19-2918; Rev 1; 1/04 PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets Features The MAX8506/MAX8507/MAX8508 integrate a PWM stepdown DC-DC regulator and a 75m (typ) bypass FET to power the PA in WCDMA and cdmaOneTM cell phones. The supply voltage range is from 2.6V to 5.5V, and the guaranteed output current is 600mA. One megahertz PWM switching allows for small external components. The MAX8506 and MAX8507 are dynamically controlled to provide varying output voltages from 0.4V to 3.4V. The MAX8508 is externally programmed for fixed 0.75V to 3.4V output. Digital logic enables a high-power (HP) bypass mode that connects the output directly to the battery for all versions. The MAX8506/MAX8507/MAX8508 are designed so the output settles in less than 30s for a full-scale change in output voltage and load current. The MAX8506/MAX8507/MAX8508 are offered in 16-pin 4mm x 4mm thin QFN packages (0.8mm max height). Integrated 75m (typ) Bypass FET 38mV Dropout at 600mA Load Up to 94% Efficiency Dynamically Adjustable Output from 0.4V to 3.4V (MAX8506, MAX8507) Externally Fixed Output from 0.75V to 3.4V (MAX8508) 1MHz Fixed-Frequency PWM Switching 600mA Guaranteed Output Current Shutdown Mode 0.1A (typ) 16-Pin Thin QFN (4mm x 4mm, 0.8mm max Height) Ordering Information Applications WCDMA/NCDMA Cell Phones PART TEMP RANGE PIN-PACKAGE Wireless PDAs, Palmtops, and Notebook Computers MAX8506ETE -40C to +85C 16 Thin QFN MAX8507ETE -40C to +85C 16 Thin QFN Wireless Modems MAX8508ETE -40C to +85C 16 Thin QFN Pin Configurations appear at end of data sheet. cdmaOne is a trademark of CDMA Development Group. Typical Application Circuits (MAX8506/MAX8507) INPUT 2.6V TO 5.5V OUTPUT 0.4V TO 3.4V OR VBATT 4.7H 4.7F 2.2F BATTP SKIP MAX8506 MAX8507 LX BATT OUT 0.075 SHDN REF REF PWM 0.4 0.22F CURRENTLIMIT CONTROL 1MHz OSC REFIN DAC 0.3 HP COMP PGND RC* Cf* CC* GND * RC (k) CC (pF) MAX8506 1500 10 MAX8507 1000 15 Cf (pF) 100 100 Typical Application Circuits continued at end of data sheet. ________________________________________________________________ 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 MAX8506/MAX8507/MAX8508 General Description MAX8506/MAX8507/MAX8508 PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets ABSOLUTE MAXIMUM RATINGS BATTP, BATT, OUT, SHDN, SKIP, HP, REFIN, FB to GND ...........................................................-0.3V to +6V PGND to GND .......................................................-0.3V to +0.3V BATT to BATTP......................................................-0.3V to +0.3V OUT, COMP, REF to GND.......................-0.3V to (VBATT + 0.3V) LX Current (Note 1) ...............................................................1.6A OUT Current (Note 1)............................................................3.2A Output Short-Circuit Duration.....................................Continuous Continuous Power Dissipation (TA = +70C) 16-Pin Thin QFN (derate 16.9mW/C above +70C) ...1.349W 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 (V BATT = V BATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, V REFIN = 1.932V (MAX8506), V REFIN = 1.70V (MAX8507), CREF = 0.22F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER CONDITIONS Input BATT Voltage Undervoltage Lockout Threshold MIN TYP MAX 5.5 V 2.35 2.575 V 2.6 VBATT rising 2.150 Undervoltage Lockout Hysteresis 40 UNITS mV SKIP = GND (normal mode) 180 SKIP = BATT, 1MHz switching 1750 Quiescent Current in Dropout HP = BATT 775 1000 A Shutdown Supply Current SHDN = GND 0.1 5 A Quiescent Current OUT Voltage Accuracy OUT Input Resistance VREFIN = 1.932V, IOUT = 0 to 600mA (MAX8506) 3.375 3.40 3.425 VREFIN = 0.426V, IOUT = 0 to 30mA (MAX8506) 0.740 0.75 0.760 VREFIN = 1.700V, IOUT = 0 to 600mA (MAX8507) 3.375 3.40 3.425 VREFIN = 0.375V, IOUT = 0 to 30mA (MAX8507) 0.740 0.75 0.760 MAX8506 250 485 MAX8507 275 535 -1 0.1 REFIN Input Current REFIN to OUT Gain MAX8506 1.76 MAX8507 2.00 Reference Voltage Reference Load Regulation FB Voltage Accuracy FB = COMP (MAX8508) FB Input Current VFB = 1V (MAX8508) +1 1.25 1.275 V 2.5 8.5 mV 0.1 0.22 0.7275 0.75 F 0.7725 V A 0.175 0.4 0.825 VBATT = 2.6V 0.5 N-Channel On-Resistance ILX = 180mA HP/Bypass P-Channel On-Resistance IOUT = 180mA, VBATT = 3.6V A V/V 0.03 ILX = 180mA V k VBATT = 3.6V P-Channel On-Resistance A 1.225 10A < IREF < 100A Reference Bypass Capacitor 2 250 VBATT = 3.6V 0.3 VBATT = 2.6V 0.35 0.075 _______________________________________________________________________________________ 0.5 0.110 PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets (V BATT = V BATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, V REFIN = 1.932V (MAX8506), V REFIN = 1.70V (MAX8507), CREF = 0.22F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER CONDITIONS P-Channel Current-Limit Threshold MIN TYP MAX UNITS 1.00 1.25 1.50 A N-Channel Current-Limit Threshold SKIP = BATT (PWM mode) -0.6 -0.45 -0.30 SKIP = GND (normal mode) 0.03 0.05 0.07 P-Channel Pulse-Skipping Current Threshold SKIP = GND (normal mode) 0.050 0.125 0.170 A HP/Bypass P-Channel Current-Limit Threshold VOUT = 3.1V 0.8 1.5 2.5 A LX Leakage Current -2 0.01 +2 A OUT Leakage Current -2 0.01 +2 A Maximum Duty Cycle Minimum Duty Cycle 100 % SKIP = GND (normal mode) 0 SKIP = BATT 12 COMP Clamp Low Voltage 0.8 COMP Clamp High Voltage 2.0 MAX8506 Transconductance A % V V 85 150 215 MAX8507 75 130 188 MAX8508 150 260 376 0.36 0.48 0.60 V/A 0.8 1 1.2 MHz 0.4 V 1 A Current-Sense Transresistance S OSCILLATOR Internal Oscillator Frequency LOGIC INPUTS (SHDN, HP, SKIP) Logic-Input High Voltage VBATT = 2.6V to 5.5V Logic-Input Low Voltage VBATT = 2.6V to 5.5V Logic Input Current 1.6 V 0.1 THERMAL SHUTDOWN Thermal-Shutdown Temperature Thermal-Shutdown Hysteresis +160 C 15 C Note 2: Specifications to -40C are guaranteed by design, not production tested. _______________________________________________________________________________________ 3 MAX8506/MAX8507/MAX8508 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, TA = +25C, unless otherwise noted.) (See the Typical Application Circuits.) RLOAD = 15 90 EFFICIENCY vs. INPUT VOLTAGE 100 RLOAD = 15 90 MAX8506 toc03 100 MAX8506 toc01 100 EFFICIENCY vs. OUTPUT VOLTAGE IN PWM MODE MAX8506 toc02 EFFICIENCY vs. OUTPUT VOLTAGE IN NORMAL MODE 90 RLOAD = 10 80 RLOAD = 5 70 EFFICIENCY (%) EFFICIENCY (%) RLOAD = 10 80 RLOAD = 5 70 60 0.5 1.0 1.5 2.0 2.5 3.0 60 50 50 3.5 0.5 0 1.5 2.0 2.5 3.0 SKIP = GND RLOAD = 10 2.5 3.5 3.0 3.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE (V) EFFICIENCY vs. LOAD CURRENT DROPOUT VOLTAGE vs. LOAD CURRENT SUPPLY CURRENT vs. SUPPLY VOLTAGE IN PWM MODE VIN = 3.6V HP = BATT 120 80 VOUT = 1.2V; PWM 70 VOUT = 2.5V; PWM 60 90 60 30 VOUT = 1.2V; NORMAL MODE 50 100 1000 VOUT = 1.2V 3 VOUT = 0.4V 2 0 500 0 LOAD CURRENT (mA) 1000 1500 2000 2.0 LOAD CURRENT (mA) SUPPLY CURRENT vs. SUPPLY VOLTAGE IN NORMAL MODE 2.5 3.0 3.5 HEAVY-LOAD SWITCHING WAVEFORM MAX8506 toc07 SKIP = GND 900 800 VLX 2V/div VOUT = 3.4V 700 600 500 400 VOUT = 1.2V 300 VOUT AC-COUPLED 20mV/div VOUT = 0.4V 200 VOUT = 1.2V LOAD = 10 100 2.0 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 4.0 4.5 SUPPLY VOLTAGE (V) MAX8506 toc08 1000 SUPPLY CURRENT (A) 4 1 0 10 5 SUPPLY CURRENT (mA) 90 6 MAX8506 toc05 150 MAX8506 toc04 VOUT = 2.5V; NORMAL MODE 4 1.0 VOUT = 0.4V OUTPUT VOLTAGE (V) 100 1 70 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (mV) 0 VOUT = 1.2V 60 SKIP = GND 50 80 MAX8506 toc06 EFFICIENCY (%) VOUT = 3.4V EFFICIENCY (%) MAX8506/MAX8507/MAX8508 PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets 5.5 1s/div _______________________________________________________________________________________ 5.0 5.5 PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets (VBATT = VBATTP = 3.6V, SHDN = SKIP = BATT, HP = GND, TA = +25C, unless otherwise noted.) (See the Typical Application Circuits.) LIGHT-LOAD SWITCHING WAVEFORM IN PWM MODE LIGHT-LOAD SWITCHING WAVEFORM IN NORMAL MODE MAX8506 toc09 MAX8506 toc10 VLX 2V/div VLX 2V/div VOUT AC-COUPLED 5mV/div VOUT AC-COUPLED 20mV/div VOUT = 0.4V LOAD = 10, SKIP = GND VOUT = 0.4V LOAD = 10 1s/div 400s/div EXITING AND ENTERING SHUTDOWN REFIN TRANSIENT RESPONSE MAX8506 toc11 MAX8506 toc12 REFIN 1V/div SHDN 2V/div 0 SKIP = GND VOUT 1V/div VOUT 1V/div SKIP = BATT 0 VREFIN = 0.284V TO 1.420V VOUT = 1.8V, RLOAD = 10 100s/div 20s/div LINE TRANSIENT RESPONSE HP TRANSIENT RESPONSE MAX8506 toc14 MAX8506 toc13 HP 1V/div VIN 200mV/div 0 3.4V SKIP = GND VOUT 1V/div 1.8V SKIP = BATT VOUT = 1.8V, RLOAD = 10 20s/div VOUT AC-COUPLED 20mV/div VOUT = 1.2V, RLOAD = 10 20s/div _______________________________________________________________________________________ 5 MAX8506/MAX8507/MAX8508 Typical Operating Characteristics (continued) PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets MAX8506/MAX8507/MAX8508 Pin Description PIN NAME FUNCTION MAX8506 MAX8507 MAX8508 1 1 SHDN 2 2 GND Ground. Connect to PGND and directly to EP. 3 3 REF Reference Output. Output of the internal 1.25V reference. Bypass to GND with a 0.22F capacitor. 4 -- REFIN External Reference Input. Connect to the output of a digital-to-analog converter for dynamic adjustment of the output voltage. 5 5 COMP Compensation. Connect a compensation network from COMP to GND to stabilize the regulator. See the Typical Application Circuits. 6 6 HP 7 7 N.C. 8 8 PGND 9 9 LX Inductor Connection to the Drains of the Internal Power MOSFETs. LX is high impedance in shutdown mode. 10 10 BATTP Supply Voltage Input. Connect to a 2.6V to 5.5V source. Bypass BATTP to PGND with a low-ESR 2.2F capacitor. Connect BATTP to BATT. 11, 13, 15 11, 13, 15 BATT Supply Voltage Input. Connect all BATT pins to BATTP. 12, 14 12, 14 OUT Regulator Output. Connect both OUT pins directly to the output voltage. 16 16 SKIP Skip Control Input. Connect to GND or drive low to enable pulse skipping under light loads. Connect SKIP to BATT or logic high for forced-PWM mode. -- 4 FB Output Feedback Sense Input. To set the output voltage, connect FB to the center of an external resistive voltage-divider between OUT and GND. FB voltage regulates to 0.75V when HP is low. -- -- EP Exposed Pad. Connect directly to GND underneath the IC. Shutdown Control Input. Drive low for shutdown mode. Connect to BATT or logic high to enable the IC. High-Power Bypass Control Input. Drive low for OUT to regulate to the voltage set by REFIN (MAX8506/MAX8507) or the external resistors on FB (MAX8508). Drive HP high for OUT to be connected to BATT by an internal bypass PFET. No Connection. Connect to PGND. Power Ground. Connect to GND. Detailed Description The MAX8506/MAX8507/MAX8508 PWM step-down DCDC converters with integrated bypass PFET are optimized for low-voltage, battery-powered applications where high efficiency and small size are priorities. An analog control signal dynamically adjusts the MAX8506/ MAX8507s' output voltage from 0.4V to 3.4V with a settling time of 30s. The MAX8508 uses external feedback resistors to set the output voltage from 0.75V to 3.4V. The MAX8506/MAX8507/MAX8508 operate at a high 1MHz switching frequency that reduces external com- 6 ponent size. Each device includes an internal synchronous rectifier for high efficiency, which eliminates the need for an external Schottky diode. The normal operating mode uses constant-frequency PWM switching at medium and heavy loads and automatically pulse skips at light loads to reduce supply current and extend battery life. A forced-PWM mode switches at a constant frequency, regardless of load, to provide a well-controlled spectrum in noise-sensitive applications. Battery life is maximized by the low-dropout (75m) highpower mode and a 0.1A (typ) logic-controlled shutdown mode. _______________________________________________________________________________________ PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets During PWM operation, the MAX8506/MAX8507/ MAX8508 regulate the output voltage by switching at a constant frequency and then modulating the duty cycle with PWM control. The error-amp output, the main switch current-sense signal, and the slope-compensation ramp are all summed using a PWM comparator. The comparator modulates the output power by adjusting the peak inductor current during the first half of each cycle based on the output-error voltage. The MAX8506/MAX8507/MAX8508 have relatively low AC loop gain coupled with a high-gain integrator to enable the use of a small and low-valued output filter capacitor. The resulting load regulation is 0.1% at 0 to 600mA. Normal-Mode Operation Connecting SKIP to GND enables normal operation. This allows automatic PWM control at medium and heavy loads and skip mode at light loads to improve efficiency and reduce quiescent current to 180A. Operating in normal mode allows the MAX8506/MAX8507/MAX8508 to pulse skip when the peak inductor current drops below 90mA. During skip operation, the MAX8506/ MAX8507/MAX8508 switch only as needed to service the load, reducing the switching frequency and associated losses in the internal switch and synchronous rectifier. There are three steady-state operating conditions for the MAX8506/MAX8507/MAX8508 in normal mode: 1) The device performs in continuous conduction for heavy loads in a manner identical to forced-PWM mode. 2) The inductor current becomes discontinuous at medium loads, requiring the synchronous rectifier to be turned off before the end of a cycle as the inductor current reaches zero. 3) The device enters into skip mode when the converter output voltage exceeds its regulation limit before the inductor current reaches its skip threshold level. During skip mode, a switching cycle initiates when the output voltage has dropped out of regulation. The Pchannel MOSFET switch turns on and conducts current to the output-filter capacitor and load until the inductor current reaches the pulse-skipping current threshold. Then the main switch turns off and the magnetic field in the inductor collapses while current flows through the synchronous rectifier to the output filter capacitor and the load. The synchronous rectifier is turned off when the inductor current reaches zero. The MAX8506/ MAX8507/MAX8508 wait until the skip comparator senses a low output voltage again. Forced-PWM Operation Connect SKIP to BATT for forced-PWM operation. Forced-PWM operation is desirable in sensitive RF and data-acquisition applications to ensure that switching harmonics do not interfere with sensitive IF and datasampling frequencies. A minimum load is not required during forced-PWM operation since the synchronous rectifier passes reverse-inductor current as needed to allow constant-frequency operation with no load. ForcedPWM operation uses higher supply current with no load (1.75mA typ) compared to skip mode (180A typ). 100% Duty-Cycle Operation and Dropout The maximum on-time can exceed one internal oscillator cycle, which permits operation at 100% duty cycle. Near dropout, cycles can be skipped, reducing switching frequency. However, voltage ripple remains small because the current ripple is still low. As the input voltage drops even further, the duty cycle increases until the internal P-channel MOSFET stays on continuously. Dropout voltage at 100% duty cycle is the output current multiplied by the sum of the internal PMOS onresistance (400m typ) and the inductor resistance. For lower dropout, use the high-power bypass mode (75m typ). High-Power Bypass Mode A high-power bypass mode is available for use when a PA transmits at high power. This mode connects OUT to BATT through the bypass PFET. Additionally, the PWM buck converter is forced into 100% duty cycle to further reduce dropout. The dropout in the bypass PFET equals the load current multiplied by the on-resistance (75 typ) in parallel with the buck converter and inductor dropout resistance. Undervoltage Lockout (UVLO) The MAX8506/MAX8507/MAX8508 do not operate with battery voltages below the UVLO threshold of 2.35V (typ). The output remains off until the supply voltage exceeds the UVLO threshold. This guarantees the integrity of the output voltage regulation. _______________________________________________________________________________________ 7 MAX8506/MAX8507/MAX8508 PWM Control The MAX8506/MAX8507/MAX8508 use a fixed-frequency, current-mode and PWM controller capable of achieving 100% duty cycle. Current-mode feedback provides cycle-by-cycle current limiting and superior load and line response, as well as overcurrent protection for the internal MOSFET and rectifier. A comparator at the P-channel MOSFET switch detects overcurrent at 1.25A. MAX8506/MAX8507/MAX8508 PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets Synchronous Rectification An N-channel synchronous rectifier operates during the second half of each switching cycle (off-time). When the inductor current falls below the N-channel currentcomparator threshold or when the PWM reaches the end of the oscillator period, the synchronous rectifier turns off. This prevents reverse current from the output to the input in pulse-skipping mode. During PWM operation, the NEGLIM threshold adjusts to permit reverse current during light loads. This allows regulation with a constant switching frequency and eliminates minimum load requirements for fixed-frequency operation. Shutdown Mode Drive SHDN to GND to place the MAX8506/MAX8507/ MAX8508 in shutdown mode. In shutdown, the reference, control circuitry, internal switching MOSFET, and synchronous rectifier turn off and the output becomes high impedance. Input current falls to 0.1A (typ) during shutdown mode. Drive SHDN high to enable the IC. Current-Sense Comparators The MAX8506/MAX8507/MAX8508 use several internal current-sense comparators. In PWM operation, the PWM comparator terminates the cycle-by-cycle on-time and provides improved load and line response. A second current-sense comparator used across the P-channel switch controls entry into skip mode. A third current-sense comparator monitors current through the internal N-channel MOSFET to prevent excessive reverse currents and determine when to turn off the synchronous rectifier. A fourth comparator used at the P-channel MOSFET detects overcurrent. A fifth comparator used at the bypass P-channel MOSFET detects overcurrent in the HP mode or at dropout. This protects the system, external components, and internal MOSFETs under overload conditions. The MAX8506/MAX8507s' output voltage is dynamically adjustable from 0.4V to 3.4V by the use of the REFIN input. The gain from VREFIN to VOUT is internally set to 1.76 (MAX8506) or 2.00 (MAX8507). VOUT can be adjusted during operation by driving REFIN with an external DAC. The MAX8506/MAX8507 output responds to fullscale change in voltage and current in less than 30s. Using External Divider (MAX8508) The MAX8508 is intended for two-step V CC control applications where high efficiency is a priority. Select an output voltage between 0.75V and 3.4V by connecting FB to a resistive-divider between the output and GND (see the MAX8508 Typical Application Circuit). Select feedback resistor R2 in the 5k to 50k range. R1 is then given by: V R1 = R2 x OUT - 1 VFB where VFB = 0.75V. Input Capacitor Selection Capacitor ESR is a major contributor to input ripple in high-frequency DC-DC converters. Ordinary aluminumelectrolytic capacitors have high ESR and should be avoided. Low-ESR tantalum or polymer capacitors are better and provide a compact solution for space-constrained surface-mount designs. Ceramic capacitors have the lowest overall ESR. The input filter capacitor reduces peak currents and noise at the input voltage source. Connect a low-ESR bulk capacitor (2.2F to 10F) to the input. Select this bulk capacitor to meet the input ripple requirements and voltage rating rather than capacitance value. Use the following equation to calculate the maximum RMS input current: Applications Information Setting the Output Voltage Using a DAC (MAX8506/MAX8507) The MAX8506/MAX8507 are optimized for highest system efficiency when applying power to a linear PA in CDMA handsets. When transmitting at less than full power, the supply voltage to the PA is lowered in many steps from 3.4V to as low as 0.4V to greatly reduce battery current (see the Typical Application Circuits). The use of DC-DC converters such as the MAX8506/ MAX8507 dramatically extends talk time in these applications. 8 I IRMS = OUT x VOUT x (VIN - VOUT ) VIN Compensation, Stability, and Output Capacitor The MAX8506/MAX8507/MAX8508 are externally compensated by placing a resistor and a capacitor (see the Typical Application Circuits, RC and CC) in series from COMP to GND. An additional capacitor (C f) may be required from COMP to GND if high-ESR output capacitors are used. The CC capacitor integrates the current from the transimpedance amplifier, averaging output _______________________________________________________________________________________ PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets PART NUMBER INDUCTANCE (H) ESR (m) SATURATION CURRENT (A) DIMENSIONS (mm) Murata LQH32C-53 4.7 150 0.650 2.5 x 3.2 x 1.7 Sumida CDRH2D11 4.7 135 0.500 3.2 x 3.2 x 1.2 Taiyo Yuden LBLQ2016 4.7 250 0.210 1.6 x 2.0 x 1.6 D312C 4.7 200 0.790 3.6 x 3.6 x 1.2 SUPPLIER TOKO capacitor ripple. This sets the device speed for transient response and allows the use of small ceramic output capacitors because the phase-shifted capacitor ripple does not disturb the current-regulation loop. The resistor sets the proportional gain of the output error voltage by a factor of gm x RC. Increasing this resistor also increases the sensitivity of the control loop to output ripple. The resistor and capacitor set a compensation zero that defines the system's transient response. The load creates a dynamic pole, shifting in frequency with changes in load. As the load decreases, the pole frequency shifts to the left. System stability requires that the compensation zero must be placed to ensure adequate phase margin (at least 30 at unity gain). With a 4.7F output capacitor, the recommended CC and RC for the MAX8506 are 1500pF and 10k, respectively. This provides adequate phase margin over the entire output voltage and load range and optimizes the outputvoltage settling time for REFIN dynamic control. See the Typical Application Circuits for recommended CC and RC values for the MAX8507 and MAX8508. Inductor Selection A 4H to 6H inductor is recommended for most applications. For best efficiency, the inductor's DC resistance should be <400m. Saturation current (ISAT) should be greater than the maximum DC load at the PA's supply plus half the inductor current ripple. Two-step VCC applications typically require very small inductors with ISAT in the 200mA to 300mA region. See Tables 1 and 2 for recommended inductors and suppliers. PC Board Layout and Routing Table 2. Component Suppliers SUPPLIER PHONE WEBSITE Murata 770-436-1300 www.murata.com Sumida 847-956-0666 www.sumida.com Taiyo Yuden 408-573-4150 www.t-yuden.com TOKO 847-297-0070 www.tokoam.com High switching frequencies and large peak currents make PC board layout a very important part of design. Good design minimizes EMI, noise on the feedback paths, and voltage gradients in the ground plane, all of which can result in instability or regulation errors. Connect the inductor, input filter capacitor, and output filter capacitor as close together as possible and keep their traces short, direct, and wide. The external voltage- feedback network should be very close to the FB pin, within 0.2in (5mm). Keep noisy traces, such as those from the LX pin, away from the voltage-feedback network. Position the bypass capacitors as close as possible to their respective supply and ground pins to minimize noise coupling. For optimum performance, place input and output capacitors as close to the device as possible. Connect GND directly under the IC to the exposed paddle. Refer to the MAX8506 evaluation kit for an example PC board layout and routing scheme. _______________________________________________________________________________________ 9 MAX8506/MAX8507/MAX8508 Table 1. Suggested Inductors PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets MAX8506/MAX8507/MAX8508 Typical Application Circuits (MAX8508) (continued) INPUT 2.6V TO 5.5V OUTPUT 0.75V TO 3.4V OR VBATT 4.7H 4.7F 2.2F BATTP LX BATT OUT MAX8508 0.075 SKIP SHDN REF 0.4 REF CURRENTLIMIT CONTROL PWM 0.22F R1 1MHz OSC 0.3 FB R2 HP 0.75V PGND COMP GND RC 5.6k CC 2700pF Cf 100pF BATT OUT BATT SKIP BATT OUT BATT 13 MAX8506 MAX8507 12 OUT SHDN 1 11 BATT GND 2 10 BATTP REF 3 9 LX FB 4 MAX8508 5 6 7 8 5 6 7 8 PGND 4 14 HP REFIN 15 N.C. 3 16 COMP 2 REF 13 PGND GND 14 HP 1 15 N.C. SHDN 16 COMP TOP VIEW SKIP Pin Configurations THIN QFN 4mm x 4mm 12 OUT 11 BATT 10 BATTP 9 LX THIN QFN 4mm x 4mm Chip Information TRANSISTOR COUNT: 2020 PROCESS: BiCMOS 10 ______________________________________________________________________________________ PWM Step-Down DC-DC Converters with 75m Bypass FET for WCDMA and cdmaOne Handsets 24L QFN THIN.EPS PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm 21-0139 C 1 2 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. MAX8506/MAX8507/MAX8508 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.) Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MAX8506ETE+ MAX8506ETE+T MAX8508ETE+ MAX8508ETE+T MAX8507ETE+T MAX8507ETE+