LSP5502 2A Synchronous Step Down DC/DC Converter FEATURES GENERAL DESCRIPTION 2A Output Current Wide 4.5V to 27V Operating Input Range Integrated 120m Power MOSFET Switches Output Adjustable from 0.925V to 24V Up to 96% Efficiency Programmable Soft-Start Stable with Low ESR Ceramic Output Capacitors Fixed 400KHz Frequency Cycle-by-Cycle Over Current Protection Input Under Voltage Lockout 8-Pin SOP Package The LSP5502 is a monolithic synchronous buck regulator. The device integrates 120m MOSFETS that provide 2A 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 1A. This device, available in an 8-pin SOP package, provides a very compact system solution with minimal reliance on external components. TYPICAL APPLICATION Distributed Power Systems Networking Systems FPGA, DSP, ASIC Power Supplies Green Electronics/ Appliances Notebook Computers PIN ASSIGNMENT SOP-8L (TOP View) BS 1 8 SS IN 2 7 EN SW 3 6 COMP GND 4 5 FB PIN DESCRIPTION Name No. BS 1 IN 2 SW GND 3 4 FB 5 COMP 6 EN 7 SS 8 Description 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. Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in the Application Information section. Switch Output. Connect this pin to the switching end of the inductor. Ground. 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. Compensation Pin. See Stability Compensation in the Application Information section. 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. Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1F capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS unconnected. 1/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter ABSOLUTE MAXIMUM RATINGS Parameter Value Unit IN Supply Voltage -0.3 to 30 V SW Voltage -1 to VIN + 0.3 V BS Voltage VSW - 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 (JA) 70 C/W (Test on Approximately 3 in2 Copper Area 1OZ copper FR4 board) Junction to Ambient Case Resistance (JC) 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 VIN TJ Parameter Min 4.5 -20 Input Voltage Operating Junction Temperature Range Max 27 125 Unit V o C ELECTRICAL CHARACTERISTICS (VIN = 12V, TA= 25C unless otherwise specified.) Parameter Symbol Input Operating Voltage Input Holdup Voltage Feedback Voltage Feedback Overvoltage Threshold High-Side Switch-On Resistance Low-Side Switch-On Resistance High-Side Switch Leakage Upper Switch Current Limit Lower Switch Current Limit COMP to Current Limit Transconductance Error Amplifier Transconductance Error Amplifier DC Gain Switching Frequency Short Circuit Switching Frequency Maximum Duty Cycle Minimum On Time EN Shutdown Threshold Voltage EN Shutdown Threshold Voltage Hysterisis EN Lockout Threshold Voltage EN Lockout Hysterisis Test Conditions Min. VIN VOUT = 1.0V, ILOAD = 0A to 2A 4.5 VFB VOUT = 1.0V, ILOAD = 0A to 2A 4.5V VIN 20V 0.900 VEN = 0V, VSW = 0V GCOMP GEA AVEA fSW DMAX ICOMP = 10A 350 VFB = 0 VFB = 0.8V VEN Rising 1.1 Typ. 4.5 0.925 1.1 120 120 9 3.5 0.9 Max. Unit 27 V 0.950 10 4.0 5.2 A/V 800 480 400 150 90 220 1.3 A/V V/V kHz kHz % nS V 470 1.5 200 2.2 2/12 www.liteon-semi.com V V V m m A A A 2.5 210 mV 2.7 V mV Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter Supply Current in Shutdown IC Supply Current in Operation Input UVLO Threshold Rising Input UVLO Threshold Hysteresis Soft-start Current Soft-start Period Thermal Shutdown Temperature VEN = 0 VEN = 3V, VFB = 1.0V VEN Rising UVLO VSS = 0V CSS = 0.1F Hysteresis = 10C 3.80 0.3 1.4 4.05 210 6 15 160 3.0 1.5 4.40 A mA V mV A mS C FUNCTIONAL BLOCK DIAGRAM CURRENT SENSE AMPLIFIER OVP RAMP 1.1V 2 IN 5V OSCILLATOR FB 5 150/400KHz CLK M1 0.12 0.3V S Q R Q SS 8 0.925V ERROR AMPLIFIER 1 BS 3 SW 4 GND M2 0.12 CURRENT COMPARATOR 6uA COMP 6 EN 7 EN OK 2.5V 1.2V LOCKOUT COMPARATOR IN 7V Zener 1.5V OVP IN<4.10V INTERNAL REGULATORS SHUTDOWN COMPARATOR 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 voltage 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. 3/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter APPLICATION INFORMATION Output Voltage Setting Figure1. Output Voltage Setting Figure 1 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors RFB1 and RFB2 based on the output voltage. Typically, use RFB2 10k and determine RFB1 from the following equation: (1) Table 1-Recommended Resistance Values VOUT RFB1 RFB2 1.0V 1.2V 1.8V 2.5V 3.3V 5V 12V 1.0k 3.0k 9.53k 16.9k 26.1k 44.2k 121k 12k 10k 10k 10k 10k 10k 10k Inductor Selection The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. In general, select an inductance value L based on the ripple current requirement: VOUT * ( VIN - VOUT ) L= VIN f SW I OUTMAX K RIPPLE (2) where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum output current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum output current. With this inductor value, the peak inductor current is IOUT * (1 + KRIPPLE / 2). Make sure that this peak inductor current is less that the 3A current limit. Finally, select the inductor core size so that it does not saturate at 3A. Typical inductor values for various output voltages are shown in Table 1. VOUT 1.0V 1.2V 1.5V 1.8V 2.5V 3.3V 5V L 4.7uH 4.7uH 6.8H 6.8H 10H 10H 15H Table 1. Typical Inductor Values Input Capacitor 4/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter The input capacitor needs to be carefully selected to maintain 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 10F. 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 types, they can be further away if a small parallel 0.1F 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: V IN VRIPPLE = I OUTMAX K RIPPLE R ESR (3) + 8 * f SW 2 LC OUT 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 ripple. Therefore, a lower capacitance value can be used for ceramic capacitors. In the case of tantalum or electrolytic capacitors, the ripple is dominated by RESR 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 22F. For tantalum or electrolytic capacitors, choose a capacitor with less than 50m 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 MBRS130 30V,1A 30V,1A Lite-on Semiconductor Corp. International Rectifier C6 10nF 1 VIN = 12V 2 BS IN SW 15H/2A LSP5502 R4 100k 7 () C1 C2 22 uF/16V 0.1 uF EN SS GND 8 4 () C3 0.1F FB COMP R1 5 44.2k 6 C4 2.2nF R3 6.8k 5/12 www.liteon-semi.com VOUT = 5V/2A L1 3 C5 R2 10k C7 22F/10V CERAMIC x2 47pF Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter Stability Compensation CCOMP2 is needed only for high ESR output capacitor Figure 2. Stability Compensation The feedback loop of the IC is stabilized by the components at the COMP pin, as shown in Figure 2. The DC loop gain of the system is determined by the following equation: (4) The dominant pole P1 is due to CCOMP: G EA f P1 = 2 AVEA C COMP (5) The second pole P2 is the output pole: I OUT fP 2 = 2VOUT C OUT (6) The first zero Z1 is due to RCOMP and CCOMP: 1 fZ1 = 2R COMP C COMP (7) And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): 1 fP 3 = 2R COMP C COMP 2 (8) The following steps should be used to compensate the IC: STEP1. Set the crossover frequency at 1/10 of the switching frequency via RCOMP: (9) but limit RCOMP to 10k maximum. STEP2. Set the zero fZ1 at 1/4 of the crossover frequency. If RCOMP is less than 10k, the equation for CCOMP is: C COMP = 1 . 8 x 10 -5 R COMP (F ) (10) If RCOMP is limited to 10k, then the actual crossover frequency is 10/ (VOUTCOUT). Therefore: CCOMP = 1.2 x 10 -5 VOUT COUT (F ) (11) STEP3. If the output capacitor's ESR is high enough to cause a zero at lower than 4 times the crossover frequency, an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is: R ESRCOUT 1 . 1 x 10 -6 Min ,0. 012 * VOUT COUT () (12) 6/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter And the proper value for CCOMP2 is: C COMP 2 = C OUT R ESRCOUT R COMP (13) Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 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 1.5k 1.0V 22F Ceramic 10nF 100pF 1.7k 1.2V 22F Ceramic 10nF 100pF 2.2k 1.8V 22F Ceramic 6.8nF 100pF 3.6k 2.5V 22F Ceramic 4.7nF 100pF 4.7k 3.3V 22F Ceramic 3.3nF 47pF 6.8k 5V 22F Ceramic 2.2nF 47pF 3.0k 1.0V 47F SP Cap 6.8nF 470pF 3.6k 1.2V 47F SP Cap 4.7nF 330pF 5.6k 1.8V 47F SP Cap 3.3nF 220pF 6.8k 2.5V 47F SP Cap 2.2nF 200pF 10k 3.3V 47F SP Cap 2.0nF 150pF 10k 5V 47F SP Cap 2.2nF 150pF 470F/6.3V/30m 10k 1.0V 2.2nF 1nF 470F/6.3V/30m 10k 1.2V 3.3nF 1nF 470F/6.3V/30m 10k 1.8V 4.7nF 1nF 470F/6.3V/30m 10k 2.5V 6.8nF 1nF 470F/6.3V/30m 10k 3.3V 8.2nF 1nF 470F/10V/30m 10k 5V 10nF 1nF Table3. Typical Compensation for Different Output Voltages and Output Capacitors 7/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter C6 10nF 1 VIN = 12V 2 BS IN SW 15H/2A LSP5502 R4 100k 7 () C1 C2 22 uF/16V 0.1 uF EN SS GND 8 4 FB COMP R1 5 44.2k 6 C4 2.2nF () C3 0.1F C7 22F/10V CERAMIC x2 R2 10k C5 R3 6.8k VOUT = 5V/2A L1 3 47pF Figure 3 shows a sample LSP5502 application circuit generating 5V/2A output. C6 10nF 1 VIN = 12V 2 BS IN SW 4.7H/2A LSP5502 R4 100k 7 C1 C2 22F/16V 0.1F () EN SS GND 8 4 FB COMP R1 5 1k 6 () C3 C4 10nF 0.1F R3 1.5k VOUT = 1V/2A L1 3 C5 R2 12k C7 22F/6.3V CERAMIC x2 100pF Figure 4 shows a sample LSP5502 application circuit generating 1.0V/2A output. () To improve quality, it is recommended to choose a capacitance of about 1uF for C3. For system security, it is recommended to place a 0.1uF capacitor from EN Pin to ground. 8/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter TYPICAL CHARACTERISTICS Start up soft start Vin=12V, Vout=5V Iout=2A Operating status Vin=12V, Vout=5V Iout=2A ripple of Vout Vin=12V, Vout=5V Iout=3A SCP 9/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter 12Vin 5.0Vout Efficiency curve 12Vin 1.0Vout Efficiency curve VIN=8V VIN=12V VIN=18V VIN=23V Efficiency vs Input VoltageVout=5.0V) ( Vout=1.0V) Efficiency vs Input VoltageVout=5.0V) VIN=8V VIN=12V VIN=18V VIN=23V 100 90 90 80 80 (%) 100 (%) VIN=5V 70 60 70 60 Io(mA) 50 0 500 1000 1500 Io(mA) 50 2000 0 500 1000 1500 2000 ORDERING INFORMATION LSP5502 X X X Package : S: SOP8 Packing : Blank : Tube or Bulk A : Tape & Reel Temperature : C : -20 ~ 85 C MARKING INFORMATION 10/12 www.liteon-semi.com Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter PACKAGE INFORMATION Dimensions In Millimeters Dimensions In Inches Symbol A Min. Nom. Max. Min. Nom. Max. 1.35 1.6 1.75 0.053 0.063 0.069 A1 0.1 0.25 0.004 A2 1.25 1.45 1.55 0.049 0.057 0.061 B 0.31 0.41 0.51 0.012 0.016 0.02 C 0.1 0.2 0.25 0.0039 0.008 0.01 D 4.8 4.9 5 0.192 0.196 0.2 E 3.8 3.9 4 0.148 0.154 0.16 e 1.27 BSC 0.01 0.050 BSC H 5.7 6 6.3 0.224 0.236 0.248 L 0.4 0.71 1.27 0.015 0.028 0.05 0 8 11/12 www.liteon-semi.com 0 8 Rev. 1.8 LSP5502 2A Synchronous Step Down DC/DC Converter Important Notice and Disclaimer LSC reserves the right to make changes to this document and its products and specifications at any time without notice. Customers should obtain and confirm the latest product information and specifications before final design, purchase or use. LSC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does LSC assume any liability for application assistance or customer product design. LSC does not warrant or accept any liability with products which are purchased or used for any unintended or unauthorized application. No license is granted by implication or otherwise under any intellectual property rights of LSC. LSC products are not authorized for use as critical components in life support devices or systems without express written approval of LSC. 12/12 www.liteon-semi.com Rev. 1.8