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| LX1912 TM (R) VREF @ 800mV, 1.0A, 1.2MHz PWM 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 90% of VIN Output Current up to 1.0A Quiescent Current < 550A, Typical @ 23C 1.2MHz PWM Frequency Over Voltage Protection APPLICATIONS WWW .Microsemi .C OM 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. 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. 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 95% EFFICIENCY (VIN = 5V, VOUT @ 3.3V) VPWR 4.7F 2.7H 90% SW 31.6K 3.3V @ 1.0A EFFICIENCY 85% 80% 75% 70% 65% VCC LX1912 Part GND N.C. FB 30F 10K 60% 55% 50% 0.01 0.10 1.00 OUTPUT CURRENT (Amps) Figure 1 - LX1912 Circuit Topology and Typical Efficiency Performance PACKAGE ORDER INFO TA (C) 0 to +70 Input Voltage Output Voltage Range 4.0V - 6.0V Adjustable SG Plastic TSOT 6-Pin LX1912CSG Part Marking LX1912 LX1912 RoHS Compliant / Pb-free 1912 Note: Available in Tape & Reel. Append the letters "TR" to the part number. (i.e. LX1912CSG-TR) Copyright (c) 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 TM (R) VREF @ 800mV, 1.0A, 1.2MHz PWM PRODUCTION DATA SHEET ABSOLUTE MAXIMUM RATINGS 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).................................................................-40C to +125C Storage Temperature Range, TA...................................................................................... -65C to 150C Maximum Junction Temperature....................................................................................................150C Peak Package Solder Reflow Temp. (40 seconds max. 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 N.C. GND FB 1 6 SW VPWR VCC 2 5 3 4 SG PACKAGE (Top View) RoHS / Pb-free 100% Matte Tin Lead Finish N.C. - No Internal Connection THERMAL DATA SG Plastic TSOT 6-Pin 134C/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. FUNCTIONAL PIN DESCRIPTION Name VCC VPWR FB GND SW Description 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. PACKAGE DATA PACKAGE DATA Copyright (c) 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 2 LX1912 TM (R) VREF @ 800mV, 1.0A, 1.2MHz PWM PRODUCTION DATA SHEET ELECTRICAL CHARACTERISTICS Specifications apply over junction temperature of: -20C < TJ < 125C for VCC = VPWR = 5V (except where otherwise noted). Typical values are at TA=23C. Parameter Operating Range FB Input Current Error Amplifier Quiescent Operating Current Soft Start, VOUT Slew Rate P-Channel Switch ON Resistance Maximum Duty Cycle SW Leakage Current Under Voltage Lockout UVLO Under Voltage Lockout UVLO Hysteresis P-Channel Current Limit PWM Frequency PFM Mode Region Feed Back PSRR Closed Loop Load Regulation Thermal Shutdown Load Reg TSD 2 1 WWW .Microsemi .C OM Symbol VCC VFBT IFB BW IQ (Pin 4) Vo RDS(ON) D ILEAK Test Conditions Functional operation guaranteed by design 4.0V < VCC < 6.0V VFB = 0.81V Closed Loop VFB > 0.825V, RLOAD Switch Pin < 1K Initial Power On or after Short Circuit ISW = 1.0A ISW = 1.0A (assured by design, not ATE tested) VFB = 0.825V VCC Rising VCC Falling Min 4.0 784 Typ 800 40 200 500 21 0.375 80 0.01 Max 6.0 816 75 850 50 0.6 5 3.00 Units V mV nA KHz A V/mS % A V Feed Back Threshold 2.4 0.15 1.50 820 2.30 1200 100 -40 0.85 135 150 1920 A KHz mA dB %VO C ILIM FOP-PWM Io Peak Current at Switch Pin (not DC current) PWM Mode PFM Mode Load Current Crossover 1Hz < Frequency VCC < 10KHz VO = 1.2V, 50mA < IO < 1.0A, ckt figure 1 (assured by design, not ATE tested) Note 1: VIN vs VOUT ratio @ 1.0A LOAD IS SET AT VIN = VOUT + 1.0V Note 2: 1.0 amp operation @ 70C ambient depends on adequate heat sinking to keep TJ below 125C ELECTRICALS ELECTRICALS Copyright (c) 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 3 LX1912 TM (R) VREF @ 800mV, 1.0A, 1.2MHz PWM PRODUCTION DATA SHEET SIMPLIFIED BLOCK DIAGRAM WWW .Microsemi .C OM VPWR VCC UVLO Bias CL Clock And Ramp PWM S R SW 920mV REF OVP EA BG REF 800mV LX1912 GND Figure 2 - LX1912 Block Diagram PCB LAYOUT FB VOUT COUT Inductor Diode COUT COUT VIN N.C. GND FB SW VPWR VCC APPLICATIONS APPLICATIONS Rf COUT CIN Rf LX1912 GROUND Figure 3 - PCB Layout Considerations Copyright (c) 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 (R) VREF @ 800mV, 1.0A, 1.2MHz PWM PRODUCTION DATA SHEET APPLICATION NOTE 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 160C (typical) and has 20C of hysteresis. The regulator has an internal Power On Reset delay of 50100s 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. V R1 = R2 OUT - 1 V REF INDUCTOR SELECTION, CONT. The LX1912 stability performance is optimized by using an inductor value of 2.7H 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 60F 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 > 4.7F). 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 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 0.1F capacitor. 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) 2005 Rev. 1.0, 2006-09-06 APPLICATIONS APPLICATIONS Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX1912 TM (R) VREF @ 800mV, 1.0A, 1.2MHz PWM PRODUCTION DATA SHEET CHARACTERISTIC CURVES WWW .Microsemi .C OM UVLO THRESHOLDS- VIN RISING and FALLING 1.4 1.2 1 0.8 0.6 0.4 0.2 0 3 2.4 2.45 2.5 2.55 2.6 2.65 2.7 2.75 2.8 2.85 2.9 2.95 3.05 3.1 PWM Frequency vs Load Current 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 120C 0C PWM Switching Frequency, hZ 0.01 0.1 1 VIN, volts Load Current, A Figure 4- Under Voltage Lockout for VIN Figure 5 - PFM / PWM Range of Output Switch Figure 6 - Step Load Response 300mA to 800mA, L = 2.7H, COUT = 30F Figure 7- Soft Start Power On, L = 2.7H, COUT = 30F, IOUT = 0mADC CHARTS CHARTS Copyright (c) 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 6 LX1912 TM (R) VREF @ 800mV, 1.0A, 1.2MHz PWM PRODUCTION DATA SHEET PACKAGE DIMENSIONS WWW .Microsemi .C OM SG 6 Pin TSOT D e1 b E E1 e A2 E A Dim A A1 A2 b c D E E1 e1 e L L2 Note: 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 L A1 1. 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. MECHANICALS MECHANICALS Copyright (c) 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 7 LX1912 TM (R) VREF @ 800mV, 1.0A, 1.2MHz PWM PRODUCTION DATA NOTES SHEET WWW .Microsemi .C OM NOTES 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 (c) 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 |
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