LM5020 100V Current Mode PWM Controller General Description Features The LM5020 high voltage pulse-width-modulation (PWM) controller contains all of the features needed to implement single ended primary power converter topologies. Output voltage regulation is based on current-mode control, which eases the design of loop compensation while providing inherent line feed-forward. The LM5020 includes a highvoltage start-up regulator that operates over a wide input range up to 100V. The PWM controller is designed for high speed capability including an oscillator frequency range to 1MHz and total propagation delays less than 100ns. Additional features include an error amplifier, precision reference, line under-voltage lockout, cycle-by-cycle current limit, slope compensation, softstart, oscillator synchronization capability and thermal shutdown. The controller is available in both MSOP-10 and LLP-10 packages. n n n n n n n n n n n n Internal Start-up Bias Regulator Error Amplifier Precision Voltage Reference Programmable Softstart 1A Peak Gate Driver Maximum Duty Cycle Limiting (80% for LM5020-1 or 50% for LM5020-2) Programmable Line Under Voltage Lockout (UVLO) with Adjustable Hysteresis Cycle-by-Cycle Over-Current Protection Slope Compensation (LM5020-1) Programmable Oscillator Frequency with Synchronization Capability Current Sense Leading Edge Blanking Thermal Shutdown Protection Packages n MSOP-10 n LLP-10 (4 mm x 4 mm) Connection Diagram Top View 20095001 10-Lead MSOP, LLP Ordering Information NSC Package Drawing Supplied As LM5020MM-1 Order Number MSOP, 80% Duty Cycle Limit Description MUB-10A 1000 Units on Tape and Reel LM5020MMX-1 MSOP, 80% Duty Cycle Limit MUB-10A 3500 Units on Tape and Reel LM5020SD-1 LLP, 80% Duty Cycle Limit SDC-10A 1000 Units on Tape and Reel LM5020SDX-1 LLP, 80% Duty Cycle Limit SDC-10A 4500 Units on Tape and Reel LM5020MM-2 MSOP, 50% Duty Cycle Limit MUB-10A 1000 Units on Tape and Reel LM5020MMX-2 MSOP, 50% Duty Cycle Limit MUB-10A 3500 Units on Tape and Reel LM5020SD-2 LLP, 50% Duty Cycle Limit SDC-10A 1000 Units on Tape and Reel LM5020SDX-2 LLP, 50% Duty Cycle Limit SDC-10A 4500 Units on Tape and Reel © 2004 National Semiconductor Corporation DS200950 www.national.com LM5020 100V Current Mode PWM Controller October 2004 LM5020 Block Diagram 20095002 FIGURE 1. www.national.com 2 PIN NAME DESCRIPTION APPLICATION INFORMATION 1 Vin Source Input Voltage Input to start-up regulator. Input range 13V to 100V. 2 FB Feedback Signal Inverting input of the internal error amplifier. The non-inverting input is internally connected to a 1.25V reference. 3 COMP The output of the error amplifier and input to the Pulse Width Modulator COMP pull-up is provided by an internal 5K resistor which may be used to bias an opto-coupler transistor. 4 VCC Output of the internal high If an auxiliary winding raises the voltage series pass regulator. voltage on this pin above the Regulated output voltage 7.7V regulation set point, the internal series pass regulator will shutdown, reducing the controller power dissipation. 5 OUT Output of the PWM controller 6 GND Ground return 7 UVLO Line Under-Voltage Shutdown An external resistor divider from the power converter source sets the shutdown levels. The threshold of operation equals 1.25V. Hysteresis is set by a switched internal 20µA current source. 8 CS Current Sense input Current sense input for current mode control and over-current protection. Current limiting is accomplished using a dedicated current sense comparator. If the CS comparator input exceeds 0.5V the OUT pin switches low for cycle-by-cycle current limiting. CS is held low for 50ns after OUT switches high to blank leading edge current spikes. 9 RT / SYNC Oscillator timing resistor pin and synchronization input An external resistor connected from RT to GND sets the oscillator frequency. This pin will also accept synchronization pulses from an external clock. 10 SS Softstart Input An external capacitor and an internal 10µA current source set the soft-start ramp rate. 3 Gate driver output with a 1A peak current capability www.national.com LM5020 Pin Description LM5020 Absolute Maximum Ratings (Note 1) Storage Temperature -55˚C to +150˚C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Junction Temperature 150˚C Operating Ratings VIN to GND -0.3V to 100V VCC to GND -0.3V to 16V VIN Voltage -0.3V to 5.5V External Voltage applied to VCC 8V to 15V -0.3V to 7V Operating Junction Temperature -40˚C to +125˚C RT to GND All other pins to GND Power Dissipation 13V to 90V Internally Limited ESD Rating (Note 2) Human Body Model 2kV Electrical Characteristics Specifications in standard type face are for TJ= +25˚C and those in boldface type apply over the full operating junction temperature range. Unless otherwise specified: VIN = 48V, VCC = 10V, and RT = 31.6KΩ Symbol Parameter Conditions Min Typ Max 8.0 Units Startup Regulator VCCReg VCC Regulation Open ckt 7.4 7.7 VCC Current Limit (Note 4) 15 22 V I-VIN Startup Regulator Leakage VIN = 100V 150 500 µA IIN Shutdown Current VUVLO = 0V, VCC = open 250 350 µA mA VCC Supply ICC VCC UVLO (Rising) VccReg - 300mV VccReg 100mV VCC UVLO (Falling) 5.3 6.0 6.7 V 2 3 mA Supply Current Cload = 0 V Error Amplifier GBW Gain Bandwidth 4 MHz DC Gain 75 dB Input Voltage VFB = COMP COMP Sink Capability VFB = 1.5V COMP= 1V 1.225 1.25 5 17 1.275 V 1.225 1.25 1.275 V 16 20 24 µA mA Line UVLO Shutdown Shutdown Threshold Undervoltage Shutdown Hysteresis Current Source Current Limit ILIM Delay to Output CS CS step from 0 to 0.6V Time to onset of OUT Transition (90%) Cycle by Cycle CS Threshold Voltage 30 0.45 0.5 Leading Edge Blanking Time 50 CS Sink Impedance (clocked) 35 ns 0.55 V ns 55 Ω Soft Start www.national.com Softstart Current Source 7 10 13 µA Softstart to COMP Offset 0.35 0.55 0.75 V 4 (Continued) Specifications in standard type face are for TJ= +25˚C and those in boldface type apply over the full operating junction temperature range. Unless otherwise specified: VIN = 48V, VCC = 10V, and RT = 31.6KΩ Symbol Parameter Conditions Min Typ Max Units Oscillator Frequency1 (RT = 31.6k) (Note 5) 175 200 225 kHz Frequency2 (RT = 9.76k) (Note 5) 560 630 700 kHz 2.4 3.2 3.8 V Sync threshold PWM Comparator Delay to Output COMP set to 2V CS stepped 0 to 0.4V, Time to onset of OUT transition low Min Duty Cycle COMP=0V 25 0 Max Duty Cycle (-1 Device) 75 80 Max Duty Cycle (-2 Device) 50 COMP to PWM Comparator Gain 0.33 COMP Open Circuit Voltage COMP Short Circuit Current ns 85 % % % 4.3 5.2 6.1 V COMP=0V 0.6 1.1 1.5 mA Delta increase at PWM Comparator to CS 80 105 130 mV Slope Compensation Slope Comp Amplitude (LM5020-1 Device Only) Output Section Output High Saturation Iout = 50mA, VCC - VOUT 0.25 0.75 V Output Low Saturation IOUT = 100mA, VOUT 0.25 0.75 V Rise Time Cload = 1nF 18 ns Fall Time Cload = 1nF 15 ns Thermal Shutdown Tsd Thermal Shutdown Temp. 165 ˚C Thermal Shutdown Hysteresis 25 ˚C Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5kΩ resistor. Note 3: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. The limits are used to calculate National’s Average Outgoing Quality Level (AOQL). Note 4: Device thermal limitations may limit usable range. Note 5: Specification applies to the oscillator frequency. The operational frequency of the LM5020-2 devices is divided by two. 5 www.national.com LM5020 Electrical Characteristics LM5020 Typical Performance Characteristics Unless otherwise specified: TJ = 25˚C. VCC and VIN vs VIN VCC vs ICC (VIN = 48V) 20095006 20095007 Oscillator Frequency vs Temperature RT = 31.6kΩ Oscillator Frequency vs RT 20095008 20095009 Soft Start Current vs Temperature Error Amp. Gain/Phase Plot 20095010 www.national.com 20095021 6 The LM5020 High Voltage PWM controller contains all of the features needed to implement single ended primary power converter topologies. The LM5020 includes a high-voltage startup regulator that operates over a wide input range to 100V. The PWM controller is designed for high speed capability including an oscillator frequency range to 1MHz and total propagation delays less than 100ns. Additional features include an error amplifier, precision reference, line undervoltage lockout, cycle-by-cycle current limit, slope compensation, softstart, oscillator sync capability and thermal shutdown. The functional block diagram of the LM5020 is shown in Figure 1. The LM5020 is designed for current-mode control power converters, which require a single drive output, such as Flyback and Forward topologies. The LM5020 provides all of the advantages of current-mode control including line feed-forward, cycle-by-cycle current limiting and simplified loop compensation . Error Amplifier An internal high gain error amplifier is provided within the LM5020. The amplifier’s non-inverting input is internally set to a fixed reference voltage of 1.25V. The inverting input is connected to the FB pin. In non-isolated applications, the power converter output is connected to the FB pin via voltage scaling 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 amplifier 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 5K pull-up resistor between a 5V reference and COMP can be used as the pull-up for an optocoupler in isolated applications. High Voltage Start-Up Regulator The LM5020 contains an internal high voltage startup regulator, that allows the input pin (Vin) to be connected directly to line voltages as high as 100V. The regulator output is internally current limited to 15mA. 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 100µF. When the voltage on the VCC pin reaches the regulation level of 7.7V, the controller output is enabled. The controller will remain enabled until VCC falls below 6V. In typical applications, a transformer auxiliary winding is connected through a diode to the VCC pin. This winding should raise the VCC voltage above 8V to shut off the internal startup regulator. Powering VCC from an auxiliary winding improves conversion efficiency while reducing the power dissipated in the controller. The external VCC capacitor must be selected such that the capacitor maintains the Vcc voltage greater than the VCC UVLO falling threshold (6V) during the initial start-up. During a fault condition when the converter auxiliary winding is inactive, external current draw on the VCC line should be limited such that the power dissipated in the start-up regulator does not exceed the maximum power dissipation capability 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 (815V) to the two pins. Current Limit/Current Sense The LM5020 provides a cycle-by-cycle over current protection function. Current limit is accomplished by an internal current sense comparator. If the voltage at current sense comparator input exceeds 0.5V, the output will be immediately terminated. A small RC filter, located near the controller, is recommended to filter noise from the current sense signal. The CS input has an internal MOSFET which discharges the CS pin capacitance at the conclusion of every cycle. The discharge device remains on an additional 50ns after the beginning of the new cycle to attenuate the leading edge spike on the current sense signal. The LM5020 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 sense resistor. The capacitor associated with the CS filter must be located very 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 and the current sense filter network. A sense resistor located in the source of the primary power MOSFET may be used for current sensing, but a low inductance resistor is required. When designing with a current sense resistor all of the noise sensitive low power ground connections should be connected together local to the controller and a single connection should be made to the high current power ground (sense resistor ground point). Line Under Voltage Detector The LM5020 contains a line Under Voltage Lock Out (UVLO) circuit. An external set-point voltage divider from Vin to GND sets the operational range of the converter. The resistor divider must be designed such that the voltage at the UVLO pin is greater than 1.25V when Vin is in the desired operating range. If the under voltage threshold is not met, all functions of the controller are disabled and the controller remains in a low power standby state. 7 www.national.com LM5020 UVLO hysteresis is accomplished with an internal 20µA 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 voltage falls below the 1.25V 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. If an external transistor pulls the UVLO pin below the 1.25V threshold, the converter will be disabled. Detailed Operating Description LM5020 (slope compensation) to the current sense signal, this oscillation can be avoided. The LM5020-1 integrates this slope compensation by summing a current ramp generated by the oscillator with the current sense signal. Additional slope compensation may be added by increasing the source impedance of the current sense signal. Since the LM5020-2 is not capable of duty cycles greater than 50%, there is no slope compensation feature in this device. Oscillator and Sync Capability A single external resistor connected between the RT and GND pins sets the LM5020 oscillator frequency. Internal to the LM5020–2 device (50% duty cycle limited option) is an oscillator divide by two circuit. This divide by two circuit creates an exact 50% duty cycle pulse which is used internally to create a precise 50% duty cycle limit function. Because of this, the internal oscillator actually operates at twice the frequency of the output (OUT). For the LM5020–1 device the oscillator frequency and the operational output frequency are the same. To set a desired output operational frequency (F), the RT resistor can be calculated from: Soft Start The softstart feature allows the power converter to gradually reach the initial steady state operating point, thereby reducing start-up stresses and current surges. At power on, after the VCC and the line undervoltage lockout thresholds are satisfied, an internal 10µA current source charges an external capacitor connected to the SS pin. The capacitor voltage will ramp up slowly and will limit the COMP pin voltage and the duty cycle of the output pulses. LM5020-1: LM5020-2: Gate Driver and Maximum Duty Cycle Limit The LM5020 provides an internal gate driver (OUT), which can source and sink a peak current of 1 Amp. The LM5020 is available in two duty cycle limit options. The maximum output duty cycle is typically 80% for the LM5020-1 option and precisely equal to 50% for the LM5020-2 option. The maximum duty cycle function for the LM5020-2 is accomplished with an internal toggle flip-flop which ensures an accurate duty cycle limit. The internal oscillator frequency of the LM5020-2 is therefore twice the operating frequency of the PWM controller (OUT pin). The 80% maximum duty cycle limit of the LM5020-1 is determined by the internal oscillator and varies more than the 50% limit of the LM5020-2. For the LM5020-1 the internal oscillator frequency and the operational frequency of the PWM controller are equal. The LM5020 can also be synchronized to an external clock. The external clock must have a higher frequency than the free running oscillator frequency set by the RT resistor. The clock signal should be capacitively coupled into the RT pin with a 100pF capacitor. A peak voltage level greater than 3.7 Volts at the RT pin is required for detection of the sync pulse. The sync pulse width should be set between 15 to 150ns 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 a 2 Volts. The RT resistor should be located very close to the device and connected directly to the pins of the controller (RT and GND). Thermal Protection PWM Comparator / Slope Compensation Internal thermal shutdown circuitry is provided to protect the integrated circuit in the event the maximum junction temperature is exceeded. This feature prevents catastrophic failures from accidental device overheating. When activated, typically at 165 degrees Celsius, the controller is forced into a low power standby state, disabling the output driver and the bias regulator. After the temperature is reduced (typical hysteresis = 25˚C) the VCC regulator will be enabled and a softstart sequence initiated. The PWM comparator compares the current ramp signal with the loop error voltage derived from the error amplifier output. The error amplifier output voltage at the COMP pin is offset by 1.4V and then further attenuated by a 3:1 resistor divider. The PWM comparator polarity is such that 0 Volts on the COMP pin will result in a zero duty cycle at the controller output. For duty cycles greater than 50 percent, current mode control circuits are subject to sub-harmonic oscillation. By adding an additional fixed slope voltage ramp signal www.national.com 8 Typical Application Circuit: 36V - 75 VIN and 3.3V, 4.5A OUT 20095005 LM5020 9 www.national.com LM5020 Bill Of Materials ITEM PART NUMBER DESCRIPTION VALUE C 1 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µF, 100V C 2 C4532X7R2A225M CAPACITOR, CER, TDK 2.2µF, 100V C 3 C2012X7R1H103K CAPACITOR, CER, TDK 0.01µF, 50V C 4 C3216X7R2A104K CAPACITOR, CER, TDK 0.1µF, 100V C 5 C2012X7R1H103K CAPACITOR, CER, TDK 0.01µF, 50V C 6 C2012C0G1H221J CAPACITOR, CER, KEMET 220pF, 50V C 7 C2012C0G1H332J CAPACITOR, CER, TDK 3300pF, 50V C 8 C2012C0G1H101J CAPACITOR, CER, TDK 100pF, 50V C 9 C2012X7R1H104K CAPACITOR, CER, TDK 0.1µF, 50V C 10 C3216X7R1C475K CAPACITOR, CER, TDK 4.7µF, 16V C 11 C2012C0G1H102J CAPACITOR, CER, TDK 1000pF, 50V C 12 C2012C0G1H471J CAPACITOR, CER, TDK 470p, 50V C 13 C4532X7S0G107M CAPACITOR, CER, TDK 100µF, 4V C 14 C4532X7S0G107M CAPACITOR, CER, TDK 100µF, 4V C 15 A700X277M0004AT CAPACITOR, ALUM ORGANIC, KEMET 270µF, 4V D 1 CMPD2838E-NSA DIODE, SIGNAL, CENTRAL D 2 CMPD2838E-NSA DIODE, SIGNAL, CENTRAL D 3 MBRD835L DIODE, RECTIFIER, ON SEMICONDUCTOR J 1 MKDS 1/2-3.81 TERM BLK, MINI, 2 POS, PHOENIX CONTACT J 2 MKDS 1/2-3.81 TERM BLK, MINI, 2 POS, PHOENIX CONTACT Q 1 SI7898DP FET, SILICONIX 150V, 85m R 1 CRCW120610R0F RESISTOR 10 R 2 CRCW12066192F RESISTOR 61.9K R 3 CRCW08052871F RESISTOR 2.87K R 4 CRCW08051001F RESISTOR 1.00K R 5 CRCW08051502F RESISTOR 15.0K R 6 CRCW08051242F RESISTOR 12.4K R 7 CRCW08051000F RESISTOR 100 R 8 CRCW12060R47F RESISTOR 0.47 R 9 CRCW12060R47F RESISTOR 0.47 R 10 CRCW251210R0F RESISTOR 10, 1Ω R 11 CRCW08052431F RESISTOR 2.43K R 12 CRCW08051471F RESISTOR 1.47K R 13 CRCW080520R0F RESISTOR 20 T 1 B0695-A COILCRAFT TRANSFORMER, FLYBACK, EFD20 CORE T 1 PA0751 PULSE TRANSFORMER, FLYBACK, EFD20 CORE U 1 LM5020-2MM CONTROLLER, SINGLE OUT, PWM, NATIONAL Z 1 1SMB5936B DIODE, ZENER, SMB, 30V www.national.com 10 ALTERNATE LM5020 Physical Dimensions inches (millimeters) unless otherwise noted 10 Lead MSOP Package NS Package Number MUB10A 10 Lead MSOP, LLP Package NS Package Number SDC10A 11 www.national.com LM5020 100V Current Mode PWM Controller Notes National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. 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