LESHAN RADIO COMPANY, LTD. 1.5MHz 600mA Synchronous Step-Down Converter with Low Quiescent Current LR8501 Series FEATURES: constant z High efficiency : Up to 96% current z Output Current: 600mA (Typ.) step-down z 1.5MHz Constant Switching Frequency converter. It is ideal for powering portable z No Schottky Diode Required equipment which runs from a single cell z Input Voltage: 1.8V to 5.5V Lithium-Ion z 0.6V Reference Allows Low Output INTRODUCTION: The LR8501 frequency, mode is slope PWM a 1.5MHz compensated synchronous battery. 100% duty cycle provides low dropout operation, extending Voltage battery life in portable systems. In power z Low Dropout: 100% duty Cycle saving mode, 40μA quiescent current is z Low Quiescent Current: 40μA very suitable for DSP/MCU in standby z Shutdown Current: <1μA operation; and in active mode, low output z Current Mode Operation for Excellent Line and Load Transient Response ripple voltage is good enough for noise sensitive applications. The two modes can z Built-in Thermal Protection be automatically switched according to the z Package: SOT-23-5 load current. APPLICATIONS： z Cellular and Smart Phones z Digital Still and Video Cameras z Personal Information Appliances z Microprocessors Core Supplies z Wireless and DSL Modems z Portable consumer equipments PIN CONFIGURATION: ORDER INFORMATION: LR8501①②③④ Ver1.0 DESIGNATOR SYMBOL DESCRIPTION ① A ②③ Integer ④ M/MR Standard Output Voltage e.g.1.8V=②:1, ③:8 Adj=②:, ③: Package：SOT-23-5 1/11 LESHAN RADIO COMPANY, LTD. Pin Description Tabel1. PIN NUMBER PIN NAME FUNCTION 3 CE Chip Enable Pin 2 2 VSS Ground 3 5 SW External Inductor Connection Pin 4 1 VIN Power Input 5 4 VOUT/FB Output Pin/Feedback(ADJ Version) M MR 1 BLOCK DIAGRAM ABSOLUTE MAXIMUM RATINGS SYMBOL RATINGS UNITS VIN VSS-0.3~VSS+6.5 V VSS-0.3~VIN+0.3 V ISWMAX 1500 mA Pd 400 mW Operating Temperature Topr -40~+85 ℃ Junction Temperature Tj 125 ℃ Storage Temperature Tstg -40~+125 ℃ Soldering Temperature & Time Tsolder 260℃, 10s PARAMETER Input Voltage CE,SW,FB/VOUT Voltage Peak SW Sink and Source Current Power Dissipation SOT-23-5 2/11 LESHAN RADIO COMPANY, LTD. ELECTRICAL CHARACTERISTICS LR8501 Series (V IN=CE=3.6V, Ta=25℃, Test Circuit Figure1, unless otherwise specified) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Output Voltage VOUT(F) (1) IOUT =100mA VOUT×0.97 VOUT VOUT×1.03 V TA=25℃ 0.5880 0.600 0.6120 0℃≤TA≤85℃ 0.5865 0.600 0.6135 -40℃≤TA≤85℃ 0.5850 0.600 0.6150 Feedback Voltage VFB Input Voltage VIN 5.5 V Supply Current1 （Active MODE） ISS1 VFB=0.50V 270 400 μA Supply Current2 （Power Saving Mode） ISS2 VFB=0.63V 40 50 μA Shutdown Current ISHDN VCE=VSS 0.1 1.0 μA Feedback Current IFB VFB=0.65V ±30 nA Maximum Output Current IOUT － VFB Line Regulation ∆VFB VIN= 1.8V~5.5V 0.40 %/V Output Voltage Line Regulation ∆VOUT VIN= 1.8V~5.5V IOUT=10mA 0.40 %/V Output Voltage Load Regulation ∆VLOAD IOUT =1mA ~600mA 0.02 %/mA Oscillator Frequency fosc VFB=0.6V or VOUT=100% Peak Inductor Current IPK VIN=3V,VFB=0.5V or VOUT=90% 1.0 RDS(ON) OF P-CH FET RPFET ISW = 100mA 0.45 0.60 Ω RDS(ON) OF N-CH FET RNFET ISW = -100mA 0.35 0.50 Ω SW Leakage ILSW CE=0,VSW=0 or 5V, VIN=5V ±0.01 ±1 μA VIN V 0.3 V ±1 μA CE "High" Voltage(2) VCE“H” (3) VCE“L” CE "Low" Voltage 1.8 V 600 1.2 mA 1.5 1.5 CE Leakage Current ICE NOTE : 1. VOUT(F):The fixed voltage version effective output voltage. ±0.1 1.8 MHz A 2. High Voltage：Forcing CE above 1.5V enables the part. 3. Low Voltage：Forcing CE below 0.3V shuts down the device. 3/11 LESHAN RADIO COMPANY, LTD. TYPICAL APPLICATION CIRCUITS L1 2.2μH VIN VIN SW CE VOUT VSS VOUT 1.8V C1 4.7μF OFF ON C3 10μF Figure1 Basic Application Circuit TYPICAL PERFORMANCE CHARACTERISTICS (Test Figure1 above unless otherwise specified) 4/11 LESHAN RADIO COMPANY, LTD. 5/11 LESHAN RADIO COMPANY, LTD. 6/11 LESHAN RADIO COMPANY, LTD. OPERATION MAIN CONTROL LOOP IRCMP, and the switch voltage will ring. This is The LR8501 uses a constant frequency, discontinuous mode operation, and is normal current mode step-down architecture. Both the behavior for the switching regulator. At very light main (P-channel MOSFET) and synchronous loads, the LR8501 will automatically skip pulses in (N-channel discontinuous mode operation to maintain output MOSFET) switches are internal. During normal operation, the internal top power regulation. MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when SLOPE COMPENSATION the current comparator, ICOMP, resets the RS latch. Slope compensation provides stability in The peak inductor current at which ICOMP resets constant frequency architecture by preventing the RS latch, is controlled by the output of error sub-harmonic oscillations at high duty cycles. It is amplifier EA. When the load current increases, it accomplished causes a slight decrease in the feedback voltage, compensating ramp to the inductor current signal FB, relative to the 0.6V reference, which in turn, at duty cycles in excess of 50%. This slope causes the EA amplifier’s output voltage to compensated current mode PWM control provides increase until the average inductor current stable switching and cycle-by-cycle current limit matches the new load current. While the top for excellent load and line response. internally by adding a MOSFET is off, the bottom MOSFET is turned on until either the inductor current starts to reverse, as indicated by the current reversal comparator IRCMP, or the beginning of the next clock cycle. POWER SAVING MODE OPERATION At very light loads, the chip automatically enters power saving mode. In power saving mode at light load, a control circuit puts most of the MAXIMUM LOAD CURRENT circuit into sleep in order to reduce quiescent The LR8501 will operate with input voltage as current and improve efficiency at light load. When low as 1.8V, however, the maximum load current the output voltage drops to certain threshold, the decreases at lower input due to large IR drop on control circuit turns back on the oscillator and the the main switch and synchronous rectifier. The PWM control loop, boosting output backup. When slope compensation signal reduces the peak an upper threshold is reached, the control circuit inductor current as a function of the duty cycle to again puts most of circuit into sleep, reducing prevent sub-harmonic oscillations at duty cycles quiescent current. During power saving mode greater than 50%.Conversely the current limit operation, the converter positions the output increase as the duty cycle decreases. voltage slightly higher than the nominal output voltage during PWM operation, allowing additional DISCONTINUOUS MODE OPERATION headroom for voltage drop during a load transient At light loads, the inductor current may reach from light to heavy load. While the power saving zero reverse on each pulse. The bottom MOSFET mode improves light load efficiency, however, with is turned off by the current reversal comparator, the turning on and off, the noise or ripple voltage is 7/11 LESHAN RADIO COMPANY, LTD. will then be determined by the input voltage minus larger than that in the active Mode. the voltage drop across the P-channel MOSFET and the inductor. DROPOUT OPERATION As the input supply voltage decreases to a An important detail to remember is that at low value approaching the output voltage, the duty inputs supply voltages, the RDS(ON) of cycle increases toward the maximum on-time. P-channel switch increases. Therefore, the user Further reduction of the supply voltage forces the should calculate the power dissipation when the main switch to remain on for more than one cycle LR8501 is used at 100% duty cycle with low input until reaches 100% duty cycle. The output voltage voltage. the APPLICATION INFORMATION The basic LR8501 applic ation circuits are This formula has a maximum at VIN = 2VOUT, shown in Figure 1.External component selection is where IRMS = IOUT/2. This simple worst-case driven by the load requirement and begins with the condition is commonly used for design because selection of L followed by CIN and COUT. even significant deviations do not offer much relief. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low SETTING THE OUTPUT VOLTAGE Figure1 shows the basic application circuit ESR and small temperature coefficients. A 4.7μF with LR8501 adjustable output version. The ceramic capacitor for most application is sufficient. external resistor sets the output voltage according INDUCTOR SELECTION to the following equation: VOUT 0.6V 1 R2 R1 For most applications, the value of the inductor will fall in the range of 1μH to 4.7μH. Its Table 2.Resistor select for output voltage setting VOUT 1.2V 1.5V 1.8V 2.5V R1 316K 316K 316K 316K value is chosen based on the desired ripple R2 316K 470K 634K 1M current. Large value inductor lower ripple current and small value inductor result in higher ripple currents. Higher VIN or VOUT also increases the ripple current as shown in the following equation: ∆IL INPUT CAPACITOR SELECTION VOUT VIN VOUT VIN L f In continuous mode, the source current of the A reasonable starting point for setting ripple top MOSFET is a square wave of duty cycle current is △IL=240mA (40% of 600mA). The DC VOUT/VIN. To prevent large voltage transients, a current rating of the inductor should be at least low ESR input capacitor sized for the maximum equal to the maximum load current plus half the RMS current must be used. The maximum RMS ripple current to prevent core saturation. Different core materials and shapes will capacitor current is given by: CIN required IRMS IOMAX VOUT VIN VOUT VIN / change the size/current relationship of an inductor. and price/current The choice of which 8/11 LESHAN RADIO COMPANY, LTD. style inductor to use often depends more on the price vs. size requirements and any radiated field/EMI requirements than on what the LR8501 requires to operate. Table 3 shows some typical surface mount inductors that work well in LR8501 applications. Table 3.Representative Surface Mount Inductors PART NUMBER MAX DCR (mΩ) VALUE (μH) MAX DC CURRENT (A) SIZE Sumida CDRH 3D16 2.2 3.3 4.7 75 110 162 1.20 1.10 0.90 3.8×3.8 Sumida CR43 2.2 3.3 4.7 71.2 86.2 108.7 1.75 1.44 1.15 4.5×4.0 2.2 3.3 4.7 75 110 162 1.32 1.04 0.84 Sumida CDRH 4D18 ×1.8 ×3.5 4.7×4.7 ×2.0 W×L×H (mm3) PCB LAYOUT GUIDANCE When laying out the printed circuit board, the OUTPUT CAPACITOR SELECTION The selection of COUT is driven by the required effective series resistance (ESR). following suggestions should be taken to ensure proper operation of the LR8501. Typically, once the ESR requirement for COUT has 1. The power traces, including the GND trace, been met, the RMS current rating generally far the SW trace and the VIN trace should be kept exceeds the IRIPPLE requirement. The output ripple short, direct and wide to allow large current △VOUT is determined by: flow. Put enough multiply-layer pads when ∆VOUT ∆IL ESR they need to change the trace layer. 1 8fCOUT 2. Keep the switching node, SW, away from the Where f = operating frequency, COUT = output capacitance and △IL = ripple current in the sensitive FB node. 3. The FB pin should directly connect to the inductor. For a fixed output voltage, the output feedback ripple is highest at maximum input voltage since R1/R2 must be connected between the (+) △IL plate of COUT and ground. increase with input voltage. Ceramic capacitors with X5R or X7R dielectrics are recommended due to their low ESR and high ripple current. resistors. The resistive divider 4. Connect the (+) plate of CIN to the VIN pin as closely as possible. 5. Keep the (-) plate of CIN and COUT as close as possible. Figure 2a LR8501-1.8V Layout 9/11 LESHAN RADIO COMPANY, LTD. Figure 2b LR8501-Adj Layout 10/11 LESHAN RADIO COMPANY, LTD. PACKAG GING INFORMATION N z SOT23-5 Package P Ou utline Dimen nsions 11/11