19-1006; Rev 4; 4/09 KIT ATION EVALU E L B AVAILA High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter The MAX8625A PWM step-up/down regulator is intended to power digital logic, hard disk drives, motors, and other loads in portable, battery-powered devices such as PDAs, cell phones, digital still cameras (DSCs), and MP3 players. The MAX8625A provides either a fixed 3.3V or adjustable output voltage (1.25V to 4V) at up to 0.8A from a 2.5V to 5.5V input. The MAX8625A utilizes a 2A peak current limit. Maxim’s proprietary H-bridge topology* provides a seamless transition through all operating modes without the glitches commonly seen with other devices. Four internal MOSFETs (two switches and two synchronous rectifiers) with internal compensation minimize external components. A SKIP input selects a low-noise, fixedfrequency PWM mode, or a high-efficiency skip mode where the converter automatically switches to PFM mode under light loads for best light-load efficiency. The internal oscillator operates at 1MHz to allow for a small external inductor and capacitors. The MAX8625A features current-limit circuitry that shuts down the IC in the event of an output overload. In addition, soft-start circuitry reduces inrush current during startup. The IC also features True ShutdownTM, which disconnects the output from the input when the IC is disabled. The MAX8625A is available in a 3mm x 3mm, 14-pin TDFN package. Applications PDAs and Smartphones DSCs and Camcorders MP3 Players and Cellular Phones Features o o o o o Four Internal MOSFET True H-Bridge Buck/Boost Glitch-Free, Buck-Boost Transitions Minimal Output Ripple Variation on Transitions Up to 92% Efficiency 37µA (typ) Quiescent Current in Skip Mode o 2.5V to 5.5V Input Range o Fixed 3.3V or Adjustable Output o 1µA (max) Logic-Controlled Shutdown o o o o o o o True Shutdown Output Overload Protection Internal Compensation Internal Soft-Start 1MHz Switching Frequency Thermal-Overload Protection Small 3mm x 3mm, 14-Pin TDFN Package Ordering Information PINPACKAGE PART MAX8625AETD+ TOP MARK 14 TDFN-EP** ABQ Note: The device is specified over the -40°C to +85°C extended temperature range. +Denotes a lead(Pb)-free/RoHS-compliant package. **EP = Exposed pad. Battery-Powered Hard Disk Drive (HDD) Pin Configuration Typical Operating Circuit IN IN GND GND OUT OUT REF TOP VIEW 14 13 12 11 10 9 8 INPUT 2.7V TO 5.5V LX1 IN LX2 OUTPUT 3.3V OUT GND MAX8625A PWM EP + SKIP 1 2 3 4 5 6 7 LX1 LX1 LX2 LX2 ON SKIP FB SKIP TDFN-EP EP = EXPOSED PAD. ON OFF MAX8625A FB REF ON *U.S. Patent #7,298,119. True Shutdown is a trademark of Maxim Integrated Products, Inc. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX8625A General Description MAX8625A High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter ABSOLUTE MAXIMUM RATINGS IN, OUT, SKIP, ON to GND ......................................-0.3V to +6V REF, FB, to GND...............................................-0.3V, (IN + 0.3V) LX2, LX1 (Note 1).........................................................±1.5ARMS Continuous Power Dissipation (TA = +70°C) Single-Layer Board (derate 18.5mW/°C above TA = +70°C) ...................................................1482mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Note 1: LX1 and LX2 have internal clamp diodes to IN, PGND and OUT, PGND, respectively. Applications that forward bias these diodes should take care not to exceed the device's 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 = 3.6V, ON = SKIP = IN, FB = GND, VOUT = 3.3V, LX_ unconnected, CREF = C5 = 0.1µF to GND, Figure 4. TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 2) PARAMETER Supply Range UVLO Threshold SYMBOL CONDITIONS VIN UVLO VIN rising, 60mV hysteresis MIN TYP MAX 2.5 5.5 V 2.20 2.49 V 22 mA Quiescent Supply Current, FPWM Mode, Switching IIN No load, VOUT = 3.2V 15 Quiescent Supply Current, Skip Mode, Switching IIN SKIP = GND, no load 37 Quiescent Supply Current, No Switching, Skip Mode IIN SKIP = GND, FB = 1.3V 35 45 Shutdown Supply Current IIN ON = GND, TA = +25°C 0.1 1 TA = +85°C 0.2 PWM mode, VIN = 2.5V to 5.5V 3.30 IOUT = 0 to 0.5A, VIN = 2.5V to 5.5V, TA = -40°C to +85°C (Note 3) Output Voltage Accuracy (Fixed Output) -1 3.28 Average skip voltage 3.285 Load step +0.5A µA µA % V -3 1.25 µA V +1 SKIP mode, valley regulation value Output Voltage Range (Adjustable Output) UNITS % 4.00 V Maximum Output Current VIN = 3.6V 0.80 A Soft-Start L = 3.3µH; COUT = C3 + C4 = 44µF 250 mA/ms Load Regulation IOUT = 0 to 500mA 0.1 %/A Line Regulation VIN = 2.5V to 5.5V 0.03 %/V 3 µA OUT Bias Current IOUT REF Output Voltage VREF REF Load Regulation FB Feedback Threshold 2 VOUT = 3.3V VIN = 2.5V to 5.5V 1.244 IREF = 10µA VFB IOUT = 0 to full load, PWM mode; VIN = 2.5V to 5.5V 1.25 1.256 1 1.244 1.25 _______________________________________________________________________________________ V mV 1.258 V High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter (VIN = 3.6V, ON = SKIP = IN, FB = GND, VOUT = 3.3V, LX_ unconnected, CREF = C5 = 0.1µF to GND, Figure 4. TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 2) PARAMETER FB Dual-Mode Threshold SYMBOL CONDITIONS MIN TYP MAX UNITS 75 100 125 mV VFB = 1.3V, TA = +25°C 0.001 0.1 VFB = 1.3V, TA = +85°C 0.01 VFBDM FB Leakage Current IFB ON, SKIP Input High Voltage VIH 2.5V < VIN < 5.5V ON, SKIP Input Low Voltage VIL 2.5V < VIN < 5.5V ON Input Leakage Current SKIP Input Leakage Current Peak Current Limit IIHL 1.6 0.45 0.001 TA = +85°C 0.01 ISKIPH VSKIP = 3.6V ISKIPL VSKIP = 0V -2 -0.2 3 ILIMP LX1 PMOS 1700 2000 Rectifier-Off Current Threshold Idle-Mode Current Threshold (Note 4) LX1, LX2 Leakage Current RON ILX1OFF ISKIP ILXLKG Out Reverse Current ILXLKGR Minimum TON TONMIN OSC Frequency Thermal Shutdown 1 12 2300 100 Each MOSFET, TA = +25°C MOSFET On-Resistance V 2.5V < VIN < 5.5V, TA = +25°C Fault Latch-Off Delay 0.05 Each MOSFET, VIN = 2.5V to 5.5V, TA = -40°C to +85°C 125 SKIP = GND, load decreasing 100 Load increasing 300 VIN = VOUT = 5.5V, VLX1 = 0V to VIN, VLX2 = 0V to VOUT, TA = +25°C 0.01 TA = +85°C 0.2 VIN = VLX1 = VLX2 = 0V, VOUT = 5.5V, measure I (LX2), TA = +25°C 0.01 TA = +85°C 0.5 15°C hysteresis 1000 +165 µA µA mA ms Ω mA mA 1 1 25 850 V 0.1 0.2 SKIP = GND FOSCPWM µA µA µA % 1150 kHz °C Note 2: Devices are production tested at TA = +25°C. Specifications over the operating temperature range are guaranteed by design and characterization. Note 3: Limits are guaranteed by design and not production tested. Note 4: The idle-mode current threshold is the transition point between fixed-frequency PWM operation and idle-mode operation. The specification is given in terms of output load current for an inductor value of 3.3µH. For the step-up mode, the idle-mode transition varies with input to the output-voltage ratios. _______________________________________________________________________________________ 3 MAX8625A ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 3.6V, SKIP = GND, TA = +25°C, Figure 4, unless otherwise noted.) 60 50 VOUT = 3.3V VIN = 2.7V 3.0V, 3.3V, 3.6V, 4.2V, 5.0V 30 20 10 90 EFFICIENCY (%) 70 85 100mA 80 500mA 75 1 10 60 50 VOUT = 2.8V VIN = 2.7V 3.0V, 3.3V, 3.6V, 4.2V, 5.0V 40 20 10 0 2.0 1000 100 70 30 VOUT = 3.3V LOAD CURRENT = 100mA, 300mA, 500mA 65 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 0.1 1 10 1000 100 LOAD CURRENT (mA) INPUT VOLTAGE (V) LOAD CURRENT (mA) EFFICIENCY vs. LOAD CURRENT FPWM MODE (FIGURE 3) OUTPUT VOLTAGE (3.3V INTERNAL FB) vs. LOAD CURRENT OUTPUT VOLTAGE (2.8V EXTERNAL FB) vs. LOAD CURRENT (FIGURE 3) 60 50 VOUT = 3.45V VIN = 2.7V 3.0V, 3.3V, 3.6V, 4.2V, 5.0V 40 30 20 10 1 10 0 -0.5 0.5 0 -0.5 -1.0 -1.5 VOUT = 3.3V TA = +25°C, TA = -40°C, TA = +85°C, -2.0 VOUT = 2.8V TA = +25°C, TA = -40°C, TA = +85°C -1.5 -2.0 0.1 1000 100 1.0 0.5 -1.0 0 0.1 1.5 1.0 DEVIATION (%) 70 1.5 MAX8625A toc06 80 2.0 DEVIATION (%) 90 MAX8625A toc05 2.0 MAX8625A toc04 100 1 10 1000 100 0.1 1 10 1000 100 LOAD CURRENT (mA) LOAD CURRENT (mA) LOAD CURRENT (mA) OUTPUT VOLTAGE vs. INPUT VOLTAGE WITH INTERNAL FB RESISTORS OUTPUT VOLTAGE vs. INPUT VOLTAGE WITH EXTERNAL FB RESISTORS SUPPLY CURRENT vs. INPUT VOLTAGE WITH NO LOAD 3.31 3.30 3.29 3.28 LOAD: 500mA, VOUT = 3.3V TA = +25°C, TA = -40°C, TA = +85°C 2.80 2.79 2.78 2.77 2.76 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 5.5 6.0 10 1 0.1 NO LOAD VOUT = 3.3V LOAD: 500mA, VOUT = 2.8V TA = +25°C, TA = -40°C, TA = +85°C (FIGURE 3) 0.01 2.75 3.27 FPWM MODE SUPPLY CURRENT (mA) 2.81 OUTPUT VOLTAGE (V) 3.32 100 MAX8625A toc09 2.82 MAX8625A toc07 3.33 MAX8625A toc08 EFFICIENCY (%) 80 300mA 60 0.1 OUTPUT VOLTAGE (V) 90 70 0 4 100 MAX8625A toc03 80 95 EFFICIENCY (%) 90 MAX8625A toc02 100 MAX8625A toc01 100 40 EFFICIENCY vs. LOAD CURRENT FPWM MODE (FIGURE 3) SKIP-MODE EFFICIENCY vs. INPUT VOLTAGE EFFICIENCY vs. LOAD CURRENT SKIP AND FPWM MODES EFFICIENCY (%) MAX8625A High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 5.5 6.0 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5.0 5.5 6.0 High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter (VIN = 3.6V, SKIP = GND, TA = +25°C, Figure 4, unless otherwise noted.) SWITCHING WAVEFORMS VIN = 3V, LOAD = 500mA, VOUT = 3.3V MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE MAX8625A toc11 MAX8625A toc10 1000 MAXIMUM LOAD CURRENT (mA) 900 800 VOUT = 3.3V 700 VOUT 50mV/div (AC-COUPLED) VLX1 2V/div 600 500 VLX2 2V/div 400 300 ILX 500mA/div 200 100 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 1μs/div 6.0 INPUT VOLTAGE (V) SWITCHING WAVEFORMS VIN = 3.3V, LOAD = 500mA, VOUT = 3.3V SWITCHING WAVEFORMS VIN = 3.6V, LOAD = 500mA, VOUT = 3.3V MAX8625A toc12 MAX8625A toc13 VOUT 50mV/div (AC-COUPLED) VOUT 50mV/div (AC-COUPLED) VLX1 2V/div VLX1 2V/div VLX2 2V/div VLX2 2V/div ILX 500mA/div ILX 500mA/div 1μs/div 1μs/div FPWM MODE VIN = 3V, LOAD = 20mA, VOUT = 3.308V SKIP MODE VIN = 3V, LOAD = 20mA, VOUT = 3.288V MAX8625A toc15 MAX8625A toc14 VOUT 20mV/div (AC-COUPLED) OUT 20mV/div (AC-COUPLED) CH1 = VLX1 2V/div VLX1 2V/div CH2 = VLX2 2V/div VLX2 2V/div ILX 500mA/div 10μs/div ILX 500mA/div 1μs/div _______________________________________________________________________________________ 5 MAX8625A Typical Operating Characteristics (continued) Typical Operating Characteristics (continued) (VIN = 3.6V, SKIP = GND, TA = +25°C, Figure 4, unless otherwise noted.) STARTUP WAVEFORMS (FIGURE 3) VIN = 3.6V, LOAD = 30Ω, VOUT = 1.5V STARTUP WAVEFORMS VIN = 3.6V, LOAD = 5Ω, VOUT = 3.288V MAX8625A toc17 MAX8625A toc16 SHDN 2V/div SHDN 2V/div VOUT 20mV/div VOUT 500mA/div ILX 500mA/div ILX 500mA/div IBATT 100mA/div IBATT 500mA/div 2ms/div 2ms/div LOAD TRANSIENT VOUT = 3.3V LINE TRANSIENT VOUT = 3.3V, LOAD = 5.5Ω, VIN RAMP 3V TO 4V MAX8625A toc18 MAX8625A toc19 VOUT 100mV/div (DC OFFSET = 3.3V) CH2 = VOUT 50mV/div (AC-COUPLED) IBATT 250mA/div CH1 = VIN 500mV/div 3V OFFSET ILX 500mA/div 1ms/div BODE PLOT GAIN AND PHASE vs. FREQUENCY OSCILLATOR FREQUENCY vs. TEMPERATURE GAIN 1.06 144 1.04 20 108 10 72 0 36 PHASE -10 0 -20 -36 -30 -72 -108 VIN = 3.6 VOUT = 3.3V LOAD = 200mA -40 -50 -60 1 10 100 FREQUENCY (kHz) 6 180 1000 OSCILLATOR FREQUENCY (MHz) 30 PHASE (DEG) MAX8625A toc20 MAX8625A toc21 400μs/div 40 GAIN (dB) MAX8625A High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter 1.02 1.00 0.98 0.96 0.94 -144 0.92 -180 0.90 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) _______________________________________________________________________________________ High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter (VIN = 3.6V, SKIP = GND, TA = +25°C, Figure 4, unless otherwise noted.) REFERENCE vs. TEMPERATURE NO LOAD MINIMUM STARTUP VOLTAGE vs. TEMPERATURE 1.27 2.42 REFERENCE (V) MINIMUM STARTUP VOLTAGE (V) 2.44 MAX8625A toc23 VOUT = 3.3V, NO LOAD 2.46 1.28 MAX8625A toc22 2.48 2.40 2.38 2.36 1.26 1.25 1.24 2.34 2.32 VOUT = 3.3V VIN = 3.0V, 3.6V, 4.2V, 5.0V 1.23 2.30 2.28 1.22 -50 -25 0 25 50 75 100 -20 0 20 40 60 80 TEMPERATURE (°C) REFERENCE vs. TEMPERATURE WITH 300mA LOAD SHUTDOWN DUE TO OVERLOAD VIN = 3.6V, VOUT = 3.288V 100 MAX8625A toc25 MAX8625A toc24 1.28 1.27 REFERENCE (V) -40 TEMPERATURE (°C) VLX2 2V/div 1.26 VLX2 2V/div 1.25 1.24 VOUT 500mV/div VOUT = 3.3V VIN = 3.0V, 3.6V, 4.2V, 5.0V 1.23 ILX 500mA/div 1.22 -40 -20 0 20 40 60 80 100μs/div 100 TEMPERATURE (°C) BOOST-TO-BUCK TRANSITION FPWM MODE VIN = 3.6V, VOUT = 3.288V MAX8625A toc26 VOUT 100mV/div AC-COUPLED VIN 1V/div DC OFFSET = 3V ILX 200mA/div 2μs/div _______________________________________________________________________________________ 7 MAX8625A Typical Operating Characteristics (continued) High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter MAX8625A Pin Description PIN NAME FUNCTION 1, 2 LX1 Inductor Connection 1. Connect the inductor between LX1 and LX2. Both LX1 pins must be connected together externally. LX1 is internally connected to GND during shutdown. 3, 4 LX2 Inductor Connection 2. Connect the inductor between LX1 and LX2. Both LX2 pins must be connected together externally. LX2 is internally connected to GND during shutdown. 5 ON Enable Input. Connect ON to the input or drive high to enable the IC. Drive ON low to disable the IC. 6 SKIP Mode Select Input. Connect SKIP to GND to enable skip mode. This mode provides the best overall efficiency curve. Connect SKIP to IN to enable forced-PWM mode. This mode provides the lowest noise, but reduces lightload efficiency compared to skip mode. 7 FB Feedback Input. Connect to ground to set the fixed 3.3V output. Connect FB to the center tap of an external resistor-divider from the output to GND to set the output voltage to a different value. VFB regulates to 1.25V. 8 REF Reference Output. Bypass REF to GND with a 0.1µF ceramic capacitor. VREF is 1.25V and is internally pulled to GND during shutdown. 9, 10 OUT Power Output. Bypass OUT to GND with two 22µF ceramic capacitors. Both OUT pins must be connected together externally. 11, 12 GND Ground. Connect the exposed pad and GND directly under the IC. 13, 14 IN Power-Supply Input. Bypass IN to GND with two 22µF ceramic capacitors. Connect IN to a 2.5V to 5.5V supply. Both IN pins must be connected together externally. — EP Exposed Pad. Connect to GND directly under the IC. Connect to a large ground plane for increased thermal performance. Detailed Description The MAX8625A step-up/down architecture employs a true H-bridge topology that combines a boost converter and a buck converter topology using a single inductor and output capacitor (Figure 1). The MAX8625A utilizes a pulse-width modulated (PWM), current-mode control scheme and operates at a 1MHz fixed frequency to minimize external component size. A proprietary H-bridge design eliminates mode changes when transitioning from buck to boost operation. This control scheme provides very low output ripple using a much smaller inductor than a conventional H-bridge, while avoiding glitches that are commonly seen during mode transitions with competing devices. The MAX8625A switches at an internally set frequency of 1MHz, allowing for tiny external components. Internal compensation further reduces the external component count in cost- and space-sensitive applications. The MAX8625A is optimized for use in HDDs, DSCs, and other devices requiring low-quiescent current for optimal light-load efficiency and maximum battery life. 8 Control Scheme The MAX8625A basic noninverting step-up/down converter operates with four internal switches. The control logic determines which two internal MOSFETs operate to maintain the regulated output voltage. Unlike a traditional H-bridge, the MAX8625A utilizes smaller peakinductor currents, thus improving efficiency and lowering input/output ripple. The MAX8625A uses three operating phases during each switching cycle. In phase 1 (fast-charge), the inductor current ramps up with a di/dt of VIN/L. In phase 2 (slow charge/discharge), the current either ramps up or down depending on the difference between the input voltage and the output voltage (VIN - VOUT)/L. In phase 3 (discharge), the inductor current discharges at a rate of VOUT/L through MOSFETs P2 and N1 (see Figure 1). An additional fourth phase (phase 4: hold) is entered when the inductor current falls to zero during phase 3. This fourth phase is only used during skip operation. The state machine (Figure 2) decides which phase to use and when to switch phases. The converter goes through the first three phases in the same order at all _______________________________________________________________________________________ High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter IN MAX8625A LX1 LX2 P1 P2 OUT N2 N1 UVLO P1 CURRENT SENSE PWM/PFM CONTROL ON SKIP OSCILLATOR 1.25V REF Gm REFERENCE 125mV GND MAX8625A FB Figure 1. Simplified Block Diagram times. This reduces the ripple and removes any mode transitions from boost-only or buck-only to hybrid modes as seen in competing H-bridge converters. The time spent in each phase is set by a PWM controller, using timers and/or peak-current regulation on a cycle-by-cycle basis. The heart of the PWM control block is a comparator that compares the output voltage-error feedback signal and the sum of the currentsense and slope compensation signals. The currentmode control logic regulates the inductor current as a function of the output error voltage signal. The currentsense signal is monitored across the MOSFETs (P1, N1, and N2). A fixed time delay of approximately 30ns occurs between turning the P1 and N2 MOSFETs off, and turning the N1 and P2 MOSFETs on. This dead time prevents efficiency loss by preventing “shootthrough” current. Step-Down Operation (VIN > VOUT) During medium and heavy loads and V IN > V OUT , MOSFETs P1 and N2 turn on to begin phase 1 at the clock edge and ramp up the inductor current. The duration of phase 1 is set by an internal timer. During phase 2, N2 turns off, and P2 turns on to further ramp up inductor current and also transfer charge to the output. This slow charge phase is terminated on a clock edge and P1 is turned off. The converter now enters the fast discharge phase (phase 3). In phase 3, N1 turns on and the inductor current ramps down to the valley current-regulation point set by the error signal. At the end of phase 3, both P2 and N1 turn off and another phase 1 is initiated and the cycle repeats. With SKIP asserted low, during light loads when inductor current falls to zero in phase 3, the converter switches to phase 4 to reduce power consumption and avoid _______________________________________________________________________________________ 9 MAX8625A High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter FAULT TIMEOUT (ASYNCHRONOUS FROM ANYWHERE) OFF ON = 0 P1, P2 = OFF N1, N2 = ON IQ = 0μA ERROR ON = 1 P1, P2 = OFF N1, N2 = ON ON = 0 (ASYNCHRONOUS FROM ANYWHERE) TPUP REFOK = 0 OR UVLO = 0 (ASYNCHRONOUS FROM ANYWHERE) POWER-UP ON = 1, P1, P2 = OFF, N1, N2 = ON, OSC = ON AND REF = ON IF UVLO OK TRUN PHASE 2 SLOW CHARGE/ DISCHARGE OSC = ON P1, P2 = ON N1, N2 = OFF T1-2 PHASE 1 FAST-CHARGE OSC = ON P1, N2 = ON P2, N1 = OFF T1-3 T2-3 PHASE 3 FAST DISCHARGE OSC = ON P2, N1 = ON P1, N2 = OFF T3-1 T3-4 (SKIP) T4-1 PHASE 4 HOLD OSC = OFF N1, N2 = ON P1, P2 = OFF Figure 2. State Diagram shuttling current in and out of the output capacitor. If SKIP is asserted high for forced-PWM mode, phase 4 is not entered and current shuttling is allowed (and is necessary to maintain the PWM operation frequency when no load is present). Step-Up Operation (VIN < VOUT) During medium and heavy loads when VIN < VOUT, MOSFETs P1 and N2 turn on at the clock edge to ramp up the inductor current. Phase 1 terminates when the inductor current reaches the peak target current set by the PWM comparator and N2 turns off. This is followed by a slow-discharge phase (phase 2) instead of a charge phase (since VIN is less than VOUT) when P2 turns on. The slow-discharge phase terminates on a clock edge. The converter now enters the fast-discharge phase (phase 3). During phase 3, P1 turns off 10 and N1 turns on. At the end of the minimum time, both P2 and N1 turn off and the cycle repeats. If SKIP is asserted low, during light loads when inductor current falls to zero in phase 3, the converter switches to phase 4 (hold) to reduce power consumption and avoid shuttling current in and out of the output. If SKIP is high to assert forced-PWM mode, the converter never enters phase 4 and allows negative inductor current. Step-Up/Down Transition-Zone Operation (VIN = VOUT) When VIN = VOUT, the converter still goes through the three phases for moderate to heavy loads. However, the maximum time is now spent in phase 2 where inductor current di/dt is almost zero, since it is proportional to (VIN - VOUT). This eliminates transition glitches ______________________________________________________________________________________ High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter Forced-PWM Mode Drive SKIP high to operate the MAX8625A in forcedPWM mode. In this mode, the IC operates at a constant 1MHz switching frequency with no pulse skipping. This scheme is desirable in noise-sensitive applications because the output ripple is minimized and has a predictable noise spectrum. Forced PWM consumes higher supply current at light loads due to constant switching. Skip Mode Drive SKIP low to operate the MAX8625A in skip mode to improve light-load efficiency. In skip mode, the IC switches only as necessary to maintain the output at light loads, but still operates with fixed-frequency PWM at medium and heavy loads. This maximizes light-load efficiency and reduces the input quiescent current to 37µA (typ). Do not dynamically transition between skip and FPWM. The MAX8625A is not designed for dynamic transitions between FPWM and skip modes. Spikes of negative inductor current are possible when making these types of dynamic transitions. The magnitude of the spike depends on the load and output capacitance. The MAX8625A has no protection against these types of negative current spikes. Load Regulation and Transient Response During a load transient, the output voltage instantly changes due to the ESR of the output capacitors by an amount equal to their ESR times the change in load current (ΔVOUT = RESR x ΔILOAD). The output voltage then deviates further based on the speed at which the loop compensates for the load step. Increasing the output capacitance reduces the output-voltage droop. See the Capacitor Selection section. The typical application circuit limits the output transient droop to less than 3%. See the Typical Operating Characteristics section. Soft-Start Soft-start prevents input inrush current during startup. Internal soft-start circuitry ramps the peak inductor current with an internal DAC in 8ms. Once the output reaches regulation, the current limit immediately jumps to the maximum threshold. This allows full load capability as soon as regulation is reached, even if it occurs before the 8ms soft-start time is complete. When using the MAX8625A at low input voltages (close to UVLO and < 3V), it is recommended that the ON pin should not be tied to the BATT or supply voltage node directly. The ON pin should be held low for > 1ms after power to the MAX8625A is applied before it is driven high for normal operation. Shutdown Drive ON low to place the MAX8625A in shutdown mode and reduce supply current to less than 1µA. During shutdown, OUT is disconnected from IN, and LX1 and LX2 are connected to GND. Drive ON high for normal operation. Fault and Thermal Shutdown The MAX8625A contains current-limit and thermal shutdown circuitry to protect the IC from fault conditions. When the inductor current exceeds the current limit (2A for the MAX8625A), the converter immediately enters phase 3 and an internal 100ms timer starts. The converter continues to commutate through the three phases, spending most of its time in phase 1 and phase 3. If the overcurrent event continues and the output is out of regulation for the duration of the 100ms timer, the IC enters shutdown mode and the output latches off. ON must then be toggled to clear the fault. If the overload is removed before the 100ms timer expires, the timer is cleared and the converter resumes normal operation. The thermal-shutdown circuitry disables the IC switching if the die temperature exceeds +165°C. The IC begins soft-start once the die temperature cools by 15°C. ______________________________________________________________________________________ 11 MAX8625A or oscillation between the boost and buck modes as seen in other step-up/down converters. See the switching waveforms for each of the three modes and transition waveforms in the Typical Operating Characteristics section. MAX8625A High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter Applications Information 22µF ceramic capacitors at the input. Select two 22µF ceramic output capacitors. For best stability over a wide temperature range, use X5R or better dielectric. Selecting the Output Voltage The MAX8625A output is nominally fixed at 3.3V. Connect FB to GND to select the internally fixed-output voltage. For an adjustable output voltage, connect FB to the center tap of an external resistor-divider connected from the output to GND (R1 and R2 in Figure 3). Select 100kΩ for R2 and calculate R1 using the following equation: Inductor Selection The recommended inductance range for the MAX8625A is 3.3µH to 4.7µH. Larger values of L give a smaller ripple, while smaller L values provide a better transient response. This is because, for boost and stepup/down topologies, the crossover frequency is inversely proportional to the value of L for a given load and input voltage. The MAX8625A is internally compensated, and therefore, the choice of power components for stable operation is bounded. A 3.3µH inductor with 2A rating is recommended for the 3.3V fixed output with 0.8A load. ⎛V ⎞ R1 = 100kΩ × ⎜ OUT − 1⎟ ⎝ VFB ⎠ where VFB = 1.25V and VOUT is the desired output regulation voltage. VOUT must be between 1.25V and 4V. Note that the minimum output voltage is limited by the minimum duty cycle. VOUT cannot be below 1.25V. PCB Layout and Routing Good PCB layout is important to achieve optimal performance from the MAX8625A. Poor design can cause excessive conducted and/or radiated noise. Conductors carrying discontinuous currents and any high-current path should be made as short and wide as possible. Keep the feedback network (R1 and R2) very close to the IC, preferably within 0.2 inches of the FB and GND pins. Nodes with high dv/dt (switching nodes) should be kept as small as possible and routed away from FB. Connect the input and output capacitors as close as possible to the IC. Refer to the MAX8625A evaluation kit for a PCB layout example. Calculating Maximum Output Current The maximum output current provided by the MAX8625A circuit depends on the inductor value, switching frequency, efficiency, and input/output voltage. See the Typical Operating Characteristics section for the Maximum Load Current vs. Input Voltage graph. Capacitor Selection The input and output ripple currents are both discontinuous in this topology. Therefore, select at least two L 3.3μH 1 INPUT 2.7V TO 5.5V 13 14 C1, C2 22μF 2 LX1 LX1 3 4 LX2 LX2 IN IN MAX8625A 6 C3, C4 22μF R1 140kΩ U1 MODE SELECTION INPUT OUTPUT 3V 9 OUT 10 OUT FB 7 SKIP ON 5 OFF 8 R2 100kΩ ON REF C5 0.1μF 11 GND GND 12 Figure 3. Typical Application Circuit (Adjustable Output) 12 ______________________________________________________________________________________ High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter MAX8625A L 3.3μH 1 INPUT 2.7V TO 5.5V 13 14 C1, C2 22μF 2 LX1 LX1 3 4 LX2 LX2 IN IN 9 OUT 10 OUT OUTPUT 3.3V C3, C4 22μF U1 MODE SELECTION INPUT MAX8625A 6 FB 7 SKIP ON 5 OFF 8 ON REF C5 0.1μF 11 GND 12 GND Figure 4. Typical Application Circuit (Fixed 3.3V Output) Package Information Chip Information PROCESS: BiCMOS For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 14 TDFN-EP T1433-2 21-0137 ______________________________________________________________________________________ 13 MAX8625A High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. 14 ______________________________________________________________________________________ High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter COMMON DIMENSIONS PACKAGE VARIATIONS MIN. MAX. PKG. CODE N D2 E2 e JEDEC SPEC b A 0.70 0.80 T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF D 2.90 3.10 T833-2 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF E 2.90 3.10 T833-3 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF A1 0.00 0.05 T1033-1 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF L 0.20 0.40 T1033MK-1 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF SYMBOL [(N/2)-1] x e k 0.25 MIN. T1033-2 A2 0.20 REF. T1433-1 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.05 2.40 REF T1433-2 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.05 2.40 REF T1433-3F 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.05 2.40 REF ______________________________________________________________________________________ 15 MAX8625A Package Information (continued) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. MAX8625A High-Efficiency, Seamless Transition, Step-Up/Down DC-DC Converter Revision History REVISION NUMBER REVISION DATE 0 3/08 Initial release — 1 5/08 Added PCB Layout and Routing section 12 2 10/08 Updated Electrical Characteristics, Skip Mode and Soft-Start sections 3 12/08 Corrected P1 and P2 symbols in Figure 1 9 4 4/09 Corrected U.S. Patent # 1 DESCRIPTION PAGES CHANGED 2, 11 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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.