19-2740; Rev 0; 1/03 KIT ATION EVALU E L B A IL AVA 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining Lossless current sensing in the MAX1960 and MAX1961 is achieved by monitoring the drain-to-source voltage of the low-side external FET. The current limit is scalable to accommodate a wide variety of MOSFETs and load currents. The MAX1962 has 10% accurate sense-resistor-based current limiting. The MAX1960 and MAX1962 have an adjustable output voltage from 0.8V to 4.95V. The MAX1961 and MAX1962 have four preset output voltages (1.5V, 1.8V, 2.5V, and 3.3V) and feature 0.5% voltage accuracy over temperature, line, and load variations. The MAX1960 and MAX1961 also feature voltage-margining control inputs that shift the output voltage up or down by 4% for system testing. Features ♦ 0.5% Accurate Output ♦ Operates from 2.35V to 5.5V Supply ♦ Generates Low Output Voltage Down to 0.8V ♦ ♦ ♦ ♦ On-Chip Charge Pump Provides 5V Gate Drive Ceramic or Electrolytic Capacitors 94% Efficiency External Synchronization from 450kHz to 1.2MHz ♦ ♦ ♦ ♦ 500kHz/1MHz Fixed-Frequency PWM Operation Fast Transient Response Two Converters Can Operate 180° Out-of-Phase ±4% Voltage Margining for System Test ♦ 10% Accurate Current Sensing (MAX1962) ♦ Adaptive Dead Time Prevents Shoot-Through Ordering Information TEMP RANGE PIN-PACKAGE MAX1960EEP PART -40°C to +85°C 20 QSOP MAX1961EEP -40°C to +85°C 20 QSOP MAX1962EEP -40°C to +85°C 20 QSOP Typical Operating Circuit C+ INPUT 2.35V TO 5.5V CAVDD VCC MAX1960 VDD Applications VOLTAGE MARGINING AND ON/OFF ASIC, FPGA, DSP, and CPU Core and I/O Voltages Cellular Base Stations CTL1 BST CTL2 COMP DH REF LX Telecom and Network Equipment OUTPUT 0.8 TO 0.87 ✕ VIN UP TO 20A DL Server and Storage Systems GND PGND ILIM OPTIONAL SYNCHRONIZATION Pin Configurations and Selector Guide appear at the end of the data sheet. CLKOUT 180° OUT-OF-PHASE FSET/SYNC CLKOUT FB ________________________________________________________________ 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 MAX1960/MAX1961/MAX1962 General Description The MAX1960/MAX1961/MAX1962 high-current, highefficiency voltage-mode step-down DC-DC controllers operate from a 2.35V to 5.5V input and generate output voltages down to 0.8V at up to 20A. An on-chip charge pump generates a regulated 5V for MOSFET drive. Additionally, adaptive dead-time drivers allow a wide variety of MOSFETs to be used without risking shoot-through. Fixed-frequency PWM operation and external synchronization make these controllers suitable for telecom and datacom applications. The operating frequency is programmable to either 500kHz or 1MHz, or from 450kHz to 1.2MHz with an external clock. A clock output is provided to synchronize another converter for 180° out-of-phase operation. A high closed-loop bandwidth provides excellent transient response for applications with dynamic loads. MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining ABSOLUTE MAXIMUM RATINGS VCC, CTL_, CS, FSET/SYNC, SEL, EN, OUT to GND ..........................................................-0.3V to +6V ILIM, COMP, REF, FB, CLKOUT, C- to GND ..............................................-0.3V to VAVDD + 0.3V C+ to GND.............-0.3V to higher of VVCC + 1V or VVDD + 0.3V VDD, AVDD to GND ..............-0.3V to higher of VVCC - 0.3V or 6V DL to PGND ................................................-0.3V to VVDD + 0.3V BST to GND ............................................................-0.3V to +12V DH to LX ...................................................................-0.3V to +6V LX to BST..................................................................-6V to +0.3V PGND to GND, or VDD to AVDD ............................-0.3V to +0.3V Continuous Power Dissipation (TA = +70°C) 20-Pin QSOP (derate up to +70°C)..............................727mW 20-Pin QSOP (derate above +70°C) ........................9.1mW/°C Operating Temperature Range (Extended).........-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°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 (VVCC = 3.3V, Circuits of Figures 9–12, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS VCC Input Voltage Range VCC Input Voltage UVLO Rising or falling, hysteresis = 33mV (typ) VDD Input Voltage UVLO Rising or falling, hysteresis = 44mV (typ) Output Voltage MIN TYP UNITS 5.5 V 1.95 2.3 V 3.9 4.45 0.8 MAX1960/MAX1962 (measured at FB) DC Output Accuracy MAX 2.35 SEL = GND MAX1961/ SEL = REF MAX1962 (FB = VDD), SEL not connected measured at output SEL = VDD 0.796 V V 0.800 0.804 1.492 1.500 1.508 1.791 1.800 1.809 2.487 2.500 2.514 V 3.272 3.300 3.336 Positive Voltage-Margining Shift MAX1960/MAX1961 +3.8 +4 +4.2 % Negative Voltage-Margining Shift MAX1960/MAX1961 -3.8 -4 -4.2 % Load Regulation Error 0V to full load 0.08 Line Regulation Error VVCC = 2.7V to 5.5V 0.1 FB Input Bias Current COMP Discharge Resistance 1 In shutdown DC-DC Soft-Start Time Switching Frequency µA 2 3 mS 10 100 1280 450 500 550 FSET/SYNC = VCC 880 1000 1120 450 Maximum Duty Cycle f = 1MHz 80 Maximum Duty Cycle f = 500kHz 90 1200 83 Shutdown Supply Current 2 _______________________________________________________________________________________ kHz kHz % 92 11 Ω cycles FSET/SYNC = GND SYNC Frequency Range Quiescent Supply Current % +0.2 -0.2 Feedback Transconductance % % 15 mA 15 µA 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining (VVCC = 3.3V, Circuits of Figures 9–12, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER VDD Output Voltage Reference Voltage (No Load) Reference Load Regulation MAX UNITS 2.7V ≤ VVCC ≤ 5.5V, ILOAD = 1mA to 50mA CONDITIONS 4.75 MIN 5.25 V 2.35V ≤ VVCC ≤ 2.7V, ILOAD = 1mA to 35mA, C1 = 4.7µF, C6 = 22µF (Note 1) 4.45 5.25 V 2.35V ≤ VVCC ≤ 3.6V with tripler, ILOAD = 1 to 50mA (circuit of Figure 12) (Note 1) 4.75 5.25 V 1.291 V mV 1.269 TYP VOUT = 0.8V 44 1.280 3 53 VOUT = 2.0V 45 50 55 VOUT = 3.3V 38 48 58 38 50 68 mV -50µA to +50µA Positive Current-Limit Threshold (VPGND - VLX) MAX1962 Negative Current-Limit Threshold (VLX - VPGND) MAX1962, VOUT = 0.8V to 3.3V 62 mV CS Bias Current MAX1962, VCS = 3.3V 20 50 µA OUT Bias Current MAX1961/MAX1962, VOUT = 3.3V 30 50 µA Current-Limit Threshold (Positive Direction, Fixed, VPGND - VLX) MAX1960/MAX1961, ILIM = VDD 58 74 90 mV Current-Limit Threshold (Negative Direction, Fixed, VLX - VPGND) MAX1960/MAX1961, ILIM = VDD 50 67 85 mV Current-Limit Threshold (Positive Direction, Adjustable, VPGND - VLX) MAX1960/MAX1961, RILIM = 160kΩ 100 114 135 RILIM = 400kΩ 250 279 306 Current-Limit Threshold (Negative Direction, Adjustable, VLX - VPGND) MAX1960/MAX1961, RILIM = 160kΩ 90 107 125 RILIM = 400kΩ 245 271 296 Thermal-Shutdown Threshold DH Gate-Driver On-Resistance DL Gate-Driver On-Resistance (Pullup) DL Gate-Driver On-Resistance (Pulldown) 15°C hysteresis VBST - VLX = 5V, pulling up or down DL high state DL low state DH falling to DL rising +160 1.8 1.8 0.5 35 3.5 3.5 1.6 Minimum Adaptive Dead Time FSET/SYNC Pulse Width DH rising to DL falling 200 Minimum low time (Note 1) 200 FSET/SYNC Rise/Fall Time (Note 1) CTL_, FSET/SYNC, EN Input High Voltage VVCC = 2.35V to 5.5V CTL_, FSET/SYNC, EN Input Low Voltage VVCC = 2.35V to 5.5V CTL_, FSET/SYNC, EN Input Current Sinking 1mA CLKOUT VOH Sourcing 1mA 100 2.0 CLKOUT Rise/Fall Time CLOAD = 100pF (Note 1) ns V 0.01 VVCC 0.2V °C Ω Ω Ω ns -1 CLKOUT VOL mV ns 26 Minimum high time (Note 1) mV 0.8 V +1 µA 0.1 V VVCC 0.01V V 40 ns _______________________________________________________________________________________ 3 MAX1960/MAX1961/MAX1962 ELECTRICAL CHARACTERISTICS (continued) MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining ELECTRICAL CHARACTERISTICS (VVCC = 3.3V, Circuits of Figures 9–12, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS VCC Input Voltage Range MIN TYP MAX UNITS 2.35 5.50 V VCC Input Voltage UVLO Rising or falling 1.95 2.3 V VDD Input Voltage UVLO Rising or falling 3.90 4.45 V MAX1960/MAX1962 (measured at FB) 0.805 SEL = GND 0.795 1.492 SEL = REF 1.789 1.809 SEL not connected 2.482 2.517 SEL = VDD 3.272 3.339 4.2 Output Voltage DC Output Accuracy 0.8 MAX1961/MAX1962 (FB = VDD), measured at output V 1.508 V Positive Voltage-Margining Shift MAX1960/MAX1961 3.8 Negative Voltage-Margining Shift MAX1960/MAX1961 -3.8 -4.2 % -0.2 +0.2 µA 1 3 µS 100 Ω FSET/SYNC = GND 450 550 FSET/SYNC = VCC 880 1120 450 1200 FB Input Bias Current Feedback Transconductance COMP Discharge Resistance Switching Frequency In shutdown SYNC Frequency Range % kHz kHz Maximum Duty Cycle f = 1MHz 80 % Maximum Duty Cycle f = 500kHz 90 % Quiescent Supply Current 15 mA Shutdown Supply Current 15 µA VDD Output Voltage 2.7V ≤ VVCC ≤ 5.5V, ILOAD = 1mA to 50mA 4.75 5.25 2.35V ≤ VVCC ≤ 2.7V, ILOAD = 1mA to 35mA, C1 = 4.7µF, C6 = 22µF 4.45 5.25 2.35V ≤ VVCC ≤ 3.6V with tripler, ILOAD = 1mA to 50mA (circuit of Figure 12) 4.75 5.25 1.267 1.291 V Reference Voltage (No Load) V Positive Current-Limit Threshold (VCS - VOUT) MAX1962, VOUT = 2V 45 56 mV Negative Current-Limit Threshold (VOUT - VCS) MAX1962, VOUT = 2V 42 64 mV CS Bias Current MAX1962, VCS = 3.3V 50 µA OUT Bias Current MAX1961/MAX1962, VOUT = 3.3V 50 µA Current-Limit Threshold (Positive Direction, Fixed, VPGND - VLX) MAX1960/MAX1961, ILIM = VDD 58 90 mV Current-Limit Threshold (Negative Direction, Fixed, VLX - VPGND) MAX1960/MAX1961, ILIM = VDD 50 85 mV MAX1960/MAX1961, RILIM = 160kΩ 100 135 RILIM = 400kΩ 250 306 Current-Limit Threshold (Positive Direction, Adjustable, VPGND - VLX) 4 _______________________________________________________________________________________ mV 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining (VVCC = 3.3V, Circuits of Figures 9–12, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER Current-Limit Threshold (Negative Direction, Adjustable, VLX - VPGND) CONDITIONS MIN TYP MAX MAX1960/MAX1961, RILIM = 160kΩ 90 125 RILIM = 400kΩ 245 296 UNITS mV DH Gate-Driver On-Resistance VBST - VLX = 5V, pulling up or down 3.5 Ω DL Gate-Driver On-Resistance (Pullup) DL high state 3.5 Ω DL Gate-Driver On-Resistance (Pulldown) DL low state 1.6 Ω Minimum high time 200 Minimum low time 200 CTL_, FSET/SYNC, EN Input High Voltage VVCC = 2.35V to 5.5V 2.0 CTL_, FSET/SYNC, EN Input Low Voltage VVCC = 2.35V to 5.5V FSET/SYNC Pulse Width FSET/SYNC Rise/Fall Time 100 CTL_, FSET/SYNC, EN Input Current CLKOUT VOL ns -1 Sinking 1mA CLKOUT VOH Sourcing 1mA CLKOUT Rise/Fall Time CLOAD = 100pF ns V 0.8 V +1 µA 0.1 V VVCC 0.2V V 40 ns Note 1: Guaranteed by design. Note 2: Specifications at -40°C are guaranteed by design, and not production tested. _______________________________________________________________________________________ 5 MAX1960/MAX1961/MAX1962 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (Circuit of Figure 9, TA = +25°C, unless otherwise noted.) 80 VOUT = 1.8V 70 80 VOUT = 2.5V VOUT = 1.8V 70 VOUT = 1.5V 100 90 60 VOUT = 1.8V VOUT = 1.5V 70 60 50 100 10 50 0.1 1 100 10 0.1 1 100 10 LOAD CURRENT (A) LOAD CURRENT (A) LOAD CURRENT (A) EFFICIENCY vs. LOAD CURRENT WITH 15A 500kHz CIRCUIT, 5V INPUT OUTPUT VOLTAGE vs. INPUT VOLTAGE, 1MHz OUTPUT VOLTAGE vs. INPUT VOLTAGE, 500kHz VOUT = 1.8V VOUT = 1.5V 2.5 2.5V OUTPUT DROPOUT 2.0 1.5 1.8V OUTPUT 1.5V OUTPUT 1.0 1.2V OUTPUT 3.5 3.3V OUTPUT 3.0 OUTPUT VOLTAGE (V) VOUT = 2.5V 70 3.0 OUTPUT VOLTAGE (V) 90 3.3V OUTPUT MAX1960 toc05 VOUT = 3.3V 80 3.5 MAX1960 toc04 100 2.5 MAX1960 toc06 50 1 80 VOUT = 1.5V 60 0.1 VOUT = 2.5V MAX1960 toc03 90 EFFICIENCY (%) 90 VOUT = 3.3V EFFICIENCY vs. LOAD CURRENT WITH 15A 500kHz CIRCUIT, 3.3V INPUT EFFICIENCY (%) VOUT = 2.5V EFFICIENCY (%) 100 MAX1960 toc01 100 EFFICIENCY vs. LOAD CURRENT WITH 15A 1MHz CIRCUIT, 5V INPUT MAX1960 toc02 EFFICIENCY vs. LOAD CURRENT WITH 15A 1MHz CIRCUIT, 3.3V INPUT EFFICIENCY (%) 2.5V OUTPUT DROPOUT 2.0 1.5 1.8V OUTPUT 1.5V OUTPUT 1.0 1.2V OUTPUT 60 0.5 0.5 15A LOAD 15A LOAD 0 1 0.1 10 100 0 3.1 2.7 LOAD CURRENT (A) 3.5 3.9 4.3 4.7 5.1 5.5 2.7 3.1 3.5 INPUT VOLTAGE (V) FB REGULATION VOLTAGE vs. LOAD CURRENT 0.802 4.3 4.7 FREQUENCY vs. INPUT VOLTAGE 1200 MAX1960 toc07 0.803 3.9 INPUT VOLTAGE (V) 1100 FSET/SYNC = VCC MAX1960 toc08 50 1000 0.801 FREQUENCY (kHz) FB VOLTAGE (V) MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining 0.800 0.799 900 800 700 600 FSET/SYNC = GND 0.798 500 0.797 0 5 10 LOAD CURRENT (A) 6 15 20 400 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5.5 5.1 5.5 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining 700 600 500 400 300 FSET/SYNC = GND 200 5.1 5.0 4.9 VIN = 3.3V 4.8 4.7 VIN = 2.5V 4.6 5.2 C1 = 1µF C6 = 4.7µF 5.1 MAX1960 toc11 C1 = 0.47µF C6 = 2.2µF CHARGE-PUMP OUTPUT VOLTAGE vs. CHARGE-PUMP LOAD CURRENT, 500kHz CHARGE-PUMP OUTPUT VOLTAGE (V) FSET/SYNC = VCC 800 5.0 4.9 4.8 4.7 VIN = 2.5V 4.6 VIN = 3.3V 100 4.5 -15 10 35 60 4.5 50 0 85 100 150 200 C10, C11, C12 = 0.47µF C6 = 2.2µF 5.1 5.0 4.9 VIN = 2.5V 4.8 4.7 4.6 100 150 200 CHARGE-PUMP LOAD CURRENT (mA) TRIPLER CHARGE-PUMP OUTPUT VOLTAGE vs. CHARGE-PUMP LOAD CURRENT, 500kHz 5.2 CHARGE-PUMP OUTPUT VOLTAGE (V) 5.2 MAX1960 toc12 TRIPLER CHARGE-PUMP OUTPUT VOLTAGE vs. CHARGE-PUMP LOAD CURRENT, 1MHz 50 0 CHARGE-PUMP LOAD CURRENT (mA) TEMPERATURE (°C) CHARGE-PUMP OUTPUT VOLTAGE (V) C10, C11, C12 = 1µF C6 = 4.7µF 5.1 5.0 4.9 VIN = 2.5V 4.8 4.7 4.6 CIRCUIT OF FIGURE 12 CIRCUIT OF FIGURE 12 4.5 4.5 10 20 30 40 50 0 10 20 30 40 CHARGE-PUMP LOAD CURRENT (mA) CHARGE-PUMP LOAD CURRENT (mA) MAX1960/MAX1961 CURRENT-LIMIT THRESHOLD VOLTAGE vs. TEMPERATURE MAX1962 CURRENT-LIMIT THRESHOLD VOLTAGE vs. TEMPERATURE RILIM = 390kΩ 300 250 200 150 ILIM = VDD 100 50 0 52.0 50 MAX1960 toc15 350 CURRENT-LIMIT THRESHOLD VOLTAGE (mV) 0 MAX1960 toc14 -40 MAX1960 toc13 0 CURRENT-LIMIT THRESHOLD VOLTAGE (mV) FREQUENCY (kHz) 900 5.2 CHARGE-PUMP OUTPUT VOLTAGE (V) 1000 MAX1960 toc09 1100 MAX1960 toc10 CHARGE-PUMP OUTPUT VOLTAGE vs. CHARGE-PUMP LOAD CURRENT, 1MHz FREQUENCY vs. TEMPERATURE 51.5 51.0 50.5 50.0 49.5 49.0 48.5 48.0 47.5 47.0 -40 -15 10 35 TEMPERATURE (°C) 60 85 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 7 MAX1960/MAX1961/MAX1962 Typical Operating Characteristics (continued) (Circuit of Figure 9, TA = +25°C, unless otherwise noted.) MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining Typical Operating Characteristics (continued) (Circuit of Figure 9, TA = +25°C, unless otherwise noted.) VOLTAGE-MARGINING STEP RESPONSE 7.5A TO 15A TO 7.5A LOAD TRANSIENT MAX1960 toc17 MAX1960 toc16 CTL1 5V/div 5V/div CTL2 50mV/div VOUT IIN ILOAD 5A/div 200mA/div VOUT 200mV/div CIRCUIT OF FIGURE 13 50µs/div 20µs/div MAX1960/MAX1961 SHORT-CIRCUIT WAVEFORMS STARTUP/SHUTDOWN WAVEFORMS MAX1960 toc19 MAX1960 toc18 VOUT IIN 10A/div IL 10A/div CIRCUIT OF FIGURE 13 2V/div IL VOUT 20A/div 1V/div IIN 5A/div 50µs/div 1ms/div MAX1962 SHORT-CIRCUIT WAVEFORMS SYNC TIMING WAVEFORMS MAX1960 toc21 MAX1960 toc20 DH MASTER IIN 10A/div 10A/div IL VOUT VIN = 5V VOUT = 3.3V 50µs/div 8 2V/div DL MASTER CLKOUT MASTER/ SYNC SLAVE DH SLAVE DL SLAVE 200ns/div _______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining PIN NAME FUNCTION Clock Output. Connect to FSET/SYNC of a second converter to operate 180° out-ofphase. CLKOUT swings from VCC to GND. CLKOUT is low in shutdown (see the Operating Frequency and Synchronization section). MAX1960 MAX1961 MAX1962 1 1 1 CLKOUT 2 2 2 FSET/SYNC 3 3 — ILIM — — 3 EN Enable. Drive high for normal operation. Drive low or connect to GND for shutdown mode. — 4 4 SEL Preset Output Voltage Select. Allows the output to be set to one of four preset voltages (1.5V, 1.8V, 2.5V, and 3.3V). For the MAX1962, FB must be connected to VDD if SEL is to be used (see the Setting the Output Voltage section). 4 — — N.C. No Connection. Not internally connected. Output. Connect to the output. Used to sense the output voltage for internal feedback and current sense. — 8 5 OUT 5 5 — CTL1 6 6 — CTL2 — — 6 CS 7 7 7 AVDD 8 — 8 FB Frequency Set and Synchronization. Connect to GND for 500kHz operation, connect to VCC for 1MHz operation, or drive with clock signal to synchronize (between 450kHz and 1200kHz). Current Limit. Connect a resistor from ILIM to GND to set the current-sense threshold voltage. Connect ILIM to VDD to select the default threshold of 75mV. Control Pins. Controls voltage margining and shutdown. Connect both CTL1 and CTL2 high for normal operation. Connect both CTL1 and CTL2 low for shutdown. Connect CTL1 high and CTL2 low for +4% voltage margining. Connect CTL1 low and CTL2 high for -4% voltage margining. If voltage margining is not to be used, connect CTL1 and CTL2 together and use to enable/shutdown the device. Current-Sense Input. Connect to the junction of the current-sense resistor and the inductor. The MAX1962 current-sense threshold is 50mV measured from CS to OUT. Filtered Supply from VDD. Connect a 1µF bypass capacitor. AVDD is forced to VCC in shutdown. Do not apply an external load to AVDD. Feedback Input. The feedback threshold is 0.8V. Connect to the center of a resistive voltage-divider from the output to GND to set the output voltage to 0.8V or greater. On the MAX1962, connect FB to VDD to select preset output voltages (see SEL). 9 9 9 COMP 10 10 10 REF Reference Output. VREF = 1.28V. Bypass with a 0.22µF capacitor to GND. 11 11 11 GND Analog Ground. Connect to the PC board analog ground plane. Connect the PC board analog ground plane and power ground planes with a single connection. Charge-Pump Output. Provides regulated 5V to power the IC and gate drivers. Bypass with a 4.7µF ceramic capacitor for operating frequencies between 450kHz and 950kHz. Bypass with a 2.2µF ceramic capacitor for 1MHz operation. VDD is internally forced to VCC in shutdown. Do not apply an external load to VDD. 12 12 12 VDD 13 13 13 DL 14 14 14 PGND Compensation Pin. COMP is forced to GND in shutdown, UVLO, or thermal fault. Low-Side MOSFET Synchronous Rectifier Gate-Driver Output. DL is high in shutdown. Power Ground. Connect to the PC board power ground plane. _______________________________________________________________________________________ 9 MAX1960/MAX1961/MAX1962 Pin Description MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining Pin Description (continued) PIN NAME FUNCTION MAX1960 MAX1961 MAX1962 15 15 15 C- Charge-Pump Flying Capacitor Negative Connection. Use a 0.47µF ceramic capacitor at 1MHz, and 1µF between 450kHz and 950kHz. 16 16 16 C+ Charge-Pump Flying Capacitor Positive Connection. Use a 0.47µF ceramic capacitor at 1MHz and 1µF between 450kHz and 950kHz. 17 17 17 VCC Input Supply to Charge Pump 18 18 18 BST Boost Capacitor Connection. Connect a 0.1µF ceramic capacitor from BST to LX. 19 19 19 DH High-Side MOSFET Gate-Driver Output. DH is low in shutdown. 20 20 20 LX Inductor Connection Detailed Description The MAX1960/MAX1961/MAX1962 are high-current, high-efficiency voltage-mode step-down DC-DC controllers that operate from 2.35V to 5.5V input and generate adjustable voltages down to 0.8V at up to 20A. An on-chip charge pump generates a regulated 5V for driving a variety of external N-channel MOSFETs. Constant frequency PWM operation and external synchronization make these controllers suitable for telecom and datacom applications. The operating frequency is programmed externally to either 500kHz or 1MHz, or from 450kHz to 1.2MHz with an external clock. A clock output is provided to synchronize another converter for 180° out-of-phase operation. A high closed-loop bandwidth provides excellent transient response for applications with dynamic loads. Internal Charge Pump An on-chip regulated charge pump develops 5V at 50mA (max) with input voltages as low as 2.35V. The output of this charge pump provides power for the internal circuitry, bias for the low-side driver (DL), and the bias for the boost diode, which supplies the highside MOSFET gate driver (DH). The charge pump is synchronized with the DL driver signal and operates at 1/2 the PWM frequency. The external MOSFET gate charge is the dominant load for the charge pump and is proportional to the PWM switching frequency. The charge pump must supply chip-operating current plus adequate gate current for both MOSFETs at the selected operating frequency. The required charge-pump output current is given by the formula: ITOTAL = IAVDD + fOSC (QG1 + QG2) 10 where IAVDD is the current supplied to the IC through AV DD (typically 2mA), f OSC is the PWM switching frequency, Q G1 is the gate charge of the high-side MOSFET, and QG2 is the gate charge of the low-side MOSFET. The MOSFETs must be chosen such that ITOTAL does not exceed 50mA. For example, with 1MHz operation, QG1 + QG2 should be less than 48nC. Voltage Margining and Shutdown The voltage-margining feature on the MAX1960/ MAX1961 shifts the output voltage up or down by 4%. This is useful for the automatic testing of systems at high and low supply conditions to find potential hardware failures. CTL1 and CTL2 control voltage margining as outlined in Table 1. A shutdown feature is included on all three parts, which stops switching the output drivers and the charge pump, reducing the supply current to less than 15µA. For the MAX1962, drive EN high for normal operation, or low for shutdown. For the MAX1960/MAX1961, drive both CTL1 and CTL2 high for normal operation, or drive CTL1 and CTL2 low for shutdown. For a simple enable/shutdown function with no voltage margining, connect CTL1 and CTL2 together and drive as one input. Table 1. Voltage Margining Truth Table CTL1 CTL2 FUNCTION High High Normal operation High Low +4% output-voltage shift Low High -4% output-voltage shift Low Low Shutdown ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining OUT MAX1960/MAX1961/MAX1962 ILIM (MAX1960/MAX1961) CS (MAX1962) CURRENT SENSE LX PGND BST CLKOUT S OSC DH Q FSET/SYNC UVLO LX OSC VDD COMP R Q DL COMP PGND OUT (MAX1961/MAX1962) SOFT-START DAC REF ERROR AMP FB (MAX1960/MAX1962) AVDD REF FEEDBACK SELECT VDD C+ VSEL (MAX1961/MAX1962) CTL1 (MAX1960/MAX1961) CTL2 (MAX1960/MAX1961) MAX1960/ MAX1961/ MAX1962 SHUTDOWN AND VOLTAGE MARGINING OSC CHARGE PUMP CVCC GND EN (MAX1962) Figure 1. Functional Diagram MOSFET Gate Drivers Undervoltage Lockout and Soft-Start The DH and DL drivers are designed to drive logic-level N-channel MOSFETs to optimize system cost and efficiency. MOSFETs with RDSON rated at VGS 4.5V are recommended. An adaptive dead-time circuit monitors the DL output and prevents the high-side MOSFET from turning on until DL is fully off. There must be a low-resistance, low-inductance path from the DL driver to the MOSFET gate for the adaptive dead-time circuit to work properly. Otherwise, the internal sense circuitry could interpret the MOSFET gate as “off” while there is actually still charge left on the gate. Use very short, wide traces measuring no more than 20 squares (50mils to 100mils wide if the MOSFET is 1in from the IC). There are two undervoltage lockout (UVLO) circuits on the MAX1960/MAX1961/MAX1962. The first UVLO circuit monitors VCC, which must be above 2.15V (typ) in order for the charge pump to operate. The second UVLO circuit monitors the output of the charge pump. The charge-pump output, VDD, must be above 4.2V (typ) in order for the PWM converter to operate. Both UVLO circuits inhibit switching and force DL high and DH low when either VCC or VDD are below their threshold. When the monitored voltages are above their thresholds, an internal soft-start timer ramps up the erroramplifier reference voltage. The ramp occurs in eighty 10mV steps. Full output voltage is reached 1.28ms after activation with a 1MHz operating frequency. ______________________________________________________________________________________ 11 MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining Operating Frequency and Synchronization The MAX1960/MAX1961/MAX1962 operating frequency is set externally to either 500kHz or 1MHz. For 500kHz operation, connect FSET/SYNC to GND, or for 1MHz operation, connect FSET/SYNC to VDD. Alternately, an external clock from 450kHz to 1.2MHz can be applied to SYNC. A clock output (CLKOUT) that is 180° out-of-phase with the internal clock is also provided. This allows a second converter to be synchronized, and operate 180° out-ofphase with the first. To do this, simply connect CLKOUT of the first converter to FSET/SYNC of the second converter. The first converter can be set internally to 500kHz or 1MHz for this mode of operation. When the first converter is synchronized to an external clock, CLKOUT is the inverse of external clock. See the SYNC Timing Waveform in the Typical Operating Characteristics. Lossless Current Limit (MAX1960/MAX1961) increases until it reaches its maximum value, where the part enters dropout. With a switching frequency of 1MHz, the maximum duty cycle is about 83%. At 500kHz, the duty cycle can increase to about 92%, resulting in a lower dropout voltage. The duty cycle is dependent on the input voltage (VIN), the output voltage (V OUT ), and the parasitic voltage drops in the MOSFETs and the inductor (V DROP(N1), V DROP(N2), V DROP(L)). Note that V DROP(L) includes the voltage drop due to the inductor’s resistance, the drop across the current-sense resistor (if used), and any other resistive voltage drop from the LX switching node to the point where the output voltage is sensed. The duty cycle is found from: D= VOUT + VDROP(L) VIN - VDROP(N1) - VDROP(N2) Adaptive Dead Time To prevent damage in the case of excessive load current or a short circuit, the MAX1960/MAX1961 use the low-side MOSFET’s on-resistance (RDS(ON)) for current sensing. The current is monitored during the on-time of the low-side MOSFET. If the current-sense voltage (VPGND - VLX) rises above the current-limit threshold for more than 128 clock cycles, the controller turns off. The controller remains off until the input voltage is removed or the device is re-enabled with CTL1 and CTL2 (see the Setting the Current Limit section). The MAX1960/MAX1961/MAX1962 DL and DH MOSFET drivers have an adaptive dead-time circuit to prevent shoot-through current caused by high- and low-side MOSFET overlap. This allows a wide variety of MOSFETs to be used without matching FET dynamic characteristics. The DL driver will not go high until DH drives the high-side MOSFET gate to within 1V of its source (LX). The DH output will not go high until DL drives the low-side MOSFET gate to within 1V of ground. Current-Sense Resistor (MAX1962) Component selection is primarily dictated by the following criteria: The MAX1962 uses a standard current-sense resistor in series with the inductor for a 10% accurate current-limit measurement. The current-sense threshold is 50mV. This provides accurate current sensing at all duty cycles without relying on MOSFET on-resistance. CS connects to the high-side (inductor side) of the current-sense resistor and OUT connects to the low-side (output side) of the current-sense resistor. The current-sense resistor for the MAX1962 may also be replaced with a series RC network across the inductor. This method uses the parasitic resistance of the inductor for current sensing. This method is less accurate than using a current-sense resistor, but is lower cost and provides slightly higher efficiency. See the Design Procedure section for instructions on using this method. Dropout Performance The MAX1960/MAX1961/MAX1962 enter dropout when the input voltage is not sufficiently high to maintain output regulation. As input voltage is lowered, the duty cycle 12 Design Procedure Input voltage range. The maximum value (VIN(MAX)) must accommodate the worst-case high input voltage. The minimum value (VIN(MIN)) must account for the lowest input voltage after drops due to connectors, fuses, and selector switches are considered. Maximum load current. There are two values to consider: The peak load current (ILOAD(MAX)) determines the instantaneous component stresses and filtering requirements and is key in determining output capacitor requirements. ILOAD(MAX) also determines the inductor saturation rating and the design of the current-limit circuit. The continuous load current (ILOAD) determines the thermal stresses and is key in determining input capacitor requirements, MOSFET requirements, as well as those of other critical heatcontributing components. ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining MAX1960/MAX1961/MAX1962 Inductor operating point. This choice provides tradeoffs between size, transient response, and efficiency. Choosing higher inductance values results in lower inductor ripple current, lower peak current, lower switching losses, and, therefore, higher efficiency at the cost of slower transient response and larger size. Choosing lower inductance values results in large ripple currents, smaller size, and poorer efficiency, but have faster transient response. Table 2. Preset Voltages— MAX1961/MAX1962 PRESET OUTPUT VOLTAGE SEL 1.5V GND 1.8V REF 2.5V No connection 3.3V VDD Setting the Output Voltage The MAX1961 has four output voltage presets selected by SEL. Table 2 shows how each of the preset voltages are selected. The MAX1962 also has four preset output voltages, but also is adjustable down to 0.8V. To use the preset voltages on the MAX1962, FB must be connected to VDD. SEL then selects the output voltage as shown in Table 2. Both the MAX1960/MAX1962 feature an adjustable output that can be set down to 0.8V. To set voltages greater than 0.8V, Connect FB to a resistor-divider from the output (Figures 9 and 11). Use a resistor up to 10kΩ for R2 and select R1 according to the following equation: D2 Input Voltage Range The MAX1960/MAX1961/MAX1962 have an input voltage range of 2.35V to 5.5V but cannot operate at both extremes with one application circuit. The standard charge-pump doubler application circuit operates with an input range of 2.7V to 5.5V (Figures 9, 10, and 11). In order to operate down to 2.35V, the charge pump must be configured as a tripler. This circuit, however, limits the maximum input voltage to 3.6V. The schematic for the tripler charge pump is shown in Figure 2. Note that the flying capacitor between C+ and C- has been removed and C+ is not connected. D4 D5 C11 C10 C12 VCC C- MAX1960/ MAX1961/ MAX1962 C+ VDD C6 R5 10Ω AVDD C4 1µF V R1 = R2 × OUT - 1 VFB where the feedback threshold, VFB = 0.8V, and VOUT is the output voltage. D3 C10, C11, C12 500kHz 1µF 1MHz 0.47µF C6 4.7µF 2.2µF Figure 2. Tripler Charge-Pump Configuration. vides a good compromise between efficiency and economy. Choose a low-loss inductor having the lowest possible DC resistance. Ferrite core type inductors are often the best choice for performance. The inductor saturation current rating must exceed IPEAK: LIR IPEAK = ILOAD(MAX) + × ILOAD(MAX) 2 Inductor Selection Determine an appropriate inductor value with the following equation: L = VOUT × VIN - VOUT VIN × fOSC × LIR × ILOAD(MAX) The inductor current ripple, LIR, is the ratio of peak-topeak inductor ripple current to the average continuous inductor current. An LIR between 20% and 40% pro- Setting the Current Limit Lossless Current Limit (MAX1960/MAX1961) The MAX1960/MAX1961 use the low-side MOSFET’s onresistance (RDS(ON)) for current sensing. This method of current limit sets the maximum value of the inductor’s “valley” current (Figure 3). If the inductor current is higher than the valley current-limit setting at the end of the clock period, the controller skips the DH pulse. When the first current-limit event is detected, the controller initi- ______________________________________________________________________________________ 13 DH 0.22µH, 2.8mW, ILIMIT = 18A RL IPEAK L LX ILOAD INDUCTOR CURRENT MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining MAX1962 DL R R = 33Ω C C = 4.7µF IVALLEY CS TIME OUT Figure 3. Inductor Current Waveform Figure 4. Using the Inductor Resistance as a Current-Sense Resistor with the MAX1962 ates a 128 clock cycle counter. If the current limit is present at the end of this count, the controller remains off until the input voltage is removed and re-applied, or the device is re-enabled with CTL1 and CTL2. The 128-cycle counter is reset when four successive DH pulses are observed, without activating the current limit. At maximum load, the low excursion of inductor current, IVALLEY(MAX), is: accuracy is needed, use the MAX1962 with a currentsense resistor. LIR IVALLEY(MAX) = ILOAD(MAX) - × ILOAD(MAX) 2 The current-limit threshold (VCLT) is set by connecting a resistor (RILIM) from ILIM to GND. The range for this resistor is 100kΩ to 400kΩ. Set current-limit threshold as follows: VCLT = RILIM × 0.714µA Connecting ILIM to VDD sets the threshold to a default value of 75mV. To prevent the current limit from falsely triggering, VCLT divided by the low-side MOSFET RDS(ON) must exceed the maximum value of IVALLEY. The maximum value of low-side MOSFET RDS(ON) should be used: VCLT > RDS(ON)MAX x IVALLEY(MAX) A limitation of sensing current across MOSFET on-resistance is that the MOSFET on-resistance varies significantly from MOSFET to MOSFET and over temperature. Consequently, this current-sensing method may not be suitable if a precise current limit is required. If better 14 Current-Sense Resistor (MAX1962) The MAX1962 uses a current-sense resistor connected from the inductor to the output with Kelvin sense connections. The current-sense voltage is measured from CS to OUT, and has a fixed threshold of 50mV. The MAX1962 current limit is triggered when the peak voltage across the current-sense resistor, IPEAK × RSENSE, exceeds 50mV. Once current sense is triggered, the controller does not turn off, but continues to operate at the current limit. This method of current sensing is more precise due to the accuracy of the current-sense resistor. The cost of this precision is that it requires an extra component and is slightly less efficient due to the loss in the currentsense resistance. Inductor Resistance Current Sense (MAX1962) Alternately, the inductor resistance can be used to sense current in place of a current-sense resistor. To do this, connect a series RC network in parallel with the inductor (Figure 4). Choose a resistor value less than 40Ω to avoid offsets due to CS input current. Calculate the capacitor value from the formula C = 2L / (RL × R). The effective current-sense resistance (RSENSE) equals RL. Current-sense accuracy then depends on the accuracy of the inductor resistance. Note that the currentsense signal is delayed due to the RC filter time constant. Consequently, inductor current may overshoot (by as much as 2x) when a fast short occurs. ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining VDIP RESR ≤ ILOADSTEP(MAX) In applications with less severe load steps, maximum ESR may be governed by what is needed to maintain acceptable output voltage ripple: VRIPPLE(P−P) RESR ≤ LIR × ILOAD(MAX) To satisfy both load step and ripple requirements, select the lowest value from the above two equations. The capacitor is usually selected by physical size, ESR, and voltage rating, rather than by capacitance value. With current tantalum, electrolytic, and polymer capacitor technology, the bulk capacitance will also be sufficient once the ESR requirement is satisfied. When using low-capacity filter capacitors such as ceramic, capacitor size is usually determined by the capacitance needed to prevent voltage undershoot and overshoot during load transients. The overshoot voltage (VSOAR) is given by: VSOAR = L × (IPEAK )2 2 × VOUT × COUT Generally, once enough capacitance is in place to meet the overshoot requirement, undershoot at the rising load edge is no longer a problem. Input Capacitor Selection The input capacitor (CIN) reduces the current peaks drawn from the input supply and reduces noise injection. The source impedance to the input supply largely determines the value of CIN. High source impedance requires high input capacitance. The input capacitor must meet the ripple current requirement (I RMS ) imposed by the switching currents. The RMS input ripple current is given by: IRMS = ILOAD × VOUT × (VIN - VOUT ) VIN For optimal circuit reliability, choose a capacitor that has less than 10°C temperature rise at the peak ripple current. Compensation and Stability Compensation with Ceramic Output Capacitors The high switching frequency range of the MAX1960/MAX1961/MAX1962 allows the use of ceramic output capacitors. Since the ESR of ceramic capacitors is very low typically, the frequency of the associated transfer function zero is higher than the unity-gain crossover frequency and the zero cannot be used to compensate for the double pole created by the output inductor and capacitor. The solution is Type 3 compensation (Figure 5), which takes advantage of local feedback to create two zeros and three poles (Figure 6). The frequency of the poles and zeros are described below: fP1 = 0 fP2 = 1 2π × R2 × C3 1 fP3 = fLC = fZ1 = fZ2 = C1 × C2 C1 + C2 2π × R1 × 1 2π L 0 × C 0 1 2π × R1 × C1 1 2π × (R2 + R3) × C3 fZESR = 1 2π × RESR × C0 Unity-gain crossover frequency: f0 = R1 × C3 × VIN(MAX) VRAMP × 1 2π × L 0 × C 0 ______________________________________________________________________________________ 15 MAX1960/MAX1961/MAX1962 Output Capacitor Selection The output filter capacitor must have low enough effective series resistance (ESR) to meet output ripple and load transient requirements. In addition, the capacitance value must be high enough to absorb the inductor energy during load steps. In applications where the output is subject to large load transients, low ESR is needed to prevent the output from dipping too low (VDIP) during a load step: MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining VIN GAIN (dB) DH LO VOUT LX DL C0 MAX1960 R3 FB R2 C3 R4 R1 COMP fz1 fp1 C2 fz2 fp2 fp3 FREQUENCY C1 Figure 5. Type 3 Compensation Network Figure 6. Transfer Function for Type 3 Compensation where: VIN(MAX) = Maximum input voltage VRAMP = Oscillator ramp voltage = 0.85 x 106/fS, where fS = switching frequency LO = Output inductance If C2 < 10pF, it can be omitted. CO = Output capacitance The goal is to place the two zeros below crossover and the two poles above crossover so that crossover occurs with a single-pole slope. The compensation procedure is as follows: Select the crossover frequency such that: f0 < fZESR and f0 <1/5 ✕ fS C3 ≤ 2π × f0 × L 0 × C0 × VRAMP R1 × VIN Place the second pole after the ESR zero: R2 ≤ 1 2π × fZESR × C3 If: R2 < Select R1 such that: R1 >> 2 gmEA increase R1 and recalculate C1, C2, and C3. Place the second zero at the double-pole frequency: R3 ≥ where gmEA = 2mS. 1 (= 550Ω), gM Place the first zero before the double pole: 1 - R2 2π × fLC × C3 Set the output voltage: 1 C1 ≥ 2π × 0.75 × fLC × R1 Place the third pole at half the switching frequency: C2 ≥ 16 R4 = VFB × R3, VFB = 0.8V VOUT - VFB 1 2π × 0.5 × fS × R1 ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining GMOD(DC) = CO = n × CEACH The total ESR is: RESR(EACH) n The ESR zero (f ZESR ) for a parallel combination of capacitors is the same as for an individual capacitor. The feedback divider has a gain of GFB = VFB/VOUT, where VFB is 0.8V. 1 2π × CC × RC The total closed-loop gain must equal to unity at the crossover frequency, where the crossover frequency should be higher than fZESR, so that the -1 slope is used to cross over at unity gain. Also, the crossover frequency should be less than or equal to 1/5 the switching frequency. f fZESR < fC ≤ S 5 The loop-gain equation at the crossover frequency is: VFB × GEA(fC ) × GMOD(fC ) = 1 VOUT 2π LOCO The output capacitor is usually comprised of several same value capacitors connected in parallel. With n capacitors in parallel, the output capacitance is: RESR = fZEA = 1 1 2π × RESR × CO 1 2π × CC × (R0 + RC ) A zero is set by the compensation resistor and the compensation capacitor: VRAMP The zero frequency due to the output capacitor’s ESR is: fZESR = fPEA = VIN where VRAMP = 0.85 × 106 / fS. The pole frequency due to the inductor and output capacitor is: fPMOD = The transconductance error amplifier has DC gain GEA(dc) of 80dB. A dominant pole is set by the compensation capacitor (CC), the amplifier output resistance (RO), and the compensation resistor (RC): where: GEA(fC ) = gmEA × RC and: GMOD(fC ) = GMOD(DC) × (fPMOD )2 fESR × fC The compensation resistor, RC, is calculated from: RC = VOUT gmEA × VFB × GMOD(fC ) where gmEA = 2mS. Due to the under-damped (Q > 1) nature of the output LC double pole, the error-amplifier compensation zero should be approximately 0.2fPMOD to provide good phase boost. CC is calculated from: CC = 5 2π × RC × fPMOD ______________________________________________________________________________________ 17 MAX1960/MAX1961/MAX1962 Compensation with Electrolytic Output Capacitors The MAX1960/MAX1961/MAX1962 use a voltage-mode control scheme that regulates the output voltage by comparing the error-amplifier output (COMP) with a fixed internal ramp to produce the required duty cycle. The inductor and output capacitor create a double pole at the resonant frequency, which has gain drop of 40dB per decade, and phase shift of 180°. The error amplifier must compensate for this gain drop and phase shift in order to achieve a stable high-bandwidth, closed-loop system. The basic regulator loop consists of a power modulator, an output feedback divider and an error amplifier. The power modulator has DC gain set by VIN/VRAMP, with a double pole set by the inductor and output capacitor, and a single zero set by the output capacitor (CO) and its equivalent series resistance (ESR). Below are equations that define the power modulator: The DC gain of the power modulator is: MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining A small capacitor CF, can also be added from COMP to GND to provide high-frequency decoupling. CF will add another high-frequency pole (fPHF) to the error-amplifier response. This pole should be greater than 100 times the error-amplifier zero frequency to have negligible impact on the phase margin. This pole should also be less than half the switching frequency for effective decoupling: 100fZEA < fPHF < 0.5fS Select a value for fPHF in the range given above, then solve for CF using the following equation: CF = 1 2π × RC × fPHF Below is a numerical example to calculate compensation values: VIN = 3.3V VRAMP = 0.85V The power modulator gain at fC is: GMOD(fc) = VIN VRAMP = × (fPMOD )2 fZESR × fC 3 (9201)2 × = 0.102 0.85 29.3kΩ × 100kΩ Choose R1 = 8.06kΩ, then R2 = 10kΩ (see the Setting the Output Voltage section): C= VOUT 1.8 = gmEA × VFB × GMOD(fC ) 0.002 × 0.8 × 0.102 = 11kΩ CC = 5 5 = = 7863pF 2π × RC × fPMOD 2π × 11kΩ × 9201 Select C C = 8200pF (nearest standard capacitor value). VOUT = 1.8V VFB = 0.8V Select fPHF in the range 100fZEA < fPHF < 0.5fS. 184kHz < fPHF < 500kHz IOUT(max) = 15A CO = 2 x 680µF = 1360µF Select fPHF = 250kHz, then solve for CF: ESR = 0.008Ω / 2 = 0.004Ω LO = 0.22µH gmEA = 2mS fS = 1MHz fPMOD = L O × CO 1 = 1 2π × RC × fPHF = 1 = 58pF 2π × 11kΩ × 250kHz Select the nearest standard capacitor value CF = 56pF. Summary of feedback divider and compensation components: R1 = 8.06kΩ 1 2π × CF = 2π × 0.22 × 10−6 × 1360 × 10−6 = 9.201kHz R2 = 10kΩ RC = 11kΩ CC = 8200pF CF = 56pF Power MOSFET Selection fZESR = = 1 2π × CO × RESR 1 2π × 1360 × 10−6 × 0.004 = 29.3kHz Choose the crossover frequency (fC) in the range fZESR < fC < fS/5: 29.3kHz < fC < 200kHz When selecting a MOSFET, essential parameters include: (1) Total gate charge (QG) (2) Reverse transfer capacitance (CRSS) (3) On-resistance (RDS(ON)) (4) Gate threshold voltage (VTH(MIN)) (5) Turn-on/turn-off times (6) Turn-on/turn-off delays Select fC = 100kHz, this meets the criteria above, and the bandwidth is high enough for good transient response. 18 ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining ERROR AMPLIFIER MODULATOR OUTPUT FILTER V1 0.8V R1 VIN/VRAMP Gm RS R2 R3 L1 C9 V2 RESR RLOAD COUT Figure 7. Open-Loop Transfer Model At high switching rates, dynamic characteristics (parameters 1, 2, 5, and 6) that predict switching losses may have more impact on efficiency than RDS(ON), which predicts DC losses. QG includes all capacitance associated with charging the gate, and best performance is achieved with a low total gate charge. QG also helps predict the current needed to drive the gate at the selected operating frequency. This is very important because the output current from the charge pump is finite (50mA, max) and is used to drive the gates of the MOSFETs as well as provide bias for the IC. RDS(ON) is important as well, as it is used for current sensing in the MAX1960/MAX1961. RDS(ON) also causes power dissipation during the on-time of the MOSFET. Choose QG to be as low as possible. Ensure that: QG1 + QG2 ≤ 50mA fS Choose RDS(ON) to provide the desired ILOAD(MAX) at the desired current-limit threshold voltage (see the Setting the Current Limit section). MOSFET RC Snubber Circuit Fast-switching transitions can cause ringing due to resonating circuit parasitic inductance and capacitance at the switching nodes. This high-frequency ringing occurs at LX rising and falling transitions, and may introduce current-sensing errors and generate EMI. To dampen this ringing, a series RC snubber circuit can be added across each MOSFET switch (Figure 8). Typical values for the snubber components are CSNUB = 4700pF and RSNUB = 1Ω, however, the ideal values for snubber components will depend on circuit parasitics. Below is the procedure for selecting the component values of the series RC snubber circuit: 1) Connect a scope probe to measure VLX to GND, and observe the ringing frequency, fR. 2) Find the capacitor value (connected from LX to GND) that reduces the ringing frequency by half. 3) The circuit parasitic capacitance, CPAR, at LX is then equal to 1/3 of the value of the added capacitance above. ______________________________________________________________________________________ 19 MAX1960/MAX1961/MAX1962 FEEDBACK DIVIDER MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining where VIN(MAX) is the maximum value of the input voltage, tFALL and tRISE are the fall and rise time of the MOSFET, I L(PEAK) and I L(VALLEY) are the maximum peak and valley inductor current, and fS is the PWM switching frequency: IL(PEAK) = IOUT(MAX) × (1 + 0.5 × LIR) and IL(VALLEY) = IOUT(MAX) × (1 - 0.5 × LIR) where LIR is the peak-to-peak inductor ripple current divided by the load current. The total power dissipation in the high-side MOSFET is the sum of these two power losses: PD(N1) = PD(N1RESISTIVE) + PD(N1SWITCHING) For the low-side MOSFET, the worst-case power dissipation occurs at maximum input voltage: INPUT RSNUB DH MAX1960 N1 CSNUB L1 LX RSNUB DL N2 CSNUB PGND Figure 8. RC Snubber Circuit 4) The circuit parasitic inductance, LPAR, is calculated by: LPAR = 1 Applications Information (2π × fR )2 × CPAR 5) The resistor for critical dampening, RSNUB = 2π x fR x LPAR. The resistor value can be adjusted up or down to tailor the desired damping and the peak voltage excursion. 6) The capacitor, CSNUB, should be at least 2 to 4 times the value of the CPAR to be effective. 7) The snubber circuit power loss is dissipated in the resistor, PRSNUB, and can be calculated as: PRSNUB = CSNUB × (VIN )2 × fS where V IN is the input voltage, and f S is the switching frequency. Choose RSNUB power rating that exceeds the calculated power dissipation. MOSFET Power Dissipation Worst-case power dissipation occurs at duty factor extremes. For the high-side MOSFET, the worst-case power dissipation due to resistance occurs at minimum input voltage (VIN(MIN)): PD(N1RESISTIVE) = VOUT × ILOAD2 × RDS(ON) VIN(MIN) The following formula calculates switching losses for the high-side MOSFET, but is only an approximation and not a substitute for evaluation: PD(N1SWITCHING) = (IL(PEAK) × 20 VOUT PD(N2RESISTIVE) = 1 × ILOAD2 × RDS(ON) VIN(MAX) ) tFALL + IL(VALLEY) × tRISE × VIN(MAX) 2 PC Board Layout Guidelines A properly designed PC board layout is important in any switching DC-DC converter circuit. If possible, mount the MOSFETs, inductor, input/output capacitors, and current-sense resistor on the top side. Connect the ground for these devices close together on a powerground trace. Make all other ground connections to a separate analog ground plane. Connect the analog ground plane to power ground at a single point. To help dissipate heat, place high-power components (MOSFETs, inductor, and current-sense resistor) on a large PC board area. Keep high-current traces short and wide to reduce the resistance in these traces. Also make the gate drive connections (DH and DL) short and wide, measuring 10 to 20 squares (50mils to 100mils wide if the MOSFET is 1in from the controller IC). For the MAX1960/MAX1961, connect LX and PGND to the low-side MOSFET using Kelvin sense connections. For the MAX1962, connect CS and OUT to the currentsense resistor using Kelvin sense connections. Place the REF capacitor, the BST diode and capacitor, and the charge-pump components as close as possible to the IC. If the IC is far from the input capacitors, bypass VCC to GND with a 0.1µF or greater ceramic capacitor close to the VCC pin. For an example PC board layout, see the MAX1960 evaluation kit. × fS ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining MAX1960/MAX1961/MAX1962 Table 3. Component List for Application Circuits PART APP. CIRCUIT C1 1, 2, 3 15A OUTPUT 1MHz 0.47µF ceramic capacitor 15A OUTPUT 500kHz 1µF ceramic capacitor C2 1, 2, 3, 4 5 × 10µF ceramic capacitors 5 × 10µF ceramic capacitors C3 1, 2, 3, 4 2 x 680µF POSCAPs Sanyo 2R5TPD680M8 2 x 680µF POSCAPs Sanyo 2R5TPD680M8 C4 1, 2, 3, 4 1µF ceramic capacitor 1µF ceramic capacitor C5 1, 2, 3, 4 0.1µF ceramic capacitor 0.1µF ceramic capacitor C6 1, 2, 3, 4 2.2µF ceramic capacitor 4.7µF ceramic capacitor C8 1, 2, 3, 4 0.22µF ceramic capacitor 0.22µF ceramic capacitor C9 1, 2, 3, 4 (Table 4) (Table 5) C10, C11, C12 4 0.47µF ceramic capacitors 1µF ceramic capacitors C13, C14 1, 2, 3, 4 4700pF ceramic capacitors 4700pF ceramic capacitors D1 1, 2, 3, 4 Schottky diode Central CMSSH-3 Schottky diode Central CMSSH-3 D2–D5 4 Schottky diodes Central CMHSH5-2L Schottky diodes Central CMHSH5-2L L1 1, 2, 3, 4 0.22µH, 1.7mΩ inductor Sumida CDEP1040R2NC-50 0.45µH inductor Sumida CDEP1040R4MC-50 N1 1, 2, 3, 4 N-channel MOSFET International Rectifier IRLR7821 N-channel MOSFET International Rectifier IRLR7821 N2 1, 2, 3, 4 N-channel MOSFET International Rectifier IRLR7833 N-channel MOSFET International Rectifier IRLR7833 R1 1, 3 Sets output voltage Sets output voltage R2 1, 3 10kΩ ±1% resistor 10kΩ ±1% resistor R3 1, 2, 3, 4 (Table 4) (Table 5) 390kΩ ±5% resistor 390kΩ ±5% resistor 10Ω ±5% resistor 10Ω ±5% resistor 1.5mΩ ±5%, 1W resistor Panasonic ERJM1WTJ1M5U 1.5mΩ ±5%, 1W resistor Panasonic ERJM1WTJ1M5U 1Ω ±5% resistors 1Ω ±5% resistors R4 1, 2 R5 1, 2, 3, 4 R6 3, 4 R7, R8 1, 2, 3, 4 ______________________________________________________________________________________ 21 MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining Table 4. R1, R3, and C9 Component Values for 1MHz Operation VIN VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V VOUT = 1.5V R1 (kΩ) R3 (kΩ) C9 (µF) R1 (kΩ) R3 (kΩ) C9 (µF) R1 (kΩ) R3 (kΩ) C9 (µF) R1 (Ω) R3 (kΩ) C9 (µF) 5V 3.12 1.2 0.0068 2.13 9.1 0.01 1.24 6.8 0.01 876 5.5 0.01 3.3V — — — — — — 1.24 2.7 0.01 876 2.4 0.01 2.5V — — — — — — 1.24 3.9 0.01 876 3.3 0.01 Table 5. R1, R3, and C9 Component Values for 500kHz Operation VIN VOUT = 3.3V VOUT = 2.5V VOUT = 1.8V VOUT = 1.5V R1 (kΩ) R3 (kΩ) C9 (µF) R1 (kΩ) R3 (kΩ) C9 (µF) R1 (kΩ) R3 (kΩ) C9 (µF) R1 (Ω) R3 (kΩ) 5V 3.12 36 0.0033 2.13 27 0.0047 1.24 20 0.0068 876 16 0.0068 3.3V — — — 2.13 47 0.0033 1.24 30 0.0047 876 27 0.0047 2.5V — — — — — — 1.24 39 0.0033 876 33 0.0033 Table 6. Component Suppliers Selector Guide SUPPLIER PHONE WEBSITE Central Semiconductor 631-435-1110 www.centralsemi.com International Rectifier 310-322-3331 www.irf.com MAX1960 Kamaya 260-489-1533 www.kamaya.com MAX1961 Murata 814-237-1431 www.murata.com Panasonic 714-373-7939 www.panasonic.com Sanyo 619-661-6835 www.sanyo.com Sumida 847-956-0666 www.sumida.com Taiyo Yuden 408-573-4150 www.t-yuden.com 22 C9 (µF) PART MAX1962 VOLTAGE MARGINING CURRENT LIMIT OUTPUT VOLTAGE ±4% FET VDS Sensing Adjustable No ±10% with RSENSE 4 Presets or Adjustable ______________________________________________________________________________________ 4 Presets 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining MAX1960/MAX1961/MAX1962 C1 INPUT 2.7V TO 5.5V C+ C4 C- VCC AVDD C2 R5 CTL1 VDD D1 BST CTL2 COMP C6 MAX1960 R7 DH N1 C5 C9 REF C13 OUTPUT DOWN TO 0.8V L1 LX C3 R8 DL C8 R3 N2 C14 GND FSET/SYNC CLKOUT PGND ILIM R4 CLKOUT N.C. R1 FB R2 Figure 9. Application Circuit 1—MAX1960 Adjustable Output Voltage ______________________________________________________________________________________ 23 MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining C1 INPUT 2.7V TO 5.5V C+ C4 C- VCC AVDD C2 R5 CTL1 VDD D1 BST CTL2 COMP C6 MAX1961 R7 DH N1 C5 C9 REF C13 L1 OUTPUT 2.5V LX C3 R8 DL C8 R3 N2 C14 GND FSET/SYNC CLKOUT PGND ILIM R4 CLKOUT VSEL OUT Figure 10. Application Circuit 2—MAX1961 Preset Output Voltage 24 ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining MAX1960/MAX1961/MAX1962 C1 INPUT 2.7V TO 5.5V C+ C4 C- VCC AVDD C2 R5 VDD D1 EN COMP C6 BST MAX1962 R7 DH N1 C5 C9 REF C13 L1 R6 OUTPUT DOWN TO 0.8V LX C3 R8 DL C8 R3 N2 C14 GND FSET/SYNC CLKOUT CLKOUT PGND CS OUT R1 VSEL FB R2 Figure 11. Application Circuit 3—MAX1962 Adjustable Output Voltage ______________________________________________________________________________________ 25 MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining D3 D2 D4 C11 C10 INPUT 2.35V TO 3.6V C+ C12 C4 C- VCC D5 AVDD C2 R5 VDD D1 BST EN COMP C6 MAX1962 R7 DH N1 C5 C9 REF C13 LX L1 R6 OUTPUT 1.5V C3 R8 DL C8 R3 N2 C14 GND FSET/SYNC CLKOUT CLKOUT VSEL PGND CS OUT FB VDD Figure 12. Application Circuit 4—MAX1962 Tripler Configuration, Preset Output 26 ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining MAX1960/MAX1961/MAX1962 C1 0.47µF INPUT 2.7V TO 5.5V C+ C2 5 x 10µF C4 1µF C- VCC AVDD R5 10Ω CTL1 VDD CTL2 BST C6 2.2µF D1 COMP C10 33pF C9 820pF R3 10kΩ MAX1960 REF C8 0.22µF C5 0.1µF N1 R7 1Ω C13 4700pF L1 OUTPUT 2.5V, 15A LX DL N2 C3 4 x 47µF TAIYO-YUDEN JMK325BJ476MN R8 1Ω C14 4700pF GND FSET/SYNC CLKOUT DH PGND ILIM R4 390kΩ CLKOUT N.C. R9 680Ω C7 560pF R1 6.84kΩ FB R2 3.22kΩ N1 – IRLR7821 N2 – IRLR7833 Figure 13. Application Circuit—Ceramic Output Capacitors with Type 3 Compensation ______________________________________________________________________________________ 27 MAX1960/MAX1961/MAX1962 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining Pin Configurations TOP VIEW TOP VIEW CLKOUT 1 20 LX CLKOUT 1 20 LX FSET/SYNC 2 19 DH FSET/SYNC 2 19 DH ILIM 3 18 BST EN 3 N.C. (SEL) 4 17 VCC SEL 4 CTL1 5 CTL2 6 MAX1960 MAX1961 AVDD 7 16 C+ OUT 5 15 C- CS 6 14 PGND FB (OUT) 8 13 DL 18 BST 17 VCC MAX1962 16 C+ 15 C- AVDD 7 14 PGND FB 8 13 DL COMP 9 12 VDD COMP 9 12 VDD REF 10 11 GND REF 10 11 GND QSOP QSOP ( ) ARE FOR MAX1961. Chip Information TRANSISTOR COUNT: 4476 PROCESS: BiCMOS 28 ______________________________________________________________________________________ 2.35V to 5.5V, 0.5% Accurate, 1MHz PWM Step-Down Controllers with Voltage Margining QSOP.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 ____________________ 29 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1960/MAX1961/MAX1962 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.)