19-2837; Rev 1; 11/04 KIT ATION EVALU E L B A IL AVA 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET The MAX1572 is a fixed-frequency, synchronous stepdown DC-to-DC converter to power low-voltage microprocessor/DSP cores in portable equipment requiring high efficiency in a limited PC board area. The features are optimized for high efficiency over a wide load range, small external component size, low output ripple, and excellent transient response. The input supply voltage range is from 2.6V to 5.5V, while the output is internally fixed from 0.75V to 2.5V in 50mV increments with a guaranteed output current of 800mA. The high 2MHz switching allows tiny low-cost capacitors and a low-profile inductor, while the power-saving pulse-group mode reduces quiescent current to 48A (typ) with light loads. To reduce noise and RF interference, the converter can be configured to provide forced-PWM operation. The MAX1572 includes a low on-resistance internal MOSFET switch and synchronous rectifier to maximize efficiency and minimize external component count. No external diode is needed. Other features include softstart to eliminate inrush current at startup and a 170ms (min) RESET output to provide power-on/undervoltage reset. The MAX1572 is available in a 12-pin, 4mm x 4mm thin QFN package with exposed paddle. Applications Cell Phones and Smart Phones PDAs, Palmtops, and Notebook Computers MP3 and DVD Players Digital Cameras and Camcorders PCMCIA Cards Hand-Held Instruments Features Up to 97% Efficiency 2MHz PWM Switching 800mA Guaranteed Output Current Low 48A Quiescent Current Power-Saving Modes: Pulse-Group, Pulse-Skip, Forced-PWM Mode 0.75V to 2.5V Preset Output Range (in 50mV Increments) Voltage-Positioning Load Transients 5mVP-P Output Ripple Tiny 2.2H Inductor 10F Ceramic Output Capacitor Low 0.1A Shutdown Current No External Schottky Diode Required Soft-Start with Zero Inrush Current 170ms (min) RESET Output Small 12-Pin, 4mm x 4mm Thin QFN Package Ordering Information PART TEMP RANGE PIN-PACKAGE MAX1572ETC075 -40C to +85C 12 Thin QFN-EP** MAX1572ETC130 -40C to +85C 12 Thin QFN-EP** MAX1572ETC150 -40C to +85C 12 Thin QFN-EP** MAX1572ETC180 -40C to +85C 12 Thin QFN-EP** MAX1572ETC250 -40C to +85C 12 Thin QFN-EP** MAX1572ETCxyz* -40C to +85C 12 Thin QFN-EP** *xyz is for the output voltage (e.g., MAX1572ETC165 has a 1.65V output). Minimum order quantity is 2500. **EP = Exposed paddle. Selector Guide appears at end of data sheet. Pin Configuration MAX1572 PGND ABATT MODE SELECT EN1 EN2 SS OUT RESET GND EN1 10 GND 11 ABATT 12 PGND 9 8 7 MAX1572 1 2 3 GND LX LX BATT TOP VIEW SS 2.2H OUTPUT 0.75V TO 2.5V 800mA RESET INPUT 2.6V TO 5.5V BATT Typical Operating Circuit 6 EN2 5 GND 4 OUT 4mm x 4mm THIN QFN ________________________________________________________________ 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 MAX1572 General Description MAX1572 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET ABSOLUTE MAXIMUM RATINGS ABATT, BATT, EN1, EN2, RESET, OUT, SS to GND ............................................................-0.3V to +6V PGND to GND .......................................................-0.3V to +0.3V LX Current (Note 1) .............................................................2.1A Output Short-Circuit Duration ............................................Infinite Continuous Power Dissipation (TA = +70C) 12-Pin Thin QFN (derate 16.9mW/C above +70C)...1349mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Note 1: LX has internal clamp diodes to PGND and BATT. Applications that forward bias these diodes should take care not to exceed the IC's package power dissipation limits. 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 (VBATT = 3.6V, TA = +0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER CONDITIONS TYP MAX 5.5 V 2.35 2.55 V EN1 = GND, EN2 = BATT, no switching 48 80 EN1 = BATT, EN2 = GND, no switching 700 EN1 = EN2 = GND, TA = +25C 0.1 1 6 9 1.2 2.7 +0.8 +2.0 BATT Input Voltage Undervoltage Lockout Threshold Quiescent Supply Current Shutdown Supply Current MIN 2.6 VBATT rising and falling, 1% hysteresis Maximum Output Current 2.20 800 OUT Bias Current No load, EN1 = EN2 = BATT 100mA load Output-Voltage Accuracy (Voltage Positioning) -0.4 0 550mA load -1 N-Channel On-Resistance ILX = 180mA VBATT = 3.6V 0.28 VBATT = 2.6V 0.33 VBATT = 3.6V 0.18 VBATT = 2.6V 0.20 P-Channel Current-Limit Threshold N-Channel Current-Limit Threshold EN1 = EN2 = BATT N-Channel Zero-Crossing Threshold EN1 = BATT, EN2 = GND LX Output Current (Note 2) LX Leakage Current EN1 = EN2 = GND Maximum Duty Cycle Minimum Duty Cycle A % 0.3 ILX = 180mA A -2 Line Regulation P-Channel On-Resistance A mA 300mA load 800mA load UNITS %/V 0.45 0.30 1.00 1.25 1.65 -0.68 -0.52 -0.37 A 15 40 65 mA 1.4 ARMS 10 A 0.1 100 EN1 = BATT, EN2 = GND or EN1 = GND, EN2 = BATT % 0 EN1 = EN2 = BATT A 16.7 % 17.3 Switching Frequency 1.8 2 2.2 MHz SS Output Impedance 65 100 150 k 2 _______________________________________________________________________________________ 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET (VBATT = 3.6V, TA = +0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER SS Discharge Resistance EN_ Logic Input High CONDITIONS MIN EN1 = EN2 = GND VABATT > 4.2V 1.6 VABATT 4.2V 1.4 TYP MAX UNITS 100 200 V EN_ Logic Input Low EN_ Logic Input Current 0.4 V A 0.1 1 RESET Threshold Percent of nominal, measured at OUT 87 90 93 % RESET Timer Delay Time From VOUT > 90% to RESET = HI 170 200 230 ms RESET Output Low Level ISINK = 1mA 0.015 0.075 V 14 20 k RESET Internal Pullup Resistance to OUT Thermal-Shutdown Threshold 9 TJ rising Thermal-Shutdown Hysteresis 160 C 20 C ELECTRICAL CHARACTERISTICS (VBATT = 3.6V, TA = -40C to +85C, unless otherwise noted.) (Note 3) PARAMETER CONDITIONS BATT Input Voltage Undervoltage Lockout Threshold VBATT rising and falling, 1% hysteresis Quiescent Supply Current EN1 = GND, EN2 = BATT, no switching Shutdown Supply Current EN1 = EN2 = GND Maximum Output Current MIN TYP MAX UNITS 2.6 5.5 V 2.20 2.55 V 80 A 3 800 OUT Bias Current 9 No load, EN1 = EN2 = BATT Output-Voltage Accuracy (Voltage Positioning) 100mA load P-Channel On-Resistance ILX = 180mA 3.2 -1.2 A mA +2.8 A % 0.45 0.3 -0.22 A N-Channel On-Resistance ILX = 180mA N-Channel Current-Limit Threshold EN1 = EN2 = BATT N-Channel Zero-Crossing Threshold EN1 = BATT, EN2 = GND 65 mA LX Output Current (Note 2) 1.4 ARMS LX Leakage Current EN1 = EN2 = GND 10 A 17.3 % 2.2 MHz 150 k 200 Maximum Duty Cycle Minimum Duty Cycle 100 1.8 SS Output Impedance EN_ Logic Input High 10 EN1 = EN2 = BATT Switching Frequency SS Discharge Resistance -0.68 65 EN1 = EN2 = GND VABATT > 4.2V 1.6 VABATT 4.2V 1.4 % V _______________________________________________________________________________________ 3 MAX1572 ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (VBATT = 3.6V, TA = -40C to +85C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX EN_ Logic Input Low EN_ Logic Input Current RESET Threshold UNITS 0.4 V 1 A Percent of nominal, measured at OUT 87 93 % RESET Timer Delay Time From VOUT > 90% to RESET = HI 170 230 ms RESET Output Low Level ISINK = 1mA RESET Internal Pullup Resistance to OUT 9 0.2 V 20 k Note 2: Guaranteed by design, not production tested. Note 3: Specifications to -40C are guaranteed by design and not production tested. Typical Operating Characteristics (VBATT = 3.6V, VOUT = 1.5V, EN1 = GND, EN2 = BATT, TA = +25C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT WITH 2.5V OUTPUT VIN = 2.6V VIN = 3.6V 70 VIN = 5V 60 VIN = 2.6V 70 VIN = 5V VIN = 3.6V 90 60 50 40 10 100 70 VIN = 2.6V VIN = 3.6V VIN = 5V 60 40 1 10 1000 100 1 10 1000 100 LOAD CURRENT (mA) LOAD CURRENT (mA) EFFICIENCY vs. LOAD CURRENT vs. MODE OUTPUT VOLTAGE vs. LOAD CURRENT OUTPUT VOLTAGE vs. INPUT VOLTAGE WITH 100mA LOAD 1.54 FORCEDPWM MODE TA = +85C 1.52 1.50 TA = +25C 1.48 1.46 TA = -40C 1.44 50 1.53 OUTPUT VOLTAGE (V) PULSESKIP MODE 60 1.56 OUTPUT VOLTAGE (V) 80 1.55 MAX1572toc05 MAX1572toc04 PULSEGROUP MODE 70 1.58 TA = +85C MAX1572toc06 LOAD CURRENT (mA) 100 90 1000 80 50 40 1 1.51 TA = +25C TA = -40C 1.49 1.47 1.42 1.40 40 1 10 100 LOAD CURRENT (mA) 4 80 MAX1572toc03 90 50 100 EFFICIENCY (%) 80 EFFICIENCY vs. LOAD CURRENT WITH 1.5V OUTPUT MAX1572toc02 100 EFFICIENCY (%) 90 EFFICIENCY (%) EFFICIENCY vs. LOAD CURRENT WITH 1.8V OUTPUT MAX1572toc01 100 EFFICIENCY (%) MAX1572 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET 1000 1.45 0 200 400 600 LOAD CURRENT (mA) 800 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5.0 5.5 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET INPUT CURRENT vs. INPUT VOLTAGE WITH NO LOAD MAX1572toc07 50 INPUT CURRENT (A) HEAVY-LOAD SWITCHING WAVEFORMS MAX1572 toc08 60 VLX 2V/div 40 VOUT RIPPLE 30 10mV/div 20 500mA/div IL 10 ILOAD = 500mA 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 200ns/div INPUT VOLTAGE (V) LIGHT-LOAD SWITCHING WAVEFORMS SOFT-START/SHUTDOWN WAVEFORMS MAX1572 toc09 MAX1572 toc10 VLX 2V/div VOUT RIPPLE VEN2 2V/div VOUT 1V/div 20mV/div 100mA/div IIN IL 500mA/div ILOAD = 20mA 200s/div 2s/div RESET WAVEFORM LOAD TRANSIENT, FORCED-PWM MODE MAX1572 toc11 MAX1572 toc12 2V/div VEN2 VOUT 1V/div VRESET 1V/div 100mA/div IIN VOUT 100mV/div ILOAD 500mA/div ILOAD = 20mA TO 550mA 100ms/div 4s/div _______________________________________________________________________________________ 5 MAX1572 Typical Operating Characteristics (continued) (VBATT = 3.6V, VOUT = 1.5V, EN1 = GND, EN2 = BATT, TA = +25C, unless otherwise noted.) MAX1572 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET Typical Operating Characteristics (continued) (VBATT = 3.6V, VOUT = 1.5V, EN1 = GND, EN2 = BATT, TA = +25C, unless otherwise noted.) LOAD TRANSIENT, PULSE-SKIP MODE LOAD TRANSIENT, PULSE-GROUP MODE MAX1572 toc13 MAX1572 toc14 VOUT 100mV/div VOUT 100mV/div ILOAD 500mA/div ILOAD 500mA/div ILOAD = 20mA TO 550mA ILOAD = 20mA TO 550mA 4s/div 4s/div LINE TRANSIENT MAX1572 toc15 VOUT 20mV/div VIN 1V/div 200mA/div IL VIN = 3.5V TO 4.0V 40s/div 6 _______________________________________________________________________________________ 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET PIN NAME FUNCTION Active-Low RESET Output. Open-drain output with internal 14k pullup to OUT. RESET is driven LOW in shutdown. 1 RESET 2 SS 3, 5, 11 GND Ground. Connect all ground pins to the exposed paddle. OUT Output Sense Input. Connect to the output of the regulator. In shutdown, OUT is discharged internally with 14k to GND. 4 6 EN2 7 PGND 8 LX 9 BATT 10 EN1 12 ABATT Soft-Start Control. Connect a capacitor from SS to GND to set the soft-start time. Use a 1000pF or larger capacitor to eliminate inrush current during startup. With greater than 10F total output capacitance, increase CSS to COUT/10,000 for soft-start. In shutdown, SS is discharged internally with 100 to GND. Enable/Mode Control Input 2. See Table 1. Power Ground. Connect to exposed paddle. Inductor Connection. LX is high impedance in shutdown. Supply Voltage Input. Connect to a 2.6V to 5.5V source. Connect a 10F ceramic capacitor from BATT to GND. Enable/Mode Control Input 1. See Table 1. Analog Supply Input. Connect to BATT through a 10 resistor. Connect a 0.1F capacitor from ABATT to GND. Exposed Exposed Paddle. Connect to GND and PGND. Paddle -- Table 1. Mode Select Truth Table MODE EN1 EN2 Shutdown 0 0 Pulse group 0 1 Pulse skip 1 0 Forced PWM 1 1 EN2 MODE SELECT EN1 CLOCK 2MHz ABATT 0.1F 10 A zero represents EN_ being driven low or connected to GND. A 1 represents EN_ being driven high or connected to BATT. SLOPE COMP INPUT 2.6V TO 5.5V BATT CURRENT SENSE PWM CONTROL 10F LX OUTPUT 0.75V TO 2.5V 800mA 2.2H Detailed Description COUT MAX1572 PGND Figure 1 is the functional diagram. RESET PWM Control Scheme The MAX1572 uses a 2MHz fixed-frequency, pulsewidth-modulated (PWM), current-mode control scheme. The heart of the current-mode PWM controller is an open-loop comparator that compares the error amp voltage-feedback signal against the sum of the amplified current-sense signal and the slope compensation ramp. At each rising edge of the internal clock, the internal high-side P-channel MOSFET turns on until the PWM comparator trips. During this on-time, current ramps up through the inductor, sourcing current to the RESET TIMER 170ms OUT EA REFERENCE THERMAL SHUTDOWN GND SS 1000pF Figure 1. Functional Diagram _______________________________________________________________________________________ 7 MAX1572 Pin Description MAX1572 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET output and storing energy in the inductor's magnetic field. The current-mode feedback system regulates the peak inductor current as a function of the output voltage error signal. Since the average inductor current is nearly the same as the peak inductor current (assuming that the inductor value is relatively high to minimize ripple current), the circuit acts as a switch-mode transconductance amplifier. This pushes the output LC filter pole, normally found in a voltage-mode PWM, to a higher frequency. To preserve inner-loop stability and eliminate inductor staircasing, an internal slope-compensation ramp is summed into the main PWM comparator. During the second half of the switching cycle (off-time), the internal high-side P-channel MOSFET turns off and the internal low-side N-channel MOSFET turns on. Now the inductor releases the stored energy as its current ramps down while still providing current to the output. The output capacitor stores charge when the inductor current exceeds the load current and discharges when the inductor current is lower, smoothing the voltage across the load. Under overload conditions, when the inductor current exceeds the current limit, the high-side MOSFET is turned off and the low-side MOSFET remains on for the remainder of the cycle to let the inductor current ramp down. pulse-group mode. In pulse-skip mode, the output voltage ripple is lower, and the load-transient response faster. However, the quiescent current is higher than in pulse-group mode. Forced-PWM Mode In forced-PWM mode, the MAX1572 operates at a constant 2MHz switching frequency without pulse skipping. This is desirable in noise-sensitive applications, since the output ripple is minimized and has a predictable noise spectrum. Forced-PWM mode requires higher supply current with light loads due to constant switching. 100% Duty-Cycle Operation The MAX1572 can operate at 100% duty cycle. In this state, the high-side P-channel MOSFET is turned on (not switching). This occurs when the input voltage is close to the output voltage. The dropout voltage is the voltage drop due to the output current across the on-resistance of the internal P-channel MOSFET (RDS(ON)P) and the inductor resistance (RL): VDROPOUT = IOUT x ( RDS(ON)P + RL ) RDS(ON)P is given in the Electrical Characteristics section. RL, for a few recommended inductors, is given in Table 2. Pulse-Group Mode Pulse-group mode is used to minimize the supply current with a light load. In pulse-group mode, the IC shuts off most internal circuitry when VOUT is +0.8% above nominal regulation. When VOUT drops below +0.8% of the nominal regulation voltage, the IC powers up its circuits and resumes switching. Pulse-Skip Mode Pulse-skip mode is also used to minimize the supply current with a light load. The difference between pulsegroup and pulse-skip modes is that when VOUT rises above the +0.8% regulation point, pulse-group mode stops switching and completely turns off a number of circuits. Under the same conditions, pulse-skip mode stops switching but leaves all circuits on. The delay coming out of pulse-skip mode is shorter than with Load-Transient Response/ Voltage Positioning The MAX1572 uses voltage positioning that matches the load regulation to the voltage droop seen during load transients. In this way, the output voltage does not overshoot when the load is removed, which results in the total output-voltage variation being half as wide as in a conventional design. Figure 2 shows an example of a voltage-positioned and a nonvoltage-positioned load transient. Additionally, the MAX1572 uses a wide-bandwidth feedback loop to respond more quickly to a load transient than regulators using conventional integrating feedback loops. The load line used to achieve voltage positioning is shown in Figure 3. This assumes a nominal operating point of 3.6V input at 300mA load. Table 2. Recommended Inductors MANUFACTURER Murata Sumida TOKO 8 PART VALUE (H) RL (m) ISAT (mA) SIZE (mm) SHIELDED LQH32CN 2.2 97 790 2.5 x 3.2 x 2.0 No CDRH3D16 2.2 50 1200 3.8 x 3.8 x 1.8 Yes CDRH2D11 2.2 78 780 3.2 x 3.2 x 1.2 Yes D312F 2.2 170 1200 3.6 x 3.6 x 1.2 No D412F 2.2 140 1330 4.8 x 4.8 x 1.2 No _______________________________________________________________________________________ 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET VOUT (VOLTAGE POSITIONING) FORCED-PWM VIN = 3.6V CHANGE IN OUTPUT 0 VOLTAGE (%) VOUT (CONVENTIONAL) MAX1572 NORMAL OPERATION +1 VIN = 5.5V -1 VIN = 2.6V IOUT -2 0 200 400 600 800 LOAD CURRENT (mA) Figure 2. Load Transient Response, With and Without Voltage Positioning Soft-Start Soft-start is used to prevent input-current overshoot during startup. For most applications using a 10F output capacitor, connect a 1000pF capacitor from SS to GND. If a larger output capacitor is used, then use the following formula to find the value of the soft-start capacitor needed to prevent input-current overshoot: CSS = COUT /104 During soft-start, the output voltage rises from 0 to V OUT(nom) with a time constant equal to CSS times 100k (see the Typical Operating Characteristics). 170ms RESET RESET is an open-drain output with an internal 14k pullup resistor to OUT. During startup, RESET is held low until 200ms (typ) after the output voltage reaches 90% of its nominal regulation voltage. When the output voltage drops below 90% of its nominal regulation voltage, RESET pulls low again. See the Typical Operating Characteristics section for RESET waveforms during startup and shutdown. Applications Information Inductor Selection A 2.2H inductor with a saturation current of at least 1A is recommended for full-load (800mA) applications. For lower load currents, the inductor current rating may be reduced. For most applications, use an inductor with a current rating 1.25 times the maximum required output Figure 3. Voltage-Positioning Load Line current. For maximum efficiency, the inductor's DC resistance should be as low as possible. See Table 2 for recommended inductors and manufacturers. Capacitor Selection Ceramic 10F input and output capacitors are recommended for most applications. For output voltages below 1.5V, output capacitance should be increased to 22F. For best stability over a wide temperature range, use capacitors with an X5R or better dielectric. ABATT Input Filter In normal applications, an RC filter on ABATT keeps power-supply noise from entering the IC. Connect a 10 resistor between BATT and ABATT and connect a 0.1F capacitor from ABATT to GND. PC Board Layout and Routing Due to fast-switching waveforms and high-current paths, careful PC board layout is required. An evaluation kit (MAX1572EVKIT) is available to speed design. When laying out a board, minimize trace lengths between the IC, the inductor, the input capacitor, and the output capacitor. Keep these traces short, direct, and wide. Keep noisy traces, such as the LX node trace, away from OUT. The input bypass capacitors should be placed as close to the IC as possible. Connect PGND and GND directly to the exposed paddle underneath the IC. The ground connections of the input and output capacitors should be as close together as possible. _______________________________________________________________________________________ 9 Selector Guide PART VOUT (V) TOP MARK MAX1572ETC075 0.75 AABW MAX1572ETC130 1.30 AACW MAX1572ETC150 1.50 AABX MAX1572ETC180 1.80 AABY MAX1572ETC250 2.50 AABZ MAX1572ETCxyz * -- Chip Information TRANSISTOR COUNT: 3697 PROCESS: BiCMOS *xyz is for output voltage (e.g., MAX1572ETC165 has a 1.65V output). 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.) 24L QFN THIN.EPS MAX1572 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm 21-0139 10 ______________________________________________________________________________________ C 1 2 800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm 21-0139 C 2 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1572 Package Information (continued) (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.)