LX1912 VREF @ 800mV, 1.0A, 1.2MHz PWM ® TM P RODUCTION D ATA Internal Reference 800mv ±2% Accuracy (Line and Temp.) 4.0V to 6.0V Input Range Internal Soft Start Adj. Output From 0.8V to 90% of VIN Output Current up to 1.0A Quiescent Current < 550μA, Typical @ 23°C 1.2MHz PWM Frequency Over Voltage Protection bs ol et e The regulator is capable of providing an output load current of 1.0A, 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 low regulator IQ and PFM mode of operation The LX1912 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 TSOT package provides a small form factor with excellent power dissipation capability. WWW . Microsemi .C OM KEY FEATURES DESCRIPTION The LX1912 operates as a Current Mode PWM Buck regulator that switches to PFM mode with light loads. The entire regulator function is implemented with few external components. The LX1912 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. SHEET APPLICATIONS Portable Microprocessor Core Voltage Supplies 5V to 3V RoHS Compliant Product IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com PRODUCT HIGHLIGHT 4V to 6V EFFICIENCY (VIN = 5V, VOUT @ 3.3V) 95% 4.7µF 90% 2.7µH SW VCC 31.6K LX1912 Part 30µF FB GND 85% 3.3V @ 1.0A EFFICIENCY VPWR 80% 75% 70% 65% N.C. 10K 60% 55% 50% 0.01 0.10 1.00 OUTPUT CURRENT (Amps) TA (°C) 0 to +70 PACKAGE ORDER INFO Output Voltage Range 4.0V – 6.0V Adjustable Input Voltage SG Plastic TSOT 6-Pin Part Marking LX1912 O Figure 1 – LX1912 Circuit Topology and Typical Efficiency Performance RoHS Compliant / Pb-free LX1912CSG 1912 Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX1912CSG-TR) Copyright © 2005 Rev. 1.0, 2006-09-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX1912 VREF @ 800mV, 1.0A, 1.2MHz PWM ® TM P RODUCTION D ATA PACKAGE PIN OUT N.C. 1 6 SW GND 2 5 VPWR FB 3 4 VCC SG PACKAGE bs ol et e Input Voltage (VCC and VPWR).......................................................................................-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 Operating Junction Temperature Range (TJ).................................................................-40°C to +125°C Storage Temperature Range, TA...................................................................................... -65°C to 150°C Maximum Junction Temperature....................................................................................................150°C Peak Package Solder Reflow Temp. (40 seconds max. 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. (Top View) RoHS / Pb-free 100% Matte Tin Lead Finish WWW . Microsemi .C OM ABSOLUTE MAXIMUM RATINGS SHEET N.C. – No Internal Connection THERMAL DATA SG Plastic TSOT 6-Pin THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA 134°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 VCC VPWR FB GND Unregulated supply voltage input, ranging from +4V to 6.0V for internal analog control circuitry. Unregulated supply voltage for PMOSFET drain to drive the switch pin. Feedback input for setting programming output voltage. Circuit ground providing bias for IC operation and high frequency gate drive bias. Inductor and commutation diode connection point. Connects to internal PMOSFET source. Copyright © 2005 Rev. 1.0, 2006-09-06 PACKAGE DATA O SW Description Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2 LX1912 VREF @ 800mV, 1.0A, 1.2MHz PWM ® TM P RODUCTION D ATA SHEET ELECTRICAL CHARACTERISTICS Parameter Operating Range Symbol 1 Feed Back Threshold Test Conditions Min VCC Functional operation guaranteed by design 4.0 VFBT 4.0V < VCC < 6.0V 784 Typ Max Units 6.0 V mV 800 816 FB Input Current IFB VFB = 0.81V 40 75 Error Amplifier BW Closed Loop 200 IQ (Pin 4) VFB > 0.825V, RLOAD Switch Pin < 1KΩ 500 850 μA Vo Initial Power On or after Short Circuit 21 50 V/mS 0.375 0.6 Quiescent Operating Current bs ol et e Soft Start, VOUT Slew Rate P-Channel Switch ON Resistance RDS(ON) Maximum Duty Cycle D SW Leakage Current ILEAK UVLO ISW = 1.0A ISW = 1.0A (assured by design, not ATE tested) 80 VFB = 0.825V 0.01 Under Voltage Lockout VCC Rising Under Voltage Lockout VCC Falling 2.4 Peak Current at Switch Pin (not DC current) 1.50 2.30 PWM Mode 820 1200 UVLO Hysteresis P-Channel Current Limit ILIM FOP-PWM PFM Mode Region Io Feed Back PSRR Closed Loop Load Regulation Ω % 5 μA 3.00 V 1920 KHz 0.15 2 PWM Frequency nA KHz WWW . Microsemi .C OM Specifications apply over junction temperature of: -20°C < TJ < 125°C for VCC = VPWR = 5V (except where otherwise noted). Typical values are at TA=23°C. Load Reg Thermal Shutdown TSD A PFM Mode Load Current Crossover 100 1Hz < Frequency VCC < 10KHz -40 dB VO = 1.2V, 50mA < IO < 1.0A, ckt figure 1 0.85 %VO 150 °C (assured by design, not ATE tested) 135 mA Copyright © 2005 Rev. 1.0, 2006-09-06 ELECTRICALS O Note 1: VIN vs VOUT ratio @ 1.0A LOAD IS SET AT VIN = VOUT + 1.0V Note 2: 1.0 amp operation @ 70°C ambient depends on adequate heat sinking to keep TJ below 125°C Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX1912 VREF @ 800mV, 1.0A, 1.2MHz PWM ® TM P RODUCTION D ATA SHEET SIMPLIFIED BLOCK DIAGRAM WWW . Microsemi .C OM VPWR VCC UVLO Bias bs ol et e CL Clock And Ramp PWM S R SW 920mV REF EA OVP BG REF 800mV LX1912 GND Figure 2 – LX1912 Block Diagram FB PCB LAYOUT VOUT COUT Inductor O Diode COUT APPLICATIONS COUT Rf VIN N.C. SW GND VPWR FB LX1912 COUT VCC CIN Rf GROUND Figure 3 – PCB Layout Considerations Copyright © 2005 Rev. 1.0, 2006-09-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 4 LX1912 ® TM VREF @ 800mV, 1.0A, 1.2MHz PWM P RODUCTION D ATA SHEET APPLICATION NOTE bs ol et e INDUCTOR SELECTION, CONT. The LX1912 stability performance is optimized by using an inductor value of 2.7µH ±20%. 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 20 to 60µF 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 LX1912; (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 LX1912 VOUT pin and GND pin to reduce high frequency noise and decoupling the VCC, VPWR pins using a 0.1µF capacitor. O ⎡⎛ V ⎞ ⎤ R1 = R2⎢⎜⎜ OUT ⎟⎟ − 1⎥ ⎣⎢⎝ VREF ⎠ ⎦⎥ Copyright © 2005 Rev. 1.0, 2006-09-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 APPLICATIONS 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. WWW . Microsemi .C OM FUNCTIONAL DESCRIPTION The LX1912 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 50100µs 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 OVER VOLTAGE PROTECTION The over voltage comparator compares the FB pin voltage to a voltage that is 15% higher than the internal referenced VREF. Once the FB pin voltage goes 15% above the internal reference, the internal PMOS control switch is turned off, which allows the output voltage to decrease toward regulation. OUTPUT VOLTAGE PROGRAMMING Resistors R1 and R2 program the output voltage. The total impedance of both feedback resistors should not exceed 50K Ohms to ensure optimal frequency stability. The value of R1 can be determined using the following equation, note VREF is also referred to as VFBT. Page 5 LX1912 VREF @ 800mV, 1.0A, 1.2MHz PWM ® TM P RODUCTION D ATA SHEET CHARACTERISTIC CURVES WWW . Microsemi .C OM UVLO THRESHOLDS- VIN RISING and FALLING PWM Frequency vs Load Current 1.4 1 0.8 0°C 0.4 0.2 0 3.1 3.05 3 2.95 2.9 2.85 2.8 2.75 2.7 2.65 2.6 2.55 2.5 2.45 2.4 1.4.E+06 1.3.E+06 1.2.E+06 1.1.E+06 1.0.E+06 9.0.E+05 8.0.E+05 7.0.E+05 6.0.E+05 5.0.E+05 4.0.E+05 3.0.E+05 2.0.E+05 1.0.E+05 0.001 bs ol et e 120°C 0.6 PWM Switching Frequency, hZ 1.2 VIN, volts O 0.1 1 Figure 5 – PFM / PWM Range of Output Switch Figure 4– Under Voltage Lockout for VIN Figure 6 – Step Load Response 300mA to 800mA, L = 2.7µH, COUT = 30µF Figure 7– Soft Start Power On, L = 2.7µH, COUT = 30µF, IOUT = 0mADC CHARTS Copyright © 2005 Rev. 1.0, 2006-09-06 0.01 Load Current, A Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6 LX1912 VREF @ 800mV, 1.0A, 1.2MHz PWM ® TM P RODUCTION D ATA SHEET PACKAGE DIMENSIONS 6 Pin TSOT D Dim A A1 A2 b c D E E1 e1 e L L2 e1 E1 e A A2 MILLIMETERS MIN MAX 1.00 0.01 0.10 0.84 0.90 0.30 0.45 0.12 0.20 2.90 BSC 2.80 BSC 1.60 BSC 1.90 BSC 0.095 BSC 0.30 0.50 0.25 BSC INCHES MIN MAX 0.039 0.0004 0.004 0.033 0.035 0.012 0.018 0.005 0.008 0.114 BSC 0.110 BSC 0.063 BSC 0.075 BSC 0.037 BSC 0.012 0.010 BSC bs ol et e b E WWW . Microsemi .C OM SG E Note: L Dimensions do not include mold flash or protrusions; these shall not exceed 0.15mm (.006”) on any side. Lead Dimension shall not include solder coverage. Copyright © 2005 Rev. 1.0, 2006-09-06 MECHANICALS O A1 1. Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 7 LX1912 VREF @ 800mV, 1.0A, 1.2MHz PWM ® TM P RODUCTION D ATA SHEET NOTES O bs ol et e 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 © 2005 Rev. 1.0, 2006-09-06 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 8