MAX1684EEE+TG002

19-1454; Rev 2; 7/01 KIT ATION EVALU E L B AVAILA Low-Noise, 14V Input, 1A, PWM Step-Down Converters Both devices are available in a space-saving 16-QSOP package. An evaluation kit is also available to help speed designs. For a similar device in a 10-pin µMAX package with lower input voltage requirements (5.5V max), refer to the MAX1692 data sheet. Applications Cellular Phones Two-Way Radios and Walkie-Talkies Computer Peripherals Features ♦ Up to 96% Efficiency ♦ 1A Guaranteed Output Current ♦ 100% Duty Cycle in Dropout ♦ 2.7V to 14V Input Range (15V Absolute Max) ♦ ±1% Accurate Reference Output ♦ 0.24Ω P-Channel On-Resistance ♦ Synchronizable Switching Frequency ♦ Fixed-Frequency PWM Operation 300kHz (MAX1684) 600kHz (MAX1685) ♦ 150µA Normal-Mode Quiescent Current ♦ 25µA Low-Power Mode Quiescent Current ♦ 2µA Shutdown Current ♦ Dual Mode™ Fixed 3.3V (±1%) Output or Adjustable Output (1.25V to VIN) ♦ Small 16-QSOP Package ♦ Auxiliary Output (CVL): 3V/5mA Ordering Information PART TEMP RANGE PIN-PACKAGE MAX1684EEE -40°C to +85°C 16 QSOP MAX1685EEE -40°C to +85°C 16 QSOP Typical Operating Circuit OUTPUT 3.3V AT 1A INPUT 2.7V TO 14V + IN LX AIN SHDN MAX1684 MAX1685 Personal Communicators PDAs and Handy-Terminals + GND CVH CVL BOOT STBY SYNC/PWM Pin Configuration appears at end of data sheet. FB CC REF Dual Mode is a trademark of Maxim Integrated Products, Inc. ________________________________________________________________ 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 MAX1684/MAX1685 General Description The MAX1684/MAX1685 are high-efficiency, internalswitch, pulse-width modulation (PWM) step-down switching regulators intended to power cellular phones, communicating PDAs, and handy-terminals. These devices deliver a guaranteed 1A output current from two lithium-ion (Li+) batteries. Their wide-input voltage range of 2.7V to 14V gives design flexibility and allows batteries to charge from a wall cube, since the ICs operate at the higher voltages that occur when the battery is removed. The output voltage is preset to 3.3V or can be externally adjusted from 1.25V to VIN. The low on-resistance power switch and built-in synchronous rectifier provide high efficiencies of up to 96%. There are four modes of operation: fixed-frequency, normal, low-power, and shutdown. The fixed-frequency PWM mode of operation offers excellent noise characteristics. The normal mode maintains high efficiency at all loads. The low-power mode is used to conserve power in standby or when full load is not required. The shutdown mode is used to power down the device for minimal current draw. The MAX1684 runs at 300kHz for applications that require highest efficiency. The MAX1685 runs at 600kHz to allow the use of smaller external components. These devices can also be synchronized to an external clock. Other features include a 100% duty cycle for low-dropout applications, an auxiliary 3V/5mA output, and a 1% accurate reference. MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters ABSOLUTE MAXIMUM RATINGS AIN to AGND ............................................................-0.3 to +15V IN to PGND ................................................-0.3V to (VAIN + 0.3V) LX to PGND .................................................-0.5V to (VIN + 0.3V) PGND to AGND ..................................................................±0.3V SHDN to AGND .........................................-0.3V to (VAIN + 0.3V) ILIM/SS, FB, CC, BOOT, REF to AGND ....-0.3V to (VCVL + 0.3V) CVH to IN..................................................................-6V to +0.3V CVL, STBY, SYNC/PWM to AGND............................-0.3V to +6V Reference Current ..............................................................±1mA CVL Current .......................................................-1mA to +10mA LX Peak Current (Internally Limited) .....................................2.3A Continuous Power Dissipation (TA = +70°C) 16-Pin QSOP (derate 8.3mW/°C above +70°C)............667mW 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 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 = V SHDN = 6V, STBY = SYNC/PWM = CVL, VBOOT = VOUT, FB = AGND, circuit of Figure 1, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS Input Voltage Range Feedback Voltage Output Voltage (3.3V Mode) 1.251 1.264 3.296 3.333 3.368 BOOT = AGND (Note 1) IFB VFB = 1.4V V -50 50 nA 0.5 0.34 0.8 3 8 ILIM Ω Ω 1.2 1.75 2.3 A SYNC/PWM = low 285 380 475 mA STBY = low 285 380 475 mA A SYNC/PWM = high 0.15 0.4 0.9 MAX1684 -10 50 100 MAX1685 20 80 130 MAX1684 13 33 MAX1685 25 65 Normal mode, SYNC/PWM = low, VBOOT = 3.3V (Note 2) 0.9 2 Low-power mode, STBY = low, VBOOT = 3.3V (Note 2) 0.14 0.27 SYNC/PWM = low PWM mode, SYNC/PWM = high, VBOOT = 3.3V (Note 2) 2 VIN 0.24 Low-side switch, VIN = 2.7V, ILX = 200mA ILIMLP A VREF VIN = 2.7V On-Resistance, N-Channel V % VIN = 6V High-side switch, ILX = 1A Pulse-Skipping Current Threshold 0.01 1 On-Resistance, P-Channel Quiescent Power Consumption V 1.238 FB = AGND, ILOAD = 0 to 1A VIN = 5V to 14V Zero Crossing Threshold V VFB = VOUT, ILOAD = 0 to 1A Output Adjust Range Current Limit, N-Channel UNITS 14 VFB Output Current Capability Current Limit in Low-Power Mode MAX VOUT VFB = VOUT, ILOAD = 0 to 1A Current Limit in PWM Mode TYP 2.7 Output Load Regulation FB Input Current MIN mA mW _______________________________________________________________________________________ Low-Noise, 14V Input, 1A, PWM Step-Down Converters (VIN = V SHDN = 6V, STBY = SYNC/PWM = CVL, VBOOT = VOUT, FB = AGND, circuit of Figure 1, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Quiescent Supply Current in Dropout Oscillator Frequency SHDN = low ILX fOSC SYNC Capture Range TYP MAX UNITS 230 430 µA 6 µA 20 µA 2 VIN = 14V, VLX = 0 or 14V, SHDN = low MAX1684 260 300 340 MAX1685 520 600 680 MAX1684 180 350 MAX1685 360 700 Maximum Duty Cycle 100 Constant-Frequency Minimum Duty Cycle Reference Output Voltage MIN STBY = low, VIN = 2.7V Shutdown Supply Current LX Leakage Current CONDITIONS (Note 3) VREF 10 MAX1685 20 1.238 1.264 V 4 15 mV 0.2 5 mV 3.0 3.15 V 120 mV 2.5 2.6 V -5.0 -4.6 -4.1 V 2.35 2.5 2.65 V -1µA < IREF < 50µA Reference Supply Regulation 2.7V < VBOOT < 5.5V CVL Regulator Output Voltage VIN = 3V to 14V, BOOT = AGND, ICVL = 0 to 5mA CVL Dropout Voltage BOOT = AGND, ICVL = 5mA CVL Undervoltage Lockout Threshold BOOT = AGND, CVL falling edge, typical hysteresis is 40mV 2.35 CVH with Respect to VIN ICVH = -1mA BOOT Switchover Threshold BOOT falling edge, typical hysteresis is 0.1V Thermal Shutdown Threshold Typical hysteresis is +10°C (Note 4) VILIM/SS = 1.4V Logic Input High Voltage VIH Logic Input Low Voltage VIL SHDN, STBY, SYNC/PWM Logic Input Current SHDN, STBY, SYNC/PWM SYNC/PWM Pulse Width High or low period % 1.251 Reference Load Regulation ILIM/SS Source Current kHz % MAX1684 IREF = 0 kHz 2.7 160 3.3 4 °C 4.65 2 -1 500 µA V 0.7 V 1 µA ns _______________________________________________________________________________________ 3 MAX1684/MAX1685 ELECTRICAL CHARACTERISTICS (continued) MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters ELECTRICAL CHARACTERISTICS (VIN = V SHDN = 6V, STBY = SYNC/PWM = CVL, VBOOT = VOUT, FB = AGND, circuit of Figure 1, TA = -40°C to +85°C, unless otherwise noted.) (Note 5) PARAMETER SYMBOL CONDITIONS Input Voltage Range Output Feedback Voltage Output Voltage (3.3V Mode) MAX UNITS 2.7 14 V V VFB VFB = VOUT, ILOAD = 0 to 1A 1.233 1.269 VOUT FB = AGND, ILOAD = 0 to 1A 3.280 3.382 Output Current Capability VIN = 6V to 14V Output Adjust Range BOOT = AGND (Note 1) FB Input Current IFB Current Limit in PWM Mode ILIM Current Limit in Low-Power Mode ILIMLP VFB = 1.4V STBY = low 1 VIN V -50 50 nA 1.2 2.3 A 285 475 mA 2 mW Low-power mode, STBY = low, VBOOT = 3.3V (Note 2) 0.27 SHDN = low Shutdown Supply Current fOSC V A VREF Normal mode, SYNC/PWM = low, VBOOT = 3.3V (Note 2) Quiescent Power Consumption Oscillator Frequency MIN 6 µA MAX1684 240 350 MAX1685 480 700 1.232 1.268 V kHz Reference Output Voltage IREF = 0 CVL Regulator Output Voltage VIN = 3V to 14V, BOOT = AGND, ICVL = 0 to 5mA 2.7 3.15 V CVL Undervoltage Lockout Threshold BOOT = AGND, CVL falling edge, typical hysteresis is 40mV 2.4 2.6 V CVH with Respect to VIN ICVH = -1mA -5.0 -4.1 V BOOT Switchover Threshold BOOT falling edge, typical hysteresis is 0.1V 2.35 2.65 V ILIM/SS Source Current VILIM/SS = 1.4V 3.1 4.7 µA Logic Input High Voltage VIH Logic Input Low Voltage VIL SHDN, STBY, SYNC/PWM 2 0.7 V Note 1: The output adjust range with BOOT connected to VOUT is VREF to 5.5V. Connect BOOT to AGND for VOUT > 5.5V. Note 2: The quiescent power-consumption specifications include chip supply and gate-drive loss only. Divide these values by VIN (6V) to obtain quiescent currents. In normal and low-power modes, chip supply current dominates and quiescent power is proportional to VBOOT (BOOT connected to OUT). In PWM mode, gate-drive loss dominates and quiescent power is proportional to VIN ✕ (VIN - VCVH). In addition, IR losses in power switches and external components typically increase PWM quiescent power consumption by 5mW to 10mW. Note that if the device is not bootstrapped, additional power is dissipated in the CVL linear regulator. Note 3: When the duty factor (VOUT / VIN) is less than this value, the switching frequency decreases in PWM mode to maintain regulation. Note 4: Thermal shutdown is disabled in low-power mode (STBY = low) to reduce power consumption. Note 5: Specifications to -40°C are guaranteed by design, not production tested. 4 _______________________________________________________________________________________ Low-Noise, 14V Input, 1A, PWM Step-Down Converters MAX1684 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) 60 C B A: VOUT = 2.5V LP MODE B: VOUT = 1.8V LP MODE C: VOUT = 2.5V NORM MODE D: VOUT = 1.8V NORM MODE E: VOUT = 2.5V PWM MODE F: VOUT = 1.8V PWM MODE F 30 20 10 0 0.1 1 10 100 1000 A: VIN = 4V B: VIN = 5V C: VIN = 9V D: VIN = 12V MAX1684/85 toc02 10 0 0.1 1 10 100 1000 10,000 1 10 100 1000 10,000 MAX1684 EFFICIENCY vs. LOAD CURRENT (VOUT = 5V) MAX1684 EFFICIENCY vs. LOAD CURRENT (VOUT = 5V, PWM MODE) MAX1685 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V, PWM MODE) F 60 50 A: VIN = 6V LP MODE B: VIN = 9V LP MODE C: VIN = 12V LP MODE D: VIN = 6V NORMAL MODE E: VIN = 9V NORMAL MODE F: VIN = 12V NORMAL MODE 40 30 20 0.1 1 10 100 1000 80 A 70 60 50 B 40 100 C 90 70 60 VIN = 5V 50 40 VIN = 9V 30 20 A: VIN = 6V B: VIN = 9V C: VIN =12V 10 VIN = 12V 10 0 0 10,000 VIN = 4V 80 30 20 MAX1684/85 toc06 E 90 EFFICIENCY (%) E 100 MAX1684/85 toc05 D 70 1 10 100 1000 1 10,000 10 100 1000 10,000 LOAD CURRENT (mA) LOAD CURRENT (mA) LOAD CURRENT (mA) MAX1685 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) MAX1685 EFFICIENCY vs. LOAD CURRENT (VOUT = 5V PWM MODE) MAX1685 EFFICIENCY vs. LOAD CURRENT (VOUT = 5V) C A 80 D 90 80 EFFICIENCY (%) B 100 60 50 40 VIN = 6V 70 VIN = 9V 60 50 40 A: VIN = 4V LP MODE B: VIN = 12V LP MODE C: VIN = 4V NORMAL MODE D: VIN = 12V NORMAL MODE 20 10 0 1 10 100 LOAD CURRENT (mA) 1000 10,000 B A 90 80 C VIN =12V 20 60 40 A: VIN = 6V LP MODE B: VIN = 9V LP MODE C: VIN = 12V LP MODE D: VIN = 6V NORMAL MODE E: VIN = 9V NORMAL MODE F: VIN =12V NORMAL MODE 20 0 0 1 10 100 1000 LOAD CURRENT (mA) 10,000 D E 50 10 10 F 70 30 30 30 100 EFFICIENCY (%) 100 0.1 40 LOAD CURRENT (mA) C 70 B 50 20 0 MAX1684/85 toc07 EFFICIENCY (%) 10 60 30 A: VIN = 4V LP MODE B: VIN = 12V LP MODE C: VIN = 4V NORMAL MODE D: VIN = 12V NORMAL MODE 20 D LOAD CURRENT (mA) A 90 40 30 C A 70 LOAD CURRENT (mA) B 80 60 50 10,000 100 90 80 MAX1684/85 toc08 40 E MAX1684/85 toc04 50 D 90 MAX1684/85 toc09 D B 70 100 EFFICIENCY (%) A 70 80 EFFICIENCY (%) EFFICIENCY (%) 80 C A 90 EFFICIENCY (%) 90 EFFICIENCY (%) 100 MAX1684/85 toc01 100 MAX1684 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V, PWM MODE) MAX1684/85 toc03 MAX1684 EFFICIENCY vs. LOAD CURRENT (VIN = 3.3V, VOUT = 1.8V, 2.5V) 0.1 1 10 100 1000 10,000 LOAD CURRENT (mA) _______________________________________________________________________________________ 5 MAX1684/MAX1685 Typical Operating Characteristics (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE SAFE OPERATING AREA 1.4 1.3 1000 1.2 800 600 400 MAX1684/85 toc12 400 DROPOUT VOLTAGE (mV) 1.5 VOUT = 3.3V 1200 LOAD CURRENT (mA) 300 VOUT = 3.3V 200 VOUT = 5V 100 200 1.1 INDUCTOR RESISTANCE INCLUDED PWM OR NORMAL MODE 0 1.0 2 4 6 8 10 12 0 14 2 6 8 10 12 INPUT VOLTAGE (V) INPUT VOLTAGE (V) NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE MAX1684 NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE (VOUT = 3.3V, PWM MODE) 80 NORMAL MODE 60 40 16 6 8 400 600 800 1000 PWM FIXED-FREQUENCY OPERATION AREA 5.0 4.5 4.0 3.5 3.0 15 14 MAX1684 13 12 MAX1685 11 10 9 8 7 6 2.0 20 4 200 LOAD CURRENT (mA) 2.5 LOW-POWER MODE 0 INPUT VOLTAGE (V) 100 14 MAX1684/85 toc14 MAX1684/85 toc13 120 SUPPLY CURRENT (mA) 0 0 4 M AX1684/85 toc15 LOAD CURRENT (A) 1.6 MAX1684/85 toc11 1.7 DROPOUT VOLTAGE vs. LOAD CURRENT 1400 MAX1684/85 toc10 1.8 SUPPLY CURRENT (µA) MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters 10 12 2.7 4 14 5 6 7 8 9 10 11 12 0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) 6 8 10 12 14 SWITCHING WAVEFORM MAX1684/85 toc17 MAX1684/85 toc16 ILOAD 500mA/div 4 OUTPUT VOLTAGE (V) SWITCHING WAVEFORM LOAD-TRANSIENT RESPONSE 2 VOUT 20mV/div MAX1684/85 toc18 VLX 5V/div VOUT 50mV/div ILX 100mA/div 2ms/div MAX1684, ILOAD = 0.1mA TO 1A, VOUT = 3.3V, VIN = 5V, SYNC/PWM = 3.3V 6 ILX 100mA/div 1µs/div 1µs/div MAX1684, ILOAD = 100mA, VOUT = 3.3V, VIN = 5V, SYNC/PWM = 3.3V MAX1684, ILOAD = 100mA, VOUT = 3.3V, VIN = 5V, SYNC/PWM = 3.3V _______________________________________________________________________________________ Low-Noise, 14V Input, 1A, PWM Step-Down Converters STARTUP CURRENT LINE-TRANSIENT RESPONSE MAX1684/85 toc20 MAX1684/85 toc19 VSHDN 5V/div VIN 5V/div 0V VOUT 100mV/div IIN 50mA/div 10ms/div 2ms/div MAX1684, ILOAD = 100mA, VOUT = 3.3V, VIN = 5V, CILIM/SS = 0.1µF, SYNC/PWM = 3.3V MAX1684, ILOAD = 100mA, VIN = 5V TO 10V, SYNC/PWM = 3.3V Pin Description PIN NAME FUNCTION 1 CVH High-Side MOSFET Gate Bias. Bias voltage for P-channel switch. Bypass to IN with a 0.1µF capacitor. 2 AIN Analog Supply Voltage Input. Connect to IN with a 0.2in metal trace. Bypass to PGND with a 0.1µF capacitor. 3 IN 4 CVL 5 AGND 6 REF Reference Output. 1.25V reference output supplies 10µA for external loads. Bypass to AGND with 0.1µF capacitor. 7 FB Dual-Mode Feedback Input. Connect FB to VOUT for 1.25V output. Connect to an external resistor divider to adjust the output voltage. Connect to AGND to set output voltage to 3.3V. 8 CC Integrator Capacitor Connection. Connect a 0.01µF capacitor to AGND. Supply Voltage Input Logic Supply Voltage Output and IC Logic Supply. Sources 5mA for external loads. Bypass to AGND with 1µF capacitor. Analog Ground SYNC/PWM Input: For synchronized-PWM operation, drive with TTL level, 50% square wave. Connect to CVL for PWM mode. Connect to AGND for normal mode. 9 SYNC/PWM 10 ILIM/SS 11 STBY Standby Control Input. Connect to CVL for normal operation. Connect to AGND for low-power mode (Table 1). This pin overrides SYNC/PWM setting. 12 BOOT Bootstrap Input. Connection for the bootstrap switch and internal feedback path. Connect BOOT to VOUT for VOUT < 5.5V. Connect BOOT to AGND for VOUT > 5.5V. Current-Limit Adjust/Soft-Start Input. See the Current Limit and Soft-Start section. 13, 14 LX 15 SHDN Inductor Connection. Drain for internal P-channel MOSFETs. Connect inductor from LX to OUT. Active-Low Shutdown Input. Connect to ground for shutdown. SHDN can withstand the input voltage. 16 PGND Power Ground _______________________________________________________________________________________ 7 MAX1684/MAX1685 Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters 0.1µF INPUT 14V MAX 3 22µF 2 1 CVH IN LX MAX1685 PGND 15 1µF 11 OUTPUT 3.3V AT 1A COUT 100µF MBRS 130LT3 AIN 0.1µF ON/OFF L 10µH* 13, 14 AGND SHDN 4 CVL BOOT STBY 9 SYNC/PWM 16 5 12 7 synchronization to an external clock. The MAX1684/MAX1685 can operate in five modes. Setting the devices to operate in the appropriate mode for the intended application (Table 1) achieves highest efficiency. PWM Control The MAX1684/MAX1685 use an oscillator-triggered minimum/maximum on-time current-mode control scheme (Figure 2). The minimum on-time is typically 220ns unless the regulator is in dropout. The maximum on-time is 2 / f OSC, allowing operation to 100% duty cycle. Current-mode feedback provides cycle-by-cycle current limiting for superior load- and line-transient response. _______________Detailed Description At each falling edge of the internal oscillator, the internal P-channel MOSFET (main switch) turns on. This allows current to ramp up through the inductor to the load and stores energy in a magnetic field. The switch remains on until either the current-limit comparator trips, the maximum on-time expires, or the PWM comparator signals that the output is in regulation. When the switch turns off during the second half of each cycle, the inductor’s magnetic field collapses, releasing the stored energy and forcing current through the output diode to the output filter capacitor and load. The output filter capacitor stores charge when the inductor current is high and releases it when the inductor current is low, smoothing the voltage across the load. The MAX1684/MAX1685 step-down, PWM DC-DC converters provide an adjustable output from 1.25V to the input voltage. They accept inputs from 2.7V to 14V and deliver up to 1.6A. An internal MOSFET and synchronous rectifier reduce PC board area while maintaining high efficiency. Operation with up to 100% duty cycle minimizes dropout voltage. Fixed-frequency PWM operation reduces interference in sensitive communications and data-acquisition applications. A SYNC input allows During normal operation, the MAX1684/MAX1685 regulate the output voltage by switching at a constant frequency and modulating the power transferred to the load on each cycle using the PWM comparator. A multiinput comparator sums three weighted differential signals (the output voltage with respect to the reference, the main switch current sense, and the slope-compensation ramp) and changes states when a threshold is reached. It modulates output power by adjusting the ILIM/SS 10 0.1µF (OPTIONAL) FB CC 8 REF 6 0.1µF 0.01µF *SUMIDA CD54-100; USE 22µH FOR MAX1684 Figure 1. Standard Application Circuit Table 1. Operating Modes STBY SHDN H H H Fixed-frequency PWM 1.6 Clocked H H Fixed-input clock-frequency PWM 1.6 Normal L H H PFM at light loads (150mA) 1.6 Low Power X L H Low-power or standby mode Shutdown X X L Circuit disabled PWM Sync PWM 8 TYPICAL OUTPUT CAPABILITY (A) SYNC/PWM MODE FUNCTION _______________________________________________________________________________________ 160m 0 Low-Noise, 14V Input, 1A, PWM Step-Down Converters CVL IN MAX1684 MAX1685 4µA AIN SHDN CVH VH VL THERMAL SHUTDOWN MAX1684/MAX1685 ILIM/SS ILIM THRESHOLD ON CVL REF PFM CURRENT COMPARATOR REF ILIM COMPARATOR LX CONTROL AND DRIVER UNDERVOLTAGE COMPARATOR 2.5V SYNC/PWM STBY LOGIC PWM COMPARATOR OSC SYNC SLOPE COMPENSATION AND STANDBY PWM MODE CONTROL NORMAL MODE LOW-POWER MODE PGND ZERO-CROSSING COMPARATOR CVL 2.5V CC PFM COMPARATOR BOOT GM INTEGRATOR FB 0.125V AGND Figure 2. Functional Diagram _______________________________________________________________________________________ 9 MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters inductor peak current during the first half of each cycle, based on the output error voltage. The MAX1684/ MAX1685s’ loop gain is relatively low to enable the use of a small, low-value output filter capacitor. The 1.4% transient load regulation from 0 to 1A is compensated by an integrator circuit that lowers DC load regulation to 0.01% typical. Slope compensation accounts for the inductor-current waveform’s down slope during the second half of each cycle, and eliminates the inductorcurrent staircasing characteristic of current-mode controllers at high duty cycles. PFM Control In low-power mode, the MAX1684/MAX1685 switch only as needed to service the load. This reduces the switching frequency and associated losses in the P-channel switch, the synchronous rectifier, and the external inductor. During this PFM operation, a switching cycle initiates when the PFM comparator senses that the output voltage has dropped too low. The P-channel MOSFET switch turns on and conducts current to the output-filter capacitor and load. The MAX1684/MAX1685 then wait until the PFM comparator senses a low-output voltage again. In normal mode at light load (100mA), V IN can increase slightly higher before the frequency decreases. Synchronous Rectification Although the primary rectifier is an external Schottky diode, a small internal N-channel synchronous rectifier allows PWM operation at light loads. During the second half of each cycle, when the inductor current ramps below the zero-crossing threshold or when the oscillator period ends, the synchronous rectifier turns off. This keeps excess current from flowing backward through the inductor. Choose an appropriate inductor to limit the PWM ripple current through the N-channel FET to 400mAP-P. Current Limit and Soft-Start The voltage at ILIM/SS sets the PWM current limit (ILIM = 1.75A) and the low-power current limit (ILIMLP = 380mA). The PWM current limit applies when the device is in PWM mode, in synchronized PWM mode, or delivering a heavy load in normal mode (Table 1). The ILIMLP limit applies when the device is in low-power mode. An internal 4µA current source pulls ILIM/SS up to CVL. To use the maximum current-limit thresholds, leave ILIM/SS unconnected or connect it to a soft-start capacitor. Connect an external resistor from ILIM/SS to AGND to adjust the current-limit thresholds. The PWM current-limit threshold is (ILIM ✕ RILIM/SS ✕ 4µA) / VREF and is adjustable from 0.5A to 1.75A. The low-power current-limit threshold is equal to (ILIMLP ✕ RILIM/SS ✕ 4µA) / VREF and is adjustable from 110mA to 380mA. For example, when RILIM/SS is 156kΩ, the PWM current limit threshold is 0.88A and the low-power current limit threshold is 0.19A. Connect a low-value capacitor from ILIM/SS to AGND to achieve soft-start, limiting inrush current. ILIM/SS internally shorts to AGND in shutdown to discharge the soft-start capacitor. Do not connect ILIM/SS to REF or CVL. Determine the soft-start duration by: tSOFT-START = CILIM/SS(1.25V / 4µA) where tSOFT-START is the time from SHDN going high to the regulator being able to supply full load current. For example, a 0.1µF capacitor yields 31ms of soft-start. ______________________________________________________________________________________ Low-Noise, 14V Input, 1A, PWM Step-Down Converters Internal Low-Voltage Regulators and Bootstrap (BOOT) The MAX1684/MAX1685 have two internal regulators (VH and VL) that generate low-voltage supplies for internal circuitry (see the Functional Diagram). The VH regulator generates -4.6V with respect to IN to supply the P-channel switch and driver. Bypass CVH to IN with a 0.1µF capacitor. The VL regulator generates a 3V output at CVL to supply internal low-voltage blocks, as well as the N-channel switch and driver. Bypass CVL to AGND with a 1µF capacitor. To reduce the quiescent current in low-power and normal modes, connect BOOT to OUT. After startup, when VBOOT exceeds 2.6V, the internal bootstrap switch connects CVL to BOOT. This bootstrap mechanism causes the internal circuitry to be supplied from the output and thereby reduces the input quiescent current by a factor of VOUT / VIN. Do not connect BOOT to OUT if the output voltage exceeds 5.5V. Instead, connect BOOT to AGND to keep CVL regulated at 3V. CVL has a 5mA capability to supply external logic circuitry and is disabled in shutdown mode. Applications Information Output Voltage Selection Connect FB to AGND to select the internal 3.3V output mode. Connect BOOT to OUT in this configuration. To select an output voltage between 1.25V and VIN, connect FB to a resistor voltage-divider between the output and AGND (Figure 3). Select R2 in the 20kΩ to 100kΩ range. Calculate R1 as follows: R1 = R2 [( VOUT / VFB) - 1] where VFB = 1.25V. VOUT R1 MAX1684 MAX1685 C1 FB R2 Figure 3. Setting Output Voltage Connect a small capacitor across R1 to compensate for stray capacitance at the FB pin: C1 = 5 (10−7) R2 where: R2 = 100kΩ, use 4.7pF. Inductor Selection The MAX1684/MAX1685s’ high switching frequency allows the use of small surface-mount inductors. Table 2 shows a selection of suitable inductors for different output voltage ranges. Calculate the minimum inductor by: L = 0.9(VOUT - 0.3V) / (IRIPPLE MAX × fOSC) where: IRIPPLE MAX = should be less than or equal to 400mA fOSC = 300kHz (MAX1684) or 600kHz (MAX1685) Capacitor Selection Select input and output filter capacitors to service inductor currents while minimizing voltage ripple. The input filter capacitor reduces peak currents and noise at the voltage source. The MAX1684/MAX1685s’ loop gain is relatively low to enable the use of small, lowvalue output filter capacitors. Higher capacitor values provide improved output ripple and transient response. Low-ESR capacitors are recommended. Capacitor ESR is a major contributor to output ripple (usually more than 60%). Avoid ordinary aluminum electrolytic capacitors, as they typically have high ESR. Low-ESR aluminum electrolytic capacitors are acceptable and relatively inexpensive. Low-ESR tantalum capacitors are better and provide a compact solution for spaceconstrained surface-mount designs. Do not exceed the ripple-current ratings of tantalum capacitors. Ceramic capacitors offer the lowest ESR overall. Sanyo OS-CON ______________________________________________________________________________________ 11 MAX1684/MAX1685 The output current capability for each mode is determined by the following equations: IOUTMAX = ILIM - 0.5 ✕ IRIPPLE (for PWM and normal modes) IOUTMAX = 0.5 ✕ ILIMLP (for low-power mode) where: IRIPPLE = ripple current = (VIN - VOUT) ✕ VOUT / (VIN ✕ fOSC ✕ L) ILIM = current limit in PWM mode ILIMLP = current limit in low-power mode MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters capacitors have the lowest ESR of the high-value electrolytic types. Use ceramic and OS-CON capacitors for very compact, high-reliability, or wide-temperature applications, where expense is justified. When using very low ESR capacitors, such as ceramic or OS-CON, check for stability while examining load-transient response, and increase the output compensation capacitor if needed. Table 3 lists suppliers for the various components used with the MAX1684/MAX1685. Ensure that the minimum capacitance value and maximum ESR values are met: COUT > IOUT MAX / (VOUT ✕ AC Load Reg ✕ fOSC) where I OUT MAX = 1A, AC Load Reg ≅ 1.4%, and fOSC = 300kHz (MAX1684) or 600kHz (MAX1685). Output Diode Selection Use a 1A external Schottky diode (MBRS130LT3 or equivalent) for the output rectifier to pass inductor current during the start of the second half of each cycle. This diode operates before the internal N-channel MOSFET completely turns on and during high-current operation. Use a Schottky diode to avoid forward biasing the internal body diode of the N-channel MOSFET. RESR < 2 ✕ AC Load Reg ✕ VOUT/IOUT MAX Table 2. Inductor and Minimum Output Capacitor Selection MAX1684 (300kHz) VOUT (V) MAX1685 (600kHz) L (µH) MIN COUT (µF) L (µH) MIN COUT (µF) 1.25 to 2.7 22 220 10 100 2.7 to 4 22 100 10 47 4 to 6 47 68 22 33 6 to 14 68 47 33 22 Table 3. Component Suppliers SUPPLIER PHONE FAX 0.1µF CAPACITORS AVX Matsuo 803-946-0690 714-969-2591 803-626-3123 714-960-6492 Sanyo 619-661-6835 619-661-1055 Sprague 603-224-1961 603-224-1430 AIN VIN MAX1684 MAX1685 LX C1 0.1µF 22µF IN FB STBY R2 CVL INDUCTORS 847-639-6400 847-639-1469 Murata-Erie 814-237-1431 814-238-0490 Sumida 847-956-0666 847-956-0702 TDK 847-390-4373 847-390-4428 602-303-5454 602-994-6430 100µF L R1 CVH SHDN Coilcraft -VOUT -1.25V TO -5.5V MBRS 130LT3 SYNC/PWM 1µF REF 0.1µF ILIM/SS BOOT PGND AGND CC 0.01µF 0.01µF DIODES Motorola VIN, MAX = 14V - |VOUT| Figure 4. Inverting Output 12 ( R2 -VOUT = -1.25V R1 + 1 ______________________________________________________________________________________ ) Low-Noise, 14V Input, 1A, PWM Step-Down Converters PC Board Layout High switching frequencies and large peak currents make PC board layout a very important part of design. Poor design can result in excessive EMI on the feedback paths and voltage gradients in the ground plane, both of which result in instability or regulation errors. Power components such as the MAX1684/MAX1685 inductor, input filter capacitor, and output filter capacitor should be placed as close together as possible, and their traces kept short, direct, and wide, Connect their ground nodes in a star-ground configuration. Keep the extra copper on the board and integrate into ground as a pseudo-ground plane. When using external feedback, the feedback network should be close to FB, within 0.2 inch (5mm), and the output voltage feedback should be tapped as close to the output capacitor as possible. Keep noisy traces, such as those from LX, away from the voltage feedback network. Separate the noisy traces by grounded copper. Place the small bypass capacitors within 0.2 inch (5mm) of their respective inputs. The MAX1684 evaluation kit manual illustrates an example PC board layout, routing, and pseudo-ground plane. Connect AIN to IN with a short (0.2 inch) metal trace or a 1Ω resistor and bypass AIN to PGND with a 0.1µF capacitor. This acts as a lowpass filter to reduce noise at AIN. Pin Configuration TOP VIEW CVH 1 16 PGND AIN 2 15 SHDN IN 3 CVL 4 AGND 5 14 LX MAX1684 MAX1685 REF 6 13 LX 12 BOOT 11 STBY FB 7 10 ILIM/SS CC 8 9 SYNC/PWM QSOP Chip Information TRANSISTOR COUNT: 2061 ______________________________________________________________________________________ 13 MAX1684/MAX1685 Inverting Output Interchanging the ground and VOUT connections yields a negative voltage supply (Figure 4). The component selections are the same as for a positive voltage converter. The absolute maximum ratings limit the output voltage range to -1.25V to -5.5V and the maximum input voltage range to 14V -  VOUT. 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.) QSOP.EPS MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters 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. 14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.