AMS2596 3A 30V Step-Down Converter General Description Features • • The AMS2596 is a high efficiency, non-synchronous step down regulator delivering up to 3A of output current making it ideal for medium to heavy load applications. It is designed to operate with wide input voltage range of 4.5 to 30V while maintaining 1mA of supply current at no load. The output voltage is either factor programmed or set via two external resistors to as low as 1.23V. • • • • • • • • • • • • • • The regulator operates at fixed 150kHz switching frequency ensuring low output ripple across the entire load. It requires only four external components for minimum PCB footprint and lowest overall system cost. An independent Enable pin provides electrical On/Off of the regulator. When connected to logic high, the regulator shuts down and consumes less than 100µA of current. Excellent transient response is achieved with no external compensation components. The device provides under-voltage lockout, output short circuit and over-temperature protection to safeguard the device and under fault conditions. An integrated soft-start controls the ramp of the output voltage and minimizes the inrush current. VIN range: 4.5 - 30V VOUT range: 1.25V to 7V fixed output Voltage in 100mV steps Adjustable version output voltage range from 1.2V to 25V Up to 5A output current 150kHz switching frequency 900µA supply current 80uA standby quiescent current 100% Duty Cycle Excellent line and load regulation Internal Soft Start Internal compensation Under voltage lockout Current Limit Protection Over temperature protection -25°C to +125°C Temperature Range Available in SOIC-8, TO220-5, TO252-5 and TO263-5 packages Applications • • • • The AMS2596 is available in SOIC, TO220, TO252 and TO263 packages, and it is rated for -25 to +125°C temperature range. LCD Monitor and TV High Current Point of Load Regulator System Power Set Top Box Typical Application 12V C1 470uF 4 2 3 7 3/4/2010 U1 Vin LX EN LX n/c FB gnd gnd AMS2596 L1 33uH 6 D1 B540C 5 1 R1 8 R2 10.0k 2.5V C2 470uF 31.7k www.advanced-monolithic.com 1 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter Pin Description TO-263 TO-220 TO-252 Pin# SOIC-8 Pin# Symbol 1 4 VIN Input supply pin. Connect a capacitor between this pin and ground. 2 5, 6 LX Switching node - connect an inductor between this pin and the output capacitor. 3, tab 7, 8 GND 4 1 FB Feedback pin. Connect this pin to the center tab of the resistor divider. 5 2 EN Enable pin. Logic high shuts the device down and consumes 50µA of current. When connected to logic low, the device will resume normal operation. This pin should not be floating. N/A 3 NC GND (PADDLE) 9 Description Ground connection. No connect. Ground paddle to be connected to PCB ground plane. Pin Configuration 8L SOIC SO Package (S) Top View 3/4/2010 www.advanced-monolithic.com 2 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter Absolute Maximum Ratings (1) Recommended Operating Conditions (2) VIN Supply Voltage………………...….......…..….-0.3V to 30V FB feedback pin……………………...........……-0.3V to +30V EN Enable Voltage…………………….…....….-0.3V to +20V Storage Temperature Range…………...…...-65⁰C to 150⁰C Lead Temperature (Soldering 60se………….….…… 215⁰C Junction Temperature………...……………….….…… 150⁰C ESD Suceptability…………………………………………..2kV Input Voltage……………………………………..………..4.5V to 28 V Tj Operating Temperature…… ……………….…….-25⁰C to 125⁰C Electrical Characteristics Parameter Vin Thermal Information (11) 8L SOIC EP θJA ………………………………….….…...60⁰C/W (9) ……………………………….….….…....30⁰C/W TO263-5 θJA (10) ………………………………….….…....57⁰C/W TO-252 θJA (8) …………………………….….…….…….50⁰C/W TO-220 θJA TA= 25 °C and VIN=12V (unless otherwise noted). Symbol Conditions Vin Feedback Voltage Efficiency VFBSW η 4.5V ≤ VIN ≤ 30V, 0.2A ≤ ILoad ≤ 3A VIN = 12V, VOUT = 3V, ILoad = 3A Oscillator Frequency FOSC Saturation Voltage VSAT ISW out=3A Maximum Duty Cycle DMAX Minimum Duty Cycle Min. Typ. Max. Units 4.5 12 20 V 1.193 1.180 1.230 1.267 1.280 V 85 127 % 150 173 kHz 1.16 1.4/1.5 V Note 6 95 99 % DMIN Note 7 0 Current Limit ILIMSW VSW out=5V Shutdown Supply Current IVinsd VEN =0V 90 3.6 / 3.4 4.5 % 6.9 / 7.5 A nA Output Leakage Current ILK Output = 0V (Note 8) Output = -1V 2 50 30 μA Quiescent Current IQ (Note 6) 5 10 mA Standby Quiescent Current ISD ON/OFF pin = 5V (OFF) 80 200 250 μA Enable Logic Input Threshold Voltage Enable Input Current 1.3 VEN(L) Low (Regulator ON) 0.6 V VEN(H) High (Regulator OFF) 2.0 V IENH VLOGIC = 2.5V (Regular OFF) 5 5 15 µA IENL VLOGIC = 0.5V (Regular ON) 0.02 0.02 5 µA Over-temperature Sh td Notes: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. V 125 °C Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. VO = Output Voltage specified from 1.25V to 7V in 100mV increments. Typical numbers are at 25ºC and represent the most likely norm. All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Feedback pin removed from output and connected to 0V to force the output transistor switch ON. Feedback pin removed from output and connected to 12V for Fixed and Adjustable version, to force the output transistor switch OFF. With output transistor switch turned off. Junction to ambient thermal resistance (no external heat sink) for the TO-220 package mounted vertically, with the leads soldered to a printed circuit board with (1 oz.) and a heat sink approximately 1 in2. Junction to ambient thermal resistance with the TO-263 package tab soldered to a double side printed circuit board with 2.5 in2 of (1 oz.) copper area. Junction to ambient thermal resistance with the TO-252 package tab soldered to a single sided printed circuit board with 2.5 in2 of (1 oz.) copper area. Junction to ambient thermal resistance with the SO-8 EDP package soldered to a double sided printed circuit board 5 via under the package paddle crossing to the other side of PCB on 2.5 in2 1oz Cu. 3/4/2010 www.advanced-monolithic.com 3 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter Typical Characteristics 100 Efficiency (%) 90 VSW out Regulation (%) Efficiency Vout=5V, L=22µH, B540C Schottky Vin =12V 80 70 Vin =24V 60 50 Vin =30V 40 30 Load Regulation Vout =5V, L=22µH 1.0 0.6 Vin =12V 0.2 -0.2 Vin =30V -1.0 20 0.01 0.1 1 0.01 10 0.1 Efficiency Vout=3.3V, L=22µH, IRF5F30 Schottky Efficiency (%) 90 Vin =12V 80 70 60 Vin =30V Vin =23V 50 40 30 20 0.01 0.1 1 1.0 0.6 -0.2 -0.6 0.01 0.8 0.4 0.0 25 30 Switching Frequency (kHz) 1.2 20 1 10 170 Switching Frequency vs. Input Voltage Vout = 5V 166 162 158 154 5 Input Voltage (V) 3/4/2010 0.1 Output Current (A) 1.6 15 Vin =12V Vin =30V -1.0 10 No Load Input Current vs. Input Voltage Vout = 5V 10 Vin =23V 0.2 Output Current (A) 5 10 Load Regulation Vout=3.3V, L=22µH VSW out Regulation (%) 100 1 Output Current (A) Output Current (A) Input Current (mA) Vin =24V -0.6 10 15 20 25 30 Input Voltage (V) www.advanced-monolithic.com 4 Phone (925) 443-0722 Fax (925) 443-0723 A AMS2 2596 3A A 30V Step p-Down Co onverter T Typical Characteristics Switching Frequency (kHz) Output Error (%) 1 Outp put Voltage Error E vs. Inpu ut Voltage Vout = 5V, 5 Iout=2A 0.5 0 -0.5 -1 5 10 15 20 25 30 35 Switc ching Freque ency Temperrature Variation Vout=5V V, V in =12V, Io o=1A 200 180 160 140 120 -10 -45 Input Vo oltage Vin (V)) 25 60 95 5 130 A Ambient Tem mperature (ºC C) S Step p-Down Conv verter Powerr Switch Saturation Voltage V Vin =12V = Output Voltage Error (%) Vcesat (V) 1.2 Outtput Voltage Temperature T Variation 0.9 0.6 0.3 Taamb = 25⁰ C Mounted on Evaal. Board 0 0 0.7 1.4 2.1 2.8 3.5 1.60 0.80 0.00 -0.80 Iout=0 V out=5 5V -1.60 -50 30 70 110 0 150 Ambient Tem mperature (ºC C) Currrent (A) 3/4/2010 -10 www.advvanced-mono olithic.com 5 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter Typical Characteristics Load Transient 1A to 3A, Vout = 5V, Vin=12V Output Ripple V out =2.5V, Iout=1.8A, Vin=12V Vout 50mVac /div Vout 200mVac /div IL 1A/div Iout 1A/div VSW 5V/div 1 µsec/div 40 µsec/div Load Transient 500mA to 2A, Vout = 5V, Vin=12V Start-Up Response V out 100mVac /div Vout 2V /div IL 2A/div Iout 1A/div VEN 10V /div 20 µsec/div 400 µsec/div 3/4/2010 www.advanced-monolithic.com 6 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter Functional Block Diagram Vin Internal Vcc Vcc 3.3V Regulator Isense 1.23V EAout R 150kHz Oscillator FB 1 S SET CLR Q Q Σ Level Shift Vout 2 LX EAout 4 Vref 1.23V 1.3V EN Shutdown 5 Shutdown Comparator GND 3/4/2010 3 www.advanced-monolithic.com 7 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter Device Summary The AMS2596 is a high voltage fixed frequency stepdown converter with a current capability of up to 5A. The peak current mode step-down converter has internal compensation and is stable with a wide range of ceramic, tantalum, and electrolytic output capacitors. The step-down converter output voltage is sensed through an external resistive divider that feeds the negative input to an internal transconductance error amplifier. The output of the error amplifier is connected to the input to a peak current mode comparator. The inductor current is sensed as it passes through the power switch, amplified and is also fed to the current mode comparator. The error amplifier regulates the output voltage by controlling the peak inductor current passing through the power switch so that, in steady state, the average inductor current equals the load current. The step-down converter has an input voltage range of 4.5V to 20V with an output voltage as low as 0.6V. Shutdown The enable input has two levels so that the step-down converter can be enabled independently of the LDO. The enable threshold for the step-down converter is 2.0V while the enable threshold for the linear regulator output is 2.5V typical. Fault Protection Short circuit and over-temperature shutdown disable the converter and LDO in the event of an overload condition. the effect on efficiency without a detrimental effect on stability. With and inductor value selected, the ripple current can be calculated: Ipp= (Vo+Vfwd)·(1-D) ·L·Fs Using the maximum input voltage values the ripple is: Ipp= (5V+0.2V)· 1-0.44 =0.88A 22μH·150kHz Once the appropriate value is determined, the component is selected based on the DC current and the peak (saturation) current. Select an inductor that has a DC current rating greater than the full load current of the application. The DC current rating is also reflected in the DC resistance (DCR) specification of the inductor. The inductor DCR should limit the inductor loss to less than 2% of the stepdown converter output power. The peak current at full load is equal to the full load DC current plus one half of the ripple current. As mentioned before, the ripple current varies with input voltage and is a maximum at the maximum input voltage. Ipkmax=Io+ Dmin= Application Inductor The step-down converter inductor is typically selected to limit the ripple current to 40% of the full load output current. Solve for this value at the maximum input voltage where the inductor ripple current is greatest. L= Vin-Vo · L= 12V-5V · Vo Vin·Io·0.4·Fs For most applications the duty cycle of the AMS2596 step down converter is less than 50% duty and does not require slope compensation for stability. This provides some flexibility in the selected inductor value. Given the above selected value, others values slightly greater or less may be examined to determine 3/4/2010 Vo Vinmax The duty cycle can be more accurately estimated by including the drops of the external Schottky diode and the internal power switch: Dmin= Dmin= 5V =16µH 12V·3A·0.4·150kHz (Vo+Vfwd)·(1-Dmin) 2·L·Fs Vo+Vfwd Vinmax-Vo+Vfwd 5V+0.2V =0.44 12V-0.3V+0.2V Vfwd is the diode freewheeling diode drop and Vsw is the collector to emitter drop of the internal power switch. With a good estimate of the duty cycle (D) the inductor peak current can be determined: Ipkmax=3A+ www.advanced-monolithic.com 8 (5V+0.2V)·(1-0.44) =3.44A 2·22µH·150kHz Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter There are a wide range 2 and 3 Amp, shielded and non-shielded inductors available. Table 1 lists a few. Table 1. Inductor Selection Guide Dimensions (mm) Series Type W L H Sumida CDRH127 Shielded 12.3 12.3 8 CDRH127/LD Shielded 12.3 12.3 8 CDRH105R Shielded 10.3 10.5 5.1 Coilcraft MSS1246 Shielded 12 12 4.6 MSS1246T Shielded 12 12 4.6 NonDO5022P 18 15 7.1 Shielded NonDO5010H 18 15.3 7.6 Shielded Output Capacitor The optimum solution for the switching regulator is to use a large bulk capacitor for large load transients in parallel with a smaller, low ESR, X5R or X7R ceramic capacitor to minimize the switching frequency ripple. High Frequency Ripple The following equation determines the required low ESR ceramic output capacitance for a given inductor current ripple (Ipp). C= Ipp 0.88A = =36μF Fs·8·dV 150kHz·8·20mV Large Signal Transient For applications with large load transients an additional capacitor may be required to keep the output voltage within the limits required during large load transients. In this case the required capacitance can be examined for the load application and load removal. For full load to no load transient the required capacitance is 2 L·Io2 22μH·(3A) Cbulk= = =97μF Vos2 -Vo2 (5.2V)2 -(5V)2 For the application of a load pulse the capacitance required form hold up depends on the time it takes for the power supply loop to build up the inductor current 3/4/2010 to match the load current. For the AMS2596 this can be estimated to be less than 20 µsec or about three clock cycles. Cbulk= Io·t 3A·20μsec = =300μF dV 0.2V For applications that do not have any significant load transient requirements a ceramic capacitor alone is typically sufficient. Input Capacitor The low esr ceramic capacitor required at the input to filter out high frequency noise as well as switching frequency ripple. Placement of the capacitor is critical for good high frequency noise rejection. See the PCB layout guidelines section for details. Switching frequency ripple is also filtered by the ceramic bypass input capacitor. Given a desired input voltage ripple (Vripple) limit, the required input capacitor can be estimated with: Dmax= Vo+Vfwd Vinmin-Vce+Vfwd Vce is the forward voltage drop of the switching transistor and Vfwd is the external Schottky forward voltage. Dmax·Io·(1-Dmax) C= Fs·Vripple 5V 0.2V 5V +0.2V ·3A· 110V-0.3V+0.2V 10V-0.3V+0.2V =25μF = 150kHz·0.2V . Vce is the forward voltage drop of the switching transistor and Vfwd is the external Schottky forward voltage. For high voltage input converters the duty cycle is always less than 50% so the maximum ripple is at the minimum input voltage. The ripple will increase as the duty cycle approaches 50% where it is a maximum. Feedback Resistor Selection The step down converter and LDO both use a 0.6V reference voltage at the positive terminal of the error amplifier. To set the output voltage a programming resistor form the feedback node to ground must first be selected (R2,R3 of figure 4). A 10kΩ resistor is a good selection for a programming resistor. A higher value could result in an excessively sensitive feedback node while a lower value will draw more www.advanced-monolithic.com 9 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter current and degrade the light load efficiency. The equation for selecting the voltage specific resistor is: R4= Vout Vref -1 ·R3 = 5V 1.2V -1 ·10kΩ=31.67kΩ Table 2. Feedback Resistor values Vout (V) 1.8 2.5 3.3 5.0 R1,R4 (kΩ) (R2,R3=10kΩ) 4.99 10.7 17.4 31.6 the star ground shown in Figure 1. This method of grounding helps to reduce high di/dt traces, and the detrimental effect associated with them, in a step-down converter. The inductance of these traces should always be minimized by using wide traces, ground planes, and proper component placement. 6. For good thermal performance vias are required to couple the exposed tab of the SO-8 package to the PCB ground plane. The via diameter should be 0.3mm to 0.33mm positioned on a 1.2mm grid. Ion+ Ioff PCB Layout The following guidelines should be followed to insure proper layout. 1. Vin Capacitor. A low ESR ceramic bypass capacitor must be placed as close to the IC as possible. 2. Schottky Diode. During the off portion of the switching cycle the inductor current flows through the Schottky diode to the output cap and returns to the inductor through the output capacitor. The trace that connects the output diode to the output capacitor sees a current signal with a very high di/dt. To minimize the associated spiking and ringing, the inductance and resistance of this trace should be minimized by connecting the diode anode to the output capacitor return with a short wide trace. 3. Feedback Resistors. The feedback resistors should be placed as close as possible the IC. Minimize the length of the trace from the feedback pin to the resistors. This is a high impedance node susceptible to interference from external RF noise sources. 4. Inductor. Minimize the length of the SW node trace. This minimizes the radiated EMI associated with the SW node. 5. Ground. The most quiet ground or return potential available is the output capacitor return. The inductor current flows through the output capacitor during both the on time and off time, hence it never sees a high di/dt. The only di/dt seen by the output capacitor is the inductor ripple current which is much less than the di/dt of an edge to a square wave current pulse. This is the best place to make a solid connection to the IC ground and input capacitor. This node is used as 3/4/2010 Ion Ioff PCB Inductance High di/dt Ion Ioff Ion+Ioff Ion Ioff High di/dt trace reduction “Star Ground” Figure 1. Step Down Converter Layout www.advanced-monolithic.com 10 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter Output Power and Thermal Limits The AMS2596 junction temperature, Step-Down converter and LDO current capability depends on the internal dissipation and the junction to case thermal resistance of the SO8 exposed paddle package. This gives the junction temperature rise above the device paddle and PCB temperature. The temperature of the paddle and PCB will be elevated above the ambient temperature due to the total losses of the step down converter and losses of other circuits and or converters mounted to the PCB. Tjmax=Pd·θjc+Tpcb+Tamb The losses associated with the AMS2596 overall efficiency are; 1. Output Diode Conduction Losses 2. Inductor DCR Losses 3. AMS2596 Internal losses a. Power Switch Forward Conduction and Switching Losses b. Quiescent Current Losses Figure 2. AMS2596 SO-8 Evaluation Board Top The internal losses contribute to the junction temperature rise above the case and PCB temperature. The junction temperature depends on many factors and should always be verified in the final application at the maximum ambient temperature. This will assure that the device does not enter over-temperature shutdown when fully loaded at the maximum ambient temperature. Figure 3. AMS2596 SO-8 Evaluation Board Bottom 3/4/2010 www.advanced-monolithic.com 11 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter C5 3.3nF R2 R1 10.0k 31.7k 1 2 Enable 3 4 Vin gnd C3 470uF 35V C1 10uF 50V U1 FB gnd EN gnd n/c LX Vin LX AMS2596 8 gnd 7 LX 6 5 Vout L1 33uH C2 470uF D1 B540C C4 22uF gnd Figure 4. AMS2596 Evaluation Board Schematic Table 3. Evaluation Board Bill of Materials Component Value L1 C2 C1 C3 C4 C5 R2 R1 D1 U1 33 µF H 3.9A 470µF, 10V, Electrolytic 10 µF, 50V, X5R, 1210, Ceramic 470uF 35V, Electrolytic 22µF, 10V, X5R, 0805, Ceramic 3.3nF 50V, 20%, X7R, 0603 10kΩ, 0.1W, 0603 1% See table 2 5A, 40V Schottky Step-Down Converter Manufacturer Manufacturer Part Number Taiyo Yuden UMK325BJ106KM-T Taiyo Yuden Murata Various Various Diodes Inc. AMS LMK212BJ226MG-T GRM188R71H332MA01 CRCW060310K0FKEA CRCW0603xxKxFKEA B540C AMS2596 ORDERING INFORMATION PACKAGE TYPE TO-263 3/4/2010 AMS2596 ADJUSTABLE AMS2596M AMS2596 FIXEDVOLTAGE TEMP. RANGE AMS2596M-XX -25ºC to -125ºC TO-220 AMS2596T AMS2596T-XX -25ºC to -125ºC TO-252 AMS2596D AMS2596D-XX -25ºC to -125ºC SO-8 EDP AMS2596S AMS2596S-XX -25ºC to -125ºC www.advanced-monolithic.com 12 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter PACKAGE DIMENSIONS inches (millimeters) unless otherwise noted. 8 LEAD SOIC PLASTIC PACKAGES (S) 3/4/2010 www.advanced-monolithic.com 13 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter PACKAGE DIMENSIONS (continued) 5 LEAD TO-220 PLASTIC PACKAGE (T) 0.387-0.413 (9.83-10.49) 0.149-0.153 (3.77-3.87) DIA 0.170-0.190 (4.32-4.82) 0.045-0.055 (1.143-1.397) 0.240-0.260 (6.100-6.600) 0.575-0.605 (14.61-15.37) 0.460-0.500 (11.684-12.700) 0.335-0.345 (8.51-8.77) 0.980-1.070 (24.892-27.178) 0.520-0.570 (13.208-14.478) 0.062-0.072 (1.570-1.830) 0.032 TYP (0.81) 0.013-0.023 (0.330-0.584) 0.105 (2.67) TYP T (TO-220 ) AMS DRW# 042194 PLASTIC PACKAGE (D) 5 LEAD TO-252 3/4/2010 www.advanced-monolithic.com 14 Phone (925) 443-0722 Fax (925) 443-0723 AMS2596 3A 30V Step-Down Converter PACKAGE DIMENSIONS (continued) 5 LEAD TO-263 PLASTIC PACKAGE (M) 3/4/2010 www.advanced-monolithic.com 15 Phone (925) 443-0722 Fax (925) 443-0723