Product Change Notices PCN No.:20110301 Date: 03/21/2011 This is to inform you that AME5258A datasheet has been changed from Rev. A.03 to Rev. B.01. This notification is for your information and concurrence. If you require data or samples to qualify this change, please contact AME, Inc. within 30 days of receiving of this notification. If we do not receive any response from you within 30 calendar days from the date of this notification, we will consider that you have accepted this PCN. If you have any questions concerning this change, please contact: PCN Originator: Name: Bill Chou Email: [email protected] Expected 1st Device Shipment Date: N/A Earliest Year/Work Week of Changed Product: N/A Description of Change (From) : Page 5: change marking on Available Options Part Number Marking* Output Voltage Package Operating Ambient Temperature Range AME5258A-BEVADJ BWMMXX ADJ SOT-25 -40OC to +85OC Description of Change (To) : Part Number Marking* Output Voltage Package Operating Ambient Temperature Range AME5258A-BEVADJ CCWMXX ADJ SOT-25 -40OC to +85OC Reason for Change: AME5258A datasheet marking change from BWM to CCW ; that is for AME production with better traceability and management. QPM018B-B AME AME5258A n General Description The AME5258A is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. The device is available in an adjustable version. Supply current with no load is 300µA and drops to <1µA in shutdown. The 2.5V to 5.5V input voltage range makes the AME5258A ideally suited for single Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. PWM pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. At very light load, the AME5258A will automatically skip pulses in pulse skip mode operation to maintain output regulation. The AME5258A is simple to use. As with standard LDO's, Input and output capacitor are required. The only other element is a small, low cost, 2.2µH inductor.Low output voltages are easily supported with the 0.6V feedback reference voltage. And 100% duty cycle when Vin approaches Vout. n Features 1.5MHz, 800mA Synchronous Buck Converter n Applications l Cellular Phones l Digital Cameras l Portable Electronics l USB Devices l MP3 Players l LDO Replacement n Typical Application Adjustable Output Voltage VIN = 2.5V to 5.5V VIN IN C IN 4.7µF CER 2.2µH AME5258A 1.8V 800mA 22pF R1 887K FB EN GND l High Efficiency: Up to 96% l 800mA Output Current at VIN=3V VOUT SW C OUT 10µF CER R2 442K VOUT =VFB (R1+R2)/R2 l 2.5V to 5.5V Input Voltage Range l 1.5MHz Constant Frequency Operation Figure 1: 1.8V at 800mA Step-Down Requlator l No Schottky Diode Required l Low Dropout Operation: 100% Duty Cycle l 0.6V Reference Allows Low Output Voltages l Shutdown Mode Draws<1µA Supply Current l Current Mode Operation for Excellent Line and Load Transient Response l Overtemperature Protection l Internal Soft Start l Space Saving 5-Pin SOT-25 Package l Meet RoHS Standards Rev.B.01 1 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A Function Diagram IN 0.6V VFB 5 Slope COMP + 4 IN 3 SW 2 GND ∑ + - ICOMP 0.55V UVDET + SWITCHING LOGIC AND BLANKING CIRCUIT + 0.65V OVDET - + 1 0.6V VREF IRCMP - EN OSC Figure 2: Founction Block Diagram 2 Rev.B.01 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Pin Configuration SOT-25 Top View 5 ( Adjustable Output ) AME5258A-BEVADJ 4 1. EN 2. GND AME5258A 3. SW 4. IN 5. FB 1 2 3 * Die Attach: Conductive Epoxy n Pin Description Pin Number Rev.B.01 Pin Name Pin Description Enable Control Input. Forcing this pin above 1.5V enables the part. Forcing this pin below 0.3V shuts down the device. In shutdown, all functions are disabled drawing <1µA supply current. Do not leave EN floating. 1 EN 2 GND Ground Pin 3 SW Switch Node Connection to Inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. 4 IN Main Supply Pin. Must be closely decoupled to GND, Pin2, with a 4.7µF or greater ceramic capactior. 5 FB Feedback Pin. Receives the feedback voltage from an external resistive divider across the output. 3 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Ordering Information AME5258A - x x x xxx Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration B (SOT-25) 4 1. EN 2. GND 3. SW 4. IN 5. FB Package Type Number of Pins E: SOT-2X V: 5 Output Voltage ADJ: Adjustable Rev.B.01 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Available Options Part Number Marking* Output Voltage Package Operating Ambient Temperature Range AME5258A-BEVADJ CCWMXX ADJ SOT-25 -40OC to +85OC Note: 1. The first 3 places represent product code. It is assigned by AME such as CCW. 2. A bar on top of first letter represents Green Part such as CCW. 3. 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. 4. Please consult AME sales office or authorized Rep./Distributor for the availability of output voltage and package type. n Absolute Maximum Ratings Parameter Symbol Maximum Unit VIN 6 V VEN ,VFB VIN V SW Voltage VSW -0.3 to (V IN +0.3) V P-Channel Switch Source Current (DC) ISW 1 A N-Channel Switch Sink Current (DC) ISW 1 A Input Supply Voltage EN, FB Voltages ESD Classification C* Caution: Stress above the listed in absolute maximum ratings may cause permanent damage to the device. * HBM C: 4000V ~ 6000V Rev.B.01 5 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Recommended Operating Conditions Parameter Symbol Rating Unit Ambient Temperature Range TA -40 to +85 o Junction Temperature Range TJ -40 to +125 o Storage Temperature Range TSTG -65 to +150 o C C C n Thermal Information Parameter Package Thermal Resistance* (Junction to Case) SOT-25 Thermal Resistance (Junction to Ambient) SOT-25 Internal Power Dissipation SOT-25 Die Attach Conductive Epoxy Solder Iron (10 Sec)** Symbol Maximum θJC 81 o C/W θJA 260 o C/W PD 400 350 Unit mW o C * Measure θJC on center of molding compound if IC has no tab. ** MIL-STD-202G 210F 6 Rev.B.01 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Electrical Specifications TA=25oC. VIN=3.6V unless otherwise specified. Parameter Symbol Input Volatge VIN Feedback Current IFB Regulated Feedback Voltage VFB Reference Voltage Line Regulation Output Voltage Line Regulation Switch Current Limit Output Voltage Load Regulation Min Typ Max Units 5.5 V ±30 nA 0.6 0.6120 V 2.5 0.5880 ∆VFB VIN =2.5V to 5.5V 0.04 0.4 %/V REGLINE VIN =2.5V to 5.5V 0.04 0.4 %/V ICL VIN =3V, VFB=0.5V Duty Cycle < 35% 1 VLOADREG Shutdown Current ISD Quiescent Current IQ Oscillator Frequency Test Condition fOSC A 0.5 VEN =0V, VIN =4.2V VFB=0.5V or VOUT=90% VEN =VIN=4.2V VIN =2.5V & IOUT=100mA 1.2 % 0.1 1 300 450 1.5 1.8 VFB=0V or VOUT=0V 210 µA MHz kHz RDSON of P-Channel FET RDSON(P) ISW =100mA 0.4 0.6 Ω RDSON of N-Channel FET RDSON(N) ISW = -100mA 0.35 0.5 Ω Switch Leakage Current ISW ±1 µA EN Input Threshold (High) VEH EN Input Threshold (Low) VEL 0.3 EN Input Current IEN ±1 Rev.B.01 VEN =0V, VSW =0V or 5V,VIN =5V 1.5 V µA 7 AME AME5258A 1.5MHz, 800mA Synchronous Buck Converter n Detailed Description Main Control Loop Dropout Operation The AME5258A uses a constant frequency, current mode step-down architecture. Both the main (P-channel MOSFET) and synchronous (N-channel MOSFET) switches are internal. During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch, and turned off when the current comparator, ICOMP, resets the RS latch. The peak inductor current at which ICOMP resets the RS latch, is controlled by the output of error amplifier EA. When the load current increases, it causes a slight decrease in the feedback voltage, FB, relative to the 0.6V reference, which in turn,causes the EA amplifier's output voltage to increase until the average inductor current matches the new load current. While the top MOSFET is off, the bottom MOSFET is turned on until either the inductor current starts to reverse, as indicated by the current reversal comparator IRCMP, or the beginning of the next clock cycle. The comparator OVDET guards against transient overshoots >7.8% by turning the main switch off and keeping it off until the fault is removed. As the input supply voltage decreases to a value approaching the output voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage forces the main switch to remain on for more than one cycle until it reaches 100% duty cycle. The output voltage will then be determined by the input voltage minus the voltage drop across the P-channel MOSFET and the inductor. An important detail to remember is that at low input supply voltages, the RDS(ON) of the P-channel switch increases (see Typical Performance Characteristics). Therefore, the user should calculate the power dissipation when the AME5258A is used at 100% duty cycle with low input voltage. Pulse Skipping Mode Operation At light loads, the inductor current may reach zero or reverse on each pulse. The bottom MOSFET is turned off by the current reversal comparator, IRCMP, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. Short-Circuit Protection When the output is shorted to ground, the frequency of the oscillator is reduced to about 210kHz, 1/7 the nominal frequency. This frequency foldback ensures that the inductor current has more time to decay, thereby preventing runaway. The oscillator's frequency will progressively increase to 1.5MHz when VFB or VOUT rises above 0V. 8 n Application Information Inductor Selection For most applications, the value of the inductor will fall in the range of 1µH to 4.7µH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher V IN or V OUT also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is IL = 320mA (40% of 800mA). ∆ IL= VOUT 1 ⋅ VOUT (1 − ) f ⋅L VIN The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 960mA rated inductor should be enough for most applications (800mA+ 160mA). For better efficiency, choose a low DC-resistance inductor. Rev.B.01 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A Inductor Core Selection Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of more expensive ferrite or mollypermalloy cores. Actual core loss is independent of core size for a fixed inductor value but it is very dependent on the inductance selected. As the inductance increases, core losses decrease. Unfortunately, increased inductance requires more turns of wire and therefore copper losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates "hard", which means that inductance collapses abruptly when the peak design current is exceeded. This result in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate! Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don't radiate energy but generally cost more than powdered iron core inductors with similar characteristics. The choice of which style inductor to use mainly depends on the price vs. size requirements and any radiated field/EMI requirements. CIN and COUT Selection The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used.RMS current is given by : IRMS = I OUT ( max ) ⋅ VOUT ⋅ VIN VIN VOUT −1 This formula has a maximum at V IN = 2V OUT, where IRMS = IOUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life which makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Rev.B.01 Several capacitors may also be paralleled to meet size or height requirements in the design. The selection of COUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients, as well as the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, VOUT, is determined by : 1 ∆ VOUT ≤ ∆ IL ESR + 8 f ⋅ C OUT The output ripple is highest at maximum input voltage since IL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR but have lower capacitance density than other types. Tantalum capacitors have the highest capacitance density but it is important to only use types that have been surge tested for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long term reliability. Ceramic capacitors have excellent low ESR characteristics but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing Using Ceramic Input and Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. 9 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A Output Voltage Programming The output voltage is set by an external resistive divider according to the following equation : VOUT = V REF ⋅ (1 + VIN 2.5V to 5.5V 2.2µH IN R2 ) R1 SW 22pF AME5258A Where V REF equals to 0.6V typical. The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 3. 0.6V ≤ VOUT EN VOUT 1.2V C OUT 10µF CER FB 604K C IN 4.7µF CER GND 604K ≤ 5.5V Figure 4: 1.2V Step-Down Regulator R2 FB AME5258A VIN 3.3V to 5.5V R1 2.2µH IN SW 22pF GND AME5258A EN Figure 3: Setting the AME5258A Output Voltage VOUT 1.5V C OUT 10µF CER FB 475K CIN 4.7µF CER GND 316K Thermal Considerations In most applications the AME5258A does not dissipate much heat due to its high efficiency. But, in applications where the AME5258A is running at high ambient temperature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. If the junction temperature reaches approximately 160OC, both power switches will be turned off and the SW node will become high impedance. To avoid the AME5258A from exceeding the maximum junction temperature, the user will need to do some thermal analysis. The goal of the thermal analysis is to determine whether the power dissipated exceeds the maximum junction temperature of the part. The temperature rise is given by: Figure 5: 1.5V Step-Down Regulator VIN 2.7V to 5.5V 2.2µH IN SW 22pF AME5258A EN C IN 4.7µF CER VOUT 2.5V C OUT 10µF CER FB 1M GND 316K TR = ( PD)( θJA ) Where PD is the power dissipated by the regulator and θJA is the thermal resistance from the junction of the die to the ambient temperature. 10 Figure 6: 2.5V Step-Down Regulator Rev.B.01 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A VIN 3.3V to 5.5V IN SW 22pF CIN 4.7µF CER 2.2µH SW IN C OUT 10µF CER AME5258A EN VIN 3.6V to 5.5V VOUT 3V 2.2µH 22pF AME5258A FB EN FB 960K 240K Figure 7: 3V Step-Down Regulator C OUT 10µF CER 887K CIN 4.7µF CER GND VOUT 3.3V GND 196K Figure 8: 3.3V Step-Down Regulator PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the AME5258A. These items are also illustrated graphically in Figures 9. Check the following in your layout: 1. The power traces, consisting of the GND trace, the SW trace and the V IN trace should be kept short, direct and wide. 2. Does the V FB pin connect directly to the feedback resistors? The resistive divider R1/R2 must be connected between the (+) plate of COUT and ground. 3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 4. Keep the switching node, SW, away from the sensitive VFB node. 5. Keep the (-) plates of CIN and COUT as close as possible. L1 VIN SW IN AME5258A EN + C IN - C FWD VOUT + COUT - FB R2 GND R1 Figure 9: AME5258A Adjustable Voltage Regulator Layout Diagram Rev.B.01 11 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Characterization Curve(For reference only) Start-UP from Shutdown Pluse Skipping Mode RUN 2V /Div SW 5V /Div VOUT VOUT 10mV/Div 1V/Div IL IL 20mA/Div 500mA/Div VIN=3.6V VOUT=1.8V ILOAD=600mA 200µS/Div VIN=3.6V VOUT=1.8V IOUT =50mA Pluse Skipping Mode 1µS/Div Pluse Skipping Mode SW 5V/Div SW 5V/Div VOUT 10mV/Div VOUT 10mV/Div IL IL 20mA/Div VIN=3.6V VOUT=1.8V IOUT=10mA 20mA/Div 1µS/Div VIN=3.6V VOUT=1.8V IOUT=20mA Load Step 1µS/Div Efficiency vs Input Voltage 100 95 IL 500mA/Div IOUT=100mA IOUT=200mA 90 Efficiency(%) VOUT 100mV/Div AC COUPLED 85 80 75 IOUT =600mA IOUT =10mA 70 65 IOUT 500mA/Div 60 55 20µS/Div VIN=3.6V VOUT=1.8V ILOAD=0mA to 600mA 12 50 2.5 3 3.5 4 4.5 5 5.5 Input Voltage(V) Rev.B.01 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Characterization Curve(For reference only) Oscillator Frequency vs Supply Voltage Oscillator Frequency vs Temperature 2.0 2.0 1.9 1.8 1.8 Frequency(MHz) Frequency(MHz) 1.9 1.7 1.6 1.5 1.4 1.6 1.5 1.4 1.3 1.3 1.2 -50 1.7 1.2 -25 0 +25 +50 +75 +100 1.1 2.5 +125 3.5 4.5 5.5 Supply Voltage (V) o Temperature( C) VFB vs Temperature RDS(ON) vs Input Voltage 0.615 0.7 0.612 0.6 Main Switch 0.609 RDS(ON) (mΩ) VFB(V) 0.606 0.603 0.600 0.597 0.594 0.5 0.4 0.3 Synchronous Switch 0.2 0.591 0.1 0.588 0.585 -50 -25 0 +25 +50 +75 +100 0 2.5 +125 3.5 o 4.5 5.5 Temperature( C) Input Voltage(V) RDS(ON) vs Temperature Efficiency vs Load Current 0.80 6.5 100 0.75 VIN=3.6V 80 VIN =4.2V 0.60 Efficiency(%) RDS(ON) (mΩ) 0.65 90 VIN =2.7V 0.70 0.55 0.50 0.45 0.40 0.35 0.30 0.25 0.20 -50 Rev.B.01 70 60 50 40 Main Switch Synchronous Switch -25 0 +25 +50 +75 Temperature( oC) +100 V IN =2.7V V IN =3.3V V IN =4.2V 30 +125 20 1 V OUT=1.2V 10 100 1000 I OUT (mA) 13 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Characterization Curve(For reference only) Efficiency vs Load Current Efficiency vs Load Current 100 95 90 85 Efficiency(%) 80 Efficiency(%) VIN =2.7V 90 V IN =2.7V 70 VIN=3.3V 60 50 V IN =4.2V V IN =3.6V 80 75 70 V IN =4.2V 65 40 60 30 VOUT =1.5V 20 1 10 100 VOUT =1.8V 55 50 1 1000 IOUT (mA) 10 IOUT (mA) 100 1000 Output Voltage vs Load Current Efficiency vs Load Current 1.844 100 95 1.834 VIN=2.7V 1.824 85 80 VOUT (V) Efficiency(%) 90 V IN =3.6V 75 70 V IN =4.2V 1.814 1.804 65 1.794 60 VOUT =2.5V 55 50 1 10 IOUT (mA) 100 1.784 1000 1.774 0 100 200 300 400 500 600 700 800 900 I OUT (mA) Current Limit vs Input Voltage 1800 Current Limit (A) 1700 1600 1500 1400 1300 1200 1100 1000 2.5 3.0 3. 5 4.0 4.5 o 5. 0 5.5 Temperature ( C) 14 Rev.B.01 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A 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 A A A A A A A A A A A A A A A A A A A A Marking A M A M A M A M A M A M A M A M A M A M X X X X X X X X X X X X X X X X X X X X Year xxx0 xxx1 xxx2 xxx3 xxx4 xxx5 xxx6 xxx7 xxx8 xxx9 n Tape and Reel Dimension SOT-25 P W AME AME PIN 1 Carrier Tape, Number of Components Per Reel and Reel Size Rev.B.01 Package Carrier Width (W) Pitch (P) Part Per Full Reel Reel Size SOT-25 8.0±0.1 mm 4.0±0.1 mm 3000pcs 180±1 mm 15 AME 1.5MHz, 800mA Synchronous Buck Converter AME5258A n Package Dimension SOT-25 Top View Side View SYMBOLS D E H θ1 L PIN1 S1 MAX MIN MAX A 0.90 1.30 0.0354 0.0512 A1 0.00 0.15 0.0000 0.0059 b 0.30 0.55 0.0118 0.0217 D 2.70 3.10 0.1063 0.1220 E 1.40 1.80 0.0551 0.0709 1.90 BSC e 2.60 θ1 3.00 0 o 10 0.95BSC 0.10236 0.11811 0.0146BSC o 0 o 10 o 0.0374BSC A1 A S1 0.07480 BSC 0.37BSC L Front View INCHES MIN H e MILLIMETERS b 16 Rev.B.01 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. , March 2011 Document: 1265-DS5258A -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