. The inductor that works best depends upon the application’s requirements. Further, some experimentation with actual devices in-circuit is typically necessary to make the most effective choice. The LX1910 allows for a broad selection of inductor values and choosing a value between 2.2µH and 30µH supports a majority of applications. Selecting a larger inductor value can increase efficiency and reduce output voltage ripple. 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. APPLICATIONS APPLICATIONS Copyright © 2004 Rev. 1.1, 2005-02-25 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET CHARACTERISTIC CURVES W WW . Microsemi . C OM LX1910 LOAD REGULATION (Vout=1.5V) 0.15% 0.10% 0.05% 0.00% -0.05% -0.10% -0.15% -0.20% -0.25% -0.30% -0.35% 0 100 200 300 400 500 600 700 IOUT, ma CONVERSION EFFICIENCY 80% 70% 60% 50% 40% 30% 20% 10% 0 10 LX1910 Efficiency @ Vout=1.5V OUTPUT DEVIATION, % 20 30 40 50 60 70 80 90 100 OUTPUT CURRENT, ma Figure 4 Figure 5 1910 LINE REG (Vout=1.5V, Rload=15 ohms) 1.55 1.45 1.35 1.25 Vo VOLT 1.15 1.05 0.95 0.85 0.75 0.65 0.55 1 1.5 2 2.5 3 3.5 4 Vin, volts 4.5 5 5.5 6 Vo Vout Error 0.5% 0.4% 0.3% 0.2% 0.1% 0.0% -0.1% -0.2% -0.3% -0.4% -0.5% Vfb (Pin 5), Volts 1.180 1.175 1.170 1.165 1.160 1.155 -10 1.185 Feedback Voltage Thermal Stability 0 10 20 30 40 50 60 70 80 Temperature, °C Figure 6 Figure 7 GRAPHS GRAPHS Copyright © 2004 Rev. 1.1, 2005-02-25 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET CHARACTERISTIC CURVES W WW . Microsemi . C OM Figure 9– Output Load Step Response: CH1: VOUT and CH4: IOUT; Condition: VIN = 5.0V; ISTEP = 50 to 600mA Figure 10 – Switching Waveforms: PFM Mode CH3: VSW (pin 8) and CH1: VOUT; ( VIN = 5.0V; IOUT = 1mA) Figure 11 – Switching Waveforms: PWM Mode CH3: VSW (pin 8) and CH1: VOUT; (VIN = 5.0V; IOUT = 10mA) GRAPHS Copyright © 2004 Rev. 1.1, 2005-02-25 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1910 TM ® Step-Down Regulator P RODUCTION D ATA S HEET PACKAGE DIMENSIONS W WW . Microsemi . C OM DU 8-Pin Miniature Shrink Outline Package (MSOP) A Dim A B C D G H J K L M N P B H G P C N K M D L MILLIMETERS MIN MAX 2.85 3.05 2.90 3.10 – 1.10 0.25 0.40 0.65 BSC 0.38 0.64 0.13 0.18 0.95 BSC 0.40 0.70 3° 0.05 0.15 4.75 5.05 INCHES MIN MAX .112 .120 .114 .122 – 0.043 0.009 0.160 0.025 BSC 0.015 0.025 0.005 0.007 0.037 BSC 0.016 0.027 3° 0.002 0.006 0.187 0.198 Note: Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(0.006”) on any side. Lead dimension shall not include solder coverage. NOTES MECHANICALS MECHANICALS 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, 2005-02-25 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8