19-3957; Rev 0; 1/06 Current-Mode PWM Controllers with Programmable Switching Frequency The MAX15000/MAX15001 current-mode PWM controllers contain all the control circuitry required for the design of wide-input-voltage isolated and nonisolated power supplies. The MAX15000 is well suited for universal input (rectified 85VAC to 265VAC) or telecom (-36VDC to -72VDC) power supplies. The MAX15001 is well suited for low input voltage (9.5VDC to 24VDC) power supplies. The MAX15000/MAX15001 contain an internal error amplifier that regulates the tertiary winding output voltage which is used in primary-side-regulated isolated power supplies. Primary-side regulation eliminates 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. An open-drain UVLO flag output, with 210µs internal delay, allows the sequencing of a secondary-side controller. The input-supply start voltage is externally programmable with a voltage-divider. A UVLO/EN input is used to shutdown the MAX15000/ MAX15001. Internal digital soft-start eliminates output voltage overshoot. The MAX15000 has an internal bootstrap UVLO with large hysteresis that requires a minimum 23.6V for startup. The MAX15001 does not have the internal bootstrap UVLO and can be biased directly from a minimum voltage of 9.5V. The switching frequency for the MAX15000/MAX15001 is programmable with an external resistor. The MAX15000A/ MAX15001A provide a 50% maximum duty-cycle limit, while the MAX15000B/MAX15001B provide a 75% maximum duty-cycle limit. These devices are available in 10pin µMAX® packages and are rated for operation over the -40°C to +85°C temperature range. Applications 1/2, 1/4, and 1/8th Brick Power Modules Features ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ Current-Mode Control Programmable Switching Frequency Up to 625kHz Accurate UVLO Threshold (1%) Open-Drain UVLO Flag Output with Internal Delay 36V to 72V Telecom Voltage Range Universal Offline Input Voltage Range Rectified 85VAC to 265VAC (MAX15000) 9.5V to 24V Input (MAX15001) Digital Soft-Start Internal Bootstrap UVLO with Large Hysteresis (MAX15000) Internal Error Amplifier with 1.5% Accurate Reference 50µA (typ) Startup Supply Current 50% Maximum Duty-Cycle Limit (MAX15000A/MAX15001A) 75% Maximum Duty-Cycle Limit (MAX15000B/MAX15001B) 60ns Cycle-by-Cycle Current-Limit Propagation Delay Available in Tiny 10-Pin µMAX Packages Ordering Information PINPACKAGE PKG CODE MAX15000AEUB+ -40°C to +85°C 10 µMAX U10-2 MAX15000BEUB+ -40°C to +85°C 10 µMAX U10-2 MAX15001AEUB+ -40°C to +85°C 10 µMAX U10-2 MAX15001BEUB+ 10 µMAX U10-2 PART TEMP RANGE -40°C to +85°C Warning: The MAX15000/MAX15001 are designed to work with high voltages. Exercise caution. +Denotes lead-free package. Pin Configuration High-Efficiency, Isolated Telecom Power Supplies Networking/Servers Isolated Keep-Alive Power Supplies 12V Boost and SEPIC Regulators Isolated and Nonisolated High-Brightness LED Power Supplies Industrial Power Conversion Selector Guide appears at end of data sheet. µMAX is a registered trademark of Maxim Integrated Products, Inc. TOP VIEW 10 IN UVLO/EN 1 UFLG 2 MAX15000 MAX15001 9 VCC 8 NDRV FB 3 COMP 4 7 GND CS 5 6 RT 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 MAX15000/MAX15001 General Description MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency ABSOLUTE MAXIMUM RATINGS IN to GND ...............................................................-0.3V to +30V IN Clamp (Internal Shunt) Current ........................................5mA VCC to GND ............................................................-0.3V to +13V FB, COMP, UVLO/EN, RT, CS to GND .....................-0.3V to +6V UFLG to GND .........................................................-0.3V to +30V NDRV to GND ............................................-0.3V to (VCC + 0.3V) Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ........444.4mW 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 MAX15000, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ (MAX1500_A), R12 = 7.5kΩ (MAX1500_B), R15 = 1kΩ, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 19.68 21.6 23.60 V UVLO/STARTUP Bootstrap UVLO Wake-Up Level VSUVR VIN rising (MAX15000 only) Bootstrap UVLO Shutdown Level VSUVF VIN falling (MAX15000 only) 9.05 9.74 10.43 V UVLO/EN Wake-Up Threshold VULR2 UVLO/EN rising 1.218 1.23 1.242 V UVLO/EN Shutdown Threshold VULF2 UVLO/EN falling 1.14 1.17 1.20 V UVLO/EN Input Current IUVLO VUVLO/EN ≤ 2V -50 UVLO/EN Hysteresis IN Supply Current In UVLO IN Input Voltage Range ISTART VIN Bootstrap UVLO Propagation Delay UFLG Low Output Voltage VIN = 19V, MAX15000 only when in bootstrap UVLO MAX15001 only 50 9.5 UVLO/EN steps up from 1V to 1.4V UVLO/EN to UFLG Propagation Delay (Figure 3) UVLO/EN to NDRV Propagation Delay (Figure 3) +50 60 µA 24.0 V µs 0.6 tEXTR UVLO/EN steps up from 1V to 1.4V tEXTF UVLO/EN steps down from 1.4V to 1V tBUVR VIN steps up from 9V to 24V (MAX15000 only) 5 tBUVF VIN steps down from 24V to 9V (MAX15000 only) 1 VUFLG IUFLG = 5mA sinking UFLG High Output Leakage Current 90 3 UVLO/EN steps down from 1.4V to 1V 150 nA mV 3 10 ms 210 300 µs µs VUFLG = 25V 0.1 0.8 V 1 µA 10.5 V INTERNAL SUPPLY VCC Regulator Set Point IN Supply Current After Startup Shutdown Supply Current 2 VCCSP IIN VIN = 10.8V to 24V, sinking 1µA to 20mA from VCC 7.0 VIN = 24V 2 4 mA UVLO/EN = low 50 90 µA _______________________________________________________________________________________ Current-Mode PWM Controllers with Programmable Switching Frequency (VIN = +12V (for MAX15000, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ (MAX1500_A), R12 = 7.5kΩ (MAX1500_B), R15 = 1kΩ, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS GATE DRIVER Driver Output Impedance RON(LOW) Measured at NDRV sinking 100mA 2 4 RON(HIGH) Measured at NDRV sourcing 20mA 4 10 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 VPWM ICS tPWM VCOMP - VCS VCS = 0V 1.24 1.38 -4 Change in VCS = 0.1V 1.54 V +4 µA 60 ns CURRENT-LIMIT COMPARATOR Current-Limit Trip Threshold VCS CS Input Bias Current ICS Propagation Delay From Comparator Input to NDRV 900 VCS = 0V tPDCS 100mV overdrive VINC 2mA sink current (Note 2) 1000 -4 1100 mV +4 µA 60 ns IN CLAMP VOLTAGE IN Clamp Voltage 24.1 26.1 29.0 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 degrees ±1 mV FB Input Offset Voltage COMP High Voltage ICOMP = 0 COMP Low Voltage ICOMP = 0 2.8 1.1 V Source Current 0.5 mA Sink Current 0.5 mA Reference Voltage VREF (Note 3) 1.230 V Reference Voltage Accuracy -1.5 +1.5 % FB Input Bias Current -50 +50 nA COMP Short-Circuit Current 8 mA 1984 NDRV cycles 5.6 ms 31 steps 39.67 mV DIGITAL SOFT-START Soft-Start Duration tSS fSW = 350kHz Reference Voltage Steps During Soft-Start Reference Voltage Step _______________________________________________________________________________________ 3 MAX15000/MAX15001 ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (VIN = +12V (for MAX15000, bring VIN up to 23.6V for startup), 10nF bypass capacitors at IN and VCC, R12 = 15kΩ (MAX1500_A), R12 = 7.5kΩ (MAX1500_B), R15 = 1kΩ, C6 = 100nF (see the Typical Application Circuit), NDRV = open, VUVLO/EN = +1.4V, VFB = +1.0V, COMP = open, VCS = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS kHz OSCILLATOR Oscillator Frequency Range fOSC Oscillator Frequency Accuracy NDRV Switching Frequency (Note 4) fSW Maximum Duty Cycle DMAX 50 2500 fOSC = 200kHz to 800kHz -10 +10 fOSC = 50kHz to 2500kHz -20 +20 MAX1500_A, fSW = fOSC/2 25 625 MAX1500_B, fSW = fOSC/4 12.5 625.0 MAX1500_A 50 MAX1500_B 75 % kHz % Note 1: All devices are 100% tested at TA = +85°C. All limits over temperature are guaranteed by characterization. Note 2: The MAX15000 is intended for use in universal input power supplies. The internal clamp circuit at IN 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 UVLO/EN is low (shutdown mode). Externally limit the maximum current to IN (hence to clamp) to 2mA maximum when UVLO/EN is low. Clamp currents higher than 2mA may result in a clamp voltage higher than 30V, thus exceeding the absolute maximum rating for IN. For the MAX15001, do not exceed the 24V maximum operating voltage of the device. Note 3: VREF is measured with FB connected to COMP (see the Functional Diagram). Note 4: The oscillator in the MAX1500_A is capable of operating up to 2500kHz. However, the NDRV switching frequency is limited to operate up to 625kHz. Thus, the oscillator frequency for MAX1500_A must be limited to 1250kHz (maximum). Typical Operating Characteristics (VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25°C, unless otherwise noted.) 21.7 10.1 VIN (V) 21.6 MAX15000 VIN FALLING 21.5 1.236 UVLO/EN RISING 1.234 UVLO/EN (V) MAX15000 VIN RISING UVLO/EN WAKE-UP THRESHOLD vs. TEMPERATURE MAX15000 toc02 10.3 MAX15000 toc01 21.8 BOOTSTRAP UVLO SHUTDOWN LEVEL vs. TEMPERATURE 9.9 9.7 MAX15000 toc03 BOOTSTRAP UVLO WAKE-UP LEVEL vs. TEMPERATURE VIN (V) MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency 1.232 1.230 1.228 21.4 21.3 -40 9.5 -15 10 35 TEMPERATURE (°C) 4 60 85 9.3 -40 1.226 -15 10 35 TEMPERATURE (°C) 60 85 1.224 -40 -15 10 35 TEMPERATURE (°C) _______________________________________________________________________________________ 60 85 Current-Mode PWM Controllers with Programmable Switching Frequency 1.175 2.0 MAX15000 toc05 UVLO/EN FALLING VIN SUPPLY CURRENT AFTER STARTUP vs. TEMPERATURE 65 MAX15000 toc04 1.180 VIN SUPPLY CURRENT IN UVLO vs. TEMPERATURE VIN = 19V MAX15000 WHEN IN BOOTSTRAP UVLO VIN = 24V fSW = 350kHz 1.9 60 1.165 IIN (mA) 1.170 ISTART (µA) VUVLO/EN (V) MAX15000 toc06 UVLO/EN SHUTDOWN THRESHOLD vs. TEMPERATURE 55 1.8 1.7 1.160 50 1.6 1.155 -15 10 35 60 45 -40 85 -15 10 35 60 -15 10 35 60 85 TEMPERATURE (°C) TEMPERATURE (°C) VCC REGULATOR SET POINT vs. TEMPERATURE VCC REGULATOR SET POINT vs. TEMPERATURE CURRENT-LIMIT TRIP THRESHOLD vs. TEMPERATURE VIN = 19V 8.8 8.7 9.6 10mA LOAD VCC (V) 8.6 9.4 NDRV SWITCHING fSW = 350kHz 8.5 8.4 20mA LOAD 8.3 9.2 8.2 1.02 MAX15000 toc09 NDRV NOT SWITCHING 8.9 CURRENT-LIMIT TRIP THRESHOLD (V) VIN = 19V MAX15000 toc08 9.8 VCC (V) 1.5 -40 85 TEMPERATURE (°C) MAX15000 toc07 1.150 -40 +3σ 1.01 1.00 MEAN 0.99 0.98 -3σ 0.97 TOTAL NUMBER OF DEVICES = 140 8.1 35 60 -20 0 20 40 60 TEMPERATURE (°C) CURRENT-LIMIT TRIP THRESHOLD SWITCHING FREQUENCY vs. TEMPERATURE 50 40 30 20 -40 10 35 60 85 SWITCHING FREQUENCY +3σ 350 345 MEAN 340 335 -3σ 330 10 -15 TEMPERATURE (°C) MAX15000 toc11 TOTAL NUMBER OF DEVICES = 140 80 355 SWITCHING FREQUENCY (kHz) 60 PERCENTAGE OF UNITS (%) -40 85 TEMPERATURE (°C) 60 TOTAL NUMBER OF DEVICES = 140 50 MAX15000 toc12 10 0.96 PERCENTAGE OF UNITS (%) -15 MAX15000 toc10 9.0 -40 40 30 20 10 TOTAL NUMBER OF DEVICES = 140 0 0.964 325 0.978 0.993 1.007 1.022 1.036 CURRENT-LIMIT TRIP THRESHOLD (V) -40 -15 10 35 TEMPERATURE (°C) 60 85 0 326.7 333.5 340.3 347.2 354.0 360.8 SWITCHING FREQUENCY (kHz) _______________________________________________________________________________________ 5 MAX15000/MAX15001 Typical Operating Characteristics (continued) (VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25°C, unless otherwise noted.) PROPAGATION DELAY FROM CURRENT-LIMIT COMPARATOR INPUT TO NDRV vs. TEMPERATURE MAX15000A 6 MAX15000 toc14 60 MAX15000 toc13 5 UVLO/EN RISING 100 UVLO DELAY (ms) 55 tPDCS (ns) 50 4 3 2 45 206µs 1 40 10 1 10 100 0 -40 1000 UVLO/EN FALLING -15 10 35 85 60 -40 -15 10 35 TEMPERATURE (°C) TEMPERATURE (°C) UVLO/EN TO UFLG PROPAGATION DELAY vs. TEMPERATURE REFERENCE VOLTAGE vs. TEMPERATURE INPUT CURRENT vs. IN VOLTAGE 3 2 UVLO/EN FALLING 1.231 UVLO/EN = 1.4V NDRV SWITCHING AT 350kHz 1.76 INPUT CURRENT (mA) UVLO/EN RISING 1.230 1.229 1.60 1.228 -40 -15 10 35 85 60 -40 -15 TEMPERATURE (°C) 10 35 60 11 12 13 14 15 16 IN VOLTAGE (V) TEMPERATURE (°C) NDRV LOW OUTPUT IMPEDANCE vs. TEMPERATURE 2.4 MAX15000 toc19 27.0 IIN = 2mA 26.6 VIN = 24V SINKING 100mA 2.2 26.4 2.0 26.2 RON (Ω) INPUT CLAMP VOLTAGE (V) 10 85 INPUT CLAMP VOLTAGE vs. TEMPERATURE 26.8 1.68 1.64 1 0 1.72 MAX15000 toc20 4 VIN = 12V REFERENCE VOLTAGE (V) 5 1.80 MAX15000 toc17 1.232 MAX15000 toc16 6 26.0 1.8 25.8 1.6 25.6 25.4 1.4 25.2 25.0 1.2 -40 -20 0 20 40 TEMPERATURE (°C) 6 60 85 60 TIMING RESISTOR (kΩ) MAX15000 toc18 SWITCHING FREQUENCY (kHz) 1000 UVLO/EN TO NDRV PROPAGATION DELAY vs. TEMPERATURE MAX15000 toc15 SWITCHING FREQUENCY vs. TIMING RESISTOR UVLO DELAY (µs) MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency 80 -40 -15 10 35 60 TEMPERATURE (°C) _______________________________________________________________________________________ 85 17 18 19 Current-Mode PWM Controllers with Programmable Switching Frequency ERROR AMPLIFIER OPEN-LOOP GAIN AND PHASE vs. FREQUENCY SOURCING 20mA 80 40 GAIN 40 4.2 3.8 120 80 60 GAIN (dB) RON (Ω) 4.6 MAX15000 toc22 100 MAX15000 toc21 5.0 20 0 -40 0 -80 PHASE -20 PHASE (DEGREES) NDRV HIGH OUTPUT IMPEDANCE vs. TEMPERATURE -120 3.4 -40 -160 -60 3.0 -40 -15 10 35 60 85 0.1 1 10 100 -200 1k 10k 100k 1M 10M 100M FREQUENCY (Hz) TEMPERATURE (°C) Pin Description PIN 1 2 NAME FUNCTION Externally Programmable Undervoltage Lockout. UVLO/EN programs the input start voltage. Connect UVLO/EN UVLO/EN to GND to disable the device. NDRV stops switching approximately 210µs after the UVLO/EN voltage falls below 1.17V. UFLG Open-Drain Undervoltage Flag Output. UFLG is asserted low as soon as the UVLO/EN voltage falls below its threshold. 3 FB 4 COMP Error-Amplifier Inverting Input 5 CS Current-Sense Input. Current-sense connection for PWM regulation and cycle-by-cycle current limit. Connect to the high side of the sense resistor. An RC filter may be necessary to eliminate leading-edge spikes. Current-limit trip voltage is 1V. 6 RT Oscillator Timing Resistor Input. An RC network may be required to reduce jitter (see the Typical Application Circuit). 7 GND Ground Connection 8 NDRV External n-Channel MOSFET Gate Connection 9 VCC 10 IN Error-Amplifier Output Gate-Drive Supply. Internally generated supply from IN. Decouple VCC with a 10nF or larger capacitor to GND. IN Supply. Decouple with a 10nF or larger capacitor to GND. For bootstrapped operation (MAX15000), connect a startup resistor from the input supply line to IN. Connect the bias winding supply to IN also (see the Typical Operating Circuit). For the MAX15001, connect IN directly to the 9.5V to 24V supply. _______________________________________________________________________________________ 7 MAX15000/MAX15001 Typical Operating Characteristics (continued) (VUVLO/EN = +1.4V, VFB = +1V, COMP = open, VCS = 0V, TA = +25°C, unless otherwise noted.) MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency Characteristics table). The input is clamped when the devices are started with a bleed resistor (R1 in Figure 1) from a high input voltage and the UVLO/EN input is low. The clamp can safely sink up to 2mA current. Power supplies designed with the MAX15000 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 50µA of quiescent current. This low startup current and the large bootstrap UVLO hysteresis help to minimize the power dissipation across R1 even at the high end of the universal AC input voltage (265VAC). The MAX15000/MAX15001 include a cycle-by-cycle current limit that turns off the gate drive to the external MOSFET whenever the internally set threshold of 1V is exceeded. When using the MAX15000 in the bootstrapped mode, if the power-supply output is shorted, the tertiary winding voltage will drop below the internally set threshold causing the UVLO to turn off the gate drive to the external power MOSFET. This will reinitiate a startup sequence with soft-start. Detailed Description The MAX15000/MAX15001 current-mode PWM controllers are ideal for isolated and nonisolated powersupply applications. The devices offer an accurate input startup voltage programmable through the UVLO/EN input. This feature prevents the power supply from entering a brownout condition in case the input voltage sags below its minimum value. This is important since switching power supplies increases their input supply current as the input voltage drops to keep the output power constant. In addition to this externally adjustable UVLO feature, the MAX15000 also offers a bootstrap UVLO with a large hysteresis (11.9V) and very low startup and operating current, which result in an efficient universal input power supply. The switching frequency of the MAX15000/MAX15001 is programmable with an external resistor. The MAX15000 is well suited for universal input (rectified 85VAC to 265VAC) or telecom (-36VDC to -72VDC) power supplies. The MAX15001 is well suited for low-input voltage (9.5VDC to 24VDC) power supplies. The devices include an internal clamp at IN to prevent the input voltage from exceeding the absolute maximum rating (see Note 2 at the end of the Electrical D2 T1 D1 VSUPPLY VOUT R1 R2 UVLO/EN UFLG FB C2 COMP C5 R11 R3 CS 1 2 10 MAX15000 3 9 8 4 7 5 6 IN R13 VCC NDRV Q1 C4 GND RT R14 C6 C2 R15 C1 R4 R12 0V Figure 1. Nonisolated Power Supply with Programmable Input-Supply Start Voltage 8 _______________________________________________________________________________________ Current-Mode PWM Controllers with Programmable Switching Frequency MAX15000 Bootstrap UVLO In addition to the externally programmable UVLO function offered in both the MAX15000 and MAX15001, the MAX15000 includes an 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 MAX15000 attempts to start when V IN 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 the CPWM and ILIM comparators, the oscillator, and allows the output driver to switch. If VIN drops below 1.17V, the UVLO circuit shuts down the CPWM comparator, ILIM comparator, oscillator, and output driver returning the MAX15000 to the low-current startup mode. Undervoltage Lockout The MAX15000/MAX15001 provide a UVLO/EN input. The threshold for UVLO is 1.23V with 60mV hysteresis. Before any operation can commence, the voltage on UVLO/EN has to exceed 1.23V. 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/EN input to program the input-supply start voltage. For example, a reasonable start voltage for a 36V to 72V telecom range is usually 34V. Calculate the resistor-divider values, R2 and R3 (see Figure 1) by using the following formulas: R3 ≅ VULR2 VIN 500 IUVLO (VIN − VULR2 ) V −V R2 = IN ULR2 R 3 VULR2 where IUVLO is the UVLO/EN input current (50nA max), and VULR2 is the UVLO/EN wake-up threshold (1.23V). VIN is the value of the input-supply voltage where the power supply must start. The value of R3 is calculated to minimize the voltage-drop error across R2 as a result of the input bias current of the UVLO/EN input. Startup Operation The MAX15001 starts up when the voltage at IN exceeds 9.5V and the UVLO/EN input is greater than 1.23V. However, the MAX15000 requires that, in addition to meeting the specified startup conditions for the MAX15001, the voltage at IN exceeds the bootstrap UVLO threshold of 21.6V. For the MAX15000, the voltage at IN is normally derived from a tertiary winding of the transformer. However, at startup there is no energy being delivered through the transformer, hence, a special bootstrap sequence is required. Figure 2 shows the voltages at IN 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). Only 50µA of the current supplied through R1 is used by the MAX15000, 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 VIN 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 9.74V (the bootstrap UVLO lower _______________________________________________________________________________________ 9 MAX15000/MAX15001 Current-Mode Control Loop The advantages of current-mode control over voltagemode control are twofold. First, there is the feed-forward characteristic brought on by the controller’s ability to adjust for variations in the input voltage on a cycle-by-cycle basis. Secondly, the stability requirements of the current-mode controller are reduced to that of a single-pole system unlike the double pole in voltage-mode control. The MAX15000/MAX15001 use a current-mode control loop where the output of the error amplifier (COMP) is compared to the current-sense voltage at CS. When the current-sense signal is lower than the noninverting input of the PWM comparator, the output of the CPWM comparator is low and the switch is turned on at each clock pulse. When the current-sense signal is higher than the inverting input of the CPWM, the output of the CPWM comparator goes high and the switch is turned off. MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency threshold), then startup has been accomplished and sustained operation will commence. If VIN drops below 9.74V before startup is complete, the device goes back to low-current UVLO. In this case, increase the value of C1 to store enough energy to allow for the voltage at the tertiary winding to build up. UVLO Flag (UFLG) The MAX15000/MAX15001 have an open-drain undervoltage flag output (UFLG). When used with an optocoupler the UFLG output can serve to sequence a secondary-side controller. An internal 210µs delay occurs the instant the voltage on UVLO/EN drops below 1.17V until NDRV stops switching. This allows for the UFLG output to change state before the MAX15000/ MAX15001 shut down (Figure 3). When the voltage at the UVLO/EN is above the threshold, UFLG is high impedance. When UVLO/EN is below the threshold, UFLG goes low. UFLG is not affected by bootstrap UVLO (MAX15000). MAX15000 fig02 Soft-Start VCC 2V/div VIN 5V/div 0V 100ms/div The MAX15000/MAX15001 soft-start feature allows the output voltage to ramp up in a controlled manner, eliminating voltage overshoot. The MAX15000/MAX15001 reference generator that is internally connected to the error amplifier soft-starts to achieve superior control of the output voltage under heavy and light load conditions. Soft-start begins after UVLO is deasserted (VIN is above 21.6V for the MAX15000, VIN is above 9.5V for the MAX15001, and the voltage on UVLO/EN is above 1.23V). The voltage applied to the noninverting node of the amplifier ramps from 0 to 1.23V in 1984 NDRV switching cycles. Use the following formula to calculate the soft-start time (tSS): t SS = Figure 2. VIN and VCC During Startup When Using the MAX15000 in Bootstrapped Mode (Figure 1) 1984 fNDRV where fNDRV is the switching frequency at the NDRV output. Figure 4 shows the soft-start regulated output of a power supply using the MAX15000 during startup. 1.23V (±1%) 1.17V (typ) VUVLO/EN Hi-Z VUFLG LOW 3µs VNDRV 0.6µs LOW NDRV SWITCHING SHUTDOWN SHUTDOWN tEXTR 3ms tEXTF 210µs Figure 3. UVLO/EN and UFLG Operation Timing 10 ______________________________________________________________________________________ Current-Mode PWM Controllers with Programmable Switching Frequency Oscillator/Switching Frequency Use an external resistor at RT to program the MAX15000/MAX15001 internal oscillator frequency between 50kHz and 2.5MHz. The MAX15000A/ MAX15001A output switching frequency is one-half of the programmed oscillator frequency with a 50% duty cycle. The MAX15000B/MAX15001B output switching frequency is one-quarter of the programmed oscillator frequency with a 75% duty cycle. The MAX15000A/MAX15001A and MAX15000B/ MAX15001B have programmable output switching frequencies from 25kHz to 625kHz and 12.5kHz to 625kHz, respectively. Use the following formulas to determine the appropriate value of the resistor R12 (see Figure 1) needed to generate the desired output switching frequency (fSW) at the NDRV output: R12 = 1010 for the MAX15000A / MAX15001A. 2fSW R12 = 1010 for the MAX15000B / MAX15001B. 4fSW where R12 is the resistor connected from RT to GND (see Figure 1). Connect an RC network in parallel with R12 as shown in Figure 1. The RC network should consist of a 100nF capacitor C6 (for stability) in series with resistor R15 which serves to further minimize jitter. Use the following formula to determine the value of R15: 1 R15 = 88.9 × (R12) 4 For example, if R12 is 4kΩ, R15 becomes 707Ω. MAX15000 fig04 VOUT 2V/div 100mA LOAD ON/VOUT1 100mA LOAD ON/VOUT2 2ms/div Figure 4. Primary-Side Output Voltage Soft-Start During Initial Startup for the Circuit in Figure 6 Internal Error Amplifier The MAX15000/MAX15001 include an internal error amplifier to regulate the output voltage in the case of a nonisolated power supply (see Figure 1). For the circuit in Figure 1, calculate the output voltage using the following equation: R13 VOUT = 1+ V R14 REF 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 applied to this input. 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-sideregulated, isolated power supply (see Figure 6). For the circuit in Figure 6, calculate the output voltage using the following equation: N R1 VOUT = S 1+ VREF + VD6 − VD2 NT R2 where NS is the number of secondary winding turns, NT is the number of tertiary winding turns, and both V D6 and VD2 are the diode drops at the respective outputs. ______________________________________________________________________________________ 11 MAX15000/MAX15001 n-Channel MOSFET Switch Driver The NDRV output drives an external n-channel MOSFET. The internal regulator output (VCC), set to approximately 9V, drives NDRV. For the universal input voltage range, the MOSFET used must withstand the DC level of the high-line input voltage plus the reflected voltage at the primary of the transformer. Most applications that use the discontinuous flyback topology require a MOSFET rated at 600V. NDRV can source/sink in excess of 650/1000mA peak current; therefore, select a MOSFET that will yield acceptable conduction and switching losses. MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency Current Limit The current-sense resistor (R4 in Figure 1), connected between the source of the MOSFET and ground, sets the current limit. The current-limit comparator has a voltage trip level (VCS) of 1V. Use the following equation to calculate the value of R4: when fSW = 350kHz), 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 = V R4 = CS IPRI where IPRI is the peak current in the primary side of the transformer which also 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) terminates the current on-cycle within 60ns (typ). Use a small RC network to filter out the leading-edge spikes on the sensed waveform when needed. Set the corner frequency between 2MHz and 10MHz. Applications Information Startup Time Considerations for Power Supplies Using the MAX15000 The bypass capacitor at IN, C1, supplies current immediately after the MAX15000 wakes 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 9.74V 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. Typically, offline power supplies keep 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 soft-start time of the MAX15000 (approximately 5.6ms 12 (IIN + Ig )(t SS ) VHYST where IIN is the MAX15000’s internal supply current (2mA) after startup, Qgtot is the total gate charge for Q1, f SW is the MAX15000’s switching frequency (350kHz), V HYST is the bootstrap UVLO hysteresis (approximately 12V) and tSS is the internal soft-start time (5.6ms). Example: Ig = (8nC) (350kHz) ≅ 2.8mA C1 = (2mA + 2.8mA)(5.6ms) = 2.24µF 12V Choose a 2.2µF standard value (assuming 350kHz switching frequency). Assuming C1 > C2, calculate the value of R1 as follows: V C1 IC1 = SUVR (500ms) VIN(MIN) − VSUVR R1 ≅ 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 IN supply current at startup (90µA max). For example: (24V)(2.2µF) = 0.105mA (500ms) (36V) − (12V) R1 ≅ = 123.07kΩ (0.105mA) + (90µA) IC1 = Choose a 120kΩ standard value. ______________________________________________________________________________________ Current-Mode PWM Controllers with Programmable Switching Frequency Another method for bootstrapping the power supply is to use a bias winding that is in phase with the MOSFET on-time (see Figure 5). In this case, the amount of capacitance required at IN (C1) is much smaller. However, the input voltage cannot have a range greater than approximately 2:1 (primary winding voltage to bias winding voltage ratio). For hiccup-mode fault protection, make the bias winding in phase with the output, then the power-supply hiccups and soft-starts under output short-circuit conditions. The power supply does not hiccup if the bias winding is in phase with the MOSFET on-time. D1 T1 D2 VOUT VIN C4 R1 R2 UFLG R8 IN U2 OPTO TRANS. VCC MAX15000A R9 Q1 NDRV U1 U2 OPTO LED CS C3 R7 C1 GND COMP U3 TL431 R5 FB UVLO/EN RT R4 R10 C6 R6 C2 R3 R12 R15 Figure 5. Secondary-Side Regulated, Isolated Power Supply ______________________________________________________________________________________ 13 MAX15000/MAX15001 Choose a higher value for R1 than the one calculated in the previous equation if a longer startup time can be tolerated 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 time of C1 from 21.6V to 9.74V must be greater than the soft-start time of 5.6ms. FB_P IN D8 C16 1µF 35V R6 33kΩ 36V TO 72V +VIN +VIN D6 C12 15µF 35V R7 1.2kΩ D7 OPEN R12 1.2kΩ 10 12T 15T 4 C15 1µF D5 R8 OPEN 28T 35µH C10 OPEN C3 68µF 6.3V 5T 2 6 1 FB_P L1 D1 7 SGND VOUT1 5V/1.5A C13 1µF D4 C4 22µF SGND 6.3V C6 0.0047µF 250VAC D3 OPEN R1 22.6kΩ 1% 15V/100mA C5 47µF 25V 8 C2 1µF 100V C1 1µF 100V VOUT2 D2 5 T1 9 3 -VIN IN 3 R2 +VIN 2.49kΩ 1% R9 75kΩ 1% R3 1.37MΩ 1% R4 51.1kΩ L2 IN FB 10 C9 100pF 4 1 U1 COMP C14 3900pF NDRV MAX15000A UVLO/EN CS 8 C11 0.22µF R10 4.7Ω R11 100Ω 5 9 C7 0.22µF UFLG SHDN 2 1 R13 10kΩ JU1 2 VCC UFLG GND RT 8 N1 IRF7464 4 1 C8 OPEN C17 OPEN 7 56 2 3 R5 0.600Ω 1% 7 6 R14 14.3kΩ 1% UFLG_PULL R15 750Ω C19 OPEN C18 0.1µF NOTE: MOSFET N1 = IR IRF7464. Figure 6. Primary-Side-Regulated, Dual-Output, Isolated Telecom Power Supply Primary-Side-Regulated, Isolated Telecom Power Supply 5V OUTPUT LOAD REGULATION 5.6 NO LOAD AT 15V OUTPUT VIN+ = 40V VIN- = 0V 5.5 5.4 MAX15000 fig07 Figure 6 shows a complete circuit of a dual-output power supply with a telecom voltage range of 36V to 72V. An important aspect of this power supply is that it is primary-side regulated. The regulation through the tertiary winding also supplies bias for the MAX15000. In the circuit of Figure 6, cross-regulation has been improved (tertiary and 5V outputs) by using chip inductors, L1 and L2, and R7||R12 across C12. R7||R12 presents enough loading on the tertiary winding output to allow ±10% load regulation on the 5V output over a load current range from 150mA to 1.5A (Figure 7). VOUT (V) MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency 5.3 5.2 5.1 5.0 4.9 4.8 0.15 0.30 0.45 0.60 0.75 0.90 1.05 1.20 1.35 1.50 IOUT (A) Figure 7. Output Voltage Regulation for the Circuit in Figure 6 14 ______________________________________________________________________________________ Current-Mode PWM Controllers with Programmable Switching Frequency D1 MAX15000/MAX15001 L1 12V 15V R2 UFLG R5 IN Q1 NDRV VCC MAX15001 CS C4 C3 C1 C2 GND COMP R1 FB UVLO/EN RT R6 C6 R3 R12 R15 0V Figure 8. 12V to 15V Output Boost Regulator Layout Recommendations 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; therefore, minimize the surface area of the heatsink as much as possible. Keep all PC board traces carrying switching currents as short as possible to minimize current loops. Use a ground plane for best results. The pins of the µMAX package are positioned to allow easy interfacing to the external MOSFET. For universal AC input design, follow all applicable safety regulations. Offline power supplies may require UL, VDE, and other similar agency approvals. To avoid noise coupling of signals from RT to NDRV, route traces from RT away from NDRV. ______________________________________________________________________________________ 15 MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency Typical Application Circuit D2 T1 D1 R5 R2 C4 R1 UVLO/EN UFLG FB C2 + COMP 36V TO 72V C5 - R11 R3 CS 1 2 10 MAX15000 9 3 8 4 7 5 6 IN VCC NDRV Q1 GND RT R6 C6 C2 R15 16 R12 C1 R4 ______________________________________________________________________________________ VOUT Current-Mode PWM Controllers with Programmable Switching Frequency IN IN IN CLAMP 26.1V VCC VCC REGULATOR DIGITAL SOFT-START BOOTSTRAP UVLO REFERENCE 1.23V REG_OK * VL (INTERNAL 5.25V SUPPLY) 21.6V 9.74V 210µs DELAY UFLG UVLO UVLO/EN N 1.23V 1.17V COMP DRIVER S FB NDRV Q ERROR AMP R CPWM OSCILLATOR 1.4V CS GND VCS 1V MAX15000 MAX15001 ILIM RT Selector Guide PART BOOTSTRAP STARTUP VOLTAGE (V) UVLO MAX DUTY CYCLE (%) MAX15000A Yes 22 50 MAX15000B Yes 22 75 MAX15001A* No 9.5 50 MAX15001B* No 9.5 75 *MAX15000 ONLY Chip Information PROCESS: BiCMOS *The MAX15001 does not have an internal bootstrap UVLO. The MAX15001 starts operation as long as VIN is higher than 9.5V and UVLO/EN is higher than 1.23V. ______________________________________________________________________________________ 17 MAX15000/MAX15001 Functional Diagram 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.) e 10LUMAX.EPS MAX15000/MAX15001 Current-Mode PWM Controllers with Programmable Switching Frequency 4X S 10 10 INCHES H Ø0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 0.118 E2 0.114 0.199 H 0.187 L 0.0157 0.0275 L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S α 0° 6° MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.00 4.75 5.05 0.40 0.70 0.940 REF 0.177 0.270 0.500 BSC 0.090 0.200 0.498 REF 0° 6° E2 GAGE PLANE A2 c A b A1 α E1 L D1 L1 FRONT VIEW SIDE VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 10L uMAX/uSOP APPROVAL DOCUMENT CONTROL NO. 21-0061 REV. 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. 18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2006 Maxim Integrated Products Heaney Printed USA is a registered trademark of Maxim Integrated Products, Inc.