LM2742 LM2742 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages Literature Number: SNVS266B LM2742 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages General Description Features The LM2742 is a high-speed, synchronous, switching regulator controller. It is intended to control currents of 0.7A to 20A with up to 95% conversion efficiencies. Power up and down sequencing is achieved with the power-good flag, adjustable soft-start and output enable features. The LM2742 operates from a low-current 5V bias and can convert from a 1V to 16V power rail. The part utilizes a fixed-frequency, voltage-mode, PWM control architecture and the switching frequency is adjustable from 50kHz to 2MHz by setting the value of an external resistor. Current limit is achieved by monitoring the voltage drop across the on-resistance of the low-side MOSFET, which enables on-times on the order of 40ns, one of the best in the industry. The wide range of operating frequencies gives the power supply designer the flexibility to fine-tune component size, cost, noise and efficiency. The adaptive, non-overlapping MOSFET gate-drivers and high-side bootstrap structure helps to further maximize efficiency. The highside power FET drain voltage can be from 1V to 16V and the output voltage is adjustable down to 0.6V. Input power from 1V to 16V Output voltage adjustable down to 0.6V Power Good flag, adjustable soft-start and output enable for easy power sequencing Reference Accuracy: 1.5% (0C - 125C) Current limit without sense resistor Soft start Switching frequency from 50 kHz to 2 MHz 40ns typical minimum on-time TSSOP-14 package Applications POL power supply modules Cable Modems Set-Top Boxes/ Home Gateways DDR Core Power High-Efficiency Distributed Power Local Regulation of Core Power Typical Application 20087510 (c) 2007 National Semiconductor Corporation 200875 www.national.com LM2742 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages October 31, 2007 LM2742 Connection Diagram 20087511 14-Lead Plastic TSSOP JA = 155C/W Ordering Information Order Number Package Type NSC Package Drawing Supplied As LM2742MTC TSSOP-14 MTC14 94 Units, Raill LM2742MTCX TSSOP-14 MTC14 2500 Units on Tape and Reel signal to determine the duty cycle. This pin is necessary for compensating the control loop. SS (Pin 9) - Soft start pin. A capacitor connected between this pin and ground sets the speed at which the output voltage ramps up. Larger capacitor value results in slower output voltage ramp but also lower inrush current. FB (Pin 10) - This is the inverting input of the error amplifier, which is used for sensing the output voltage and compensating the control loop. FREQ (Pin 11) - The switching frequency is set by connecting a resistor between this pin and ground. SD (Pin 12) - IC Logic Shutdown. When this pin is pulled low the chip turns off both the high side and low side switches. While this pin is low, the IC will not start up. An internal 20A pull-up connects this pin to VCC. For a device which turns on the low side switch during shutdown, see the pin compatible LM2737. HG (Pin 14) - Gate drive for the high-side N-channel MOSFET. This signal is interlocked with LG to avoid shoot-through problems. Pin Descriptions BOOT (Pin 1) - Supply rail for the N-channel MOSFET gate drive. The voltage should be at least one gate threshold above the regulator input voltage to properly turn on the high-side NFET. LG (Pin 2) - Gate drive for the low-side N-channel MOSFET. This signal is interlocked with HG to avoid shoot-through problems. PGND (Pins 3, 13) - Ground for FET drive circuitry. It should be connected to system ground. SGND (Pin 4) - Ground for signal level circuitry. It should be connected to system ground. VCC (Pin 5) - Supply rail for the controller. PWGD (Pin 6) - Power Good. This is an open drain output. The pin is pulled low when the chip is in UVP, OVP, or UVLO mode. During normal operation, this pin is connected to VCC or other voltage source through a pull-up resistor. ISEN (Pin 7) - Current limit threshold setting. This sources a fixed 50A current. A resistor of appropriate value should be connected between this pin and the drain of the low-side FET. EAO (Pin 8) - Output of the error amplifier. The voltage level on this pin is compared with an internally generated ramp www.national.com 2 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VCC BOOTV LG and HG to GND (Note 3) Junction Temperature Storage Temperature Soldering Information 7V 21V -2V to 21V 150C -65C to 150C 260C 235C 2 kV Operating Ratings Supply Voltage (VCC) Junction Temperature Range 4.5V to 5.5V -40C to +125C Thermal Resistance (JA) 155C/W Electrical Characteristics VCC = 5V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA=TJ=+25C. Limits appearing in boldface type apply over full Operating Temperature Range. Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Symbol VFB_ADJ VON Parameter FB Pin Voltage UVLO Thresholds Min Typ Max VCC = 4.5V, 0C to +125C Conditions 0.591 0.6 0.609 VCC = 5V, 0C to +125C 0.591 0.6 0.609 VCC = 5.5V, 0C to +125C 0.591 0.6 0.609 VCC = 4.5V, -40C to +125C 0.589 0.6 0.609 VCC = 5V, -40C to +125C 0.589 0.6 0.609 VCC = 5.5V, -40C to +125C 0.589 0.6 0.609 Rising Falling 4.2 3.6 SD = 5V, FB = 0.55V Fsw = 600kHz Units V V 1 1.5 SD = 5V, FB = 0.65V Fsw = 600kHz 0.8 1.7 Shutdown VCC Current SD = 0V 0.15 0.4 tPWGD1 PWGD Pin Response Time FB Voltage Going Up 6 s tPWGD2 PWGD Pin Response Time FB Voltage Going Down 6 s 20 A IQ-V5 Operating VCC Current 2 mA 2.2 ISD ISS-ON ISS-OC ISEN-TH SD Pin Internal Pull-up Current SS Pin Source Current SS Pin Sink Current During Over Current SS Voltage = 2.5V 0C to +125C -40C to +125C 8 5 SS Voltage = 2.5V ISEN Pin Source Current Trip Point 0C to +125C -40C to +125C 11 11 0.7 15 15 95 35 28 50 50 mA A A 65 65 A ERROR AMPLIFIER GBW G Error Amplifier Unity Gain Bandwidth 5 MHz Error Amplifier DC Gain 60 dB SR Error Amplifier Slew Rate IFB FB Pin Bias Current FB = 0.55V FB = 0.65V 6 IEAO EAO Pin Current Sourcing and Sinking VEAO = 2.5, FB = 0.55V VEAO = 2.5, FB = 0.65V 2.8 0.8 VEA Error Amplifier Maximum Swing Minimum Maximum 1.2 3.2 0 0 3 15 30 V/A 100 155 nA mA V www.national.com LM2742 Lead Temperature (soldering, 10sec) Infrared or Convection (20sec) ESD Rating Absolute Maximum Ratings (Note 1) LM2742 Symbol Parameter Conditions Min Typ Max Units BOOT = 12V, EN = 0 0C to +125C -40C to +125C 95 95 160 215 A GATE DRIVE IQ-BOOT BOOT Pin Quiescent Current RDS1 Top FET Driver Pull-Up ON resistance BOOT-SW = 5V@350mA 3 RDS2 Top FET Driver Pull-Down ON resistance BOOT-SW = 5V@350mA 2 RDS3 Bottom FET Driver Pull-Up ON resistance BOOT-SW = 5V@350mA 3 RDS4 Bottom FET Driver Pull-Down ON resistance BOOT-SW = 5V@350mA 2 RFADJ = 590k 50 RFADJ = 88.7k 300 OSCILLATOR fOSC D ton-min PWM Frequency Max Duty Cycle RFADJ = 42.2k, 0C to +125C 500 600 700 RFADJ = 42.2k, -40C to +125C 490 600 700 kHz RFADJ = 17.4k 1400 RFADJ = 11.3k 2000 fPWM = 300kHz fPWM = 600kHz 90 88 % 40 ns Minimum on-time LOGIC INPUTS AND OUTPUTS VSD-IH SD Pin Logic High Trip Point VSD-IL SD Pin Logic Low Trip Point 0C to +125C -40C to +125C 1.3 1.25 1.6 1.6 PWGD Pin Trip Points FB Voltage Going Down 0C to +125C -40C to +125C 0.413 0.410 0.430 0.430 0.446 0.446 V FB Voltage Going Up 0C to +125C -40C to +125C 0.691 0.688 0.710 0.710 0.734 0.734 V VPWGD-TH-LO VPWGD-TH-HI VPWGD-HYS PWGD Pin Trip Points PWGD Hysteresis 2.6 FB Voltage Going Down FB Voltage Going Up 35 110 V 3.5 V mV Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device operates correctly. Operating Ratings do not imply guaranteed performance limits. Note 2: The human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin. Note 3: The LG and HG pin can have -2V to -0.5V applied for a maximum duty cycle of 10% with a maximum period of 1 second. There is no duty cycle or maximum period limitation for a LG and HG pin voltage range of -0.5V to 21V. www.national.com 4 LM2742 Typical Performance Characteristics Efficiency (VO = 1.5V) FSW = 300kHz, TA = 25C Efficiency (VO = 3.3V) FSW = 300kHz, TA = 25C 20087512 20087513 VCC Operating Current vs Temperature FSW = 600kHz, No-Load Bootpin Current vs Temperature for BOOTV = 12V FSW = 600kHz, Si4826DY FET, No-Load 20087515 20087514 Bootpin Current vs Temperature with 5V Bootstrap FSW = 600kHz, Si4826DY FET, No-Load PWM Frequency vs Temperature for RFADJ = 43.2k 20087516 20087517 5 www.national.com LM2742 RFADJ vs PWM Frequency (in 100 to 800kHz range), TA = 25C RFADJ vs PWM Frequency (in 900 to 2000kHz range), TA = 25C 20087518 20087519 VCC Operating Current Plus Boot Current vs PWM Frequency (Si4826DY FET, TA = 25C) Switch Waveforms (HG Falling) VIN = 5V, VO = 1.8V IO = 3A, CSS = 10nF FSW = 600kHz 20087520 20087523 Switch Waveforms (HG Rising) VIN = 5V, VO = 1.8V IO = 3A, FSW = 600kHz Start-Up (No-Load) VIN = 10V, VO = 1.2V CSS = 10nF, FSW = 300kHz 20087524 www.national.com 20087521 6 LM2742 Start-Up (Full-Load) VIN = 10V, VO = 1.2V IO = 10A, CSS = 10nF FSW = 300kHz Start Up (No-Load, 10x CSS) VIN = 10V, VO = 1.2V CSS = 100nF, FSW = 300kHz 20087526 20087522 Start Up (Full Load, 10x CSS) VIN = 10V, VO = 1.2V IO = 10A, CSS = 100nF FSW = 300kHz Start Up (Into 1.2V Pre-Bias) VIN = 12V, VO = 2.5V No Load, No Soft Start Capacitor FSW = 300kHz 20087548 20087525 Start Up (Into 1.2V Pre-Bias) VIN = 12V, VO = 2.5V No Load, CSS = 10nF FSW = 300kHz Shutdown VIN = 12V, VO = 1.2V IO = 10A, CSS = 10nF FSW = 300kHz 20087527 20087549 7 www.national.com LM2742 Shutdown (No Load) VIN = 12V, VO = 1.2V IO = 10A, CSS = 10nF FSW = 300kHz Load Transient Response (IO = 0 to 4A) VIN = 12V, VO = 1.2V FSW = 300kHz 20087528 20087533 Load Transient Response (IO = 4 to 0A) VIN = 12V, VO = 1.2V FSW = 300kHz Line Transient Response (VIN =5V to 12V) VO = 1.2V, IO = 5A FSW = 300kHz 20087529 20087530 Line Transient Response (VIN =12V to 5V) VO = 1.2V, IO = 5A FSW = 300kHz Line Transient Response VO = 1.2V, IO = 5A FSW = 300kHz 20087532 20087531 www.national.com 8 Peak Current During Current Limit VIN = 12V, VO = 3.3V, ILIM = 4A, FSW = 300kHz, L = 15 H 20087553 20087552 Block Diagram 20087501 9 www.national.com LM2742 Peak Current During Current Limit VIN = 12V, VO = 3.3V, ILIM = 4A, FSW = 300kHz, L = 15 H LM2742 correctly. For a BOOT of 12V, the initial gate charging current is 2A, and the initial gate discharging current is typically 6A. Application Information THEORY OF OPERATION The LM2742 is a voltage-mode, high-speed synchronous buck regulator with a PWM control scheme. It is designed for use in set-top boxes, thin clients, DSL/Cable modems, and other applications that require high efficiency buck converters. It has power good (PWRGD), and output shutdown (SD). Current limit is achieved by sensing the voltage VDS across the low side FET. During current limit the high side gate is turned off and the low side gate turned on. The soft start capacitor is discharged by a 95A source (reducing the maximum duty cycle) until the current is under control. START UP When VCC exceeds 4.2V and the shutdown pin SD sees a logic high the soft start capacitor begins charging through an internal fixed 10A source. During this time the output of the error amplifier is allowed to rise with the voltage of the soft start capacitor. This capacitor, CSS, determines soft start time, and can be determined approximately by: 20087502 FIGURE 1. BOOT Supplied by Charge Pump In a system without a separate, higher voltage, a charge pump (bootstrap) can be built using a diode and small capacitor, Figure 1. The capacitor serves to maintain enough voltage between the top FET gate and source to control the device even when the top FET is on and its source has risen up to the input voltage level. The LM2742 gate drives use a BiCMOS design. Unlike some other bipolar control ICs, the gate drivers have rail-to-rail swing, ensuring no spurious turn-on due to capacitive coupling. An application for a microprocessor might need a delay of 3ms, in which case CSS would be 12nF. For a different device, a 100ms delay might be more appropriate, in which case CSS would be 400nF. (390 10%) During soft start the PWRGD flag is forced low and is released when the voltage reaches a set value. At this point this chip enters normal operation mode and the Power Good flag is released. Since the output is floating when the LM2742 is turned off, it is possible that the output capacitor may be precharged to some positive value. During start-up, the LM2742 operates fully synchronous and will discharge the output capacitor to some extent depending on the output voltage, soft start capacitance, and the size of the output capacitor. POWER GOOD SIGNAL The power good signal is the or-gated flag representing overvoltage and under-voltage protection. If the output voltage is 18% over it's nominal value, VFB = 0.7V, or falls 30% below that value, VFB = 0.41V, the power good flag goes low. It will return to a logic high whenever the feedback pin voltage is between 70% and 118% of 0.6V. The power good pin is an open drain output that can be pulled up to logic voltages of 5V or less with a 10k resistor. NORMAL OPERATION While in normal operation mode, the LM2742 regulates the output voltage by controlling the duty cycle of the high side and low side FETs. The equation governing output voltage is: VO = 0.6 x (RFB1 + RFB2) / RFB1 UVLO The 4.2V turn-on threshold on VCC has a built in hysteresis of 0.6V. Therefore, if VCC drops below 3.6V, the chip enters UVLO mode. UVLO consists of turning off the top FET, turning off the bottom FET, and remaining in that condition until VCC rises above 4.2V. As with shutdown, the soft start capacitor is discharged through a FET, ensuring that the next start-up will be smooth. The PWM frequency is adjustable between 50kHz and 2MHz and is set by an external resistor, RFADJ, between the FREQ pin and ground. The resistance needed for a desired frequency is approximately: CURRENT LIMIT Current limit is realized by sensing the voltage across the low side FET while it is on. The RDSON of the FET is a known value, hence the current through the FET can be determined as: MOSFET GATE DRIVERS The LM2742 has two gate drivers designed for driving Nchannel MOSFETs in a synchronous mode. Power for the drivers is supplied through the BOOT pin. For the high side gate (HG) to fully turn on the top FET, the BOOT voltage must be at least one VGS(th) greater than Vin. (BOOT 2*Vin) This voltage can be supplied by a separate, higher voltage source, or supplied from a local charge pump structure. In a system such as a desktop computer, both 5V and 12V are usually available. Hence if Vin was 5V, the 12V supply could be used for BOOT. 12V is more than 2*Vin, so the HG would operate www.national.com VDS = I * RDSON The current through the low side FET while it is on is also the falling portion of the triangle wave inductor current. The current limit threshold is determined by an external resistor, RCS, connected between the switch node and the ISEN pin. A constant current of 50 A is forced through RCS, causing a fixed voltage drop. This fixed voltage is compared against VDS and if the latter is higher, the current limit of the chip has 10 which ensures enough time for correct operation of the current sensing circuitry. See the plots entitled Peak Current During Current Limit in the Typical Performance Characteristics section. In order to minimize the time period in which peak inductor current exceeds the current limit threshold, the IC also discharges the soft start capacitor through a fixed 95 A source. The output of the LM2727/37 internal error amplifier is limited by the voltage on the soft start capacitor. Hence, discharging the soft start capacitor reduces the maximum duty cycle D of the controller. During severe current limit this reduction in duty cycle will reduce the output voltage if the current limit conditions last for an extended time. Output inductor current will be reduced in turn to a flat level equal to the current limit threshold. The third benefit of the soft start capacitor discharge is a smooth, controlled ramp of output voltage when the current limit condition is cleared. During the first few nanoseconds after the low side gate turns on, the low side FET body diode conducts. This causes an additional 0.7V drop in VDS. The range of VDS is normally much lower. For example, if RDSON were 10m and the current through the FET was 10A, VDS would be 0.1V. The current limit would see 0.7V as a 70A current and enter current limit immediately. Hence current limit is masked during the time it takes for the high side switch to turn off and the low side switch to turn on. RCS = RDSON(LOW) * ILIM/50A For example, a conservative 15A current limit in a 10A design with a minimum RDSON of 10m would require a 3.3k resistor. Because current sensing is done across the low side FET, no minimum high side on-time is necessary. In the current limit mode the LM2727/37 will turn the high side off and the keep low side on for as long as necessary. The LM2727/37 enters current limit mode if the inductor current exceeds the current limit threshold at the point where the high side FET turns off and the low side FET turns on. (The point of peak inductor current. See .) Note that in normal operation mode the high side FET always turns on at the beginning of a clock cycle. In current limit mode, by contrast, the high side FET on pulse is skipped. This causes inductor current to fall. Unlike a normal operation switching cycle, however, in a current limit mode switching cycle the high side FET will turn on as soon as inductor current has fallen to the current limit threshold. The LM2727/37 will continue to skip high side FET pulses until the inductor current peak is below the current limit threshold, at which point the system resumes normal operation. SHUT DOWN If the shutdown pin SD is pulled low, the LM2742 discharges the soft start capacitor through a MOSFET switch. The high side and low side switches are turned off. The LM2742 remains in this state until SD is released. DESIGN CONSIDERATIONS The following is a design procedure for all the components needed to create the circuit shown in Figure 4 in the Example Circuits section, a 5V in to 1.2V out converter, capable of delivering 10A with an efficiency of 85%. The switching frequency is 300kHz. The same procedures can be followed to create many other designs with varying input voltages, output voltages, and output currents. Input Capacitor The input capacitors in a Buck switching converter are subjected to high stress due to the input current waveform, which is a square wave. Hence input caps are selected for their ripple current capability and their ability to withstand the heat generated as that ripple current runs through their ESR. Input rms ripple current is approximately: 20087550 FIGURE 2. Current Limit Threshold Unlike a high side FET current sensing scheme, which limits the peaks of inductor current, low side current sensing is only allowed to limit the current during the converter off-time, when inductor current is falling. Therefore in a typical current limit plot the valleys are normally well defined, but the peaks are variable, according to the duty cycle. The PWM error amplifier and comparator control the off pulse of the high side FET, even during current limit mode, meaning that peak inductor current can exceed the current limit threshold. Assuming that the output inductor does not saturate, the maximum peak inductor current during current limit mode can be calculated with the following equation: The power dissipated by each input capacitor is: Here, n is the number of capacitors, and indicates that power loss in each cap decreases rapidly as the number of input caps increase. The worst-case ripple for a Buck converter occurs during full load, when the duty cycle D = 50%. In the 5V to 1.2V case, D = 1.2/5 = 0.24. With a 10A maximum load the ripple current is 4.3A. The Sanyo 10MV5600AX aluminum electrolytic capacitor has a ripple current rating of 2.35A, up to 105C. Two such capacitors make a conservative design that allows for unequal current sharing between Where TOSC is the inverse of switching frequency fOSC. The 200ns term represents the minimum off-time of the duty cycle, 11 www.national.com LM2742 been reached. RCS can be found by using the following equation: LM2742 A good range for Io is 25 to 50% of the output current. In the past, 30% was considered a maximum value for output currents higher than about 2Amps, but as output capacitor technology improves the ripple current can be allowed to increase. Plugging in the values for output current ripple, input voltage, output voltage, switching frequency, and assuming a 40% peak-to-peak output current ripple yields an inductance of 1.5H. The output inductor must be rated to handle the peak current (also equal to the peak switch current), which is (Io + 0.5*Io). This is 12A for a 10A design. The Coilcraft D05022-152HC is 1.5H, is rated to 15Arms, and has a DCR of 4m. individual caps. Each capacitor has a maximum ESR of 18m at 100 kHz. Power loss in each device is then 0.05W, and total loss is 0.1W. Other possibilities for input and output capacitors include MLCC, tantalum, OSCON, SP, and POSCAPS. Input Inductor The input inductor serves two basic purposes. First, in high power applications, the input inductor helps insulate the input power supply from switching noise. This is especially important if other switching converters draw current from the same supply. Noise at high frequency, such as that developed by the LM2742 at 1MHz operation, could pass through the input stage of a slower converter, contaminating and possibly interfering with its operation. An input inductor also helps shield the LM2742 from high frequency noise generated by other switching converters. The second purpose of the input inductor is to limit the input current slew rate. During a change from no-load to full-load, the input inductor sees the highest voltage change across it, equal to the full load current times the input capacitor ESR. This value divided by the maximum allowable input current slew rate gives the minimum input inductance: Output Capacitor The output capacitor forms the second half of the power stage of a Buck switching converter. It is used to control the output voltage ripple (Vo) and to supply load current during fast load transients. In this example the output current is 10A and the expected type of capacitor is an aluminum electrolytic, as with the input capacitors. (Other possibilities include ceramic, tantalum, and solid electrolyte capacitors, however the ceramic type often do not have the large capacitance needed to supply current for load transients, and tantalums tend to be more expensive than aluminum electrolytic.) Aluminum capacitors tend to have very high capacitance and fairly low ESR, meaning that the ESR zero, which affects system stability, will be much lower than the switching frequency. The large capacitance means that at switching frequency, the ESR is dominant, hence the type and number of output capacitors is selected on the basis of ESR. One simple formula to find the maximum ESR based on the desired output voltage ripple, Vo and the designed output current ripple, Io, is: In the case of a desktop computer system, the input current slew rate is the system power supply or "silver box" output current slew rate, which is typically about 0.1A/s. Total input capacitor ESR is 9m, hence V is 10*0.009 = 90 mV, and the minimum inductance required is 0.9H. The input inductor should be rated to handle the DC input current, which is approximated by: In this example, in order to maintain a 2% peak-to-peak output voltage ripple and a 40% peak-to-peak inductor current ripple, the required maximum ESR is 6m. Three Sanyo 10MV5600AX capacitors in parallel will give an equivalent ESR of 6m. The total bulk capacitance of 16.8mF is enough to supply even severe load transients. Using the same capacitors for both input and output also keeps the bill of materials simple. In this case IIN-DC is about 2.8A. One possible choice is the TDK SLF12575T-1R2N8R2, a 1.2H device that can handle 8.2Arms, and has a DCR of 7m. Output Inductor The output inductor forms the first half of the power stage in a Buck converter. It is responsible for smoothing the square wave created by the switching action and for controlling the output current ripple. (Io) The inductance is chosen by selecting between tradeoffs in output ripple, efficiency, and response time. The smaller the output inductor, the more quickly the converter can respond to transients in the load current. If the inductor value is increased, the ripple through the output capacitor is reduced and thus the output ripple is reduced. As shown in the efficiency calculations, a smaller inductor requires a higher switching frequency to maintain the same level of output current ripple. An increase in frequency can mean increasing loss in the FETs due to the charging and discharging of the gates. Generally the switching frequency is chosen so that conduction loss outweighs switching loss. The equation for output inductor selection is: Mosfets MOSFETS are a critical part of any switching controller and have a direct impact on the system efficiency. In this case the target efficiency is 85% and this is the variable that will determine which devices are acceptable. Loss from the capacitors, inductors, and the LM2742 itself are detailed in the Efficiency section, and come to about 0.54W. To meet the target efficiency, this leaves 1.45W for the FET conduction loss, gate charging loss, and switching loss. Switching loss is particularly difficult to estimate because it depends on many factors. When the load current is more than about 1 or 2 amps, conduction losses outweigh the switching and gate charging losses. This allows FET selection based on the RDSON of the FET. Adding the FET switching and gate-charging losses to the equation leaves 1.2W for conduction losses. The equation for conduction loss is: PCnd = D(I2o * RDSON *k) + (1-D)(I2o * RDSON *k) The factor k is a constant which is added to account for the increasing RDSON of a FET due to heating. Here, k = 1.3. The Si4442DY has a typical RDSON of 4.1m. When plugged into www.national.com 12 LM2742 the equation for PCND the result is a loss of 0.533W. If this design were for a 5V to 2.5V circuit, an equal number of FETs on the high and low sides would be the best solution. With the duty cycle D = 0.24, it becomes apparent that the low side FET carries the load current 76% of the time. Adding a second FET in parallel to the bottom FET could improve the efficiency by lowering the effective RDSON. The lower the duty cycle, the more effective a second or even third FET can be. For a minimal increase in gate charging loss (0.054W) the decrease in conduction loss is 0.15W. What was an 85% design improves to 86% for the added cost of one SO-8 MOSFET. The following shows an efficiency calculation to complement the Circuit of Figure 4. Output power for this circuit is 1.2V x 10A = 12W. Chip Operating Loss PIQ = IQ-VCC *VCC 2mA x 5V = 0.01W FET Gate Charging Loss Control Loop Components The circuit is this design example and the others shown in the Example Circuits section have been compensated to improve their DC gain and bandwidth. The result of this compensation is better line and load transient responses. For the LM2742, the top feedback divider resistor, Rfb2, is also a part of the compensation. For the 10A, 5V to 1.2V design, the values are: Cc1 = 4.7pF 10%, Cc2 = 1nF 10%, Rc = 229k 1%. These values give a phase margin of 63 and a bandwidth of 29.3kHz. PGC = n * VCC * QGS * fOSC The value n is the total number of FETs used. The Si4442DY has a typical total gate charge, Q GS, of 36nC and an rds-on of 4.1m. For a single FET on top and bottom: 2*5*36E-9*300,000 = 0.108W FET Switching Loss PSW = 0.5 * Vin * IO * (tr + tf)* fOSC The Si4442DY has a typical rise time tr and fall time tf of 11 and 47ns, respectively. 0.5*5*10*58E-9*300,000 = 0.435W FET Conduction Loss Support Capacitors and Resistors The Cinx capacitors are high frequency bypass devices, designed to filter harmonics of the switching frequency and input noise. Two 1F ceramic capacitors with a sufficient voltage rating (10V for the Circuit of Figure 4) will work well in almost any case. RIN and CIN are standard filter components designed to ensure smooth DC voltage for the chip supply. Depending on noise, RIN should be 10 to 100, and CIN should be between 0.1 and 2.2 F. CBOOT is the bootstrap capacitor, and should be 0.1F. (In the case of a separate, higher supply to the BOOT pin, this 0.1F cap can be used to bypass the supply.) Using a Schottky device for the bootstrap diode allows the minimum drop for both high and low side drivers. The On Semiconductor BAT54 or MBR0520 work well. Rp is a standard pull-up resistor for the open-drain power good signal, and should be 10k. If this feature is not necessary, it can be omitted. RCS is the resistor used to set the current limit. Since the design calls for a peak current magnitude (Io + 0.5 * Io) of 12A, a safe setting would be 15A. (This is well below the saturation current of the output inductor, which is 25A.) Following the equation from the Current Limit section, use a 3.3k resistor. RFADJ is used to set the switching frequency of the chip. Following the equation in the Theory of Operation section, the closest 1% tolerance resistor to obtain fSW = 300kHz is 88.7k. CSS depends on the users requirements. Based on the equation for CSS in the Theory of Operation section, for a 3ms delay, a 12nF capacitor will suffice. PCn = 0.533W Input Capacitor Loss 4.282*0.018/2 = 0.164W Input Inductor Loss PLin = I2in * DCRinput-L 2.822*0.007 = 0.055W Output Inductor Loss PLout = I2o * DCRoutput-L 102*0.004 = 0.4W System Efficiency EFFICIENCY CALCULATIONS A reasonable estimation of the efficiency of a switching controller can be obtained by adding together the loss is each current carrying element and using the equation: 13 www.national.com LM2742 Example Circuits 20087503 FIGURE 3. 5V-16V to 3.3V, 10A, 300kHz This circuit and the one featured on the front page have been designed to deliver high current and high efficiency in a small package, both in area and in height The tallest component in this circuit is the inductor L1, which is 6mm tall. The compensation has been designed to tolerate input voltages from 5 to 16V. 20087504 FIGURE 4. 5V to 1.2V, 10A, 300kHz This circuit design, detailed in the Design Considerations section, uses inexpensive aluminum capacitors and off-the-shelf inductors. It can deliver 10A at better than 85% efficiency. www.national.com Large bulk capacitance on input and output ensure stable operation. 14 LM2742 20087505 FIGURE 5. 5V to 1.8V, 3A, 600kHz The example circuit of Figure 5 has been designed for minimum component count and overall solution size. A switching frequency of 600kHz allows the use of small input/output capacitors and a small inductor. The availability of separate 5V and 12V supplies (such as those available from desk-top computer supplies) and the low current further reduce com- ponent count. Using the 12V supply to power the MOSFET drivers eliminates the bootstrap diode, D1. At low currents, smaller FETs or dual FETs are often the most efficient solutions. Here, the Si4826DY, an asymmetric dual FET in an SO-8 package, yields 92% efficiency at a load of 2A. 20087506 FIGURE 6. 3.3V to 0.8V, 5A, 500kHz The circuit of Figure 6 demonstrates the LM2742 delivering a low output voltage at high efficiency (87%). A separate 5V supply is required to run the chip, however the input voltage can be as low as 2.2 15 www.national.com LM2742 20087507 FIGURE 7. 1.8V and 3.3V, 1A, 1.4MHz, Simultaneous The circuits in Figure 7 are intended for ADSL applications, where the high switching frequency keeps noise out of the data transmission range. In this design, the 1.8 and 3.3V outputs come up simultaneously by using the same softstart capacitor. Because two current sources now charge the same capacitor, the capacitance must be doubled to achieve the www.national.com same softstart time. (Here, 40nF is used to achieve a 5ms softstart time.) A common softstart capacitor means that, should one circuit enter current limit, the other circuit will also enter current limit. The additional compensation components Rc2 and Cc3 are needed for the low ESR, all ceramic output capacitors, and the wide (3x) range of Vin. 16 LM2742 20087508 FIGURE 8. 12V Unregulated to 3.3V, 3A, 750kHz This circuit shows the LM2742 paired with a cost effective solution to provide the 5V chip power supply, using no extra components other than the LM78L05 regulator itself. The input voltage comes from a 'brick' power supply which does not regulate the 12V line tightly. Additional, inexpensive 10uF ceramic capacitors (Cinx and Cox) help isolate devices with sensitive databands, such as DSL and cable modems, from switching noise and harmonics. 20087509 FIGURE 9. 12V to 5V, 1.8A, 100kHz In situations where low cost is very important, the LM2742 can also be used as an asynchronous controller, as shown in the above circuit. Although a a schottky diode in place of the bottom FET will not be as efficient, it will cost much less than the FET. The 5V at low current needed to run the LM2742 could come from a zener diode or inexpensive regulator, such as the one shown in Figure 8. Because the LM2742 senses current in the low side MOSFET, the current limit feature will not function in an asynchronous design. The ISEN pin should be left open in this case. 17 www.national.com LM2742 TABLE 1. Bill of Materials for Typical Application Circuit ID Part Number U1 LM2742 Q1, Q2 Si4884DY L1 RLF7030T-1R5N6R1 Type Synchronous Controller Size Parameters Qty. Vendor TSSOP-14 TSSOP-14 1 NSC N-MOSFET Inductor SO-8 30V, 13m, 15nC 1 Vishay 7.1x7.1x3.2mm 1.5H, 6.1A 9.6m 1 TDK TDK Cin1, Cin2 C2012X5R1J106M MLCC 0805 10F 6.3V 2 Cinx C3216X7R1E105K Capacitor 1206 1F, 25V 1 TDK Co1, Co2 6MV2200WG 10mm D 20mm H 2200F 6.3V125m 2 Sanyo Cboot VJ1206X104XXA Capacitor 1206 0.1F, 25V 1 Vishay Cin C3216X7R1E225K Capacitor 1206 2.2F, 25V 1 TDK AL-E Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay Cc1 VJ1206A2R2KXX Capacitor 1206 2.2pF 10% 1 Vishay Cc2 VJ1206A181KXX Capacitor 1206 180pF 10% 1 Vishay Rin CRCW1206100J Resistor 1206 10 5% 1 Vishay Rfadj CRCW12066342F Resistor 1206 63.4k 1% 1 Vishay Rc1 CRCW12063923F Resistor 1206 392k 1% 1 Vishay Rfb1 CRCW12061002F Resistor 1206 10k 1% 1 Vishay Rfb2 CRCW12061002F Resistor 1206 10k 1% 1 Vishay Rcs CRCW1206222J Resistor 1206 2.2k 5% 1 Vishay TABLE 2. Bill of Materials for Circuit of Figure 3 (Identical to BOM for 1.5V except as noted below) ID Part Number Type Size Parameters Qty. Vendor L1 RLF12560T-2R7N110 Inductor 12.5x12.8x6mm 2.7H, 14.4A 4.5m 1 TDK Co1, Co2, Co3, Co4 10TPB100M POSCAP 7.3x4.3x2.8mm 100F 10V 1.9Arms 4 Sanyo Cc1 VJ1206A6R8KXX Capacitor 1206 6.8pF 10% 1 Vishay Cc2 VJ1206A271KXX Capacitor 1206 270pF 10% 1 Vishay Cc3 VJ1206A471KXX Capacitor 1206 470pF 10% 1 Vishay Rc2 CRCW12068451F Resistor 1206 8.45k 1% 1 Vishay Rfb1 CRCW12061102F Resistor 1206 11k 1% 1 Vishay Qty. Vendor 1 NSC TABLE 3. Bill of Materials for Circuit of Figure 4 ID Part Number Type Synchronous Controller U1 LM2742 Q1 Si4442DY N-MOSFET Q2 Si4442DY N-MOSFET D1 BAT-54 Lin SLF12575T-1R2N8R2 L1 D05022-152HC Cin1, Cin2 Cinx Size Parameters TSSOP-14 SO-8 30V, 4.1m, @ 4.5V, 36nC 1 Vishay SO-8 30V, 4.1m, @ 4.5V, 36nC 1 Vishay SOT-23 30V 1 Vishay Inductor 12.5x12.5x7.5mm 12H, 8.2A, 6.9m 1 Coilcraft Inductor 22.35x16.26x8mm 1.5H, 15A,4m 1 Coilcraft 10MV5600AX Aluminum Electrolytic 16mm D 25mm H 5600F10V 2.35Arms 2 Sanyo Schottky Diode C3216X7R1E105K Capacitor 1206 1F, 25V 1 TDK Co1, Co2, Co3 10MV5600AX Aluminum Electrolytic 16mm D 25mm H 5600F10V 2.35Arms 2 Sanyo Cboot VJ1206X104XXA Capacitor 1206 0.1F, 25V 1 Vishay Cin C3216X7R1E225K Capacitor 1206 2.2F, 25V 1 TDK Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay www.national.com 18 Part Number Cc1 VJ1206A4R7KXX Cc2 VJ1206A102KXX Rin Type Size Parameters Qty. Vendor Capacitor 1206 4.7pF 10% 1 Vishay Capacitor 1206 1nF 10% 1 Vishay CRCW1206100J Resistor 1206 10 5% 1 Vishay Rfadj CRCW12068872F Resistor 1206 88.7k 1% 1 Vishay Rc1 CRCW12062293F Resistor 1206 229k 1% 1 Vishay Rfb1 CRCW12064991F Resistor 1206 4.99k 1% 1 Vishay Rfb2 CRCW12064991F Resistor 1206 4.99k 1% 1 Vishay Rcs CRCW1206152J Resistor 1206 1.5k 5% 1 Vishay Qty. Vendor 1 NSC 30V, 24m/ 8nC Top 16.5m/ 15nC 1 Vishay TABLE 4. Bill of Materials for Circuit of Figure 5 ID Part Number U1 LM2742 Type Q1/Q2 Si4826DY L1 DO3316P-222 Inductor 12.95x9.4x 5.21mm 2.2H, 6.1A, 12m 1 Coilcraft Cin1 10TPB100ML POSCAP 7.3x4.3x3.1mm 100F 10V 1.9Arms 1 Sanyo Co1 4TPB220ML POSCAP 7.3x4.3x3.1mm 220F 4V 1.9Arms 1 Sanyo Cc C3216X7R1E105K Capacitor 1206 1F, 25V 1 TDK Cin C3216X7R1E225K Capacitor 1206 2.2F, 25V 1 TDK Synchronous Controller Size Parameters TSSOP-14 Asymetric Dual N-MOSFET SO-8 Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay Cc1 VJ1206A100KXX Capacitor 1206 10pF 10% 1 Vishay Cc2 VJ1206A561KXX Capacitor 1206 560pF 10% 1 Vishay Rin CRCW1206100J Resistor 1206 10 5% 1 Vishay Rfadj CRCW12064222F Resistor 1206 42.2k 1% 1 Vishay Rc1 CRCW12065112F Resistor 1206 51.1k 1% 1 Vishay Rfb1 CRCW12062491F Resistor 1206 2.49k 1% 1 Vishay Rfb2 CRCW12064991F Resistor 1206 4.99k 1% 1 Vishay Rcs CRCW1206272J Resistor 1206 2.7k 5% 1 Vishay Qty. Vendor 1 NSC TABLE 5. Bill of Materials for Circuit of Figure 6 ID Part Number U1 LM2742 Type Q1 Si4884DY N-MOSFET SO-8 30V, 13.5m, @ 4.5V 15.3nC 1 Vishay Q2 Si4884DY N-MOSFET SO-8 30V, 13.5m, @ 4.5V 15.3nC 1 Vishay D1 BAT-54 SOT-23 30V 1 Vishay Lin P1166.102T Inductor 7.29x7.29 3.51mm 1H, 11A 3.7m 1 Pulse L1 P1168.102T Inductor 12x12x4.5 mm 1H, 11A, 3.7m 1 Pulse Cin1 10MV5600AX Aluminum Electrolytic 16mm D 25mm H 5600F 10V 2.35Arms 1 Sanyo Synchronous Controller Schottky Diode Size Parameters TSSOP-14 Cinx C3216X7R1E105K Capacitor 1206 1F, 25V 1 TDK Co1, Co2, Co3 16MV4700WX Aluminum Electrolytic 12.5mm D 30mm H 4700F 16V 2.8Arms 2 Sanyo Cboot VJ1206X104XXA Capacitor 1206 0.1F, 25V 1 Vishay Cin C3216X7R1E225K Capacitor 1206 2.2F, 25V 1 TDK Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay 19 www.national.com LM2742 ID LM2742 ID Part Number Type Cc1 VJ1206A4R7KXX Capacitor Cc2 VJ1206A681KXX Capacitor Rin CRCW1206100J Rfadj Rc1 Size Parameters Qty. Vendor 1206 4.7pF 10% 1 Vishay 1206 680pF 10% 1 Vishay Resistor 1206 10 5% 1 Vishay CRCW12064992F Resistor 1206 49.9k 1% 1 Vishay CRCW12061473F Resistor 1206 147k 1% 1 Vishay Rfb1 CRCW12061492F Resistor 1206 14.9k 1% 1 Vishay Rfb2 CRCW12064991F Resistor 1206 4.99k 1% 1 Vishay Rcs CRCW1206332J Resistor 1206 3.3k 5% 1 Vishay Qty. Vendor 1 NSC 30V, 24m/ 8nC Top 16.5m/ 15nC 1 Vishay TABLE 6. Bill of Materials for Circuit of Figure 7 ID Part Number U1 LM2742 Type Q1/Q2 Si4826DY Assymetric Dual N-MOSFET Schottky Diode Synchronous Controller Size Parameters TSSOP-14 SO-8 D1 BAT-54 SOT-23 30V 1 Vishay Lin RLF7030T-1R0N64 Inductor 6.8x7.1x3.2mm 1H, 6.4A, 7.3m 1 TDK Inductor L1 RLF7030T-3R3M4R1 6.8x7.1x3.2mm 3.3H, 4.1A, 17.4m 1 TDK Cin1 C4532X5R1E156M MLCC 1812 15F 25V 3.3Arms 1 Sanyo Co1 C4532X5R1E156M MLCC 1812 15F 25V 3.3Arms 1 Sanyo Cboot VJ1206X104XXA Capacitor 1206 0.1F, 25V 1 TDK Cin C3216X7R1E225K Capacitor 1206 2.2F, 25V 1 TDK Css VJ1206X393KXX Capacitor 1206 39nF, 25V 1 Vishay Cc1 VJ1206A220KXX Capacitor 1206 22pF 10% 1 Vishay Cc2 VJ1206A681KXX Capacitor 1206 680pF 10% 1 Vishay Cc3 VJ1206A681KXX Capacitor 1206 680pF 10% 1 Vishay Rin CRCW1206100J Resistor 1206 10 5% 1 Vishay Rfadj CRCW12061742F Resistor 1206 17.4k 1% 1 Vishay Rc1 CRCW12061072F Resistor 1206 10.7k 1% 1 Vishay Rc2 CRCW120666R5F Resistor 1206 66.5 1% 1 Vishay Rfb1 CRCW12064991F Resistor 1206 4.99k 1% 1 Vishay Rfb2 CRCW12061002F Resistor 1206 10k 1% 1 Vishay Rcs CRCW1206152J Resistor 1206 1.5k 5% 1 Vishay TABLE 7. Bill of Materials for 3.3V Circuit of Figure 7 (Identical to BOM for 1.8V except as noted below) ID Part Number L1 RLF7030T-4R7M3R4 Cc1 VJ1206A270KXX Cc2 VJ1206X102KXX Cc3 Rc1 Rc2 Parameters Qty. Vendor 6.8x7.1x 3.2mm 4.7H, 3.4A, 26m 1 TDK Capacitor 1206 27pF 10% 1 Vishay Capacitor 1206 1nF 10% 1 Vishay VJ1206A821KXX Capacitor 1206 820pF 10% 1 Vishay CRCW12061212F Resistor 1206 12.1k 1% 1 Vishay CRCW12054R9F Resistor 1206 54.9 1% 1 Vishay Rfb1 CRCW12062211F Resistor 1206 2.21k 1% 1 Vishay Rfb2 CRCW12061002F Resistor 1206 10k 1% 1 Vishay www.national.com Type Inductor Size 20 ID Part Number Type U1 LM2742 Synchronous Controller U2 LM78L05 Q1/Q2 Qty. Vendor TSSOP-14 1 NSC Voltage Regulator SO-8 1 NSC Si4826DY Assymetric Dual N-MOSFET SO-8 30V, 24m/ 8nC Top 16.5m/ 15nC 1 Vishay Schottky Diode SOT-23 30V 1 Vishay 6.8x7.1x3.2mm 1H, 6.4A, 7.3m 1 TDK D1 BAT-54 Lin RLF7030T-1R0N64 Inductor Inductor L1 SLF12565T-4R2N5R5 Cin1 16MV680WG Cinx C3216X5R1C106M Co1 Co2 Cox Cboot Size Parameters 12.5x12.5x6.5mm 4.2H, 5.5A, 15m 1 TDK D: 10mm L: 12.5mm 680F 16V 3.4Arms 1 Sanyo MLCC 1210 10F 16V 3.4Arms 1 TDK 16MV680WG MLCC 1812 15F 25V 3.3Arms 1 Sanyo C3216X5R10J06M MLCC 1206 10F 6.3V 2.7A VJ1206X104XXA Capacitor 1206 0.1F, 25V 1 Vishay Al-E TDK Cin C3216X7R1E225K Capacitor 1206 2.2F, 25V 1 TDK Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay Cc1 VJ1206A8R2KXX Capacitor 1206 8.2pF 10% 1 Vishay Cc2 VJ1206X102KXX Capacitor 1206 1nF 10% 1 Vishay Cc3 VJ1206X472KXX Capacitor 1206 4.7nF 10% 1 Vishay Rfadj CRCW12063252F Resistor 1206 32.5k 1% 1 Vishay Rc1 CRCW12065232F Resistor 1206 52.3k 1% 1 Vishay Rc2 CRCW120662371F Resistor 1206 2.37 1% 1 Vishay Rfb1 CRCW12062211F Resistor 1206 2.21k 1% 1 Vishay Rfb2 CRCW12061002F Resistor 1206 10k 1% 1 Vishay Rcs CRCW1206202J Resistor 1206 2k 5% 1 Vishay Qty. Vendor 1 NSC 30V, 15m, 11.5nC 1 Vishay SO-8 30V, 3A 1 ON 12.5x12.8x 4.7mm 47H, 2.7A 53m 1 TDK TABLE 9. Bill of Materials for Circuit of Figure 9 ID Part Number U1 LM2742 Q1 Si4894DY D2 MBRS330T3 L1 SLF12565T-470M2R4 D1 MBR0520 Cin1 16MV680WG Cinx C3216X5R1C106M Co1, Co2 16MV680WG Cox C3216X5R10J06M Cboot Type Synchronous Controller Size N-MOSFET SO-8 Schottky Diode Inductor Parameters TSSOP-14 Schottky Diode 1812 20V 0.5A 1 ON Al-E 1206 680F, 16V, 1.54Arms 1 Sanyo 1206 MLCC 10F, 16V, 3.4Arms 1 TDK D: 10mm L: 12.5mm 680F 16V 26m 2 Sanyo MLCC 1206 10F, 6.3V 2.7A 1 TDK VJ1206X104XXA Capacitor 1206 0.1F, 25V 1 Vishay Al-E Cin C3216X7R1E225K Capacitor 1206 2.2F, 25V 1 TDK Css VJ1206X123KXX Capacitor 1206 12nF, 25V 1 Vishay Cc1 VJ1206A561KXX Capacitor 1206 56pF 10% 1 Vishay Cc2 VJ1206X392KXX Capacitor 1206 3.9nF 10% 1 Vishay Cc3 VJ1206X223KXX Capacitor 1206 22nF 10% 1 Vishay Rfadj CRCW12062673F Resistor 1206 267k 1% 1 Vishay Rc1 CRCW12066192F Resistor 1206 61.9k 1% 1 Vishay Rc2 CRCW12067503F Resistor 1206 750k 1% 1 Vishay Rfb1 CRCW12061371F Resistor 1206 1.37k 1% 1 Vishay 21 www.national.com LM2742 TABLE 8. Bill of Materials for Circuit of Figure 8 LM2742 ID Part Number Rfb2 CRCW12061002F Rcs CRCW1206122F www.national.com Type Size Parameters Qty. Vendor Resistor 1206 10k 1% 1 Vishay Resistor 1206 1.2k 5% 1 Vishay 22 LM2742 Physical Dimensions inches (millimeters) unless otherwise noted TSSOP-14 Pin Package NS Package Number MTC14 23 www.national.com LM2742 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH www.national.com/webench Audio www.national.com/audio Analog University www.national.com/AU Clock Conditioners www.national.com/timing App Notes www.national.com/appnotes Data Converters www.national.com/adc Distributors www.national.com/contacts Displays www.national.com/displays Green Compliance www.national.com/quality/green Ethernet www.national.com/ethernet Packaging www.national.com/packaging Interface www.national.com/interface Quality and Reliability www.national.com/quality LVDS www.national.com/lvds Reference Designs www.national.com/refdesigns Power Management www.national.com/power Feedback www.national.com/feedback Switching Regulators www.national.com/switchers LDOs www.national.com/ldo LED Lighting www.national.com/led PowerWise www.national.com/powerwise Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors Wireless (PLL/VCO) www.national.com/wireless THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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