LSP5502 LITEON | Alldatasheet
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2A Synchronous Step Down DC/DC Converter 1/11 R e v . 1 . 7 www.liteon-semi.com PIN ASSIGNMENT SS EN COMP FB BS IN SW GND (TOP View) SOP-8L PIN DESCRIPTION Name No. Description BS 1 Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 0.01uF capacitor between BS and SW. IN 2 Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in the Application Information section. SW 3 Switch Output. Connect this pin to the switching end of the inductor. GND 4 Ground. FB 5 Feedback Input. The voltage at this pin is regulated to 0.925V. Connect to the resistor divider between output and ground to set output voltage. COMP 6 Compensation Pin. See Stability Compen sation in the Application Information section. EN 7 Enable Input. When higher than 2.5V, this pin turns the IC on. When lower than 1.3V, this pin turns the IC off. Output voltage is discharged when the IC is off. This pin should not be left open. SS 8 Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1µF capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS unconnected. TYPICAL APPLICATION z Distributed Power Systems z Networking Systems z FPGA, DSP, ASIC Power Supplies z Green Electronics/ Appliances z Notebook Computers GENERAL DESCRIPTION The LSP5502 is a monolithic synchronous buc k regulator. The device integrates 120m Ω MOSFETS that provide 2 A continuous load current over a wide operating input voltage of 4.5V to 27V. Current mode control provides fast transient response and cycle-by-cycle current limit. An adjustable soft-start prevents inrush current at turn on. In shutdown mode, the supply current drops below 1µA. This device, available in an 8-pin SOP package, provides a very compact system solution with minimal reliance on external components. FEATURES z 2A Output Current z Wide 4.5V to 27V Operating Input Range z Integrated 120mΩ Power MOSFET Switches z Output Adjustable from 0.925V to 24V z Up to 96% Efficiency z Programmable Soft-Start z Stable with Low ESR Ceramic Output Capacitors z Fixed 400KHz Frequency z Cycle-by-Cycle Over Current Protection z Input Under Voltage Lockout z 8-Pin SOP Package Free Datasheet http://www.nDatasheet.com
2A Synchronous Step Down DC/DC Converter 2/11 R e v . 1 . 7 www.liteon-semi.com ABSOLUTE MAXIMUM RATINGS Parameter Value Unit IN Supply Voltage -0.3 to 30 V SW Voltage -1 to V IN + 0.3 V BS Voltage V SW – 0.3 to VSW + 6 V EN, FB, COMP Voltage -0.3 to 6 V Continuous SW Current Internally limited A Junction to Ambient Thermal Resistance (θJA) (Test on Approximately 3 in2 Copper Area 1OZ copper FR4 board) 70 °C/W Junction to Ambient Case Resistance (θJC) 20 °C/W Maximum Power Dissipation 0.76 W Operating Temperature -20 to 85 °C Storage Temperature -55 to 150 °C Lead Temperature (Soldering, 10 sec) 300 °C (Note: Exceeding these limits may damage the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability.) Recommended Operating Conditions Symbol Parameter Min Max Unit VIN Input Voltage 4.5 27 V TJ Operating Junction Te mperature Range -20 125 oC ELECTRICAL CHARACTERISTICS (VIN = 12V, TA= 25°C unless otherwise specified.) Parameter Symbol Test Conditions Min. Typ. Max. Unit Input Operating Voltage V IN V OUT = 1.0V, ILOAD = 0A to 2A 4.5 27 V Input Holdup Voltage V OUT = 1.0V, ILOAD = 0A to 2A 4.5 V Feedback Voltage V FB 4.5V ≤ VIN ≤ 20V 0.900 0.925 0.950 V Feedback Overvoltage Threshold 1.1 V High-Side Switch-On Resistance 120 m Ω Low-Side Switch-On Resistance 120 m Ω High-Side Switch Leakage VEN = 0V, VSW = 0V 9 10 µA Upper Switch Current Limit 3.5 4.0 A Lower Switch Current Limit 0.9 A COMP to Current Limit Transconductance GCOMP 5.2 A/V Error Amplifier Transconductance G EA ∆ICOMP = ±10µA 800 µA/V Error Amplifier DC Gain A VEA 480 V/V Switching Frequency f SW 350 400 470 kHz Short Circuit Switching Frequency V FB = 0 150 kHz Maximum Duty Cycle D MAX V FB = 0.8V 90 % Minimum On Time 220 nS EN Shutdown Threshold Voltage VEN Rising 1.1 1.3 1.5 V EN Shutdown Threshold Voltage Hysterisis 200 mV EN Lockout Threshold Voltage 2.2 2.5 2.7 V EN Lockout Hysterisis 210 mV Free Datasheet http://www.nDatasheet.com
2A Synchronous Step Down DC/DC Converter 3/11 R e v . 1 . 7 www.liteon-semi.com 0.12Ȥ 0.12 Ȥ Supply Current in Shutdown V EN = 0 0.3 3.0 µA IC Supply Current in Operation V EN = 3V, VFB = 1.0V 1.4 1.5 mA Input UVLO Threshold Rising UV LO VEN Rising 3.80 4.05 4.40 V Input UVLO Threshold Hysteresis 210 mV Soft-start Current VSS = 0V 6 µA Soft-start Period CSS = 0.1µF 15 mS Thermal Shutdown Temperature Hysteresis = 10°C 160 °C FUNCTIONAL BLOCK DIAGRAM INTERNAL REGULATORS FB SS COMP EN Zener 1.1V 0.3V 0.925V 2.5V 1.5V OVP SHUTDOWN COMPARATOR ERROR AMPLIFIER LOCKOUT COMPARATOR EN OK 6uA OSCILLATOR 150/400KHz RAMP CLK 1.2V OVP IN<4.10V IN CURRENT COMPARATOR CURRENT SENSE AMPLIFIER IN BS SW GND S Q R Q FUNCTIONAL DESCRIPTION The LSP5502 is a synchronous rectified, cur-rent-mode, step-down regulator. It regulates in-put voltages from 4.5V to 23V down to an out-put voltage as low as 0.925V, and supplies up to 2A of load current. The LSP5502 uses current-mode control to regulate the output voltage. The output voltage is measured at FB through a resistive voltage divider and amplified through the internal trans-conductance error amplifier. The voltage at the COMP pin is compared to the switch current measured internally to control the output voltage. The converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output voltage. Since the high side MOSFET requires a gate volt age greater than the input voltage, a boost capacitor connected between SW and BS is needed to drive the high side gate. The boost capacitor is charged from the internal 5V rail when SW is low. When the LSP5502 FB pin exceeds 20% of the nominal regulation voltage of 0.925V, the over volt-age comparator is tripped and the COMP pin and the SS pin are discharged to GND, forcing the high-side switch off. Free Datasheet http://www.nDatasheet.com
ripple current being 30% of the maximum output current. inductor values for various output voltages are shown in Table 1. Table 1. Typical Inductor Values
2A Synchronous Step Down DC/DC Converter 5/11 R e v . 1 . 7 www.liteon-semi.com The input capacitor needs to be carefully selected to mainta in sufficiently low ripple at the supply input of the converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor during switching, its ESR also affects efficiency. The input capacitance needs to be higher than 10 µF. The best choice is the ceramic type; however, low ESR tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the output current. The input capacitor should be placed close to the IN and G pins of the IC, with the shortest traces possible. In the case of tantalum or electrolytic ty pes, they can be further away if a small parallel 0.1 µF ceramic capacitor is placed right next to the IC. Output Capacitor The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: ESRRIPPLEOUTMAXRIPPLE RKIV = OUTLCSWf INV 2•8 + (3) where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the case of ceramic output capacitors, RESR is very small and does not contribute to the rippl e. Therefore, a lower capacitance value can be used for ceramic capacitors. In the case of tantalum or electrolytic capacitors, the ripple is dominated by R ESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR. For ceramic output capacitors, typically choose a capacitance of about 22µF. For tantalum or electrolytic capacitors, choose a capacitor with less than 50mΩ ESR. Optional Schottky Diode During the transition between high-side switch and low-side switch, the body diode of the low side power MOSFET conducts the inductor current. The forward voltage of this body diode is high. An optional Schottky diode may be paralleled between the SW pin and GND pin to improve overall efficiency. Table 2 lists example Schottky diodes and their Manufacturers. Table 2-Diode Selection Guide Part Number Voltage/Current Rating Vendor B130 30V,1A Lite-on Semiconductor Corp. MBRS130 30V,1A International Rectifier VIN = 12V LSP5502 IN EN FB SW C1 C2 0.1uF 47pF 10nF 10k 6.8k COMP 100k BS 2.2nF 8 6 SS 0.1uF 22uF/16V 15uH/2A 44.2k VOUT = 5V/2A B130/SK13 (Option) GND C7 22µF/10V CERAMIC Free Datasheet http://www.nDatasheet.com
Figure 2. Stability Compensation but limit RCOMP to 10kΩ maximum.
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2A Synchronous Step Down DC/DC Converter 7/11 R e v . 1 . 7 www.liteon-semi.com And the proper value for CCOMP2 is: COMP ESRCOUTOUT 2COMP R RCC = (13) Though CCOMP2 is unnecessary when the output capacitor ha s sufficiently low ESR, a small value C COMP2 such as 100pF may improve stability against PCB layout parasitic effects. Table 3 shows some calculated results based on the compensation method above. VOUT COUT RCOMP CCOMP CCOMP2 1.0V 22µF Ceramic 1.5kƸ 10nF 100pF 1.2V 22µF Ceramic 1.7kƸ 10nF 100pF 1.8V 22µF Ceramic 2.2kƸ 6.8nF 100pF 2.5V 22µF Ceramic 3.6kƸ 4.7nF 100pF 3.3V 22µF Ceramic 4.7kƸ 3.3nF 47pF 5V 22µF Ceramic 6.8kƸ 2.2nF 47pF 1.0V 47µF SP Cap 3.0kƸ 6.8nF 470pF 1.2V 47µF SP Cap 3.6kƸ 4.7nF 330pF 1.8V 47µF SP Cap 5.6kƸ 3.3nF 220pF 2.5V 47µF SP Cap 6.8kƸ 2.2nF 200pF 3.3V 47µF SP Cap 10kƸ 2.0nF 150pF 5V 47µF SP Cap 10kƸ 2.2nF 150pF 1.0V 470µF/6.3V/30mƸ 10k Ƹ 2.2nF 1nF 1.2V 470µF/6.3V/30mƸ 10k Ƹ 3.3nF 1nF 1.8V 470µF/6.3V/30mƸ 10k Ƹ 4.7nF 1nF 2.5V 470µF/6.3V/30mƸ 10k Ƹ 6.8nF 1nF 3.3V 470µF/6.3V/30mƸ 10k Ƹ 8.2nF 1nF 5V 470µF/10V/30mƸ 10k Ƹ 10nF 1nF Table3. Typical Compensation for Different Output Voltages and Output Capacitors Free Datasheet http://www.nDatasheet.com
2A Synchronous Step Down DC/DC Converter 9/11 R e v . 1 . 7 www.liteon-semi.com TYPICAL CHARACTERISTICS Start up soft start Vin=12V, Vout=5V Iout=2A Operating status Vin=12V, Vout=5V Iout=2A r i p p l e o f V o u t V i n = 1 2 V , V o u t = 5 V I o u t = 3 A S C P Free Datasheet http://www.nDatasheet.com
2A Synchronous Step Down DC/DC Converter 10/11 R e v . 1 . 7 www.liteon-semi.com &GGJDJFODZWT*OQVU7PMUBHFč7PVU *P N" ȫ 7*/ 7*/ 7*/ 7*/ &GGJDJFODZWT*OQVU7PMUBHFč7PVU *P N" ȫ 7*/ 7 7*/ 7*/ 7 7*/ 7*/ 12Vin 5.0Vout Efficiency curve 12Vin 1.0Vout Efficiency curve ORDERING INFORMATION LSP5502 X X X Package : S: SOP8 Packing : Blank : Tube or Bulk A : Tape & Reel C : -20 ~ 85 C Temperature : MARKING INFORMATION ( Vout=1.0V) Free Datasheet http://www.nDatasheet.com
2A Synchronous Step Down DC/DC Converter 11/11 R e v . 1 . 7 www.liteon-semi.com PACKAGE INFORMATION Dimensions In Millimeters Dimensions In Inches A1 0.1 0.25 0.004 0.01 e 1.27 BSC 0.050 BSC θ 0 ο 8ο 0 ο 8ο Free Datasheet http://www.nDatasheet.com