19-2066; Rev 1; 9/01 ABLE KIT AVAIL N IO T A U L EVA Current-Mode PWM Controllers for Isolated Power Supplies Features ♦ Available in a Tiny 6-Pin SOT23 Package An undervoltage lockout (UVLO) circuit with large hysteresis coupled with low startup and operating current reduce power dissipation in the startup resistor and allow use of ceramic bypass capacitors. The 262kHz switching frequency is internally trimmed to ±12% accuracy; this allows the optimization of the magnetic and filter components resulting in compact, cost-effective power supplies. The MAX5021 with 50% maximum duty cycle and MAX5022 with 75% maximum duty cycle are recommended for forward converters and flyback converters, respectively. The MAX5021/MAX5022 are available in 6-pin SOT23, 8-pin µMAX, and 8-pin DIP packages and are rated for operation over the -40°C to +85°C temperature range. ♦ Fixed Switching Frequency of 262kHz ±12% ♦ 50µA Typical Startup Current ♦ 1.2mA Typical Operating Current ♦ Large UVLO Hysteresis of 14V ♦ 50% Maximum Duty Cycle Limit (MAX5021) ♦ 75% Maximum Duty Cycle Limit (MAX5022) ♦ 60ns Cycle-by-Cycle Current-Limit Response Time Ordering Information PART MAX DUTY CYCLE MAX5021EUT 50% -40°C to +85°C 6 SOT23-6 AASQ MAX5021EUA 50% -40°C to +85°C 8 µMAX MAX5021EPA 50% -40°C to +85°C 8 PDIP Standby Power Supplies MAX5022EUT 75% -40°C to +85°C 6 SOT23-6 Isolated Power Supplies MAX5022EUA 75% -40°C to +85°C 8 µMAX — Isolated Telecom Power Supplies MAX5022EPA 75% -40°C to +85°C 8 PDIP — Applications Universal Off-Line Power Supplies Mobile Phone Chargers TEMP. RANGE PINTOP PACKAGE MARK — — AASR WARNING: The MAX5021/MAX5022 are designed to work with high voltages. Exercise caution! Pin Configuration Typical Operating Circuit VSUPPLY VOUT TOP VIEW CS 1 GND 2 VCC VIN MAX5021 MAX5022 OPTO NDRV MAX5021 MAX5022 NDRV 3 SOT23 GND 6 OPTO OPTO 1 5 VIN 4 VCC VIN 2 VCC 3 MAX5021 MAX5022 N.C. 4 8 CS 7 GND 6 NDRV 5 N.C. PDIP/µMAX CS ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX5021/MAX5022 General Description The MAX5021/MAX5022 current-mode PWM controllers contain all the control circuitry required for the design of wide input voltage range isolated power supplies. These devices are well suited for use in universal input (85VAC to 265VAC) off-line or telecom (-36VDC to -72VDC) power supplies. MAX5021/MAX5022 Current-Mode PWM Controllers for Isolated Power Supplies ABSOLUTE MAXIMUM RATINGS VIN to GND .............................................................-0.3V to +30V VCC to GND ............................................................-0.3V to +13V NDRV to GND.............................................-0.3V to (VCC + 0.3V) CS, OPTO to GND ....................................................-0.3V to +6V NDRV Short-Circuit to GND........................................Continuous Continuous Power Dissipation (TA = +70°C) 6-Pin SOT23 (derate 8.7mW/°C above +70°C).............696mW 8-Pin µMAX (derate 4.5mW/°C above +70°C) ..............362mW 8-Pin PDIP (derate 9.1mW/°C above +70°C)................727mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-55°C to +150°C Lead Temperature (soldering 10s) ..................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = +11V to +28V, VCS = 0, OPTO is unconnected, 10nF bypass capacitors at VIN and VCC, NDRV unconnected, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VIN = +12V, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS UNDERVOLTAGE LOCKOUT/STARTUP Undervoltage Lockout Wakeup Level VUVR VIN rising 22 24 26 V Undervoltage Lockout Shutdown Level VUVF VIN falling 9.3 10 10.9 V 50 85 µA 28 V VIN Supply Current at Startup VIN Range Undervoltage Lockout Propagation Delay ISTART VIN = +22V VIN 11 TUVR VIN steps up from +9V to +26V 5 TUVF VIN steps down from +26V to +9V 1 µs INTERNAL SUPPLY VCC Regulator Set Point VIN Supply Current after Startup VCCSP IIN VIN = +11V to +28V, sourcing 1µA to 5mA from VCC 7.0 10.5 VIN = +28V, OPTO connected to GND 0.9 2.43 VIN = +28V, OPTO unconnected (Note 2) 0.4 V mA GATE DRIVER Driver Output Impedance Driver Peak Sink Current Driver Peak Source Current RON(LOW) Measured at NDRV sinking 5mA RON(HIGH) Measured at NDRV sourcing 5mA 10 20 20 40 Ω ISINK 250 mA ISOURCE 150 mA PWM COMPARATOR Comparator Offset Voltage CS Input Bias Current Propagation Delay from Comparator Input to NDRV Minimum On-Time VOPWM VOPTO - VCS ICS TPWM 600 750 -2 25mV overdrive TON(MIN) 900 mV +2 µA 60 ns 150 ns CURRENT-LIMIT COMPARATOR Current-Limit Trip Threshold VCS Current-Limit Propagation Delay from Comparator Input to NDRV TCL 2 540 25mV overdrive 600 60 _______________________________________________________________________________________ 660 mV ns Current-Mode PWM Controllers for Isolated Power Supplies (VIN = +11V to +28V, VCS = 0, OPTO is unconnected, 10nF bypass capacitors at VIN and VCC, NDRV unconnected, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VIN = +12V, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 230 kHz OSCILLATOR Switching Frequency fSW Maximum Duty Cycle DMAX 262 290 MAX5021 50 51 MAX5022 75 76 5.5 V 6.2 7.9 kΩ % OPTO INPUT OPTO Pullup Voltage VOPTO OPTO Pullup Resistance ROPTO OPTO sourcing 10µA 4.5 Note 1: All devices are 100% tested at TA = +25°C. All limits over temperature are guaranteed by characterization. Note 2: This minimum current after startup is a safeguard that prevents the VIN pin voltage from rising in the event that OPTO and NDRV become unconnected. Typical Operating Characteristics (VIN = 15V, TA = +25°C, unless otherwise noted.) UNDERVOLTAGE LOCKOUT vs. TEMPERATURE 24.1 24.0 VIN FALLING 10.1 10.0 9.9 53 52 MAX5021/22 toc03 24.2 10.2 MAX5021/22 toc02 UNDERVOLTAGE LOCKOUT (V) VIN RISING UNDERVOLTAGE LOCKOUT (V) MAX5021/22 toc01 24.3 STARTUP CURRENT vs. TEMPERATURE STARTUP CURRENT (µA) UNDERVOLTAGE LOCKOUT vs. TEMPERATURE VIN = 23.0V 51 50 49 48 23.9 9.8 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 47 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) _______________________________________________________________________________________ 3 MAX5021/MAX5022 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (VIN = 15V, TA = +25°C, unless otherwise noted.) 1.45 9.06 VIN = 28.0V VCS = 0 OPTO = UNCONNECTED 9.03 1.40 40 60 80 7.70 -40 -20 TEMPERATURE (°C) 40 60 80 -40 MEAN 600 -3σ 15 10 0 570 20 40 60 540 80 560 270 +3σ 265 MEAN 255 -3σ 580 600 620 640 245 660 -40 -20 CURRENT SENSE DELAY vs. TEMPERATURE 10 5 MAX5021/22 toc11 70 65 60 55 0 50 280 OSCILLATOR FREQUENCY (kHz) 4 40 60 80 290 6 UNDERVOLTAGE LOCKOUT DELAY (µs) 15 270 20 UNDERVOLTAGE LOCKOUT DELAY vs. TEMPERATURE 75 CURRENT SENSE DELAY (ns) 20 MAX5021/22 toc10 TOTAL NUMBER OF DEVICES = 200 260 0 TEMPERATURE (°C) 25 250 80 260 CURRENT SENSE THRESHOLD (mV) OSCILLATOR FREQUENCY 240 60 TOTAL NUMBER OF DEVICES = 50 275 TEMPERATURE (°C) 230 40 250 TOTAL NUMBER OF DEVICES = 50 0 20 280 5 -20 0 OSCILLATOR FREQUENCY vs. TEMPERATURE TOTAL NUMBER OF DEVICES = 200 20 FREQUENCY (%) +3σ 580 -20 TEMPERATURE (°C) 25 MAX5021/22 toc07 CURRENT SENSE THRESHOLD (mV) 630 -40 20 CURRENT SENSE THRESHOLD 640 610 0 TEMPERATURE (°C) CURRENT SENSE THRESHOLD vs. TEMPERATURE 620 7.90 MAX5021/22 toc12 20 OSCILLATOR FREQUENCY (kHz) 0 MAX5021/22 toc08 -20 8.00 7.80 9.00 -40 8.10 MAX5021/22 toc09 1.50 9.09 VIN = 10.8V 5mA LOAD ON VCC VCS = 0 OPTO = UNCONNECTED 8.20 MINIMUM VCC (V) 9.12 MAXIMUM VCC (V) 1.55 8.30 MAX5021/22 toc05 VIN = 28.0V VOPTO = VCS = 0 SUPPLY CURRENT (mA) 9.15 MAX5021/22 toc04 1.60 590 MINIMUM VCC vs. TEMPERATURE MAXIMUM VCC vs. TEMPERATURE MAX5021/22 toc06 SUPPLY CURRENT vs. TEMPERATURE FREQUENCY (%) MAX5021/MAX5022 Current-Mode PWM Controllers for Isolated Power Supplies 5 VIN RISING 4 3 2 VIN FALLING 1 0 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -40 -20 0 20 40 TEMPERATURE (°C) _______________________________________________________________________________________ 60 80 Current-Mode PWM Controllers for Isolated Power Supplies PIN SOT23 PDIP µMAX NAME 1 8 CS FUNCTION Current Sense Connection for PWM Regulation and Overcurrent Protection. The current-limit comparator threshold is internally set to 0.6V. 2 7 GND Power-Supply Ground 3 6 NDRV External N-Channel MOSFET Gate Connection 4 3 VCC Gate Drive Supply. Internally regulated down from VIN. Decouple with a 10nF or larger capacitor to GND. 5 2 VIN IC Supply. Decouple with a 10nF or larger capacitor to GND. Connect a startup resistor (Rs) from the input supply line to VIN. Connect to bias winding through diode rectifier. See Typical Operating Circuit. 6 1 OPTO — 4, 5 N.C. Optocoupler Transistor Collector Connection. Connect emitter of optocoupler to GND. The OPTO has an internal pullup resistor with a typical value of 6.2kΩ. No Connection. Do not make connections to these pins. Detailed Description The MAX5021/MAX5022 are current-mode PWM controllers that have been specifically designed for use in isolated power supplies. An undervoltage lockout circuit (UVLO) with a large hysteresis (14V) along with very low startup and operating current result in highefficiency, universal input power supplies. Both devices can be used in power supplies capable of operating from a universal 85VAC to 265VAC line or the telecom voltage range of -36VDC to -72VDC. Power supplies designed with these devices use a high-value startup resistor, RS, (series combination of R1 and R2) that charges a reservoir capacitor, C2 (see Figure 1). During this initial period while the voltage is less than the UVLO start threshold, the IC typically consumes only 50µA of quiescent current. This low startup current and the large UVLO hysteresis combined with the use of a ceramic capacitor C2 keeps the power dissipation in RS to less than 1/4W even at the high end of the universal AC input voltage (265VAC). The MAX5021/MAX5022 include a cycle-by-cycle current limit which turns off the gate drive to the external MOSFET during an overcurrent condition. If the output on the secondary side of transformer T1 is shorted, the tertiary winding voltage will drop below the 10V threshold causing the UVLO circuit to turn off the gate drive to the external power MOSFET, thus re-initiating the startup sequence. Startup Figure 2 shows the voltages on VIN and VCC during startup. Initially, both VIN and VCC are 0V. After the line voltage is applied, C2 charges through the startup resistor, RS, to an intermediate voltage at which point the internal reference and regulator begin charging C3 (see Figure 1). The bias current consumed by the device during this period is only 50µA; the remaining input current charges C2 and C3. Charging of C3 stops when the V CC voltage reaches approximately 9.5V, while the voltage across C2 continues rising until it reaches the wakeup level of 24V. Once VIN exceeds the UVLO threshold, NDRV begins switching the MOSFET, transferring energy to the secondary and tertiary outputs. If the voltage on the tertiary output builds to higher than 10V (UVLO lower threshold), then startup has been accomplished and sustained operation will commence. If VIN drops below 10V before startup is complete, then the IC goes back into UVLO. In this case, increase the value of C2 and/or use a MOSFET with a lower gatecharge requirement. Startup Time Considerations The VIN bypass capacitor C2 supplies current immediately after wakeup. The size of C2 will determine the number of cycles available for startup. Large values for C2 will increase the startup time, but will also supply more gate charge, allowing for more cycles after wakeup. If the value of C2 is too small, VIN will drop below 10V because _______________________________________________________________________________________ 5 MAX5021/MAX5022 Pin Description MAX5021/MAX5022 Current-Mode PWM Controllers for Isolated Power Supplies L CENTRAL SEMICONDUCTOR CBR1-D100S AC L2 470µH 85VAC TO N 265VAC IN G C1 10µF 400V AC R8 1.2kΩ R1 360kΩ D1 RS = R1 + R2 C9 10µF 400V R2 360kΩ D1 250mA, 75V CENTRAL SEMICONDUCTOR CMPD914 C3 0.22µF 3T 8T R11 10Ω C4 150µF 6.3V +5V OUT VCC R10 10Ω C7 1000pF OPTO C5 0.01µF TEXAS INSTRUMENTS TLV431AIDBV VIN U1 C6 0.1µF R4 24.9kΩ 1% R3 1kΩ 1% OPTO C2 0.22µF MAX5022 OPTO FAIRCHILD CNY17-3 D2 CTX03-15256 3A, 40V T1 ON SEMICONDUCTOR MBRS340T3 480µH, 60T R5 8.06kΩ 1% N1 INTERNATIONAL RECTIFIER IRFRC20 NDRV NOTE: ALL RESISTORS ARE 5% UNLESS OTHERWISE SPECIFIED. CS GND R9 240kΩ C8 8200pF R6 10Ω RCS 1.78Ω 1% Figure 1. Universal 5W Off-Line Standby Power Supply 6 25 IC COMES OUT OF UVLO (WAKEUP) 20 VIN, VCC (V) NDRV did not switch enough times to build up sufficient voltage across the tertiary output to power the device. The device will go back into UVLO and will not start. Use a low-leakage ceramic or film capacitor for C2 and C3. As a rule of thumb, off-line power supplies keep typical startup times to less than 500ms even in low-line conditions (85VAC input). Size the startup resistor, RS, to supply the maximum startup bias of the IC (85µA) plus the additional current required for charging the capacitors C2 and C3 in less than 500ms. This resistor dissipates continuous power in normal operation, despite the fact that it is only used during the startup sequence. Therefore it must be chosen to provide enough current for the low-line condition as well as have an appropriate power rating for the high-line condition (265VAC). In most cases, split the value into two resistors connected in series for the required voltage of approximately 400VDC. The typical value for C2 and C3 is 220nF. The startup resistor, RS, provides both the maximum quiescent current of 85µA and the charging current for C2 and C3. Bypass capacitor C3 charges to 9.5V and C2 charges VIN SUPPLIED BY C2 15 VIN 10 VIN SUPPLIED BY TERTIARY WINDING (NORMAL OPERATION) VCC BYPASS CAPACITOR FULLY CHARGED 5 VCC VCC DROPS SLIGHTLY WHEN NDRV BEGINS SWITCHING 0 0 50 100 TIME (ms) 150 200 Figure 2. VIN and VCC During Startup to 24V all within the desired time period of 500ms, for an overall average charging current of 15µA. Hence, the startup resistor must provide a total of at least 100µA. Developing 100µA from an input voltage of _______________________________________________________________________________________ Current-Mode PWM Controllers for Isolated Power Supplies Undervoltage Lockout (UVLO) The device will attempt to start when VIN exceeds the UVLO threshold of 24V. During startup, the UVLO circuit keeps the CPWM comparator, ILIM comparator, oscillator, and output driver shut down to reduce current consumption (Functional Diagram). Once V IN reaches 24V, the UVLO circuit turns on both the CPWM and ILIM comparators, as well as the oscillator, and allows the output driver to switch. If VIN drops below 10V, the UVLO circuit will shut down the CPWM comparator, ILIM comparator, oscillator, and output driver returning the MAX5021/MAX5022 to the startup mode. N-Channel MOSFET Switch Driver The NDRV pin drives an external N-channel MOSFET. The NDRV output is supplied by the internal regulator (VCC), which is internally set to approximately 9V. For the universal input voltage range, the MOSFET used must be able to withstand the DC level of the high-line input voltage plus the reflected voltage at the primary of the transformer. For most applications that use the discontinuous flyback topology, this requires a MOSFET rated at 600V. NDRV can source/sink 150mA/ 250mA peak current, thus select a MOSFET that will yield acceptable conduction and switching losses. Internal Oscillator The internal oscillator switches at 1.048MHz and is divided down to 262kHz by two D flip-flops. The MAX5021 inverts the Q output of the last D flip-flop to provide a duty cycle of 50% (Figure 3). The MAX5022 performs a logic NAND operation on the Q outputs of both D flip-flops to provide a duty cycle of 75%. D OSCILLATOR 1.048MHz Q D Q Q Q Figure 3. Internal Oscillator 262kHz WITH 50% (MAX5021) 262kHz WITH 75% (MAX5022) Optocoupler Feedback The MAX5021/MAX5022 do not include an internal error amplifier and are recommended for use in optocoupler feedback power supplies. Isolated voltage feedback is achieved by using an optocoupler and a shunt regulator as shown in the Typical Operating Circuit. The output voltage set point accuracy is a function of the accuracy of the shunt regulator and resistor divider. When a TLV431 shunt regulator is used for output voltage regulation, the output voltage is set by the ratio of R4 and R5 (Figure 1). Output voltage is given by the following equation: R4 VOUT = VREF × 1 + R5 where VREF = 1.24V for the TLV431. During normal operation, the optocoupler feedback pin (OPTO) is pulled up through a 6.2kΩ resistor to the internal supply voltage of 5.25V. When the device is in UVLO, OPTO is disconnected from the 5.25V regulator and connected to ground (Functional Diagram). This helps initial startup by reducing the current consumption of the device. Current Limit The current limit is set by a current sense resistor, RCS, connected between the source of the MOSFET and ground. The CS input has a voltage trip level (VCS) of 600mV. Use the following equation to calculate the value of RCS: V RCS = CS IPRI where IPRI is the peak current in the primary that flows through the MOSFET. When the voltage produced by this current through the current sense resistor exceeds the current-limit comparator threshold, the MOSFET driver (NDRV) will quickly terminate the current ON-cycle, typically within 60ns. In most cases a small RC filter will be required to filter out the leading-edge spike on the sense waveform. Set the corner frequency at a few MHz. Applications Information Universal Off-Line Power Supply Figure 1 shows the design of a 5V/1A isolated power supply capable of operating from a line voltage of 85VAC to 265VAC. This circuit is implemented in the MAX5022EVKIT. _______________________________________________________________________________________ 7 MAX5021/MAX5022 85VAC (corresponding to 120VDC) to the 24V wakeup level results in a resistor value of about 1MΩ. If we assume RS values between 750kΩ and 1MΩ, then at the high-line voltage of 265VAC (corresponding to 374VDC) power dissipation will be between 140mW to 190mW. A single 1/4W resistor or a series combination of two 1/4W resistors is adequate. MAX5021/MAX5022 Current-Mode PWM Controllers for Isolated Power Supplies T1 VOUT RS C2 VIN VCC C3 MAX5022 OPTO GND NDRV CS -36VDC TO -72VDC IN Figure 4. -48VDC Input to +5V Output WARNING! DANGEROUS AND LETHAL VOLTAGES ARE PRESENT IN OFF-LINE CIRCUITS! USE EXTREME CAUTION IN THE CONSTRUCTION, TESTING, AND USE OF OFF-LINE CIRCUITS. Isolated Telecom Power Supply Figure 4 shows a -48VDC telecom power supply capable of generating an isolated +5V output. To achieve best performance, a star ground connection is recommended to avoid ground loops. For example, the ground returns for the power-line input filter, power MOSFET switch, and sense resistor should be routed separately through wide copper traces to meet at a single system ground connection. Layout Recommendations All printed circuit board traces carrying switching currents must be kept as short as possible, and the current loops they form must be minimized. The pins of the SOT23 package have been placed to allow simple interfacing to the external MOSFET. The order of these pins directly corresponds to the order of a TO-220 or similar package MOSFET. For universal AC input design all applicable safety regulations must be followed. Off-line power supplies may require UL, VDE, and other similar agency approvals. These agencies can be contacted for the latest layout and component rules. Chip Information TRANSISTOR COUNT: 519 PROCESS: BiCMOS Typically there are two sources of noise emission in a switching power supply: high di/dt loops and high dv/dt surfaces. For example, traces that carry the drain current often form high di/dt loops. Similarly the heatsink of the MOSFET presents a dv/dt source, thus the surface area of the heatsink must be minimized as much as possible. 8 _______________________________________________________________________________________ Current-Mode PWM Controllers for Isolated Power Supplies IN VIN VCC VCC REGULATOR REG_OK UVLO IN REFERENCE 1.25V 24V 10V GND VL (INTERNAL 5.25V SUPPLY) 6.2kΩ DRIVER S Q NDRV R OPTO CPWM 0.75V OSCILLATOR 262kHz* CS GND VOPWM VCS 0.6V *MAX5021: 50% MAXIMUM DUTY CYCLE MAX5022: 75% MAXIMUM DUTY CYCLE ILIM _______________________________________________________________________________________ 9 MAX5021/MAX5022 Functional Diagram Current-Mode PWM Controllers for Isolated Power Supplies 6LSOT.EPS MAX5021/MAX5022 Package Information PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 8L uMAX/uSOP APPROVAL DOCUMENT CONTROL NO. 21-0036 10 REV. J 1 1 ______________________________________________________________________________________ Current-Mode PWM Controllers for Isolated Power Supplies PDIPN.EPS Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX5021/MAX5022 Package Information (continued)