AME AME5285 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter n General Description n Applications l TV The AME5285 is a Synchronous Rectified Step-Down Converter with internal power MOSFETs. It achieves 5A continous output current over a wide switching frequency range with excellent load and line regulation. Current mode operation provides fast transient response and eases of loop stabilization. Internal soft-start minimizes the inrush supply current at startup. The circuit protection includes cycle-by cycle current limiting, output short circuit frequency protection and thermal shutdown. This device is available in SOP-8/PP package with exposed pad for low thermal resistance. l Distributed Power Systems l Pre-Regulator for Linear Regulators n Typical Application L1 1.5µH VIN 5V CIN 10µF IN OFF ON SW EN AME5285 R1 6K VOUT 1V 5A COUT 22µF FB COMP n Features l 5A Output Current C2 Optional C1 680pF R3 5.1K GND FREQ R2 24K RFREQ 30K l 55mΩ/45mΩ Internal Power MOSFET Switch l Stable with Low ESR Output Ceramic Capacit -ors l Up to 95% Efficiency l Less than 10µA Shutdown Current l Wide Switching Frequency Range from 300KHz~1.4MHz l Thermal Shutdown l Cycle by cycle Over Current Protection and Hiccup l Output Adjustable from 0.8V to VIN l Short Circuit Frequency Protection l Green Products Meet RoHS Standards Rev. B.01 1 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Functional Block Diagram IN CURRENT SENSE EN ENABLE CURRENT LIMIT UVLO FREQ OSC SW SLOPE + + COMP SOFT START EA - GND + 0.8V VREF - LOGIC + OVP 2 - 0.9V SW PWM OTP FB DRIVER IRCMP + PGND Rev. B.01 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Pin Configuration SOP-8/PP Top View 8 7 6 AME5285-AZAxxx 5 1. COMP 2. GND 3. EN AME5285 4. IN 5. SW 1 2 3 6. SW 4 7. FREQ 8. FB * Die Attach: Conductive Epoxy Note: Connect exposed pad (heat sink on the back) to GND. n Pin Description Pin Number Pin Name Rev. B.01 Pin Description 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. 1 COMP 2 GND 3 EN Enable. Internal pull high with a resistor. Pull EN below 0.6V to shut down the regulator. 4 IN Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Bypass IN to GND with a suitable large capacitor to eliminate noise on the input to the IC. 5, 6 SW 7 FREQ 8 FB Ground. Connect the exposed pad to GND. 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. Frequency Adjust Pin. Add a resistor from this pin to ground determines the switching frequency. 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 0.8V. 3 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Ordering Information AME5285 - x x x xxx Output Voltage Number of Pins Package Type Pin Configuration Pin Configuration A (SOP-8/PP) 4 1. COMP 2. GND 3. EN 4. IN 5. SW 6. SW 7. FREQ 8. FB Package Type Z: SOP/PP Number of Pins A: 8 Output Voltage ADJ: Adjustable Rev. B.01 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Absolute Maximum Ratings Parameter Maximum Unit Supply Voltage -0.3V to +6V V Switch voltage -0.7V to V IN +0.7V V EN, FB, COMP, FREQ to GND -0.3V to V IN +0.3V V HBM 2 kV MM 200 V Symbol Rating Unit Ambient Temperature Range TA -40 to +85 Junction Temperature Range TJ -40 to +125 Storage Temperature Range T STG -65 to +150 ESD Classification n Recommended Operating Conditions Parameter o C n Thermal Information Parameter Package Die Attach Thermal Resistance* (Junction to Case) Thermal Resistance (Junction to Ambient) Symbol Maximum θ JC Unit 15 o SOP-8/PP Internal Power Dissipation Conductive Epoxy θJA 75 PD 1.333 C/W mW Maximum Junction Temperature 150 o C Lead Temperature (Soldering 10Sec)** 260 o C * Measure θJC on backside center of Exposed Pad. ** MIL-STD-202G 210F Rev. B.01 5 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Electrical Specifications VIN=5V, TA=25oC, unless otherwise noted. Parameter Symbol Test Condition Min Input Voltage Range 3 Input UVLO 2 VEN=5V Quiescent Current (No Switching) Shutdown Current ISHDN VEN=0V Feedback Voltage VFB 0.784 Feedback Current I FB -50 Typ 2.3 Units 5.5 V 2.6 V 450 µA 10 µA 0.8 0.816 V 50 nA Load Regulation 0A<IOUT<5A 0.25 % Line Regulation 3.3V<VIN<5.5V 0.25 %/V EN Voltage High 1.5 V EN V EN Voltage Low EN Leakage Current Switching Frequency Short-Circuit Frequency 0.4 IENLK FSW V VEN=3V 4 µA RFREQ=NC 300 KHz RFREQ =120KΩ 600 KHz RFREQ=47K Ω 1 MHz RFREQ=30K Ω 1.4 MHz 0.25 FSW 8.5 A -2 A FSWSC High-side Switch Current Limit 6 Low-side Switch Current Limit Maximum Duty Cycle 100 Minimum On Time % 100 ns Error Amp Voltage Gain AEA 600 V/V Error Amp Tranconductance GEA 390 µ A/V 0.1 µA Switch Leakage Current I SWLK VSW =0V, VEN=0V High-side Switch On Resistance RDSON,HI 55 mΩ Low-side Switch On Resistance RDSON,LO 45 mΩ Thermal Shutdown Protection OTP OTH 6 Max Rising Hysteresis 170 o 20 o C C Rev. B.01 AME AME5285 n Detailed Description Normal Operation The AME5285 uses a user adjustable frequency, current mode step-down architecture with internal MOSFET switch. During normal operation, the internal high-side (PMOS) switch is turned on each cycle when the oscillator sets the SR latch, and turned off when the comparator resets the SR latch. The peak inductor current at which comparator resets the SR latch is controlled by the output of error amplifier EA. While the high-side switch is off, the low-side switch turns on until either the lowside current limit reached or the beginning of the next switching cycle. 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter Short Circuit Protection When the output is shorted to ground, the frequency of the oscillator is reduced to about 1/4 of the normal frequency to ensure that the inductor current has more time to decay, thereby preventing runaway. Meanwhile, AME5285 enters hiccup mode, the average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. Dropout Operation The output voltage is dropped from the input supply for the voltage which across the high-side switch. 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 high-side switch to remain on for more than one cycle until it reaches 100% duty cycle. Soft-Start The AME5285 employs internal soft-start circuitry to reduce supply inrush current during startup conditions. Over Temperature Protection The In most applications the AME5285 does not dissipate much heat due to high efficiency. But, in applications where the AME5285 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 170oC, the internal high-side power switch will be turned off and the SW switch will become high impedance. Rev. B.01 7 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Application Information Inductor Selection For most applications, the value of the inductor will fall in the range of 2.2µH 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 VOUT also increase the ripple current ∆IL: V 1 ∆I L = VOUT 1 − OUT f ×L VIN Capacitor Selection In continuous mode, the source current of the top MOSFET is a square wave of duty cycle VOUT/VIN. To prevent large voltage transients, a low ESR input capacitor sized for maximum RMS current must be used. The maximum RMS capacitor current is given by: ≅ I OMAX When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for given value and size. Output Voltage Programming The output voltage of the AME5285 is set by a resistive divider according to the following formula: A reasonable inductor current ripple is usually set as 1/3 to 1/5 of maximum out current. 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. For better efficiency, choose a low DCR inductor. CIN requires IRMS For a fixed output voltage, the output ripple is highest at maximum input voltage since ∆IL increases with input voltage. VOUT (V IN − VOUT ) VIN R1 V OUT = 0 .8 × 1 + Volt . R 2 Some standard value of R1, R2 for most commonly used output voltage values are listed in Table 1. VOUT(V) R1(KΩ) R2(KΩ ) 1.1 7.5 20 1.2 10 20 1.5 17.4 20 1.8 30 24 2.5 51 24 3.3 75 24 This formula has a maximum at VIN =2V OUT, where IRMS=IOUT/2. For simplification, use an input capacitor with a RMS current rating greater than half of the maximum load current. The selection of COUT is driven by the required effective series resistance (ESR). Typically, once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement. The output ripple ∆VOUT is determined by: 1 ∆VOUT ≅ ∆I L ESR + 8 fCOUT 8 Rev. B.01 AME AME5285 Loop Compensation The AME5285 employs peak current mode control for easy use and fast transient response. Peak current mode control eliminates the double pole effect of the output LC filter. It greatly simplifies the compensation loop design. With peak current mode control, the buck power stage can be simplified to be a one-pole and one-zero system in frequency domain. The pole can be calculated by: f P1 = 1 2π × C OUT × R L The zero is a ESR zero due to output capacitor and its ESR. It can be calculated by: f Z1 = 1 2π × C OUT × ESRCOUT Where COUT is the output capacitor, RL is load resistance; ESRCOUT is the equivalent series resistance of output capacitor. The compensation design is to shape the converter close loop transfer function to get desired gain and phase. For most cases, a series capacitor and resistor network connected to the COMP pin sets the pole-zero and is adequate for a stable high-bandwidth control loop. In the AME5285, FB pin and COMP pin are the inverting input and the output of internal transconductance error amplifier (EA). A series RC and CC compensation network connected to COMP pin provides one pole and one zero: for RC<<AEA/GEA f P2 = 1 GEA ≈ A 2π × CC × AEA 2π × CC × RC + EA G EA fZ2 = 1 2 π × C C × RC Rev. B.01 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter where GEA is the error amplifier transconductance AEA is the error amplifier voltage gain RC is the compensation resistor CC is the compensation capacitor The desired crossover frequency fC of the system is defined to be the frequency where the control loop has unity gain. It is also called the bandwidth of the converter. In general, a higher bandwidth means faster response to load transient. However, the bandwidth should not be too high because of system stability concern. When designing the compensation loop, converter stability under all line and load condition must be considered. Usually, it is recommended to set the bandwidth to be less than 1/10 of switching frequency. Using selected crossover frequency, fC, to calculate RC: RC = f C × VOUT 2π × COUT × VFB GEA × GCS where GCS is the current sense circuit transconductance. The compensation capacitor CC and resistor RC together make zero. This zero is put somewhere close to the pole fP1 of selected frequency. CC is selected by: CC = COUT × RL RC Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, V OUT immediately shifts by an amount equal to (∆ILOAD × ESR), where ESR is the effective series resistance of COUT. ∆ILOAD also begins to charge or discharge COUT, which generates a feedback error signal. The regulator loop then acts to return VOUT to its steadystate value. During this recovery time VOUT can be monitored for overshoot or ringing that would indicate a stability problem. 9 AME AME5285 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter Efficiency Considerations Although all dissipative elements in the circuit produce losses, one major source usually account for most of the losses in AME5285 circuits: I2R losses. The I2R loss dominates the efficiency loss at medium to high load currents. The I2R losses are calculated from the resistances of the internal switches, RSW, and external inductor RL. In continuous mode, the average output current flowing through inductor L is "chopped" between the main switch and the synchronous switch. Thus the series resistance looking into the SW pin is a function of both top and bottom MOSFET RDS(ON) and the duty cycle (D) as follows: RSW = (RDS(ON)TOP)(D) + (RDS(ON)BOTTOM )(1-D) The RDS(ON) for both the top and bottom MOSFETs can be obtained from Electrical Characteristics table. Thus, to obtained I2R losses, simply add RSW to RL and multiply the result by the square of the average output current. Other losses including CIN and COUT ESR dissipative losses and inductor core losses generally account for less than 2% total additional loss. Thermal Considerations In most application the AME5285 does not dissipate much heat due to its high efficiency. But, in applications where the AME5285 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 170oC, both power switches will be turned off and the SW switch will become high impedance. 10 Rev. B.01 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Typical Operating Circuit VIN 3V to 5V CIN 10µF L 1 3 Chip Enable 4 SW IN EN R1 AME5285 COMP 7 FREQ R3 2 RFREQ GND COUT 8 FB C1 C2 Optional VOUT 5,6 GND R2 9 (Exposed pad) V OUT(V) CIN (µF) R1(KΩ ) R2(KΩ ) R3(KΩ ) C1(pF) L(µH) COUT(µF ) 3.3 10 75 24 25 680 2.2 22 2.5 10 51 24 20 680 2.2 22 1.8 10 30 24 15 680 1.5 22 1.5 10 21 24 13 680 1.5 22 1.2 10 12 24 11 680 1.5 22 1.1 10 6 24 8.2 680 1.5 22 Table 1. Recommended Components Selectin for fsw = 1.4MHz The ground area must provide adequate heat dissipating area to the thermal pad andusing multiple vias to help thermal dissipation. R3 Connect the FB pin directly to feedback R2 resistors. C1 COMP 1 8 FB V OUT R1 GND 2 GND 7 FREQ RFREQ GND EN 3 6 SW V IN 4 5 SW SW V IN SW pad should be connected together to Inductor by wide and short trace, keep sensitive components away from this trace. L1 C IN must be placed between V IN and GND as close as CIN possible Place the input and output capacitors as close to the IC as possible COUT V OUT Figure 3. AME5285 Regulators Layout Diagram Rev. B.01 11 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Characterization Curve Efficiency vs. Output Current Efficiency vs. Output Current 100 100 90 90 VOUT=3.3V 80 70 Effici ency(%) Efficiency(%) 80 60 50 40 30 VOUT =1V 60 50 40 30 VIN =5V RFREQ= 30K 20 20 10 0 70 VNI =5V RFREQ= 30 K 10 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 0 5.0 0 0 .5 1 .0 Output Current(A) 3. 0 3. 5 4.0 4. 5 5.0 100 90 90 VOUT=3.3V 80 Efficiency(%) 80 Efficiency(%) 2 .5 Efficiency vs. Output Current 100 70 60 50 40 70 V OUT=1V 60 50 40 30 30 20 20 VIN =5V R FREQ=NC 10 VIN =5V RFREQ=NC 10 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Output Current(A) 12 2 .0 Output Current(A) Efficiency vs. Output Current 0 1.5 4.0 4.5 5.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Output Current(A) Rev. B.01 AME AME5285 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter n Characterization Curve (Contd.) Load Step Load Step 1 1 2 2 Time (100µSec/DIV) Time (100µSec/DIV) VIN = 5V VOUT = 3.3V IOUT = 1mA to 5A R =30K VIN = 5V VOUT = 1V IOUT = 1mA to 5A R =30K FREQ FREQ 1) VOUT = 100mV/div 2) IL = 2A/div 1) VOUT = 50mV/div 2) IL = 2A/div Power ON from EN Power ON form VIN 1 1 2 2 3 3 Time (2.0ms /DIV) VIN = 5V VOUT = 3.3V R =NC FREQ 1) VEN = 2V/div 2) VOUT = 2V/div 3) IL = 5A/div Rev. B.01 Time (5.0ms /DIV) VIN = 5V VOUT = 3.3V R =NC FREQ 1) VIN = 2V/div 2) VOUT = 2V/div 3) IL = 5A/div 13 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Characterization Curve (Contd.) Power Off from EN Power Off from VIN 1 1 2 2 3 3 Time (5.0ms /DIV) Time (5.0ms / DIV) VIN = 5V VOUT = 3.3V R =NC VIN = 5V VOUT = 3.3V R =NC FREQ FREQ 1) VEN = 2V/div 2) VOUT = 2V/div 3) IL = 5A/div 1) VIN = 2V/div 2) VOUT = 2V/div 3) IL = 5A/div Short Circuit Test Quiescent Current vs. Input Voltage 490 1 V IN =5V V OUT =3.3V 2 Quiescent Current (µA) 480 470 460 450 440 430 420 410 V OUT=3.3V RFREQ=N C 400 3 390 Time (100ms/DIV) 380 3.5 4.0 4.5 5.0 Input Voltage(V) VIN = 5V VOUT = 3.3V R =NC FREQ 1) VIN = 5V/div 2) VOUT = 2V/div 3) IL = 5A/div 14 Rev. B.01 AME 5A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter AME5285 n Tape and Reel Dimension SOP-8PP P PIN 1 W AME AME Carrier Tape, Number of Components Per Reel and Reel Size 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 n Package Dimension SOP-8PP TOP VIEW SIDE VIEW D1 θ E1 E2 E L1 C PIN 1 D A1 Rev. B.01 MILLIMETERS INCHES MIN MAX MIN MAX A 1.350 1.750 0.053 0.069 A1 0.000 0.150 0.000 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 0.050 b 0.310 0.510 0.012 0.020 D 4.720 5.120 0.186 0.202 1.270 BSC e e FRONT VIEW A A2 b SYMBOLS 0.050 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 o 8 15 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. , November 2012 Document: A005-DS5285-B.01 Corporate Headquarter AME, Inc. 8F, 12, WenHu St., Nei-Hu Taipei 114, Taiwan . Tel: 886 2 2627-8687 Fax: 886 2 2659-2989