A5268

A5268 ANPEC | Alldatasheet

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1 Rev.B.02 C ie l 3A Output Current l Wide 4.75V to 28V Operating Input Range l Integrated Power MOSFET Switches l Output Adjustable from 0.925V to 25V l Up to 95% Efficiency l Programmable Soft Start l Stable with Low ESR Ceramic Output Capacitors l Cycle-by Cycle Over Current Protection l Fixed 340KHz Frequency l Input Under Voltage Lockout l System Protected by Over-current Limiting, Over-voltage Protection and Thermal Shut- down l Thermally Enhanced SOP-8/PP Package l Green Products Meet RoHS Standards The A5268 is a fixed frequency monolithic synchro- nous 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. Shutdown mode reduces the input supply current to less than 1µA. An adjustable soft-start prevents inrush current at turn-on. This device is available in SOP-8/PP package with ex- posed pad for low thermal resistance. n General Description n Features n Applications S l Distributed Power System l Networking System l FPGA, DSP, ASIC Power Supplies l Notebook Computers n Typical Application IN EN GND SW COMP FB VIN 12V 15µH/3.4ABS SS 10µF/35V 100KΩ 10nF 44.2KΩ 1% 10KΩ 1% 22µF/10V 0.1µF 3.3nF R3 6.98KΩ 1% VOUT A5268 A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

2 Rev.B.02 n Functional Block Diagram 1.1V 0.3V 0.925V 2.5V 1.5V CURRENT SENSE AMP LOCKOUT CMP SHUTDOWN CMP MH ML OVP CLK EA SLOPE CLAMP COMP 6uA OTP OVP UVP UVLO S Q R LOGIC SW BS VIN GND OVDET osc PWM IN INTERNAL REGULATORS IRCMP OTDET EN SS FB A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

3 Rev.B.02 C ie n Pin Configuration SOP-8/PP Top View A5268 1. BS 2. IN 3. SW 4. GND 5. FB 6. COMP 7. EN Die Attach: 8. SS Conductive Epoxy Note: The area enclosed by dashed line represents Exposed Pad and connect to GND. 1 32 4 5678 A5268 A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

4 Rev.B.02 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 N- Channel 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. S W is the s witching 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 resisti ve 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. E N 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. 8 SS Soft-start Control Input. SS controls the so ft-start period. Connect a capacitor from SS to GND to set the soft-start period. Add a 0.1 µF capacitor set the soft-start period to 15mS. To disable the soft start feature, leave the SS unconnected. A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

5 Rev.B.02 C ie n Absolute Maximum Ratings n Recommended Operating Conditions Parameter Maximum Unit Supply Voltage -0.3V to +30V V Switch Voltage -1V to VIN+0.3 V Boost Switch Voltage -0.3V to VSW + 6 V All Other Pins -0.3V to +6 V EN Voltage -0.3V to VIN V ESD Classification (HBM) 2 kV ESD Classification (MM) 200 v Parameter Rating Unit Ambient Temperature Range -40 to +85 oC Junction Temperature Range -40 to +125 oC Storage Temperature Range -65 to +150 oC A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

6 Rev.B.02 n Thermal Information * Measure θ JC on backside center of Exposed Pad. ** MIL-STD-202G 210F Parameter Package Die Attach Symbol Maximum Unit Thermal Resistance* (Junction to Case) SOP-8/PP θ JC 19 Thermal Resistance (Junction to Ambient) SOP-8/PP θ JA 84 Internal Power Dissipation SOP-8/PP PD 1450 mW 150 350 oC oC / W Maximum Junction Temperature Solder Iron(10 Sec)** Conductive Epoxy A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

7 Rev.B.02 C ie n Electrical Specifications VIN = 12V, TA = 25OC, unless otherwise noted. Parame ter Symbol Min Typ Max Units Shutdown Current ISHDN 1 3.0 µA Supply Current 1.3 1.5 mA Feedback Voltage VFB 0.90 0.925 0.95 V OVP Threshold Voltage 1.10 V Error Amplifier Voltage Gain AEA 400 V/V Error Amplifier Transconductance GEA 800 µA/V 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 10 µA High-side Switch Current Limit 4 5.8 A Low-side Switch Current Limit 1.25 A COMP to Current Sense Transconductance GCS 5.2 A/V 300 340 380 KHz 270 400 KHz Short Circuit Oscillation Frequency fOSC,SCR 116 KHz Maximum Duty Cycle DMAX 90 % Minimum On Time tON,MIN 220 nS 3.8 4.05 4.3 V 3.5 4.7 V Input Undervoltage Lockout Hysteresis VUVLO,H YST 210 mV Soft-Start Current Source ISS 6 µA Soft-Start Period tSS 15 mS 2.2 2.5 2.7 V 2.2 2.7 V VFB =0.8V VSS = 0V CSS = 0.1µF EN Lockout Threshold Voltage VEN TA = 25OC VFB = 0V Input Undervoltage Lockout VUVLO VIN rising, TA = 25OC -40OC<=TA<=+85OC -40OC<=TA<=+85OC From Drain to Source Current Limit Oscillation Frequency fOSC,CL TA = 25OC -40OC<=TA<=+85OC VEN = 0V, V SW = 0V Minimum Duty Cycle Δ IC = ±10µA Test Condition VEN = 0V VEN = 3V, V FB = 1.2V 4.75V <= V IN<=28V A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

8 Rev.B.02 n Electrical Specifications (Contd.) VIN = 12V, TA = 25OC, unless otherwise noted. Parame ter Symbol Min Typ Max Units EN Shutdown Threshold Voltage 1.1 1.56 2 V EN Shutdown Threshold Voltage Hysteresis 210 mV EN Lockout Hysteresis 210 mV Thermal Shutdown Temperature OTP 160 OC Thermal Shutdown Hysteresis OTH 20 OCRestore, temperature decreasing VEN Rising Shutdown, temperature increasing Test Condition A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

9 Rev.B.02 C ie n Detailed Description Oscillator Frequency The internal free running oscillator sets the P WM fre- quency at 340KHz. Enable and Soft start The EN Pin provides electrical on/off control of the regu- lator. Once the EN pin voltage exceeds the lockout thresh- old 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 1.1V will disable the regulator and activate the shutdown mode. To limit the start-up inrush current, a soft-start circuit is used to r amp up the refer- ence voltage from 0V to its final value, linearly. The soft- start time is 15 ms typicall y. Under Voltage Lockout (UVLO) The A5268 incorporates an under voltage lockout cir- cuit to keep the device disabled when VIN (the input volt- age) is below the UVLO start threshold voltage. During power up, internal circuits are held inactive and the soft start is grounded until VIN exceeds the UVLO start thresh- old voltage. Once the UVLO start threshold voltage is reached, the soft start is released and device start-up be- gins. The device operates until VIN falls below the UVLO stop threshold voltage. The typical hysteresis in the UVLO comparator is 210mV. Over-Current Protection Overcurrent limiting is implemented by monitoring the current through the high side MOSFET. If this current ex- ceeds the over-current threshold limit, the overcurrent in- dicator is set true. The system will ignore the over-current indicator for the leading edge blanking time at the begin- ning of each cycle to avoid any turn-on noise glitches. Once overcurrent indicator is set true. The high-side MOSFET is turned off for the rest of the cycle after a propa- gation delay. This over-current limiting mode is called cycle-by-cycle current limiting. Over-voltage Protection The A5268 has an over-voltage protection (OVP) cir- cuit to minimize voltage overshoot when recovering from output fault conditions. The OVP circuit include an over- voltage comparator to compare the FB pin voltage and a threshold of 120% x VFB. Once the FB pin voltage is higher than the threshold, the COMP pin and the SS pin are dis- charged to GND, forcing the high-side MOSFET off. When the FB pin voltage drops lower than the threshold, the high- side MOSFET will be enabled again. Thermal Shutdown The A5268 protects itself from overheating with an internal thermal shutdown circuit. If the junction tempera- ture 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. Component Selection Setting the Output Voltage The output voltage is using a resistive voltage divider con- nected from the output voltage to FB. It divides the output voltage down to the feedback voltage by the ratio: the output voltage is: RR RVV OUTFB 925.0 R RRVOUT +×= A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

10 Rev.B.02 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 induc- tor 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: Where fs is the switching frequenc y, VIN is the input voltage, VOUT is the output voltage, and Δ IL is the peak-to- peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current, calculated by: Where ILOAD is the load current. The choice of which style inductor to use mainly depends on the price vs. size re- quirements and any EMI constraints. Input Capacitor The input current to the step-down converter is discon- tinuous, 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 capaci- tors 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: At VIN = 2V OUT, where IC1 = ILOAD/2 is the worst-c ase condition occurs. For simplification, use an input capaci- tor with a RMS current rating greater than half of the maxi- mum load current. When using ceramic capacitors, make sure that they have enough capacitance to provide suffi- cient charge to prevent excessive voltage ripple at input. When using electrolytic or tantalum c apacitors, 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: 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 c apacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: Where RESR is the equivalent series resistance (ESR) value of the output capacitor and C2 is the output capaci- tance value. When using cer amic capacitors, the impedance at the switching frequency is dominated by the capacitance which is the main cause for the output voltage ripple. For simpli- fication, the output voltage ripple can be estimated by: When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: The characteristics of the output capacitor also affect the stability of the regulation system. The A5268 can be optimized for a wide range of capacitance and ESR values.  −××= IN OUT IN OUT LOADC V V V VII 11  −×Δ×= IN OUT Ls OUT V V If VL 1 IN OUT s OUT LOADLP V V Lf VII 12 IN OUT IN OUT s LOAD IN V V V V fC IV 11 ××+×  −××=Δ 28

11 CfRV

V Lf VV s ESR IN OUT s OUT OUT IN OUT s OUT OUT V V CLf VV 128 ESR IN OUT s OUT OUT RV V Lf VV ×  −××=Δ 1 A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

11 Rev.B.02 C ie n Detailed Description (Contd.) Compensation Components A5268 has current mode control for easy compensa- tion 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: Where VFB is the feedback voltage (0.925V), AVEA 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: Where GEA is the error amplifier transconductance. The system has one zero of importance, due to the com- pensation capacitor (C3) and the compensation resistor (R3). This zero is located at: 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 c apacitance of the output capacitor, is located at: In this case, a third pole set by the compensation ca- pacitor (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: The goal of compensation design is to shape the con- verter 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 insta- bility. 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: 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) be- low one-forth of the crossover frequency provides suffi- cient phase margin. Determine C3 by the following equation: Where R3 is the compensation resistor. OUT FB EACSLOADVDC V VAGRA ×××= VEA EA P AC Gf ××= 32 p LOAD P RCf ××= 22 p 332 RCfZ ××= p ESR ESR RCf ××= 22 p 362 RCfP ××= p FB OUT CSEAFB OUT CSEA C V V GG fsC V V GG fCR ×× ××= 1.022223 pp CfRC ××> 32 43 p A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

12 Rev.B.02 3. Determine if the second compensation capacitor (C6) is required. It is required if the ESR zero of the output capaci- tor is located at less than half of the switching frequency, or the following relationship is valid: If this is the case, then add the second compensation ca- pacitor (C6) to set the pole fP3 at the location of the ESR zero. Determine C6 by the equation: 222 1 S ESR f RC <××p n Detailed Description (Contd.) 26 R RCC ESR×= A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

13 Rev.B.02 C ie n Characterization Curve Efficiency vs. Output Current Efficiency vs. Output Current Frequency vs. Temperature 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 -50 -25 0 +25 +50 +75 +100 +125 Frequency(KHz) Temperature (oC) VIN = 12V VIN = 12V VOUT = 5V IOUT = 3000mA C SS = 0.1µF 1) EN = 5V/div 2) VOUT = 2V/div 3) IL = 2A/div 4) IOUT = 2A/div Start-Up form EN 4mS / div 100 100 1000 10000 Output Current (mA) Efficiency(%) VOUT = 3.3V VIN = 12V CIN = 20µF COUT = 44µF L = 10µH 100 100 1000 10000 Output Current (mA) Efficiency(%) VOUT = 5V VIN = 12V CIN = 20µF COUT = 44µF L = 15µH A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

14 Rev.B.02 Power Off from EN n Characterization Curve VIN = 12V VOUT = 5V IOUT = 3000mA C SS = 0.1µF 1) EN = 5V/div 2) VOUT = 5V/div 3) IL = 2A/div 4) IOUT = 2A/div Load Step Load Step Load Step VIN = 12V VOUT = 3.3V IOUT = 0mA to 3000mA C SS = 470pF, T A =25 O C 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div 400mS / div 200mS / div 200mS / div VIN = 12V VOUT = 5V IOUT = 0mA to 3000mA C SS = 470pF, T A =25 O C 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div 200mS / div VIN = 12V VOUT = 3.3V IOUT = 500mA to 3000mA C SS = 470pF, T A =25 O C 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

15 Rev.B.02 C ie Load Step 200mS / div VIN = 12V VOUT = 5V IOUT = 500mA to 3000mA C SS = 470pF, T A =25 O C 1) VCOMP = 1V/div 2) VOUT = 500mV/div 3) IL = 2A/div 4) IOUT = 2A/div Stead State Test 2mS / div VIN = 12V VOUT = 5V IOUT = 0mA C SS = 470pF 1) VIN = 50V/div 2) VCOMP = 20mV/div 3) IL = 500mA/div 4) IOUT = 500mA/div n Characterization Curve A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter

16 Rev.B.02 n Date Code Rule 1: January 7: July 2: February 8: August 3: March 9: September 4: April A: October 5: May B: November 6: June C: December Month Code n Tape and Reel Dimension Carrier Tape, Number of Components Per Reel and Reel Size SOP-8/PP 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 PIN 1 W P ANPEC ANPEC A5268 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter