KIT ATION EVALU E L B A AVAIL 19-2590; Rev 1; 11/03 Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies The MAX5052/MAX5053 current-mode PWM controllers contain all the control circuitry required for the design of wide-input-voltage isolated and nonisolated power supplies. The MAX5052 is well suited for universal input (rectified 85VAC to 265VAC) or telecom (-36VDC to -72VDC) power supplies. The MAX5053 is well suited for low-input-voltage (10.8VDC to 24VDC) power supplies. The MAX5052/MAX5053 contain an internal error amplifier that regulates the tertiary winding output voltage. This implements a primary-side regulated, isolated power supply, eliminating the need for an optocoupler. An input undervoltage lockout (UVLO) is provided for programming the input-supply start voltage and to ensure proper operation during brownout conditions. The input-supply start voltage is externally programmable with a voltage-divider. To shutdown the device, the UVLO pin is pulled low. Internal digital soft-start reduces output voltage overshoot. The internal thermal shutdown circuit protects the device in the event the junction temperature exceeds +130°C. The MAX5052 has an internal bootstrap UVLO with large hysteresis that requires a minimum voltage of 23.6V for startup. The MAX5053 does not have the internal bootstrap UVLO and can be biased directly from a minimum voltage of 10.8V. 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 MAX5052A/ MAX5053A are offered with a 50% maximum duty-cycle limit. The MAX5052B/MAX5053B are offered with a 75% maximum duty-cycle limit. These devices are available in 8-pin µMAX packages and operate over the -40°C to +85°C temperature range. Applications Universal Input AC Power Supplies Industrial Power Conversion Isolated Telecom Power Supplies Isolated Keep-Alive Circuits Networking Systems 12V Boost Regulators Computer Systems/ Servers 12V SEPIC Regulators Features ♦ Available in a Tiny 8-Pin µMAX Package ♦ Current-Mode Control ♦ 50W Output Power ♦ Universal Offline Input Voltage Range Rectified 85VAC to 265VAC (MAX5052) ♦ VIN Directly Driven from 10.8V to 24V Input (MAX5053) ♦ Digital Soft-Start ♦ Programmable Input Startup Voltage ♦ Internal Bootstrap UVLO with Large Hysteresis (MAX5052) ♦ Internal Error Amplifier with 1% Accurate Reference ♦ Thermal Shutdown ♦ 45µA (typ) Startup Supply Current ♦ 1.4mA (typ) Operating Supply Current ♦ Fixed Switching Frequency of 262kHz ±12% ♦ 50% Maximum Duty-Cycle Limit (MAX5052A/MAX5053A) ♦ 75% Maximum Duty-Cycle Limit (MAX5052B/MAX5053B) ♦ 60ns Cycle-by-Cycle Current-Limit Response Time Ordering Information PART TEMP RANGE PIN-PACKAGE MAX5052AEUA -40°C to +85°C 8 µMAX MAX5052BEUA -40°C to +85°C 8 µMAX MAX5053AEUA -40°C to +85°C 8 µMAX MAX5053BEUA -40°C to +85°C 8 µMAX Warning: The MAX5052/MAX5053 are designed to work with high voltages. Exercise caution. Pin Configuration TOP VIEW UVLO/EN 1 FB 2 COMP 3 MAX5052 MAX5053 CS 4 Functional Diagram/Typical Operating Circuit/Selector Guide appear at end of data sheet. 8 VIN 7 VCC 6 NDRV 5 GND µMAX ________________________________________________________________ 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 MAX5052/MAX5053 General Description MAX5052/MAX5053 Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies ABSOLUTE MAXIMUM RATINGS VIN to GND .............................................................-0.3V to +30V VCC to GND ............................................................-0.3V to +13V FB, COMP, UVLO, CS to GND .................................-0.3V to +6V NDRV to GND.............................................-0.3V to (VCC + 0.3V) Continuous Power Dissipation (TA = +70°C) 8-Pin µMAX (derate 4.5mW/°C above +70°C) ..............362mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range ............................-65°C to +150°C Junction Temperature ......................................................+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 = +12V (for MAX5052, VIN must first be brought up to 23.6V for startup), 10nF bypass capacitors at VIN and VCC, CNDRV = 0, VUVLO = +1.4V, VFB = +1.0V, VCOMP = floating, VCS = 0V, typical values are measured at TA = +25°C, TA = -40°C to + 85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 19.68 21.6 23.60 V UNDERVOLTAGE LOCKOUT/STARTUP Bootstrap UVLO Wake-Up Level VSUVR VIN rising (MAX5052 only) Bootstrap UVLO Shutdown Level VSUVF VIN falling (MAX5052 only) 9.05 9.74 10.43 V UVLO/EN Wake-Up Threshold VULR2 UVLO/EN rising 1.188 1.28 1.371 V UVLO/EN Shutdown Threshold VULF2 UVLO/EN falling 1.168 1.23 1.291 V UVLO/EN Input Current IUVLO TJ = +125°C UVLO/EN Hysteresis VIN Supply Current In Undervoltage Lockout VIN Range UVLO/EN Propagation Delay Bootstrap UVLO Propagation Delay ISTART VIN = +19V, for MAX5052 only when in bootstrap UVLO VIN 25 nA 50 mV 45 10.8 tEXTR UVLO/EN steps up from +1.1V to +1.4V 12 tEXTF UVLO/EN steps down from +1.4V to +1.1V 1.8 tBUVR VIN steps up from +9V to +24V 5 tBUVF VIN steps down from +24V to +9V 1 VCCSP VIN = +10.8V to +24V, sinking 1µA to 20mA from VCC 90 µA 24 V µs µs INTERNAL SUPPLY VCC Regulator Set Point VIN Supply Current After Startup IIN Shutdown Supply Current 7 VIN = +24V 1.4 UVLO/EN = low 10.5 V 2.5 mA 90 µA GATE DRIVER Driver Output Impedance RON(LOW) Measured at NDRV sinking, 100mA 2 4 RON(HIGH) Measured at NDRV sourcing, 20mA 4 12 Driver Peak Sink Current Driver Peak Source Current Ω 1 A 0.65 A PWM COMPARATOR Comparator Offset Voltage CS Input Bias Current Comparator Propagation Delay Minimum On-Time 2 VOPWM ICS tPWM tON(MIN) VCOMP - VCS VCS = 0V VCS = +0.1V 1.15 1.38 -2 1.70 V +2 µA 60 ns 150 ns _______________________________________________________________________________________ Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies (VIN = +12V (for MAX5052, VIN must first be brought up to 23.6V for startup), 10nF bypass capacitors at VIN and VCC, CNDRV = 0, VUVLO = +1.4V, VFB = +1.0V, VCOMP = floating, VCS = 0V, typical values are measured at TA = +25°C, TA = -40°C to + 85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 262 291 320 mV +2 µA CURRENT-LIMIT COMPARATOR Current-Limit Trip Threshold VCS CS Input Bias Current ICS Propagation Delay From Comparator Input to NDRV tPWM Switching Frequency fSW Maximum Duty Cycle DMAX VCS = 0V -2 50mV overdrive 60 230 ns 262 290 MAX505_A 50 50.5 MAX505_B 75 76 26.1 29.0 kHz % VIN CLAMP VOLTAGE VIN Clamp Voltage VINC 2mA sink current, MAX5052 only (Note 3) 24.1 V ERROR AMPLIFIER Voltage Gain RLOAD = 100kΩ 80 dB Unity-Gain Bandwidth RLOAD = 100kΩ, CLOAD = 200pF 2 MHz Phase Margin RLOAD = 100kΩ, CLOAD = 200pF 65 FB Input Offset Voltage degrees 3 COMP Pin Clamp Voltage High 2.2 3.5 Low 0.4 1.1 mV V Source Current 0.5 mA Sink Current 0.5 mA Reference Voltage VREF (Note 2) 1.218 1.230 Input Bias Current COMP Short-Circuit Current 1.242 V 50 nA 8 mA Thermal-Shutdown Temperature 130 °C Thermal Hysteresis 25 °C 15,872 clock cycles Reference Voltage Steps During Soft-Start 31 steps Reference Voltage Step 40 mV THERMAL SHUTDOWN DIGITAL SOFT-START Soft-Start Duration Note 1: All devices are 100% tested at TA = +85°C. All limits over temperature are guaranteed by characterization. Note 2: VREF is measured with FB connected to the COMP pin (see Functional Diagram). Note 3: The MAX5052 is intended for use in universal input power supplies. The internal clamp circuit is used to prevent the bootstrap capacitor (C1 in Figure 1) from charging to a voltage beyond the absolute maximum rating of the device when EN/UVLO is low. The maximum current to VIN (hence to clamp) when UVLO is low (device in shutdown) must be externally limited to 2mA, max. Clamp currents higher than 2mA may result in clamp voltage higher than 30V, thus exceeding the absolute maximum rating for VIN. For the MAX5053, do not exceed the 24V maximum operating voltage of the device. _______________________________________________________________________________________ 3 MAX5052/MAX5053 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (UVLO = +1.4V, VFB = +1V, VCOMP = floating, VCS = 0V, TA = +25°C, unless otherwise noted.) 21.55 10.1 MAX5052 VIN FALLING UVLO/EN WAKE-UP THRESHOLD vs. TEMPERATURE 1.280 UVLO/EN RISING 1.275 MAX5052 toc03 MAX5052 VIN RISING MAX5052 toc01 21.60 BOOTSTRAP UVLO SHUTDOWN LEVEL vs. TEMPERATURE MAX5052 toc02 BOOTSTRAP UVLO WAKE-UP LEVEL vs. TEMPERATURE 10.0 21.45 UVLO/EN (V) VIN (V) VIN (V) 21.50 9.9 21.40 1.270 1.265 1.260 9.8 21.35 1.255 9.7 -20 0 20 40 60 80 1.250 -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) UVLO/EN SHUTDOWN THRESHOLD vs. TEMPERATURE VIN SUPPLY CURRENT IN UNDERVOLTAGE LOCKOUT vs. TEMPERATURE VIN SUPPLY CURRENT AFTER STARTUP vs. TEMPERATURE UVLO/EN FALLING 52 51 50 1.25 1.5 MAX5052 toc05 1.30 MAX5052 toc04 -40 VIN = 19V MAX5052 WHEN IN BOOTSTRAP UVLO MAX5053 WHEN UVLO/EN IS LOW VIN = 24V MAX5052 toc06 21.30 1.4 1.20 48 IIN (mA) ISTART (µA) UVLO/EN (V) 49 47 1.3 46 45 1.15 1.2 44 43 -20 0 20 40 60 80 0 20 40 60 -20 0 20 40 60 VCC REGULATOR SET POINT vs. TEMPERATURE CURRENT-LIMIT TRIP THRESHOLD vs. TEMPERATURE VIN = 10.8V 8.8 8.7 10mA LOAD VCC (V) 9.5 8.5 8.4 9.4 20mA LOAD 8.3 NDRV OUTPUT IS SWITCHING 9.3 8.2 8.1 9.2 -20 0 20 40 TEMPERATURE (°C) 60 80 310 CURRENT-LIMIT TRIP THRESHOLD (mV) MAX5052 toc07 8.9 MAX5052 toc08 VCC REGULATOR SET POINT vs. TEMPERATURE 8.6 -40 -40 80 TEMPERATURE (°C) NDRV OUTPUT IS NOT SWITCHING, VFB = 1.5V 9.6 -20 TEMPERATURE (°C) VIN = 19V NO LOAD 9.7 -40 TEMPERATURE (°C) 9.8 4 1.1 42 -40 TOTAL NUMBER OF DEVICES = 100 +3σ 305 80 300 295 MEAN 290 285 280 -3σ 275 270 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -40 -20 0 20 40 TEMPERATURE (°C) _______________________________________________________________________________________ 60 80 MAX5052 toc09 1.10 VCC (V) MAX5052/MAX5053 Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies SWITCHING FREQUENCY vs. TEMPERATURE 15 10 5 260 255 250 -3σ 270 280 290 300 310 10 -20 0 20 40 60 80 230 240 250 260 270 280 SWITCHING FREQUENCY (kHz) PROPAGATION DELAY FROM CURRENT-LIMIT COMPARATOR INPUT TO NDRV vs. TEMPERATURE UVLO/EN PROPAGATION DELAY vs. TEMPERATURE REFERENCE VOLTAGE vs. TEMPERATURE 60 55 50 -20 0 20 40 60 80 VIN = 12V 1.229 1.228 1.227 1.226 UVLO/EN FALLING 1.225 -40 -20 0 20 40 60 -40 80 -20 0 20 40 60 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) INPUT CURRENT vs. INPUT CLAMP VOLTAGE INPUT CLAMP VOLTAGE vs. TEMPERATURE NDRV OUTPUT IMPEDANCE vs. TEMPERATURE 9 INPUT CLAMP VOLTAGE (V) 8 7 6 5 4 IIN = 2mA 26.8 26.6 2.2 2.1 1.9 26.2 1.8 1.7 25.8 1.6 25.6 1.5 2 25.4 1.4 1 25.2 1.3 0 25.0 3 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0 INPUT VOLTAGE (V) VIN = 24V SINKING 100mA 2.0 26.4 26.0 80 MAX5052 toc18 27.0 MAX5052 toc16 10 RON (Ω) -40 UVLO/EN RISING REFERENCE VOLTAGE (V) 65 1.230 MAX5052 toc14 MAX5052 toc13 70 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 290 MAX5052 toc15 TEMPERATURE (°C) UNDERVOLTAGE LOCKOUT DELAY (µs) CURRENT-LIMIT TRIP THRESHOLD (mV) 75 MAX5052 toc12 15 0 -40 320 20 5 240 260 tPWM (ns) MEAN 245 0 INPUT CURRENT (mA) 265 TOTAL NUMBER OF DEVICES = 200 25 PERCENTAGE OF UNITS (%) 20 270 MAX5052 toc17 PERCENTAGE OF UNITS (%) 25 TOTAL NUMBER OF DEVICES = 100 +3σ 275 SWITCHING FREQUENCY 30 MAX5052 toc11 TOTAL NUMBER OF DEVICES = 200 280 SWITCHING FREQUENCY (kHz) 30 MAX5052 toc10 CURRENT-LIMIT TRIP THRESHOLD 1.2 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX5052/MAX5053 Typical Operating Characteristics (continued) (UVLO = +1.4V, VFB = +1V, VCOMP = floating, VCS = 0V, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (UVLO = +1.4V, VFB = +1V, VCOMP = floating, VCS = 0V, TA = +25°C, unless otherwise noted.) ERROR AMP OPEN-LOOP GAIN AND PHASE vs. FREQUENCY NDRV OUTPUT IMPEDANCE vs. TEMPERATURE 4.8 4.6 100 30 80 10 GAIN 60 4.4 GAIN (dB) 4.2 4.0 3.8 50 -10 40 -30 20 -50 0 -70 PHASE -20 -90 3.6 -40 -110 3.4 -60 -130 3.2 -80 -150 3.0 -100 -40 -20 0 20 40 60 0.1 80 1 10 100 1k PHASE (DEGREES) VIN = 24V SOURCING 20mA MAX5052 toc20 120 MAX5052 toc19 5.0 RON (Ω) MAX5052/MAX5053 Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies -170 10k 100k 1M 10M 100M FREQUENCY (Hz) TEMPERATURE (°C) Pin Description PIN NAME FUNCTION 1 UVLO/EN Externally Programmable Undervoltage Lockout. UVLO programs the input start voltage. Connect UVLO to GND to disable the device. 2 FB 3 COMP Error-Amplifier Inverting Input Error-Amplifier Output Current-Sense Connection for PWM Regulation and Overcurrent Protection. Connect to high side of sense resistor. An RC filter may be necessary to eliminate leading-edge spikes. 4 CS 5 GND 6 NDRV 7 VCC Gate-Drive Supply. Internally regulated down from VIN. Decouple with a 10nF or larger capacitor to GND. 8 VIN IC Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX5052) connect a startup resistor from the input supply line to VIN. Connect the bias winding supply to this point as well (see the Typical Operating Circuit). For the MAX5053, connect VIN directly to 10.8V to 24V supply. Power-Supply Ground External N-Channel MOSFET Gate Connection Detailed Description The MAX5052/MAX5053 are current-mode PWM controllers that have been specifically designed for use in isolated and nonisolated power-supply applications. A bootstrap UVLO with a large hysteresis (11.9V), very low startup current, and low operating current result in efficient universal-input power supplies. In addition to the internal bootstrap UVLO, these devices also offer programmable input startup voltage programmed through the UVLO/EN pin. This feature is useful in preventing the power supply from entering a brownout condition, in case the input voltage drops below its minimum value. This is important since switching power 6 supplies increases their input supply current as the input voltage drops in order to keep the output power constant. The MAX5052 is well suited for universal input (rectified 85VAC to 265VAC) or telecom (-36VDC to -72VDC) power supplies. The MAX5053 is well suited for low-input-voltage (10.8VDC to 24VDC) power supplies. Power supplies designed with the MAX5052 use a high-value startup resistor, R1, that charges a reservoir capacitor, C1 (see Figure 1). During this initial period, while the voltage is less than the internal bootstrap UVLO threshold, the device typically consumes only 45µA of quiescent current. This low startup current and the large bootstrap UVLO hysteresis helps to minimize _______________________________________________________________________________________ Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies (max). V IN is the value of the input-supply voltage where the power supply must start. T1 VSUPPLY D2 R2 R1 VOUT C4 V − VULR2 R2 = IN × R3 VULR2 Q1 VIN C1 VCC MAX5052 C2 R5 NDRV CS C3 COMP FB R4 GND R6 UVLO/EN R3 0V Figure 1. Nonisolated Power Supply with Programmable InputSupply Start Voltage the power dissipation across R1 even at the high end of the universal AC input voltage (265VAC). The MAX5052/MAX5053 include a cycle-by-cycle current limit that turns off the gate drive to the external MOSFET during an overcurrent condition. When using the MAX5052 in the bootstrapped mode (if the powersupply output is shorted), the tertiary winding voltage drops below the 10V threshold causing the UVLO to turn off the gate drive to the external power MOSFET. This reinitiates a startup sequence with soft-start. MAX5052/MAX5053 Undervoltage Lockout The MAX5052/MAX5053 have an input voltage UVLO/EN pin. The threshold for this UVLO is 1.28V. Before any operation can commence, the voltage on this pin has to exceed 1.28V. The UVLO circuit keeps the CPWM comparator, ILIM comparator, oscillator, and output driver shut down to reduce current consumption (see the Functional Diagram). Use this UVLO function to program the input-supply start voltage. For example, a reasonable start voltage for a 36V to 72V telecom range might be set at 34V. Calculate the divider resistor values, R2 and R3 (see Figure 1) by using the following formulas: R3 ≅ where IUVLO is the UVLO/EN pin input current (50nA), and VULR2 is the UVLO/EN wake-up threshold. VULR2 × VIN 500 × IUVLO ( VIN − VULR2 ) The value of R3 is calculated to minimize the voltagedrop error across R2 as a result of the input bias current of the UVLO/EN pin. VULR2 = 1.28V, IUVLO = 50nA MAX5052 Bootstrap Undervoltage Lockout In addition to the externally programmable UVLO function offered in both the MAX5052 and MAX5053, the MAX5052 has an additional internal bootstrap UVLO that is very useful when designing high-voltage power supplies (see the Functional Diagram). This allows the device to bootstrap itself during initial power-up. The MAX5052 attempts to start when VIN exceeds the bootstrap UVLO threshold of 21.6V. During startup, the UVLO circuit keeps the CPWM comparator, ILIM comparator, oscillator, and output driver shut down to reduce current consumption. Once VIN reaches 21.6V, 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 9.7V, the UVLO circuit will shut down the CPWM comparator, ILIM comparator, oscillator, and output driver returning the MAX5052/MAX5053 to the startup mode. MAX5052 Startup Operation Normally VIN is derived from a tertiary winding of the transformer. However, at startup there is no energy delivered through the transformer, hence, a special bootstrap sequence is required. Figure 2 shows the voltages on VIN and VCC during startup. Initially, both VIN and VCC are 0V. After the line voltage is applied, C1 charges through the startup resistor, R1, to an intermediate voltage. At this point, the internal regulator begins charging C2 (see Figure 1). The MAX5052 uses only 45µA of the current supplied by R1, and the remaining input current charges C1 and C2. The charging of C2 stops when the VCC voltage reaches approximately 9.5V, while the voltage across C1 continues rising until it reaches the wake-up level of 21.6V. Once V IN exceeds the bootstrap UVLO threshold, NDRV begins switching the MOSFET and transfers energy to the secondary and tertiary outputs. If the voltage on the tertiary output builds to higher than 9.9V (the bootstrap UVLO lower threshold), then startup has been accomplished and sustained operation commences. _______________________________________________________________________________________ 7 MAX5052/MAX5053 D1 MAX5052/MAX5053 Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies VCC 2V/div MAX5052 VIN PIN 5V/div where IIN is the MAX5052’s internal supply current after startup (1.4mA), Qgtot is the total gate charge for Q1, fSW is the MAX5052’s switching frequency (262kHz), Vhyst is the bootstrap UVLO hysteresis (12V) and tss is the internal soft-start time (60ms). For example: Ig = (8nC) (262kHz) ≅ 2.1mA 0V C1= 100ms/div Figure 2. VIN and VCC During Startup when Using the MAX5052 in Bootstrapped Mode (Figure 1) If VIN drops below 9.9V before startup is complete, the device goes back to low-current UVLO. In this case, increase the value of C1 in order to store enough energy to allow for the voltage at tertiary winding to build up. Startup Time Considerations For Power Supplies Using the MAX5052 The VIN bypass capacitor, C1, supplies current immediately after wake up (see Figure 1). The size of C1 and the connection configuration of the tertiary winding determine the number of cycles available for startup. Large values of C1 increase the startup time but also supply gate charge for more cycles during initial startup. If the value of C1 is too small, VIN drops below 9.9V because NDRV does not have enough time to switch and build up sufficient voltage across the tertiary output which powers the device. The device goes back into UVLO and does not start. Use a low-leakage capacitor for C1 and C2. As a rule of thumb, offline power supplies keep typical startup times to less than 500ms even in low-line conditions (85VAC input for universal offline or 36VDC for telecom applications). Size the startup resistor, R1, to supply both the maximum startup bias of the device (90µA) and the charging current for C1 and C2. The bypass capacitor, C2, must charge to 9.5V and C1 to 24V, all within the desired time period of 500ms. Because of the internal 60ms soft-start time of the MAX5052, C1 must store enough charge to deliver current to the device for at least this much time. To calculate the approximate amount of capacitance required, use the following formula: Ig = Qgtot × fSW C1 = 8 (IIN + Ig ) (tSS ) Vhyst (1.4m A+ 2.1m A) (6 0m s) =1 7.5µF (1 2V) choose 15µF standard value. Assuming C1 > C2, calculate the value of R1 as follows: V × C1 IC1 = SUVR (500ms) R1 = VIN(MIN) − VSUVR IC1 + ISTART where VIN(MIN) is the minimum input supply voltage for the application (36V for telecom), VSUVR is the bootstrap UVLO wake-up level (23.6V max.), ISTART is the VIN supply current at startup (90µA, max). For example: IC1 = R1 = (24V) (15µF) = 0.72mA (500ms) (36V) − (12V) (0.72mA) + (90µA) = 29.6kΩ choose 32kΩ standard value. Choose a higher value for R1 than the one calculated above if longer startup time can be tolerated in order to minimize power loss on this resistor. The above startup method is applicable to a circuit similar to the one shown in Figure 1. In this circuit, the tertiary winding has the same phase as the output windings. Thus, the voltage on the tertiary winding at any given time is proportional to the output voltage and goes through the same soft-start period as the output voltage. The minimum discharge voltage of C1 from 22V to 10V must be greater than the soft-start time of 60ms. Another method for bootstrapping the power supply is to have a separate bias winding than the one used for regulating the output voltage and to connect the bias winding so that it is in phase with the MOSFET ON time (see Figure 3). The amount of capacitance required is much _______________________________________________________________________________________ Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies T1 +VIN D2 R2 R1 MAX5052/MAX5053 D1 VOUT C4 Q1 VIN U1 NDRV R8 C1 VCC MAX5052 R7 U2 OPTO TRANS COMP R9 CS U2 OPTO LED R4 GND U3 TL431 R5 FB R6 C2 C3 UVLO/EN R10 R3 -VIN Figure 3. Secondary-Side Regulated, Isolated Power Supply smaller. However, in this mode, the input voltage range has to be roughly 2:1. Another consideration is if the bias winding is in phase with the output, then the power supply hiccups and soft-start under output short-circuit conditions. Whereas, this property is lost if the bias winding is in phase with the MOSFET ON time. 1V/div Soft-Start The MAX5052/MAX5053 soft-start feature allows the load voltage to ramp up in a controlled manner, eliminating output voltage overshoot. Soft-start begins after UVLO is deasserted. The voltage applied to the noninverting node of the amplifier ramps from 0 to 1.23V in over a 60ms soft-start timeout period. Figure 4 shows the 5V output of the power-supply circuit in Figure 5 during startup. Note the staircase increase of the output voltage. This is a result of the digital soft-starting technique used. Unlike other devices, the MAX5052/MAX5053 reference voltage to the internal amplifier is soft-started; this method results in superior control of the output voltage under heavy- and light-load conditions. 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 9.5V. 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 offline applications that use the discontinuous flyback topology, this requires a MOSFET rated at 600V. NDRV can source/sink in excess of the 0V 10ms/div Figure 4. Output Voltage Soft-Start During Initial Startup for the Circuit of Figure 5 650mA/1000mA peak current, so select a MOSFET that yields 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 MAX5052A/MAX5053A invert the Q output of the last D flip-flop to provide a duty cycle of 50% (Figure 6). The MAX5052B/MAX5053B perform a logic NAND operation on the Q outputs of both D flip-flops to provide a duty cycle of 75%. _______________________________________________________________________________________ 9 MAX5052/MAX5053 Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies IN FB_P D8 C16 15µF 35V R6 33kΩ D6 R7 1.2kΩ C12 0.22µF L2 D2 9 VOUT2 (+15V/0.1A) C5 47µF 25V 10 D7* OPEN R12 1.2kΩ T1 5 4 8 C15 1µF D5 SGND +VIN +VIN 3 C1 1µF 100V C2 1µF 100V C10* OPEN R8* OPEN 6 D3* OPEN R1 22.6kΩ 1% VOUT1 (+5V/1.5A) L1 C3 68µF 6.3V 2 1 FB_P D1 7 D4 C13 1µF C4 22µF 6.3V SGND C6 0.0047µF 250VAC IN 2 R2 2.49kΩ 1% 3 COMP C14 0.022µF +VIN VIN C11 0.22µF C9 2200pF R9 4.3kΩ R3 1MΩ 1% 7 C7 0.22µF R4 42.2kΩ 1% NDRV U1 UVLO/EN R10 0Ω VCC CS 4 C8 OPEN GND 56 5 78 N1 4 6 MAX5052A 1 -VIN FB 8 12 3 R11 100Ω R5 0.17Ω 1% SHDN *COMPONENTS MARKED "OPEN" ARE OPTIONAL. (SEE MAX5052A EV KIT DATA SHEET.) JU1 Figure 5. Primary Regulated, Dual-Output, Isolated Telecom Power Supply D OSCILLATOR 1.048MHz Q D Q 262kHz WITH 50% (MAX5052A/MAX5053A) Q Q 262kHz WITH 75% (MAX5052B/MAX5053B) Figure 6. Internal Oscillator Internal Error Amplifier The MAX5052/MAX5053 include an internal error amplifier that can be used to regulate the output voltage in the case of a nonisolated power supply (see Figure 1) Calculate the output voltage using the following equation: R5 VOUT = 1 + VREF R6 10 where VREF = 1.23V. The amplifier’s noninverting input is internally connected to a digital soft-start circuit that gradually increases the reference voltage during startup and is applied to this pin. This forces the output voltage to come up in an orderly and well-defined manner under all load conditions. The error amplifier may also be used to regulate the tertiary winding output which implements a primary-side regulated, isolated power supply (see Figure 5). Calculate the output voltage using the following equation: VOUT1 = NS NT R1 VREF + VD6 1 + R2 − VD1 where NS is the number of secondary turns for VOUT1, NT is the number of tertiary winding turns, and both VD6 and VD1 are the diode drops at the respective outputs. ______________________________________________________________________________________ Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies 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 µMAX package have been placed to allow easy interfacing to the external MOSFET. For universal AC input design, all applicable safety regulations must be followed. Offline power supplies may require UL, VDE, and other similar agency approvals. These agencies can be contacted for the latest layout and component rules. 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. 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. 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) quickly terminates the current ON-cycle, typically within 60ns. In most cases, a small RC filter is required to filter out the leading-edge spike on the sense waveform. Set the corner frequency at a few megahertz. Applications Information Primary Regulated, Isolated Telecom Power Supply Figure 5 shows a complete design of a dual-output power supply with a telecom voltage range of 36V to 72V. An important aspect of this power supply is its primary-side regulation. This regulation, through the tertiary winding, also acts as bias winding for the MAX5052. In the circuit of Figure 5, cross-regulation has been improved (tertiary and 5V outputs) by using chip inductors, L1 and L2, and R7||R2. R7||R2 presents enough loading on the tertiary winding output to allow ±5% load regulation on the 5V output over a load current range from 150mA to 1.5A. 5V OUTPUT LOAD REGULATION Chip Information TRANSISTOR COUNT: 1449 PROCESS: BiCMOS L1 D1 12V 15V 6.0 5.8 R2 5.4 VOUT (V) C4 Q1 5.6 VIN 5.2 C1 5.0 VCC MAX5053 C2 4.8 R5 NDRV CS C3 COMP R1 GND R6 4.6 FB 4.4 4.2 UVLO/EN R3 4.0 0.15 0.35 0.55 0.75 0.95 1.15 1.35 0V IOUT (A) Figure 7. Output Voltage Regulation for the Figure 5 Circuit Figure 8. 12V to 15V Out Boost Regulator ______________________________________________________________________________________ 11 MAX5052/MAX5053 Current Limit The current-sense resistor (RCS), connected between the source of the MOSFET and ground, sets the current limit. The CS input has a voltage-trip level (V CS) of 291mV. Use the following equation to calculate the value of RCS: V RCS = CS IPRI MAX5052/MAX5053 Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies Functional Diagram VIN VCC VCC IN VIN CLAMP 26.1V REGULATOR BOOTSTRAP UVLO VL ** REFERENCE 1.23V DIGITAL SOFT-START REG_OK 21.6V 9.74V (INTERNAL 5.25V SUPPLY) UVLO UVLO 1.28V 1.23V COMP DRIVER S Q FB NDRV R ERROR AMP CPWM OSCILLATOR 262kHz* CS 1.4V VOPWM GND THERMAL SHUTDOWN VCS 0.3V MAX5052/MAX5053 *MAX5052A/MAX5053A: 50% MAXIMUM DUTY CYCLE, MAX5052B/MAX5053B: 75% MAXIMUM DUTY CYCLE. **MAX5052 ONLY. ILIM Typical Operating Circuit D1 T1 VSUPPLY C4 R1 R2 D4 Q1 VIN C1 FB R6 CS C3 COMP VOUT BOOTSTRAP UVLO STARTUP VOLTAGE MAX5052A Yes 22V 50% MAX5052B Yes 22 V 75% MAX5053A No 10.8V* 50% MAX5053B No 10.8V* 75% R4 GND *The MAX5053 does not have an internal bootstrap UVLO. The MAX5053 starts operation as long as the VCC pin is higher than 7V (the guaranteed output with a VIN pin voltage of 10.8V) and the UVLO/EN pin is high. UVLO/EN R3 0V 12 MAX DUTY CYCLE NDRV VCC MAX5052 C2 R5 PART D2 R7 C5 Selector Guide ______________________________________________________________________________________ Current-Mode PWM Controllers with an Error Amplifier for Isolated/Nonisolated Power Supplies E ÿ 0.50±0.1 8 INCHES DIM A A1 A2 b H c D e E H 0.6±0.1 1 L 1 α 0.6±0.1 S BOTTOM VIEW D MIN 0.002 0.030 MAX 0.043 0.006 0.037 0.014 0.010 0.007 0.005 0.120 0.116 0.0256 BSC 0.120 0.116 0.198 0.188 0.026 0.016 6∞ 0∞ 0.0207 BSC 8LUMAXD.EPS 4X S 8 MILLIMETERS MAX MIN 0.05 0.75 1.10 0.15 0.95 0.25 0.36 0.13 0.18 2.95 3.05 0.65 BSC 2.95 3.05 4.78 5.03 0.41 0.66 0∞ 6∞ 0.5250 BSC TOP VIEW A1 A2 e A c b α L SIDE VIEW FRONT VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 8L uMAX/uSOP APPROVAL DOCUMENT CONTROL NO. 21-0036 REV. J 1 1 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 ____________________ 13 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX5052/MAX5053 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)