AME. 3A, 28V, 340KHz Synchronous Rectified Step-Down Converter AME5268. Features. General Description. Applications. Typical Application

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1 568 General Description The 568 is a fixed frequency monolithic synchronous buck regulator that accepts input voltage from 4.75 to 8. Two NMOS switches with low on-resistance are integrated on the die. urrent mode topology is used for fast transient response and good loop stability. Shutdown mode reduces the input supply current to less than µa. An adjustable soft-start prevents inrush current at turn-on. This device is available in SOP-8/PP package with exposed pad for low thermal resistance. Applications Distributed Power System Networking System FPGA, DSP, ASI Power Supplies Notebook omputers Features 3A Output urrent Wide 4.75 to 8 Operating Input Range Integrated Power MOSFET Switches Output Adjustable from 0.95 to 5 Up to 95% Efficiency Programmable Soft Start Stable with Low ESR eramic Output apacitors ycle-by ycle Over urrent Protection Fixed 340KHz Frequency Input Under oltage Lockout System Protected by Over-current Limiting, Over-voltage Protection and Thermal Shutdown Thermally Enhanced SOP-8/PP Package Green Products Meet RoHS Standards Typical Application ie IN 5 0nF 0µF/35 x 4 0.µF R4 00KΩ IN BS EN SW 568 SS GND 3 3.3nF S OMP FB R3 6.98KΩ% L 5µH/3.4A R 44.KΩ% R 0KΩ% OUT 5 3A µf/0 x

2 568 Functional Block Diagram. ODET OP FB URRENT SENSE AMP 0.3 SLOPE IN 5 osc LK BS OMP S Q MH 6uA 0.95 EA LAMP PWM R LOGI SW ML SS OP OTP UP OTDET ULO IRMP EN.5 LOKOUT MP.5 IN INTERNAL REGULATORS GND SHUTDOWN MP

3 568 Pin onfiguration SOP-8/PP Top iew AZAxxx. BS. IN 3. SW 4. GND 5. FB 6. OMP 7. EN Die Attach: 8. SS onductive Epoxy Note: The area enclosed by dashed line represents Exposed Pad and connect to GND. ie 3

4 568 Pin Description Pin Number Pin Name Pin Description BS IN 3 SW High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N- hannel MOSFET switch. onnect a 0nF or greater capacitor from SW to BS to power the high side switch. Power Input. IN supplies the power to the I, as well as the step-down converter switches. Drive IN with a 4.75 to 8 power source. Bypass IN to GND with a suitable large capacitor to eliminate noise on the input to the I. Power Switching Output. SW is the switching node that supplies power to the output. onnect the output L 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. onnect the exposed pad to pin 4. 5 FB 6 OMP 7 EN 8 SS 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 ompensation Node. OMP is used to compensate the regulation control loop. onnect a series R network from OMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from OMP to GND is required. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than.7 to turn on the regulator, drive it lower than. to turn it off. Pull up to the IN pin with 00KΩ resister for automatic start up. Soft-start ontrol Input. SS controls the soft-start period. onnect a capacitor from SS to GND to set the soft-start period. Add a 0.µF capacitor set the soft-start period to 5mS. To disable the soft start feature, leave the SS unconnected. 4

5 568 Ordering Information x x x xxx Output oltage Number of Pins Package Type Pin onfiguration Pin onfiguration Package Type Number of Pins Output oltage A. BS Z: SOP/PP A: 8 ADJ: Adjustable. IN 3. SW 4. GND 5. FB 6. OMP 7. EN 8. SS (SOP-8/PP) ie 5

6 568 Available Options Part Number 568-AZAADJ Marking A568 AMyMXX Output oltage Package Operating Ambient Temperature Range ADJ SOP-8/PP -40 O to +85 O Note:. The first places represent product code. It is assigned by such as AM.. y is year code and is the last number of a year. Such as the year code of 008 is A bar on top of first letter represents Green Part such as A The last 3 places MXX represent Marking ode. It contains M as date code in "month", XX as LN code and that is for internal use only. Please refer to date code rule section for detail information. 5. Please consult sales office or authorized Rep./Distributor for the availability of output voltage and package type. 6

7 568 Absolute Maximum Ratings Parameter Maximum Unit Supply oltage -0.3 to +30 Switch oltage - to IN +0.3 Boost Switch oltage -0.3 to SW + 6 All Other Pins -0.3 to +6 EN oltage -0.3 to IN ESD lassification (HBM) k ESD lassification (MM) 00 v Recommended Operating onditions Parameter Rating Unit Ambient Temperature Range -40 to +85 o Junction Temperature Range -40 to +5 o Storage Temperature Range -65 to +50 o ie 7

8 568 Thermal Information Parameter Package Die Attach Symbol Maximum Unit Thermal Resistance* (Junction to ase) Thermal Resistance (Junction to Ambient) SOP-8/PP θ J 9 SOP-8/PP onductive Epoxy θ JA 84 o / W Internal Power Dissipation SOP-8/PP P D 450 mw Maximum Junction Temperature Solder Iron(0 Sec)** o * Measure θ J on backside center of Exposed Pad. ** MIL-STD-0G 0F 8

9 568 Electrical Specifications IN =, T A = 5 O, unless otherwise noted. Parameter Symbol Test ondition Min Typ Max Units Shutdown urrent I SHDN EN = µa Supply urrent EN = 3, FB =..3.5 ma Feedback oltage FB 4.75 <= IN <= OP Threshold oltage.0 Error Amplifier oltage Gain A EA 400 / Error Amplifier Transconductance G EA I = ±0µA 800 µa/ High-side Switch On Resistance R DS,ON,HI 35 mω Low-side Switch On Resistance R DS,ON,LO 05 mω Switch Leakage urrent I SW,LK EN = 0, SW = 0 0 µa High-side Switch urrent Limit Minimum Duty ycle A Low-side Switch urrent Limit From Drain to Source.5 A OMP to urrent Sense Transconductance G S 5. A/ T A = 5 O KHz urrent Limit Oscillation Frequency f OS,L -40 O <=T A <=+85 O KHz Short ircuit Oscillation Frequency f OS,SR FB = 0 6 KHz Maximum Duty ycle D MAX 90 % ie FB =0.8 Minimum On Time t ON,MIN 0 ns Input Undervoltage Lockout ULO IN rising, T A = 5 O Input Undervoltage Lockout Hysteresis -40 O <=T A <=+85 O ULO,HYST 0 m Soft-Start urrent Source I SS SS = 0 6 µa Soft-Start Period t SS SS = 0.µF 5 ms EN Lockout Threshold oltage EN T A = 5 O -40 O <=T A <=+85 O

10 568 Electrical Specifications (ontd.) IN =, T A = 5 O, unless otherwise noted. Parameter Symbol Test ondition Min Typ Max Units EN Shutdown Threshold oltage EN Rising..56 EN Shutdown Threshold oltage Hysteresis 0 m EN Lockout Hysteresis 0 m Thermal Shutdown Temperature OTP Shutdown, temperature increasing 60 O Thermal Shutdown Hysteresis OTH Restore, temperature decreasing 0 O 0

11 568 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. onnecting the pin to ground or to any voltage less than. 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 0 to its final value, linearly. The softstart time is 5 ms typically. Over-voltage Protection The 568 has an over-voltage protection (OP) circuit to minimize voltage overshoot when recovering from output fault conditions. The OP circuit include an overvoltage comparator to compare the FB pin voltage and a threshold of 0% x FB. Once the FB pin voltage is higher than the threshold, the OMP 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 568 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 30 O below the thermal shutdown trip point. Under oltage Lockout (ULO) The 568 incorporates an under voltage lockout circuit to keep the device disabled when IN (the input voltage) is below the ULO start threshold voltage. During power up, internal circuits are held inactive and the soft start is grounded until IN exceeds the ULO start threshold voltage. Once the ULO start threshold voltage is reached, the soft start is released and device start-up begins. The device operates until IN falls below the ULO stop threshold voltage. The typical hysteresis in the ULO comparator is 0m. ie omponent Selection Setting the Output oltage The output voltage is using a resistive voltage divider connected from the output voltage to FB. It divides the output voltage down to the feedback voltage by the ratio: FB = O U T R R + R Over-urrent 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: OUT R + R = 0.95 R 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.

12 568 Detailed Description (ontd.) 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: OUT L = f s IL Where fs is the switching frequency, IN is the input voltage, OUT is the output voltage, and I L is the peak-topeak inductor ripple current. hoose an inductor that will not saturate under the maximum inductor peak current, calculated by: Where I LOAD 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 apacitor OUT IN OUT ILP = ILOAD + f s L The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the A current while maintaining the D input voltage. Use low ESR capacitors for the best performance. eramic capacitors are preferred, but tantalum or low-esr electrolytic capacitors will also be suggested. hoose X5R or X7R dielectrics when using ceramic capacitors. Since the input capacitor () absorbs the input switching current, it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: O U T I IL O A D I N O U T = I N OUT IN At IN = OUT, where I = I LOAD / 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.µF, should be placed as close to the I as possible. The input voltage ripple for low ESR capacitors can be estimated by: ILOAD OUT IN = f s IN Where is the input capacitance value. Output apacitor OUT The output capacitor () is required to maintain the D output voltage. eramic, 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: OUT OUT = f s L OUT IN Where R ESR is the equivalent series resistance (ESR) value of the output capacitor and 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: When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: OUT OUT OUT = R ESR f s L IN The characteristics of the output capacitor also affect the stability of the regulation system. The 568 can be optimized for a wide range of capacitance and ESR values. IN R OUT OUT = 8 f s L ESR OUT IN + 8 f s

13 568 Detailed Description (ontd.) ompensation omponents 568 has current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the OMP pin. OMP 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 D gain of the voltage feedback loop is given by: A D = RLOAD G S AEA OUT Where FB is the feedback voltage (0.95), A EA is the error amplifier voltage gain, G S is the current sense transconductance and R LOAD 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 (3) and the output resistor of the error amplifier. These poles are located at: f P G EA = π 3 A EA f P = π R LOAD Where G EA is the error amplifier transconductance. The system has one zero of importance, due to the compensation capacitor (3) and the compensation resistor ie (R3). This zero is located at: f Z = π 3 R3 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 = π R ESR FB In this case, a third pole set by the compensation capacitor (6) 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 = π 6 R3 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.. hoose the compensation resistor (R3) to set the desired crossover frequency. Determine R3 by the following equation: π f O U T π 0. fs R 3 = < GE A G S FB GE A G S Where f is the desired crossover frequency which is typically below one tenth of the switching frequency.. hoose the compensation capacitor (3) to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero (fz) below one-forth of the crossover frequency provides sufficient phase margin. Determine 3 by the following equation: 4 3 > π R3 f Where R3 is the compensation resistor. O U T FB 3

14 568 Detailed Description (ontd.) 3. Determine if the second compensation capacitor (6) 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: π R S ESR f < If this is the case, then add the second compensation capacitor (6) to set the pole fp3 at the location of the ESR zero. Determine 6 by the equation: R 6 = R3 ESR 4

15 568 haracterization urve Efficiency vs. Output urrent Efficiency vs. Output urrent Efficiency(%) OUT = 3.3 IN = IN = 0µF OUT = 44µF L = 0µH Output urrent (ma) Efficiency(%) OUT = 5 IN = IN = 0µF OUT = 44µF L = 5µH Output urrent (ma) Frequency(KHz) Frequency vs. Temperature IN = Temperature ( o ) ie 3 4 IN = OUT = 5 I OUT = 3000mA SS = 0.µF ) EN = 5/div ) OUT = /div 3) I L = A/div 4) I OUT = A/div Start-Up form EN 4mS / div 5

16 568 haracterization urve Power Off from EN Load Step IN = OUT = 5 I OUT = 3000mA SS = 0.µF ) EN = 5/div ) OUT = 5/div 3) I L = A/div 4) I OUT = A/div 400mS / div IN = OUT = 3.3 I OUT = 0mA to 3000mA SS = 470pF, T =5 O ) OMP = /div ) OUT = 500m/div 3) I L = A/div 4) I OUT = A/div A 00mS / div Load Step Load Step mS / div IN = OUT = 5 I OUT = 0mA to 3000mA SS = 470pF, T =5 O ) OMP = /div ) OUT = 500m/div 3) I L = A/div 4) I OUT = A/div A 4 00mS / div IN = OUT = 3.3 I OUT = 500mA to 3000mA SS = 470pF, T =5 O ) OMP = /div ) OUT = 500m/div 3) I L = A/div 4) I OUT = A/div A 6

17 568 haracterization urve Load Step Stead State Test mS / div IN = OUT = 5 I OUT = 500mA to 3000mA SS = 470pF, T =5 O ) OMP = /div ) OUT = 500m/div 3) I L = A/div 4) I OUT = A/div A 4 IN = OUT = 5 I OUT = 0mA SS = 470pF ) IN = 50/div ) OMP = 0m/div 3) I L = 500mA/div 4) I OUT = 500mA/div ms / div ie 7

18 568 Date ode Rule Month ode : January 7: July : February 8: August 3: March 9: September 4: April A: October 5: May B: November 6: June : December Tape and Reel Dimension SOP-8/PP P PIN W arrier Tape, Number of omponents Per Reel and Reel Size Package arrier Width (W) Pitch (P) Part Per Full Reel Reel Size SOP-8/PP.0±0. mm 4.0±0. mm 500pcs 330± mm 8

19 568 Package Dimension SOP-8/PP TOP IEW D 0' SIDE IEW E E E L D A A b e A FRONT IEW SYMBOLS MILLIMETERS INHES MIN MAX MIN MAX ie A A A E E L b D e.70 BS 0.05 BS q' 0 o 8 o 0 o 8 o E D

20 Life Support Policy: These products of, Inc. are not authorized for use as critical components in life-support devices or systems, without the express written approval of the president of, Inc., 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., Inc., February 0 Document: 3003-DS568-B.0 orporate Headquarter, Inc. 8F,, WenHu St., Nei Hu Taipei, Taiwan. 4 Tel: Fax: