MAX1644EAE+TG52

19-1457; Rev 3; 8/05 KIT ATION EVALU LE B A IL A AV 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches The MAX1644 constant-off-time, PWM step-down DCDC converter is ideal for use in applications such as PC cards, CPU daughter cards, and desktop computer bus-termination boards. The device features internal synchronous rectification for high efficiency and reduced component count. It requires no external Schottky diode. The internal 0.10Ω PMOS power switch and 0.10Ω NMOS synchronous-rectifier switch easily deliver continuous load currents up to 2A. The MAX1644 produces a preset +3.3V or +2.5V output voltage or an adjustable output from +1.1V to VIN. It achieves efficiencies as high as 95%. The MAX1644 uses a unique current-mode, constantoff-time, PWM control scheme, which includes an Idle Mode™ to maintain high efficiency during light-load operation. The programmable constant-off-time architecture sets switching frequencies up to 350kHz, allowing the user to optimize performance trade-offs between efficiency, output switching noise, component size, and cost. The device also features an adjustable soft-start to limit surge currents during start-up, a 100% duty cycle mode for low-dropout operation, and a lowpower shutdown mode that disconnects the input from the output and reduces supply current below 1µA. The MAX1644 is available in a 16-pin SSOP package. Applications Features ♦ ±1% Output Accuracy ♦ 95% Efficiency ♦ Internal PMOS and NMOS Switches 70mΩ On-Resistance at VIN = +4.5V 100mΩ On-Resistance at VIN = +3V ♦ Output Voltage +3.3V or +2.5V Pin-Selectable +1.1V to VIN Adjustable ♦ +3V to +5.5V Input Voltage Range ♦ 360µA (max) Operating Supply Current ♦ < 1µA Shutdown Supply Current ♦ Programmable Constant-Off-Time Operation ♦ 350kHz (max) Switching Frequency ♦ Idle Mode Operation at Light Loads ♦ Thermal Shutdown ♦ Adjustable Soft-Start Inrush Current Limiting ♦ 100% Duty Cycle During Low-Dropout Operation ♦ Output Short-Circuit Protection ♦ 16-Pin SSOP Package Ordering Information +5V to +3.3V/+2.5V Conversion CPU I/O Supply PART +3.3V PC Card and CardBus Applications Notebook and Subnotebook Computers Desktop Bus-Termination Boards CPU Daughter Card Supply TEMP RANGE PIN-PACKAGE MAX1644EAE 40°C to +85°C 16 SSOP MAX1644EAE+ 40°C to +85°C 16 SSOP +Denotes lead-free package. Pin Configuration Typical Operating Circuit TOP VIEW INPUT +3V TO +5.5V IN LX MAX1644 FB VCC OUTPUT +1.1V TO VIN PGND 16 LX IN 2 15 PGND 14 LX LX 3 IN 4 MAX1644 GND COMP 6 REF SS TOFF 7 13 PGND 12 VCC SS 5 FBSEL SHDN COMP TOFF SHDN 1 11 FBSEL 10 REF 9 FB 8 GND RTOFF SSOP Idle Mode is a trademark of Maxim Integrated Products, Inc. A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES. ________________________________________________________________ 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 MAX1644 General Description MAX1644 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches ABSOLUTE MAXIMUM RATINGS VCC, IN to GND ........................................................-0.3V to +6V Continuous Power Dissipation (TA = +70°C) IN to VCC .............................................................................±0.3V SSOP (derate 16.7mW/°C above +70°C; GND to PGND.....................................................................±0.3V part mounted on 1 in.2 of 1oz. copper) ............................1.2W Operating Temperature Range ...........................-40°C to +85°C All Other Pins to GND.................................-0.3V to (VCC + 0.3V) LX Current (Note 1)...........................................................±3.75A Storage Temperature Range .............................-65°C to +150°C REF Short Circuit to GND Duration ............................Continuous Lead Temperature (soldering, 10s) ................................ +300°C ESD Protection .....................................................................±2kV Note 1: LX has internal clamp diodes to PGND and IN. 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 (VIN = VCC = +3.3V, FBSEL = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Input Voltage Preset Output Voltage SYMBOL VOUT Adjustable Output Voltage Range DC Load Regulation Error Reference Voltage VDO TYP ILOAD = 0 to 2A, VFB = VOUT 3.366 VIN = VCC = 3V to 5.5V, FBSEL = VCC 2.500 2.525 2.550 VIN = VCC = 3V to 5.5V, FBSEL = REF 1.089 1.100 1.111 VREF VIN FBSEL = GND 1 FBSEL = REF, VCC, or unconnected 2 FBSEL = GND 0.2 FBSEL = REF, VCC, or unconnected 0.4 VIN = VCC = 3V, ILOAD = 1A, FBSEL = VCC VREF V % mV 1.100 1.111 V 0.5 1 mV VIN = 4.5V 70 150 VIN = 3V 100 200 RON, P ILX = 0.5A NMOS Switch On-Resistance RON, N ILX = 0.5A VIN = 4.5V 70 150 VIN = 3V 100 200 ILIMIT 2.5 2.9 IIM 0.25 mΩ mΩ 3.3 A 2.5 A 0.45 0.65 A RMS LX Output Current 350 kHz No-Load Supply Current IIN + ICC VFB = 1.2V 240 360 µA Shutdown Supply Current ICC(SHDN) SHDN = GND 0.2A): t OFF = where: (VIN – VOUT − VPMOS ) fPWM ( VIN − VPMOS + VNMOS ) tOFF = the programmed off-time VIN = the input voltage VOUT = the output voltage VNMOS = the voltage drop across the internal PMOS power switch VPMOS = the voltage drop across the internal NMOS synchronous-rectifier switch _______________________________________________________________________________________ 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches Inductor Selection Three key inductor parameters must be specified: inductor value (L), peak current (IPEAK), and DC resistance (RDC). The following equation includes a constant, denoted as LIR, which is the ratio of peakto-peak inductor AC current (ripple current) to maximum DC load current. A higher value of LIR allows smaller inductance but results in higher losses and ripple. A good compromise between size and losses is found at approximately a 25% ripple-current to loadcurrent ratio (LIR = 0.25), which corresponds to a peak inductor current 1.125 times higher than the DC load current: L = VOUT × tOFF IOUT × LIR where: IOUT = maximum DC load current LIR = ratio of peak-to-peak AC inductor current to DC load current, typically 0.25 The peak inductor current at full load is 1.125 · IOUT if the above equation is used; otherwise, the peak current is calculated by: IPEAK = IOUT + Capacitor Selection The input filter capacitor reduces peak currents and noise at the voltage source. Use a low-ESR and lowESL capacitor located no further than 5mm from IN. Select the input capacitor according to the RMS input ripple-current requirements and voltage rating: ( VOUT VIN − VOUT ESR > 1% × L tOFF Stable operation requires the correct output filter capacitor. When choosing the output capacitor, ensure that: COUT ≥ (tOFF / VOUT) ✕ (64µFV / µs) With an AC load regulation setting of 1%, the COUT requirement doubles, and the minimum ESR of the output capacitor is halved. Integrator Amplifier An internal transconductance amplifier fine tunes the output DC accuracy. A capacitor, CCOMP, from COMP to VCC compensates the transconductance amplifier. For stability, choose: CCOMP ≥ 470pF A large capacitor value maintains a constant average output voltage but slows the loop response to changes in output voltage. A small capacitor value speeds up the loop response to changes in output voltage but decreases stability. Choose the capacitor values that result in optimal performance. Setting the AC Loop Gain VOUT × tOFF 2 × L Choose an inductor with a saturation current at least as high as the peak inductor current. To minimize loss, choose an inductor with a low DC resistance. IRIPPLE = ILOAD The output filter capacitor affects the output voltage ripple, output load-transient response, and feedback loop stability. For stable operation, the MAX1644 requires a minimum output ripple voltage of VRIPPLE ≥ 2% · VOUT (with 2% load regulation setting). The minimum ESR of the output capacitor should be: The MAX1644 allows selection of a 1% or 2% AC loadregulation error when the adjustable output voltage mode is selected (Table 2). A 2% setting is automatically selected in preset output voltage mode (FBSEL connected to VCC or unconnected). A 2% load-regulation error setting reduces output filter capacitor requirements, allowing the use of smaller and less expensive capacitors. Selecting a 1% load-regulation error reduces transient load errors, but requires larger capacitors. ) VIN _______________________________________________________________________________________ 9 MAX1644 f PWM = switching frequency in PWM mode (IOUT > 0.2A) Select RTOFF according to the formula: RTOFF = (tOFF - 0.07µs) (150kΩ / 1.26µs) Recommended values for RTOFF range from 39kΩ to 470kΩ for off-times of 0.4µs to 4µs. MAX1644 2A Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches Soft-Start Soft-start allows a gradual increase of the internal current limit to reduce input surge currents at start-up and at exit from shutdown. A charging capacitor, C SS , placed from SS to GND sets the rate at which the internal current limit is changed. Upon power-up, when the device comes out of undervoltage lockout (2.6V typ) or after the SHDN pin is pulled high, a 5µA constant-current source charges the soft-start capacitor and the voltage on SS increases. When the voltage on SS is less than approximately 0.7V, the current limit is set to zero. As the voltage increases from 0.7V to approximately 1.8V, the current limit is adjusted from 0 to 2.9A. The voltage across the soft-start capacitor changes with time according to the equation: VSS = 5μA × t CSS The soft-start current limit varies with the voltage on the soft-start pin, SS, according to the equation: ILIMIT = (VSS - 0.7V) · 2.7A/V, for VSS > 0.7V The constant-current source stops charging once the voltage across the soft-start capacitor reaches 1.8V (Figure 3). Circuit Layout and Grounding Good layout is necessary to achieve the MAX1644’s intended output power level, high efficiency, and low noise. Good layout includes the use of a ground plane, appropriate component placement, and correct routing of traces using appropriate trace widths. The following points are in order of decreasing importance: 1) Minimize switched-current and high-current ground loops. Connect the input capacitor’s ground, the output capacitor’s ground, and PGND together. 10 SHDN 0 1.8V VSS (V) 0.7V 0 2.9A ILIMIT (A) 0 t Figure 3. Soft-Start Current Limit over Time 2) Connect the input filter capacitor less than 5mm away from IN. The connecting copper trace carries large currents and must be at least 2mm wide, preferably 5mm. 3) Place the LX node components as close together and as near to the device as possible. This reduces resistive and switching losses as well as noise. 4) A ground plane is essential for optimum performance. In most applications, the circuit is located on a multilayer board, and full use of the four or more layers is recommended. Use the top and bottom layers for interconnections and the inner layers for an uninterrupted ground plane. ___________________Chip Information TRANSISTOR COUNT: 1758 ______________________________________________________________________________________ 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches SSOP.EPS 2 1 INCHES E H MILLIMETERS DIM MIN MAX MIN MAX A 0.068 0.078 1.73 1.99 A1 0.002 0.008 0.05 0.21 B 0.010 0.015 0.25 0.38 C D 0.20 0.09 0.004 0.008 SEE VARIATIONS E 0.205 e 0.212 0.0256 BSC 5.20 MILLIMETERS INCHES D D D D D 5.38 MIN MAX MIN MAX 0.239 0.239 0.278 0.249 0.249 0.289 6.07 6.07 7.07 6.33 6.33 7.33 0.317 0.397 0.328 0.407 8.07 10.07 8.33 10.33 N 14L 16L 20L 24L 28L 0.65 BSC H 0.301 0.311 7.65 7.90 L 0.025 0∞ 0.037 8∞ 0.63 0∞ 0.95 8∞ N A C B e L A1 D NOTES: 1. D&E DO NOT INCLUDE MOLD FLASH. 2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006"). 3. CONTROLLING DIMENSION: MILLIMETERS. 4. MEETS JEDEC MO150. 5. LEADS TO BE COPLANAR WITHIN 0.10 MM. PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, SSOP, 5.3 MM APPROVAL DOCUMENT CONTROL NO. 21-0056 REV. C 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11 © 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc. MAX1644 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.)