AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n General Description n Features The AME5268 is a fixed frequency monolithic synchronous buck regulator that accepts input voltage from 4.75V to 28V. Two NMOS switches with low on-resistance are integrated on the die. Current mode topology is used for fast transient response and good loop stability. l 3A Output Current Shutdown mode reduces the input supply current to less than 1µA. An adjustable soft-start prevents inrush current at turn-on. l Up to 95% Efficiency l Wide 4.75V to 28V Operating Input Range l Integrated Power MOSFET Switches l Output Adjustable from 0.925V to 25V l Programmable Soft Start l Stable with Low ESR Ceramic Output This device is available in SOP-8/PP package with exposed pad for low thermal resistance. Capacitors l Cycle-by Cycle Over Current Protection l Fixed 340KHz Frequency n Applications l Input Under Voltage Lockout l System Protected by Over-current Limiting, l Distributed Power System Over-voltage Protection and Thermal Shut- l Networking System down l FPGA, DSP, ASIC Power Supplies l Thermally Enhanced SOP-8/PP Package l Notebook Computers l All AME’ s Lead Free Products Meet RoHS Standards C ie n Typical Application C5 10nF VIN 12V C1 10µF/35V x2 R4 100KΩ L1 15µH/3.4A BS IN EN VOUT 5V 3A SW AME5268 SS GND C4 0.1µF Rev.B.01 FB S COMP C3 3.3nF R3 6.98KΩ1% R1 44.2K Ω1% R2 10KΩ1% C2 22µF/10V x2 1 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Function Block Diagram 1.1V OVDET OVP CURRENT SENSE AMP FB 0.3V VIN SLOPE 5V osc CLK BS S Q MH COMP 6uA PWM LOGIC R SW 0.925V EA CLAMP ML SS OVP OTP UVP OTDET UVLO IRCMP GND EN IN 2.5V 1.5V INTERNAL REGULATORS LOCKOUT CMP SHUTDOWN CMP 2 Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Pin Configuration SOP-8/PP Top View 8 7 6 5 AME5268-AZA 1. BS 2. IN 3. SW AME5268 4. GND 5. FB 6. COMP 1 2 3 4 7. EN Die Attach: 8. SS Conductive Epoxy Note: The area enclosed by dashed line represents Exposed Pad and connect to GND. C ie Rev.B.01 3 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Pin Description Pin Number Pin Name Pin Description 1 BS High-Side Gate Drive Boost Input. BS supplies the drive for the high-side NChannel MOSFET switch. Connect a 10nF or greater capacitor from SW to BS to power the high side switch. 2 IN Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with a 4.75V to 28V power source. Bypass IN to GND with a suitable large capacitor to eliminate noise on the input to the IC. 3 SW Power Switching Output. SW is the switching node that supplies power to the output. Connect the output LC filter from SW to the output load. Note that a capacitor is required from SW to BS to power the high-side switch. 4 GND Ground. Connect the exposed pad to pin 4. 5 FB Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback reference voltage is 0.925V. 6 COMP Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from COMP to GND is required. 7 EN Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than 2.7V to turn on the regulator, drive it lower than 1.1V to turn it off. Pull up to the IN pin with 100KΩ resister for automatic start up. SS Soft-start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. Add a 0.1µF capacitor set the soft-start period to 15mS. To disable the soft start feature, leave the SS unconnected. 8 4 Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Ordering Information AME5268 - x x x xxx Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration A (SOP-8/PP) 1. BS 2. IN 3. SW 4. GND 5. FB 6. COMP 7. EN 8. SS Package Type Z: SOP/PP Number of Pins A: 8 Output Voltage ADJ: Adjustable C ie Rev.B.01 5 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Available Options Part Number Marking Output Voltage Package Operating Ambient Temperature Range AME5268-AZAADJ A5268 AMyMXX ADJ SOP-8/PP -40OC to +85OC Note: 1. The first 2 places represent product code. It is assigned by AME such as AM. 2. y is year code and is the last number of a year. Such as the year code of 2008 is 8. 3. A bar on top of first letter represents Green Part such as A5268. 4. The last 3 places MXX represent Marking Code. It contains M as date code in "month", XX as LN code and that is for AME internal use only. Please refer to date code rule section for detail information. 5. Please consult AME sales office or authorized Rep./Distributor for the availability of output voltage and package type. 6 Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Absolute Maximum Ratings Parameter Maximum Unit Supply Voltage -0.3V to +30V V Switch Voltage -1V to VIN +0.3 V -0.3V to VSW + 6 V All Other Pins -0.3V to +6 V EN Voltage -0.3V to VIN V Boost Switch Voltage B* ESD Classification Caution: Stress above the listed absolute maximum rating may cause permanent damage to the device. HBM B: 2000V ~ 3999V n Recommended Operating Conditions Parameter Rating Unit Ambient Temperature Range -40 to +85 o C Junction Temperature Range -40 to +125 o C -65 to +150 o C Storage Temperature Range C ie Rev.B.01 7 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Thermal Information Parameter Package Thermal Resistance* (Junction to Case) SOP-8/PP Die Attach Symbol Maximum θJC 19 Unit o Thermal Resistance (Junction to Ambient) SOP-8/PP Internal Power Dissipation SOP-8/PP Maximum Junction Temperature Conductive Epoxy θJA 84 PD 1450 C/W mW 150 o Solder Iron(10 Sec)** C 350 * Measure θJC on backside center of Exposed Pad. ** MIL-STD-202G 210F 8 Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Electrical Specifications VIN = 12V, TA = 25OC, unless otherwise noted. Parameter Shutdown Current Symbol Test Condition ISHDN Supply Current Feedback Voltage VFB Typ Max Units VEN = 0V 1 3.0 µA VEN = 3V, VFB = 1.2V 1.3 1.5 mA 0.925 0.95 V 4.75V <= VIN <=28V Min 0.90 OVP Threshold Voltage 1.10 V 400 V/V 800 µA/V Error Amplifier Voltage Gain AEA Error Amplifier Transconductance GEA High-side Switch On Resistance RDS,ON,HI 135 mΩ Low-side Switch On Resistance RDS,ON,LO 105 mΩ Switch Leakage Current ISW,LK ∆IC = ±10µA High-side Switch Current Limit Minimum Duty Cycle Low-side Switch Current Limit From Drain to Source COMP to Current Sense Transconductance fOSC,CL Short Circuit Oscillation Frequency fOSC,SCR DMAX Minimum On Time t ON,MIN Input Undervoltage Lockout VUVLO TA = 25OC 300 -40OC<=TA <=+85OC C VFB = 0V 270 VFB =0.8V ie VIN rising, TA = 25OC O O -40 C<=TA <=+85 C Input Undervoltage Lockout Hysteresis 4 GCS Current Limit Oscillation Frequency Maximum Duty Cycle 10 VEN = 0V, VSW = 0V 3.8 5.8 A 1.25 A 5.2 A/V 340 380 KHz 400 KHz 116 KHz 90 % 220 nS 4.05 3.5 VUVLO,HYST µA 4.3 V 4.7 V 210 mV Soft-Start Current Source ISS VSS = 0V 6 µA Soft-Start Period t SS CSS = 0.1µF 15 mS EN Lockout Threshold Voltage Rev.B.01 VEN TA = 25OC 2.2 -40OC<=TA <=+85OC 2.2 2.5 2.7 V 2.7 V 9 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Electrical Specifications (Contd.) VIN = 12V, TA = 25OC, unless otherwise noted. Parameter Symbol EN Shutdown Threshold Voltage 10 Test Condition Min Typ Max Units VEN Rising 1.1 1.56 2 V EN Shutdown Threshold Voltage Hysteresis 210 mV EN Lockout Hysteresis 210 mV Thermal Shutdown Temperature OTP Shutdown, temperature increasing 160 O C Thermal Shutdown Hysteresis OTH Restore, temperature decreasing 20 O C Rev.B.01 AME AME5268 n Detailed Description Oscillator Frequency The internal free running oscillator sets the PWM frequency at 340KHz. Enable and Soft start The EN Pin provides electrical on/off control of the regulator. Once the EN pin voltage exceeds the lockout threshold voltage, the regulator starts operation and the soft start begins to ramp. If the EN pin voltage is pulled below the lockout threshold voltage, the regulator stops switching and the soft start resets. Connecting the pin to ground or to any voltage less than 0.5V will disable the regulator and activate the shutdown mode. To limit the start-up inrush current, a soft-start circuit is used to ramp up the reference voltage from 0V to its final value, linearly. The softstart time is 15 ms typically. 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter Over-voltage Protection The AME5268 has an over-voltage protection (OVP) circuit to minimize voltage overshoot when recovering from output fault conditions. The OVP circuit include an overvoltage comparator to compare the FB pin voltage and a threshold of 120% x V FB. Once the FB pin voltage is higher than the threshold, the COMP pin and the SS pin are discharged to GND, forcing the high-side MOSFET off. When the FB pin voltage drops lower than the threshold, the highside MOSFET will be enabled again. Thermal Shutdown The AME5268 protects itself from overheating with an internal thermal shutdown circuit. If the junction temperature exceeds the thermal shutdown trip point, the voltage reference is grounded and the high-side MOSFET is turned off. The part is restarted under control of the soft start circuit automatically when the junction temperature drops 30OC below the thermal shutdown trip point. Under Voltage Lockout (UVLO) Component Selection The AME5268 incorporates an under voltage lockout circuit to keep the device disabled when VIN (the input voltage) is below the UVLO start threshold voltage. During Setting the Output Voltage power up, internal circuits are held inactive and the soft start is grounded until V IN exceeds the UVLO start threshThe output voltage is using a resistive voltage divider conold voltage. Once the UVLO start threshold voltage is C nected from the output voltage to FB. It divides the output reached, the soft start is released and device start-up bevoltage down to the feedback voltage by the ratio: gins. The device operates until VIN falls below the UVLO stop threshold voltage. The typical hysteresis in the UVLO i e R2 comparator is 210mV. VFB = VOUT R1 + R2 Over-Current Protection Overcurrent limiting is implemented by monitoring the current through the high side MOSFET. If this current exceeds the over-current threshold limit, the overcurrent indicator is set true. The system will ignore the over-current indicator for the leading edge blanking time at the beginning of each cycle to avoid any turn-on noise glitches. the output voltage is: VOUT = 0.925 × R1 + R 2 R2 Once overcurrent indicator is set true. The high-side MOSFET is turned off for the rest of the cycle after a propagation delay. This over-current limiting mode is called cycle-by-cycle current limiting. Rev.B.01 11 AME AME5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter n Detailed Description (Contd.) Inductor The inductor is required to supply constant current to the load while being driven by the switched input voltage. A larger value inductor will have a larger physical size, higher series resistance, and lower saturation current. It will result in less ripple current that will in turn result in lower output ripple voltage. Make sure that the peak inductor current is below the maximum switch current limit. Determine inductance is to allow the peak-to peak ripple current to be approximately 30% of the maximum switch current limit. The inductance value can be calculated by: L= VOUT VOUT × 1 − fs × ∆IL VIN Where fs is the switching frequency, VIN is the input voltage, VOUT is the output voltage, and ∆IL is the peak-topeak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current, calculated by: ILP = ILOAD + VOUT VOUT × 1 − 2 × fs × L VIN Where ILOAD is the load current. The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI constraints. Input Capacitor The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the AC current while maintaining the DC input voltage. Use low ESR capacitors for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors will also be suggested. Choose X5R or X7R dielectrics when using ceramic capacitors. Since the input capacitor (C1) absorbs the input switching current, it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: VOUT VOUT IC 1 = I LOAD × × 1 − VIN VIN 12 At VIN = 2V OUT, where IC1 = ILOAD /2 is the worst-case condition occurs. For simplification, use an input capacitor with a RMS current rating greater than half of the maximum load current. When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input. When using electrolytic or tantalum capacitors, a high quality, small ceramic capacitor, i.e. 0.1µF, should be placed as close to the IC as possible. The input voltage ripple for low ESR capacitors can be estimated by: ∆VIN = I LOAD VOUT VOUT × × 1 − C1× fs VIN VIN Where C1 is the input capacitance value. Output Capacitor The output capacitor (C2) is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: ∆VOUT = VOUT VOUT 1 × 1 − × RESR + fs × L VIN 8 × fs × C 2 Where RESR is the equivalent series resistance (ESR) value of the output capacitor and C2 is the output capacitance value. When using ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance which is the main cause for the output voltage ripple. For simplification, the output voltage ripple can be estimated by: ∆VOUT = VOUT VOUT × 1 − 2 8 × fs × L × C 2 VIN When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: ∆VOUT = VOUT VOUT × 1 − × RESR fs × L VIN The characteristics of the output capacitor also affect the stability of the regulation system. The AME5268 can be optimized for a wide range of capacitance and ESR values. Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Detailed Description (Contd.) Compensation Components AME5268 has current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP is the output of the internal transconductance error amplifier. A series capacitor-resistor combination sets a pole-zero combination to govern the characteristics of the control system. The DC gain of the voltage feedback loop is given by: AVDC = RLOAD × GCS × AEA × VFB VOUT Where VFB is the feedback voltage (0.925V), A VEA is the error amplifier voltage gain, GCS is the current sense transconductance and RLOAD is the load resistor value. The system has two poles of importance. One is due to the output capacitor and the load resistor, and the other is due to the compensation capacitor (C3) and the output resistor of the error amplifier. These poles are located at: f P1 = GEA 2π × C3 × AVEA fP 2 = 1 2π × C 2 × RLOAD C Where GEA is the error amplifier transconductance. The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor ie (R3). This zero is located at: fZ 1 = 1 2π × C 3 × R 3 The system may have another zero of importance, if the output capacitor has a large capacitance and/or a high ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at: f ESR = Rev.B.01 1 2π × C 2 × RESR In this case, a third pole set by the compensation capacitor (C6) and the compensation resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. This pole is located at: f P3 = 1 2π × C 6 × R 3 The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover frequency where the feedback loop has the unity gain is important. Lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause system instability. A good standard is to set the crossover frequency below one-tenth of the switching frequency. To optimize the compensation components, the following procedure can be used. 1. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine R3 by the following equation: R3 = 2π × C 2 × fC VOUT 2π × C 2 × 0.1× fs VOUT × < × GEA × GCS VFB GEA × GCS VFB Where fC is the desired crossover frequency which is typically below one tenth of the switching frequency. 2. Choose the compensation capacitor (C3) to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero (fZ1) below one-forth of the crossover frequency provides sufficient phase margin. Determine C3 by the following equation: C3 > 4 2π × R3 × f C Where R3 is the compensation resistor. 13 AME AME5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter n Detailed Description (Contd.) 3. Determine if the second compensation capacitor (C6) is required. It is required if the ESR zero of the output capacitor is located at less than half of the switching frequency, or the following relationship is valid: 1 fS < 2π × C 2 × RESR 2 If this is the case, then add the second compensation capacitor (C6) to set the pole fP3 at the location of the ESR zero. Determine C6 by the equation: C6 = 14 C 2 × RESR R3 Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Characterization Curve(For reference only) Efficiency vs. Output Current Efficiency vs. Output Current 90 80 80 70 70 Efficiency(%) 100 90 Efficiency(%) 100 60 50 VOUT = 3.3V VIN = 12V C IN = 20µF C OUT = 44µF L = 10µH 40 30 20 10 60 50 40 20 10 0 0 100 1000 VOUT = 5V VI N = 12V CI N = 20µF COUT = 44µ F L = 15µH 30 10000 100 1000 Output Current(mA) Output Current(mA) Frequency vs. Temperature Start-Up form EN 10000 400 390 380 Frequency(KHz) 370 1 360 350 340 330 2 320 310 C 300 3 290 280 VIN = 12V 270 260 -50 ie -25 0 +25 +50 +75 +100 4 +125 4mS / div Temperature (oC) VIN = 12V VOUT = 5V IOUT = 3000mA C = 0.1µF SS 1) EN = 5V/div 2) VOUT = 2V/div 3) IL = 2A/div 4) IOUT = 2A/div Rev.B.01 15 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Characterization Curve(For reference only) Power Off from EN Load Step 1 1 2 2 3 3 4 4 VIN = 12V VOUT = 5V IOUT = 3000mA C = 0.1µF 200µS / div VIN = 12V VOUT = 3.3V IOUT = 0mA to 3000mA O C = 470pF, T =25 C 400µS / div SS SS 1) EN = 5V/div 2) VOUT = 5V/div 3) IL = 2A/div 4) IOUT = 2A/div A 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div Load Step Load Step 1 1 2 2 3 3 4 4 200µS / div VIN = 12V VOUT = 5V IOUT = 0mA to 3000mA O C = 470pF, T =25 C SS A 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div 16 200µS / div VIN = 12V VOUT = 3.3V IOUT = 500mA to 3000mA O C = 470pF, T =25 C SS A 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Characterization Curve(For reference only) Load Step Stead State Test 1 1 2 2 3 3 4 4 200µS / div 2µS / div VIN = 12V VOUT = 5V IOUT = 500mA to 3000mA O C = 470pF, T =25 C SS VIN = 12V VOUT = 5V IOUT = 0mA C = 470pF A SS 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div 1) VIN = 50V/div 2) VCOMP = 20mV/div 3) IL = 500mA/div 4) IOUT = 500mA/div C ie Rev.B.01 17 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Date Code Rule Month Code 1: January 7: July 2: February 8: August 3: March 9: September 4: April A: October 5: May B: November 6: June C: December n Tape and Reel Dimension SOP-8/PP P PIN 1 W AME AME Carrier Tape, Number of Components Per Reel and Reel Size 18 Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size SOP-8/PP 12.0±0.1 mm 4.0±0.1 mm 2500pcs 330±1 mm Rev.B.01 AME 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268 n Package Dimension SOP-8/PP TOP VIEW SIDE VIEW D1 0' E1 E2 E L1 C 1 D FRONT VIEW A1 e A A2 b CSYMBOLS ie INCHES MIN MAX MIN MAX A 1.350 1.750 0.053 0.069 A1 0 0.150 0 0.006 A2 1.350 1.600 0.053 0.063 C 0.100 0.250 0.004 0.010 E 3.750 4.150 0.148 0.163 E1 5.700 6.300 0.224 0.248 L1 0.300 1.270 0.012 0.05 b 0.310 0.510 0.012 0.020 D 4.700 5.120 0.185 0.202 e Rev.B.01 MILLIMETERS 1.270 BSC 0.05 BSC θ' 0 E2 2.150 2.513 0.085 0.099 D1 2.150 3.402 0.085 0.134 o 8 o 0 o 8 o 19 www.ame.com.tw E-Mail: [email protected] Life Support Policy: These products of AME, Inc. are not authorized for use as critical components in life-support devices or systems, without the express written approval of the president of AME, Inc. AME, Inc. reserves the right to make changes in the circuitry and specifications of its devices and advises its customers to obtain the latest version of relevant information. AME, Inc. , July 2010 Document: 3003-DS5268-B.01 Corporate Headquarter AME, Inc. 2F, 302 Rui-Guang Road, Nei-Hu District Taipei 114, Taiwan. Tel: 886 2 2627-8687 Fax: 886 2 2659-2989