LM5041BSDX

LM5041B Cascaded PWM Controller May 1, 2009 LM5041B Cascaded PWM Controller General Description The LM5041B PWM controller contains all of the features necessary to implement either current-fed or voltage-fed push-pull or bridge power converters. These “Cascaded” topologies are well suited for multiple output and higher power applications. The LM5041B includes these four control outputs: the buck stage controls (HD and LD) and the push-pull control outputs (PUSH and PULL). Push-pull outputs are driven at 50% nominal duty cycle at one half of the switching frequency of the buck stage and can be configured for either a guaranteed overlap time (for current-fed applications) or a guaranteed non-overlap time (for voltage-fed applications). Push-pull stage MOSFETs can be driven directly from the internal gate drivers while the buck stage requires an external driver such as the LM5102. The LM5041B includes a highvoltage start-up regulator that operates over a wide input range of 15V to 100V. The PWM controller is designed for high-speed capability including an oscillator frequency range up to 1 MHz and total propagation delays of less than 100 ns. Additional features include line Under-Voltage Lock-Out (UVLO), Soft-Start, an error amplifier, precision voltage reference, and thermal shutdown. The differences between LM5041, LM5041A and LM5041B are as follows: In the LM5041A and the LM5041B version, the hiccup mode over-current protection is not employed and the VCC bias regulator is not disabled by a low state at the SS pin. In the LM5041B version, both the high and low side buck stage gate drivers are forced to a low state when the controller is disabled. In the LM5041 and the LM5041B version, the buck stage controller is disabled by either a low state at the UVLO pin or a low state at the SS pin. Also in the LM5041B version, the REF pin 5V regulator is not disabled by a UVLO pin low state. Features ■ Internal Start-up Bias Regulator ■ Programmable Line Under-Voltage Lockout (UVLO) with ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Adjustable Hysteresis Current Mode Control Internal Error Amplifier with Reference Cycle-by-cycle Over-Current Protection Leading Edge Blanking Programmable Push-Pull Overlap or Dead Time Internal 1.5A Push-Pull Gate Drivers Programmable Soft-Start Programmable Oscillator with Sync Capability Precision Reference Thermal Shutdown Applications ■ Telecommunication Power Converters ■ Industrial Power Converters ■ Multi-Output Power Converters Packages ■ TSSOP-16 ■ LLP-16 (5x5 mm) Thermally Enhanced Typical Application Circuit 30086401 Simplified Cascaded Push-Pull Power Converter © 2009 National Semiconductor Corporation 300864 www.national.com LM5041B Connection Diagram 30086402 16-Lead TSSOP, LLP Ordering Information Order Number LM5041BMTC LM5041BMTCX LM5041BSD LM5041BSDX Package Type TSSOP-16 TSSOP-16 LLP-16 LLP-16 NSC Package Drawing MTC-16 MTC-16 SDA-16A SDA-16A Supplied As 92 Units per anti-static tube 2500 Units on Tape and Reel Coming Soon Coming Soon Pin Descriptions Pin # 1 2 3 4 Pin Name VIN FB COMP REF Pin Description Source Input Voltage Feedback Signal Output of the Internal Error Amplifier Precision 5 volt reference output Main Buck PWM control output Buck Sync Switch control output Pin Application Information Input to start-up regulator. Input range 15V to 100V. Inverting input for the internal error amplifier. The non-inverting input is connected to a 0.75V reference. There is an internal 5 kΩ resistor pull-up on this pin. The error amplifier provides an active sink. Maximum output current: 10 mA. Locally decouple with a 0.1 µF capacitor. Reference stays low until the VCC UV are satisfied. Buck switch PWM control output. The maximum duty cycle clamp for this output corresponds to an off time of typically 240 ns per cycle. The LM5101 or LM5102 Buck stage gate driver can be used to level shift and drive the Buck switch MOSFET. Sync Switch control output. Inversion of HD output during normal operation. The LM5101 or LM5102 lower drive can be used to drive the synchronous rectifier switch. 5 HD 6 LD 7 VCC Output of the internal high voltage start-up If an auxiliary winding raises the voltage on this pin above the regulation set-point, the regulator. Regulated to internal start-up regulator will shutdown, reducing the IC power dissipation. 9 volts. Output of the push-pull Output of the push-pull gate driver. Output capability of 1.5A peak . drivers Output of the push-pull Output of the push-pull gate driver. Output capability of 1.5A peak. drivers Power ground Analog ground Connect directly to analog ground. Connect directly to power ground. 8 9 10 11 PUSH PULL PGND AGND www.national.com 2 LM5041B Pin # Pin Name CS Pin Description Current sense input Pin Application Information Current sense input to the PWM comparator (current mode control). There is a 50 ns leading edge blanking on this pin. If CS exceeds 0.5V, the PWM controller will go into cycle by cycle current limit. An external capacitor and an internal 10 µA current source, set the soft-start ramp. Both HD and LD will be forced to a low state if the SS pin is below the shutdown threshold of 0.45V. 12 13 SS Soft-Start control 14 TIME An external resistor (RSET) sets the overlap time or dead time for the push-pull outputs. Push-Pull overlap and A resistor connected between TIME and GND produces overlap. A resistor connected dead time control between TIME and REF produces dead time. Oscillator timing resistor pin and sync Line Under-Voltage Shutdown An external resistor sets the oscillator frequency. This pin will also accept an external oscillator. An external divider from the power source sets the shutdown levels. Threshold of operation equals 2.5V. Hysteresis is set by a switched internal current source (20 µA). The exposed die attach pad of the LLP package should be connected to a PCB thermal pad at ground potential. For additional information on using National Semiconductor's No Pull Back LLP package, please refer to Application Note AN-1187: Leadless Leadframe Package (LLP). 15 16 RT / SYNC UVLO LLP DAP SUB Die substrate 3 www.national.com LM5041B Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN to GND VCC to GND All Other Inputs to GND Junction Temperature Storage Temperature Range 100V 16V -0.3 to 7V 150°C -65°C to +150°C ESD Rating(Note 2) Lead temperature (Note 3) Wave Infrared Vapor Phase ±2 kV 4 seconds at 260°C 10 seconds at 240°C 75 seconds at 219°C (Note 1) 15 to 90V -40°C to +125°C Operating Ratings VIN Junction Temperature Electrical Characteristics Unless otherwise stated the following conditions apply: VIN = 48V, VCC = 10V, RT = 26.7 kΩ, RSET = 20 kΩ. (Note 4). Limits in standard type are for TJ = 25°C only; limits in boldface type apply over the Operating Junction Temperature (TJ) range of -40°C to +125°C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Symbol Startup Regulator VCC Reg VCC Regulation VCC Current Limit I-VIN Startup Regulator Leakage (external Vcc Supply) Shutdown Current (Iin) VCC Supply VCC Under-Voltage Lock-Out Threshold VCC Under-Voltage Lock-Out Hysteresis Supply Current (ICC) Error Amplifier GBW Gain Bandwidth DC Gain Input Voltage COMP Sink Capability Reference Supply Ref Voltage VREF Ref Voltage Regulation Ref Current Limit Current Limit CS Step from 0 to 0.6V Time to Onset of OUT Transition (90%) CL = 0 IREF = 0 mA IREF = 0 to 10 mA 4.85 15 5 25 20 5.15 50 V mV mA VFB = COMP VFB = 1.5V, COMP= 1V 0.735 4 3 80 0.75 8 0.765 MHz dB V mA CL = 0 VCC rising VCC Reg 400 mV 1.7 VCC Reg 275 mV 2.1 3 2.6 4 V V mA Open circuit (Note 4) VIN = 100V UVLO = 0V, VCC = open 8.7 15 9 25 145 350 9.3 500 450 V mA µA µA Parameter Conditions Min Typ Max Units ILIM Delay to Output - 40 - ns Cycle by Cycle Threshold Voltage Leading Edge Blanking Time CS Sink Current (clocked) Soft-Start Soft-Start Current Source Soft-Start to COMP Offset Shutdown Threshold CS = 0.3V 0.45 2 7 0.35 0.25 0.5 50 5 10 0.55 0.5 0.55 13 0.75 0.75 V ns mA µA V V www.national.com 4 LM5041B Symbol Oscillator Frequency1 Frequency2 Parameter Conditions Min 180 175 515 - Typ Max 220 225 685 3.5 Units RT = 26.7 kΩ RT = 7.87 kΩ 200 600 3 kHz kHz V Sync threshold PWM Comparator Delay to Output Max Duty Cycle Min Duty Cycle COMP to PWM Comparator Gain COMP Open Circuit Voltage COMP Short Circuit Current Slope Compensation Slope Comp Amplitude UVLO Shutdown Under-Voltage Shutdown Under-voltage Shutdown Hysteresis Current Source Buck Stage Outputs Output High level Output High Saturation Output Low Saturation Rise Time Fall Time Push-Pull Outputs Overlap Time Dead Time Output High Saturation Output Low Saturation Rise Time Fall Time Thermal Shutdown TSD Thermal Shutdown Temp. Thermal Shutdown Hysteresis Thermal Resistance θJA Thermal Resistance Junction to Ambient TSSOP Package LLP Package RSET = 20 kΩ Connected to GND, 50% to 50% Transitions RSET = 20kΩ Connected to REF, 50% to 50% Transitions IOUT = 50 mA VCC - VOUT IOUT = 100 mA CL = 1 nF CL = 1 nF IOUT = 10 mA, REF = VOUT IOUT = −10 mA CL = 100 pF CL = 100 pF Delta increase at PWM Comparator to CS FB = 0V FB = 0V, COMP = 0V COMP = 2V, CS stepped 0 to 0.4V Time to onset of OUT transition low TS = Oscillator Period COMP = 0V 4.1 0.6 25 (Ts-240ns) / Ts 0.32 4.8 1 0 5.5 1.4 ns % % V mA - 110 - mV 2.44 16 2.5 20 2.56 24 V µA - 5 (VREF) 0.5 0.5 10 10 1 1 - V V V ns ns 60 65 - 90 95 0.25 0.5 20 20 165 25 125 32 120 125 0.5 1 - ns ns V V ns ns °C °C °C/W °C/W Note 1: 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 does not guarantee specific performance limits. For guaranteed specifications and conditions, see the Electrical Characteristics. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Test Method is per JESD-22-A114. Note 3: For detailed information on soldering plastic TSSOP and LLP packages, please refer to Application Note AN-1520: A Guide to Board Layout for Best Thermal Resistance for Exposed Packages , Application Note AN-1187: Leadless Leadframe Package (LLP) , or go to www.national.com/packaging for more information. Note 4: Device thermal limitations may limit usable range. 5 www.national.com LM5041B Typical Performance Characteristics VCC and VIN vs VIN VCC vs ICC 30086408 30086409 SS Pin Current vs Temp Frequency vs RT 30086415 30086410 Overlap Time vs RSET Dead Time vs RSET 30086411 30086412 www.national.com 6 LM5041B Overlap Time vs Temp Dead Time vs Temp 30086413 30086414 Error Amplifier Gain Phase 30086416 7 www.national.com LM5041B Block Diagram Simplified Block Diagram 30086403 www.national.com 8 LM5041B Detailed Operating Description The LM5041B PWM controller contains all of the features necessary to implement either current-fed or voltage-fed push-pull or bridge power converters. These “Cascaded” topologies are well suited for multiple output and higher power applications. The LM5041B includes these four control outputs: the buck stage controls (HD and LD) and the push-pull control outputs (PUSH and PULL). Push-pull outputs are driven at 50% nominal duty cycle at one half of the switching frequency of the buck stage and can be configured for either a guaranteed overlap time (for current-fed applications) or a guaranteed non-overlap time (for voltage-fed applications). Push-pull stage MOSFETs can be driven directly from the internal gate drivers while the buck stage requires an external driver such as the LM5102. The LM5041B includes a highvoltage start-up regulator that operates over a wide input range of 15V to 100V. The PWM controller is designed for high-speed capability including an oscillator frequency range up to 1 MHz and total propagation delays of less than 100 ns. Additional features include line Under-Voltage Lock-Out (UVLO), Soft-Start, an error amplifier, precision voltage reference, and thermal shutdown. Line Under-Voltage Detector The LM5041B contains a line Under-Voltage Lock-Out (UVLO) circuit. An external set-point resistor divider from VIN to ground sets the operational range of the converter. The divider must be designed such that the voltage at the UVLO pin will be greater than 2.5V when VIN is in the desired operating range. If the Under-Voltage threshold is not met, both HD and LD will be forced to low state and VCC regulator will be disabled while the push-pull outputs continue switching until the REF pin voltage falls below approximately 3V. ULVO hysteresis is accomplished with an internal 20 µA current source that is switched on or off into the impedance of the set-point divider. When the UVLO threshold is exceeded, the current source is activated to instantly raise the voltage at the UVLO pin. When the UVLO pin falls below the 2.5V threshold, the current source is turned off causing the voltage at the UVLO pin to fall. The UVLO pin can also be used to implement a remote enable / disable function. By shorting the UVLO pin to ground, the converter can be disabled. Buck Stage Control Outputs The LM5041B Buck switch maximum duty cycle clamp ensures that there will be sufficient off time each cycle to recharge the bootstrap capacitor used in the high side gate driver. The Buck switch is guaranteed to be off, and the sync switch on, for at least 250 ns per switching cycle. The Buck stage control outputs (LD and HD) are CMOS buffers with logic levels of 0 to 5V. During any fault state or Under-Voltage off state, both HD and LD state will be forced to low by the buck stage control. High Voltage Start-Up Regulator The LM5041B contains an internal high-voltage start-up regulator, thus the input pin (Vin) can be connected directly to the line voltage. The regulator output is internally current limited to 15 mA. When power is applied, the regulator is enabled and sources current into an external capacitor connected to the Vcc pin. The recommended capacitance range for the Vcc regulator is 0.1µF to 100 µF. When the voltage on the Vcc pin reaches the regulation point of 9V, the internal voltage reference (REF) reaches its regulation point of 5V, and the softstart capacitor is charged above its shutdown threshold, the controller outputs are enabled. The Buck stage outputs will remain enabled until Vcc falls below 7V, the REF pin voltage falls below approximately 3V, the SS pin is forced below the 0.45V shutdown threshold or the line Under-Voltage Lock-Out detector indicates that Vin is out of range. The push-pull outputs continue switching until the REF pin voltage falls below approximately 3V. In typical applications, an auxiliary transformer winding is connected through a diode to the Vcc pin. This winding must raise the Vcc voltage above 9.3V to shut off the internal start-up regulator. Powering VCC from an auxiliary winding improves efficiency while reducing the controller's power dissipation. The recommended capacitance range for the Vref regulator output is 0.1µF to 10 µF. The external VCC capacitor must be sized such that the capacitor maintains a VCC voltage greater than 7V during the initial start-up. During a fault mode when the converter auxiliary winding is inactive, external current draw on the VCC line should be limited so the power dissipated in the start-up regulator does not exceed the maximum power dissipation of the controller. An external start-up or other bias rail can be used instead of the internal start-up regulator by connecting the VCC and the VIN pins together and feeding the external bias voltage into the two pins. Push-Pull Outputs The push pull outputs operate continuously at a nominal 50% duty cycle. A distinguishing feature of the LM5041B is the ability to accurately configure either dead time (both-off) or overlap time (both-on) on the complementary push-pull outputs. The overlap/dead time magnitude is controlled by a resistor connected to the TIME pin on the controller. The TIME pin holds one end of the resistor at 2.5V and the other end of the resistor should be connected to either REF for dead time control setting or to GND for overlap control. The polarity of the current in the TIME is detected by the LM5041B The magnitude of the overlap/dead time can be calculated as follows: Overlap Time (ns) = (3.66 x RSET) + 7 Overlap Time in ns, RSET connected to GND, RSET in kΩ Dead Time (ns) = (3.69 x RSET) + 21 Dead Time in ns, RSET connected to REF, RSET in kΩ Recommended RSET programming range: 10 kΩ to 100 kΩ Current-fed designs require a period of overlap to insure there is a continuous path for the buck inductor current. Voltage-fed designs require a period of dead time to insure there is no time when the push-pull transformer acts as a shorted turn to the low impedance sourcing node. The push-pull outputs alternate continuously under all conditions provided REF the voltage is greater than 3V. 9 www.national.com LM5041B 30086404 PWM Comparator The PWM comparator compares the slope compensated current ramp signal to the loop error voltage from the internal error amplifier (COMP pin). This comparator is optimized for speed in order to achieve minimum controllable duty cycles. The comparator polarity is such that 0V on the COMP pin will produce zero duty cycle in the buck stage. Error Amplifier An internal high gain wide-bandwidth error amplifier is provided within the LM5041B. The amplifier’s non-inverting input is tied to a 0.75V reference. The inverting input is connected to the FB pin. In non-isolated applications the power converter output is connected to the FB pin via the voltage setting resistors. Loop compensation components are connected between the COMP and FB pins. For most isolated applications the error amplifier function is implemented on the secondary side of the converter and the internal error amp is not used. The internal error amplifier is configured as an open drain output and can be disabled by connecting the FB pin to ground. An internal 5 kΩ pull-up resistor between the 5V reference and the COMP pin can be used as the pull-up for an opto-coupler in isolated applications. sense resistor. The capacitor associated with the CS filter must be placed close to the device and connected directly to the pins of the controller (CS and GND). If a current sense transformer is used, both leads of the transformer secondary should be routed to the sense resistor, which should also be located close to the IC. A resistor may be used for current sensing instead of a transformer, located in the push-pull transistor sources, but a low inductance type of resistor is required. When designing with a sense resistor, all of the noise sensitive low power grounds should be connected together around the IC and a single connection should be made to the high current power ground (sense resistor ground point). Oscillator and Sync Capability The LM5041B oscillator is set by a single external resistor connected between the RT pin and GND. To set a desired oscillator frequency (F), the necessary RT resistor can be calculated from: Current Limit/Current Sense The LM5041B provides cycle-by-cycle over-current protection. If the voltage at the CS comparator (CS pin voltage plus slope comp voltage) exceeds 0.5V the present buck stage duty cycle is terminated (cycle by cycle current limit). A small RC filter located near the controller is recommended to filter current sense signals at the CS pin. An internal MOSFET discharges the external CS pin for an additional 50 ns at the beginning of each cycle to reduce the leading edge spike that occurs when the buck stage MOSFET is turned on. The LM5041B current sense and PWM comparators are very fast, and may respond to short duration noise pulses. Layout considerations are critical for the current sense filter and The buck stage will switch at the oscillator frequency and each push-pull output will switch at half the oscillator frequency in a push-pull configuration. The LM5041B can also be synchronized to an external clock. The external clock must have a higher frequency than the free running frequency set by the RT resistor. The clock signal should be capacitively coupled into the RT pin with a 100 pF capacitor. A peak voltage level greater than 3V is required for detection of the sync pulse. The sync pulse width should be set in the 15 ns to 150 ns range by the external components. The RT resistor is always required, whether the oscillator is free running or externally synchronized. The voltage at the RT pin is internally regulated to 2V. The RT resistor should be located very close to the device and connected directly to the pins of the IC (RT and GND). www.national.com 10 LM5041B Slope Compensation The PWM comparator compares the current sense signal to the voltage at the COMP pin. The output stage of the internal error amplifier generally drives the COMP pin. At duty cycles greater than 50%, current mode control circuits are subject to sub-harmonic oscillation. By adding an additional fixed ramp signal (slope compensation) to the current sense ramp, oscillations can be avoided. The LM5041B integrates this slope compensation by buffering the internal oscillator ramp and summing a current ramp generated by the oscillator internally with the current sense signal. Additional slope compensation may be provided by increasing the source impedance of the current sense signal. Thermal Protection Internal Thermal Shutdown circuitry is provided to protect the integrated circuit in the event that the maximum junction temperature is exceeded. When activated, typically at 165 degrees Celsius, the controller is forced into a low-power standby state, disabling the output drivers and the bias regulator. This feature is provided to prevent catastrophic failures from accidental device overheating. Differences Between LM5041, LM5041A and LM5041B There are five differences between LM5041, LM5041A and LM5041B. In the LM5041A and the LM5041B versions, the hiccup mode over-current protection is not employed and the VCC bias regulator is not disabled by SS pin shutdown state. In the LM5041B version, both HD and LD will be low state when the PWM controller disabled. In the LM5041 and the LM5041B version, PWM controller is disabled by either a UVLO pin low state or SS pin shutdown state. Also in the LM5041B version, the REF pin output is not disabled by a UVLO pin low state. However, if VCC does not receive power from an external source, the UVLO pin low state will disable the internal VCC regulator and a VCC under-voltage condition will eventually disable REF as the VCC voltage falls. Soft-Start and Shutdown The soft-start feature allows the power converter to gradually reach the initial steady state operating point, thereby reducing start-up stresses and surges. At power on, a 10 µA current is sourced out of the soft-start pin (SS) to charge an external capacitor. The capacitor voltage will ramp up slowly and will limit the maximum duty cycle of the buck stage. In the event of a fault as indicated by VCC Under-voltage, line Under-voltage the output drivers are disabled and the soft-start capacitor is discharged to 0.7V. When the fault condition is no longer present, a soft-start sequence will begin again and buck stage duty cycle will gradually increase as the soft-start capacitor is charged. The SS pin also serves as an enable input of HD and LD. Both HD and LD will be forced to a low state if the SS pin is below the shutdown threshold of 0.45V. Differences Between LM5041, LM5041A and LM5041B ITEM Hiccup mode over-current protection VCC disabled by SS shutdown REF disabled by UVLO pin low state BUCK controller disabled by SS shutdown BUCK driver states when the controller disabled LM5041 Available Yes Yes Yes HD : LOW LD :HIGH LM5041A N/A No Yes No HD : LOW LD : HIGH LM5041B N/A No No Yes HD : LOW LD : LOW Logic Table MODE Normal Operation UVLO Shutdown SS Shutdown CONTROLS UVLO HIGH SS DEVICE LM5041 LM5041A LM5041B LM5041 LOW LM5041A LM5041B LM5041 HIGH LOW LM5041A LM5041B GND 9V GND 5V LOW GND GND LOW HIGH LOW HIGH LOW LOW 50% Duty Cycle LOW 9V 5V PWM PWM 50% Duty Cycle PIN STATES VCC REF HD LD PUSH&PULL 11 www.national.com LM5041B Typical Application 30086406 FIGURE 1. Simplified Cascaded Half-Bridge www.national.com 12 LM5041B Application Circuit: Input 35V to 80V, Output 2.5V, 50A 30086407 13 www.national.com LM5041B Physical Dimensions inches (millimeters) unless otherwise noted Molded TSSOP-16 NS Package Number MTC16 16-Lead LLP Surface Mount Package NS Package Number SDA16A www.national.com 14 LM5041B Notes 15 www.national.com LM5041B Cascaded PWM Controller Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers Audio Clock and Timing Data Converters Interface LVDS Power Management Switching Regulators LDOs LED Lighting Voltage Reference PowerWise® Solutions Serial Digital Interface (SDI) Temperature Sensors Wireless (PLL/VCO) www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/vref www.national.com/powerwise www.national.com/sdi www.national.com/tempsensors www.national.com/wireless WEBENCH® Tools App Notes Reference Designs Samples Eval Boards Packaging Green Compliance Distributors Design Support www.national.com/webench www.national.com/appnotes www.national.com/refdesigns www.national.com/samples www.national.com/evalboards www.national.com/packaging www.national.com/quality/green www.national.com/contacts www.national.com/quality www.national.com/feedback www.national.com/easy www.national.com/solutions www.national.com/milaero www.national.com/solarmagic www.national.com/AU Quality and Reliability Feedback/Support Design Made Easy Solutions Mil/Aero SolarMagic™ Analog University® THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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