LX12973 VREF @ 800mV, 1.5A, 1.1MHZ PWM ® TM P RODUCTION D ATA S HEET KEY FEATURES DESCRIPTION APPLICATIONS/BENEFITS WWW . Microsemi .C OM Internal Reference 800mv ±2% Accuracy (Line and Temp.) 4.5V to 5.5V Input Range Internal Soft Start Adj. Output From 0.8V to VIN Output Current (I >1.5A) Quiescent Current < 550µA, typ at 23°C 1.1MHz PWM Frequency Micro Lead-frame, Thin MO229, 6-Pin Package The regulator is capable of providing an output load current of 1.5A, 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 low regulator IQ and PFM mode of operation The LX12973 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 MO-229 package provides a small form factor with excellent power dissipation capability. The LX12973 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 LX12973 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. 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 4.0 to 6V EFFICIENCY vs Iout (Vin=5V) Top Vo=3.375V, Lower Vo=1.25V 4 VINPOWER N/C 5 VINANALOG 4.7uF SWITCH 100% 6 3.3uH . 3 FB 90% 80% C . 2 GND 1.2V @ 1.5A 25K 1 10 70% 20uF 50K C= 680p 60% Ground Plane Tie-in 50% 40% 30% 1 mA 10 100 1000 10000 LX12973 Figure 1 – LX12973 Circuit Topology and Typical Efficiency Performance PACKAGE ORDER INFO Input Voltage Output Voltage Range LD Plastic MO229 6 Pin (3mm²) RoHS Compliant / Pb-free 0 to 125 4.5V – 5.5V Adjustable LX12973CLD 2987 (D/C) MSC TJ (°C) Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX12973CLD-TR) Copyright © 2000 Rev. 1.1, 2005-05-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LX12973 VREF @ 800mV, 1.5A, 1.1MHZ PWM ® 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. THERMAL DATA: Note: Heatsink pad on bottom should be connected to ground or left floating. “ LD” PACKAGE THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA (ASSUMES NO AMBIENT AIRFLOW) 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 Package Peak Temp. for Solder Reflow (40 seconds max. exposure) ............. 260°C (+0, -5) 25-40°C/W (PCB layout dependent) Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the thermal performance of the device/pc-board system. 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 < T < 125oC for VIN = 5V (except where otherwise noted). Typical values are at TA=23°C. Parameter ` Symbol Operating Range VIN 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 Feed Back Threshold VFBT Quiescent Operating Current Soft Start, Vout Slew Rate P-Channel Switch ON Resistance IQ (Pin 5) Vo RDS(ON) ISW = 1.0A ISW = 1.0A (assured by design, not ATE tested) 80 nA Khz 100 Ω % 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 © 2000 Rev. 1.1, 2005-05-05 Load Reg TSD (assured by design, not ATE tested) 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 ELECTRICALS Maximum Duty Cycle A mA Page 2 LX12973 VREF @ 800mV, 1.5A, 1.1MHZ PWM ® TM P RODUCTION D ATA S HEET SIMPLIFIED BLOCK DIAGRAM WWW . Microsemi .C OM VIN CL Σ CLOCK AND RAMP PWM S R SWITCH EA BG REF 800MV FEEDBACK GROUND Figure 2 – LX12973 Block Diagram Vout Cout INDUCTOR DIODE Vin Gnd n/ c FB Cs Sw Cout Rf C in Vpwr Cout APPLICATIONS LX12973 Vin Rs Cout Rf Ground Figure 3 – PCB Layout Considerations Copyright © 2000 Rev. 1.1, 2005-05-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 3 LX12973 VREF @ 800mV, 1.5A, 1.1MHZ PWM ® TM 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 ⎠ ⎦⎥ 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 © 2000 Rev. 1.1, 2005-05-05 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 LX12973; (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 LX12973 VOUT pin and GND pin to reduce high frequency noise and decoupling the VIN pin using a 0.1uF capacitor. The LX12973 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 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, CONT. The LX12973 allows for a broad selection of inductor values and choosing a value between 2.2µH and 22µH supports 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 StepLoad response. WWW . Microsemi .C OM FUNCTIONAL DESCRIPTION The LX12973 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 50-100us 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. LX12973 VREF @ 800mV, 1.5A, 1.1MHZ PWM ® TM P RODUCTION D ATA S HEET CHARACTERISTIC CURVES WWW . Microsemi .C OM CH2:VOUT CH1:SWITCH Figure 4– Step Load Response 250ma-1.2A 3.3uH, 40uF 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 -25 0 25 50 75 100 125 150 GRAPHS TEMPERATURE, °C Figure 6 – Power On and Soft Start For Iout 10ma to 1amp Figure 7– Vout Temperature Stability Copyright © 2000 Rev. 1.1, 2005-05-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 5 LX12973 VREF @ 800mV, 1.5A, 1.1MHZ PWM ® 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 A1 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 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. NOTES 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 © 2000 Rev. 1.1, 2005-05-05 Microsemi Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 6