LTC3576

FEATURES n LTC3576/LTC3576-1 Switching Power Manager with USB On-the-Go + Triple Step-Down DC/DCs DESCRIPTION The LTC®3576/LTC3576-1 are highly integrated power management and battery charger ICs for Li-Ion/Polymer battery applications. They each include a high efficiency, bidirectional switching PowerPath™ manager with automatic load prioritization, a battery charger, an ideal diode, a controller for an external high voltage switching regulator and three general purpose step-down switching regulators with I2C adjustable output voltages. The internal switching regulators automatically limit input current for USB compatibility and can also generate 5V at 500mA for USB on-the-go applications when powered from the battery. Both the USB and external switching regulator power paths feature Bat-Track optimized charging to provide maximum power to the application from supplies as high as 38V. An overvoltage circuit protects the LTC3576/LTC3576-1 from damage due to high voltage on the VBUS or WALL pins with just two external components. The LTC3576/LTC3576-1 are available in a low profile 38-pin (4mm × 6mm × 0.75mm) QFN package. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Bat-Track and PowerPath are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 6522118, 6404251. n n n n n n n n Bidirectional Switching Regulator with BatTrack™ Adaptive Output Control Provides Efficient Charging and a 5V Output for USB On-The-Go Bat-Track Control of External High Voltage StepDown Switching Regulator Overvoltage Protection Guards Against Damage “Instant-On” Operation with Discharged Battery Triple Step-Down Switching Regulators with I2C Adjustable Outputs (1A/400mA/400mA IOUT) 180mΩ Internal Ideal Diode + External Ideal Diode Controller Powers the Load in Battery Mode Li-Ion/Polymer Battery Charger (1.5A Max ICHG) Battery Float Voltage: 4.2V (LTC3576), 4.1V (LTC3576-1) Compact (4mm × 6mm × 0.75mm) 38-pin QFN Package APPLICATIONS n n n HDD-Based Media Players GPS, PDAs, Digital Cameras, Smart Phones Automotive Compatible Portable Electronics TYPICAL APPLICATION High Efficiency PowerPath Manager with Overvoltage Protection and Triple Step-Down Regulator AUTOMOTIVE FIREWIRE, ETC. USB OR 5V AC ADAPTER LT3653 PowerPath Switching Regulator Efficiency to System Load (PVOUT/PVBUS) 100 90 TO OTHER LOADS EFFICIENCY (%) OVERVOLTAGE PROTECTION EXTERNAL HIGH VOLTAGE BUCK CONTROLLER USB COMPLIANT BIDIRECTIONAL SWITCHING REGULATOR CC/CV BATTERY CHARGER CHARGE LTC3576/LTC3576-1 T ALWAYS ON LDO TRIPLE HIGH EFFICIENCY STEP-DOWN SWITCHING REGULATORS I2C PORT 1 2 3 0V OPTIONAL 80 70 60 50 40 30 BAT = 4.2V BAT = 3.3V + Li-Ion 3.3V/20mA 0.8V TO 3.6V/400mA 0.8V TO 3.6V/400mA 0.8V TO 3.6V/1A RST 2 RTC/LOW POWER LOGIC MEMORY I/O CORE μPROCESSOR I 2C 3576 TA01 20 10 0 10 VBUS = 5V IBAT = 0mA 10x MODE 100 LOAD CURRENT (mA) 1000 3576 TA01b ENABLE CONTROLS 6 3576f 1 LTC3576/LTC3576-1 ABSOLUTE MAXIMUM RATINGS (Notes 1, 2, 3) PIN CONFIGURATION TOP VIEW ILIM1 ILIM0 VBUS VBUS VOUT BAT 31 IDGATE 30 CHRG 29 PROG 28 ACPR 27 WALL 39 26 VC 25 FB2 24 VIN2 23 SW2 22 EN2 21 RST3 20 FB3 13 14 15 16 17 18 19 VIN3 SW3 SCL SDA EN3 NC NC SW VBUS, WALL (Transient) t < 1ms, Duty Cycle < 1% .......................................... –0.3V to 7V VBUS, WALL (Static), BAT, VIN1, VIN2, VIN3, VOUT, ENOTG, NTC, SDA, SCL, DVCC, RST3, CHRG ................................................ –0.3V to 6V ILIM0, IILIM1 .........–0.3V to Max(VBUS, VOUT, BAT) + 0.3V EN1, EN2, EN3 ...............................–0.3V to VOUT + 0.3V FBx (x = 1, 2, 3) ..............................–0.3V to VINx + 0.3V IOVSENS...................................................................10mA ICLPROG ....................................................................3mA ICHRG, IRST3 ............................................................50mA IPROG ........................................................................2mA ILDO3V3 ...................................................................30mA ISW1, ISW2 (Continuous) .......................................600mA ISW, ISW3, IBAT, IVOUT (Continuous) ..............................2A Maximum Junction Temperature........................... 125°C Operating Temperature Range.................. –40°C to 85°C Storage Temperature Range................... –65°C to 125°C 38 37 36 35 34 33 32 CLPROG 1 LDO3V3 2 NTCBIAS 3 NTC 4 OVGATE 5 OVSENS 6 FB1 7 VIN1 8 SW1 9 EN1 10 ENOTG 11 DVCC 12 UFE PACKAGE 38-LEAD (4mm 6mm) PLASTIC QFN TJMAX = 125°C, θJA = 34°C/W EXPOSED PAD (PIN 39) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH LTC3576EUFE#PBF LTC3576EUFE-1#PBF TAPE AND REEL LTC3576EUFE#TRPBF LTC3576EUFE-1#TRPBF PART MARKING 3576 35761 PACKAGE DESCRIPTION 38-Lead (4mm × 6mm) Plastic QFN 38-Lead (4mm × 6mm) Plastic QFN TEMPERATURE RANGE –40°C to 85°C –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS SYMBOL VBUS IVBUS(LIM) PARAMETER Input Supply Voltage Total Input Current PowerPath Switching Regulator—Step-Down Mode The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless otherwise noted. CONDITIONS MIN 4.35 1× Mode 5× Mode 10× Mode Low Power Suspend Mode High Power Suspend Mode 1× Mode 5×, 10× Modes Low/High Power Suspend Modes l l l l l TYP MAX 5.5 UNITS V mA mA mA mA mA mA mA mA 3576f 82 440 800 0.32 1.6 90 472 880 0.39 2.05 7 17 0.045 100 500 1000 0.5 2.5 IVBUSQ (Note 4) Input Quiescent Current 2 LTC3576/LTC3576-1 ELECTRICAL CHARACTERISTICS SYMBOL hCLPROG (Note 4) PARAMETER Ratio of Measured VBUS Current to CLPROG Program Current The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless otherwise noted. CONDITIONS 1x Mode 5x Mode 10x Mode Low Power Suspend Mode High Power Suspend Mode 1x Mode, BAT = 3.3V 5x Mode, BAT = 3.3V 10x Mode, BAT = 3.3V Low Power Suspend Mode High Power Suspend Mode Switching Modes Suspend Modes Rising Threshold Falling Threshold Rising Threshold Falling Threshold 1x, 5x, 10x Modes, 0V < BAT < 4.2V, IVOUT = 0mA, Battery Charger Off USB Suspend Modes, IVOUT = 250μA 3.4 4.5 1.8 3.95 MIN TYP 210 1160 2200 9.6 56 121 667 1217 0.31 2 1.18 100 4.30 4.00 200 50 BAT + 0.3 4.6 2.25 0.18 0.30 1x Mode (Note 5) 5x Mode (Note 5) 10x Mode (Note 5) Closed Loop 0mA ≤ IVBUS ≤ 500mA, VOUT > 3.2V l MAX UNITS mA/mA mA/mA mA/mA mA/mA mA/mA mA mA mA mA mA V mV IVOUT(POWERPATH) VOUT Current Available Before Discharging Battery 0.26 1.6 0.41 2.4 VCLPROG VUVLO VDUVLO VOUT CLPROG Servo Voltage in Current Limit VBUS Undervoltage Lockout VBUS to BAT Differential Undervoltage Lockout VOUT Voltage 4.35 V V mV mV 4.7 4.7 2.7 V V MHz Ω Ω A A A Ω fOSC RPMOS_ POWERPATH Switching Frequency PMOS On-Resistance NMOS On-Resistance RNMOS_ POWERPATH IPEAK_POWERPATH Peak Inductor Current Limit 1 2 3 10 4.75 2.9 550 –150 680 0 1.8 1.38 1.15 2.5 2.6 2.8 7.2 4.2 0 3.55 4.3 1.1 30 60 BAT + 0.3 100 100 VOUT 0 4.4 45 2.9 5.25 5.5 150 RSUSP VBUS VOUT IVBUS IPEAK IOTGQ VCLPROG VOUT(UVLO) tSCFAULT VWALL ΔVWALL VOUT IWALLQ RACPR VHACPR VLACPR Suspend LDO Output Resistance Output Voltage Input Voltage Output Current Limit VBUS Leakage Current in Shutdown Peak Inductor Current Limit VOUT Quiescent Current Output Current Limit Servo Voltage VOUT UVLO—VOUT Falling VOUT UVLO—VOUT Rising Short-Circuit Fault Delay Absolute WALL Input Threshold Differential WALL Input Threshold Regulation Target Under VC Control WALL Quiescent Current ACPR Pull-Down Strength ACPR High Voltage ACPR Low Voltage PowerPath Switching Regulator—Step-Up Mode (USB On-the-Go) V V mA nA A mA V V V ms V V mV mV V μA Ω V V 3576f On-the-Go Disabled, VBUS < UVLO (Note 5) VOUT = 3.8V, IVBUS = 0mA (Note 6) VBUS < 4V and PMOS Switch Off Rising Threshold Hysteresis WALL-BAT Falling Hysteresis Bat-Track Switching Regulator Control 3 LTC3576/LTC3576-1 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER Overvoltage Protection Overvoltage Protection Threshold VOVCUTOFF OVGATE Output Voltage VOVGATE tRISE Battery Charger VFLOAT OVGATE Time to Reach Regulation BAT Regulated Output Voltage The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless otherwise noted. CONDITIONS With 6.2k Series Resistor VOVSENS < VOVCUTOFF VOVSENS > VOVCUTOFF OVGATE CLOAD = 1nF LTC3576 LTC3576-1 MIN 6.1 TYP 6.35 1.88•VOVSENS 0 1.25 4.200 4.200 4.100 4.100 1030 206 3.6 28 1.000 0.100 100 1030 100 2.85 135 –100 4 0.5 0.1 65 0.18 110 MAX 6.7 12 UNITS V V V ms V V V V mA mA μA μA V V mV mA/mA mA V mV mV Hour Hour mA/mA mV μA Ω °C l l ICHG IBAT Constant Current Mode Charger Current Battery Drain Current RPROG = 1k RPROG = 5k VBUS > VUVLO, Suspend Mode, IVOUT = 0μA VBUS = 0V, IVOUT = 0μA (Ideal Diode Mode) 4.179 4.165 4.079 4.065 980 185 4.221 4.235 4.121 4.135 1065 223 6 45 VPROG VPROG_TRKL VC/10 hPROG ITRKL VTRKL ΔVTRKL ΔVRECHRG tTERM tBADBAT hC/10 VCHRG ICHRG RON_CHG TLIM NTC VCOLD PROG Pin Servo Voltage PROG Pin Servo Voltage in Trickle Charge BAT < VTRKL C/10 Threshold Voltage at PROG Ratio of IBAT to PROG Pin Current Trickle Charge Current BAT < VTRKL, RPROG = 1k Trickle Charge Threshold Voltage BAT Rising Trickle Charge Hysteresis Voltage Recharge Battery Threshold Voltage Safety Timer Termination Period Bad Battery Termination Time End of Charge Current Ratio CHRG Pin Output Low Voltage CHRG Pin Leakage Current Battery Charger Power FET OnResistance (Between VOUT and BAT) Junction Temperature in Constant Temperature Mode Threshold Voltage Relative to VFLOAT Timer Starts When VBAT = VFLOAT BAT < VTRKL (Note 7) ICHRG = 5mA VCHRG = 5V 2.7 –75 3.3 0.4 0.085 3.0 –125 5 0.6 0.112 100 1 Cold Temperature Fault Threshold Voltage Rising Threshold Hysteresis Hot Temperature Fault Threshold Voltage NTC Disable Threshold Voltage NTC Leakage Current Forward Voltage Internal Diode On-Resistance Dropout Diode Current Limit Falling Threshold Hysteresis Falling Threshold Hysteresis NTC = NTCBIAS = 5V IVOUT = 10mA IVOUT = 200mA 75 76.5 1.5 34.9 1.5 1.7 50 78 %NTCBIAS %NTCBIAS %NTCBIAS %NTCBIAS %NTCBIAS mV nA mV Ω A 3576f VHOT VDIS INTC Ideal Diode VFWD RDROPOUT IMAX_DIODE 33.4 0.7 –50 36.4 2.7 50 15 0.18 2 4 LTC3576/LTC3576-1 ELECTRICAL CHARACTERISTICS SYMBOL VLDO3V3 RCL_LDO3V3 ROL_LDO3V3 VIL VIH IPD1 I2C Port DVCC IDVCC VDVCC(UVLO) ADDRESS VIH, SDA, SCL VIL, SDA, SCL IPD2, SDA, SCL VOL fSCL tBUF tHD_STA tSU_STA tSU_STO tHD_DAT(O) tHD_DAT(I) tSU_DAT tLOW tHIGH tf tr tSP VIN1,2,3 VOUT(UVLO) Input Supply DVCC Current DVCC UVLO I2C Address Input High Threshold Input Low Threshold Pull-Down Current Digital Output Low (SDA) Clock Operating Frequency Bus Free Time Between Stop and Start Condition Hold Time After (Repeated) Start Condition Repeated Start Condition Setup Time Stop Condition Setup Time Data Hold Time Output Data Hold Time Input Data Setup Time SCL Low Period SCL High Period SDA/SCL Fall Time SDA/SCL Rise Time Input Spike Suppression Pulse Width Input Supply Voltage VOUT UVLO—VOUT Falling VOUT UVLO—VOUT Rising Switching Frequency FBx Input Current Maximum Duty Cycle SWx Pull-Down in Shutdown VFB1,2,3 = 0.85V (Note 8) VIN1,2,3 Connected to VOUT Through Low Impedance. Switching Regulators are Disabled in UVLO 2.7 2.5 2.6 2.8 2.25 1.3 0.6 0.6 0.6 0 0 100 1.3 0.6 20 20 300 300 50 5.5 2.9 2.7 50 10 900 ISDA = 3mA 2 0.4 400 70 30 SCL/SDA = 0kHz, DVCC = 3.3V 1.6 0.5 1.0 0001001[0] %DVCC %DVCC μA V kHz μs μs μs μs ns ns ns μs μs ns ns ns V V V MHz nA % kΩ 5.5 V μA V PARAMETER Regulated Output Voltage Closed-Loop Output Resistance Dropout Output Resistance Logic Low Input Voltage Logic High Input Voltage ILIM0, ILIM1, EN1, EN2, EN3, ENOTG, SCL, SDA Pull-Down Current 1.2 2 Always On 3.3V LDO Supply 0mA < ILDO3V3 < 20mA 3.1 3.3 2.7 23 0.4 3.5 V Ω Ω V V μA The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless otherwise noted. CONDITIONS MIN TYP MAX UNITS Logic (ILIM0, ILIM1, EN1, EN2, EN3, ENOTG, and SCL, SDA when DVCC = 0V) General Purpose Switching Regulators 1, 2 and 3 fOSC IFB1,2,3 D1,2,3 RSW1,2,3_PD 1.8 –50 100 3576f 5 LTC3576/LTC3576-1 ELECTRICAL CHARACTERISTICS SYMBOL IVIN1,2,3 PARAMETER Pulse Skip Mode Input Current Burst Mode Input Current LDO Mode Input Current Shutdown Input Current Limit VFBHIGH1,2,3 VFBLOW1,2,3 VLSB1,2,3 RLDO_CL1,2,3 RLDO_OL1,2,3 ILIM1,2 IOUT1,2 RP1,2 RN1,2 ILIM3 IOUT3 RP3 RN3 tRST3 Maximum Servo Voltage Minimum Servo Voltage VFB1,2 Servo Voltage Step Size LDO Mode Closed-Loop ROUT LDO Mode Open-Loop ROUT PMOS Switch Current Limit Available Output Current PMOS RDS(ON) NMOS RDS(ON) PMOS Switch Current Limit Available Output Current PMOS RDS(0N) NMOS RDS(ON) Power-On Reset Time for Switching Regulator VFB3 Within 92% of Final Value to RST3 Hi-Z Pulse Skip/Burst Mode Operation (Note 5) LDO Mode 1300 50 0.18 0.3 230 VFB1,2,3 = VOUT1,2 3 = 0.8V (Note 11) Pulse Skip/Burst Mode Operation (Note 5) LDO Mode 600 50 0.6 0.7 1800 2800 ® The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBUS = 5V, BAT = 3.8V, DVCC = 3.3V, RCLPROG = 3.01k, unless otherwise noted. CONDITIONS IOUT1,2,3 = 0μA (Note 9) IOUT1,2,3 = 0μA (Note 9) IOUT1,2,3 = 0μA (Note 9) IOUT1,2,3 = 0μA, FB1,2,3 = 0V Full Scale (1,1,1,1) (Note 10) Zero Scale (0,0,0,0) (Note 10) l MIN TYP 90 20 15 MAX 35 25 1 0.82 0.445 UNITS μA μA μA μA V V mV Ω Ω 0.78 0.405 0.80 0.425 25 0.25 2.5 900 General Purpose Switching Regulator 1 and 2 1300 mA mA Ω Ω mA mA Ω Ω ms General Purpose Switching Regulator 3 Burst Mode is a registered trademark of Linear Technology Corporation. Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3576E/LTC3576E-1 are guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: The LTC3576E/LTC3576E-1 include overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. Note 4: Total input current is the sum of quiescent current, IVBUSQ, and measured current given by VCLPROG/RCLPROG • (hCLPROG + 1). Note 5: The current limit features of this part are intended to protect the IC from short term or intermittent fault conditions. Continuous operation above the maximum specified pin current rating may result in device degradation or failure. Note 6: The bidirectional switcher’s supply current is bootstrapped to VBUS and in the application will reflect back to VOUT by (VBUS/VOUT) • 1/efficiency. Total quiescent current is the sum of the current into the VOUT pin plus the reflected current. Note 7: hC/10 is expressed as a fraction of the measured full charge current with indicated PROG resistor. Note 8: VOUT not in UVLO. Note 9: FBx above regulation such that regulator is in sleep. Specification does not include resistive divider current reflected back to VINx. Note 10: Applies to pulse skip and Burst Mode operation only. Note 11: Inductor series resistance adds to open-loop ROUT. 3576f 6 LTC3576/LTC3576-1 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified. Ideal Diode V-I Characteristics 1.0 INTERNAL IDEAL DIODE WITH SUPPLEMENTAL EXTERNAL VISHAY Si2333 PMOS RESISTANCE (Ω) 0.25 Ideal Diode Resistance vs Battery Voltage 4.50 VOUT Voltage vs Load Current (Battery Charger Disabled) BAT = 4V 0.8 CURRENT (A) 0.20 INTERNAL IDEAL DIODE VOUT (V) 0.15 4.25 0.6 INTERNAL IDEAL DIODE ONLY 0.4 4.00 BAT = 3.4V 3.75 0.10 INTERNAL IDEAL DIODE WITH SUPPLEMENTAL EXTERNAL VISHAY Si2333 PMOS 0.2 VBUS = 5V 0 0.04 0.12 0.16 0.08 FORWARD VOLTAGE (V) 0.20 3576 G01 0.05 3.50 0 0 2.7 3.0 3.6 3.9 3.3 BATTERY VOLTAGE (V) 4.2 3576 G02 3.25 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 3576 G03 USB Limited Load Current vs Battery Voltage (Battery Charger Disabled) 900 800 700 LOAD CURRENT (mA) CURRENT (mA) 600 500 400 300 200 100 0 2.7 3.0 3.9 3.6 3.3 BATTERY VOLTAGE (V) 4.2 3576 G04 Battery and VBUS Currents vs Load Current 750 600 VBUS CURRENT CHARGE CURRENT (mA) 500 400 Battery Charge Current vs Temperature RPROG = 2k VBUS = 5V 5x MODE 500 250 BATTERY CURRENT (CHARGING) 0 VBUS = 5V BAT = 3.8V 5x MODE RCLPROG = 3.01k BATTERY CURRENT RPROG = 1k (DISCHARGING) 0 100 200 300 400 500 600 700 800 900 1000 LOAD CURRENT (mA) 3576 G05 THERMAL REGULATION 300 200 100 0 –40 –20 –250 –500 0 20 40 60 80 TEMPERATURE (°C) 100 120 3576 G06 PowerPath Switching Regulator Transient Response 100 VOUT 50mV/DIV AC COUPLED EFFICIENCY (%) 90 PowerPath Switching Regulator Efficiency vs Load Current 95 90 1x MODE 80 70 60 50 EFFICIENCY (%) 5x, 10x MODE 85 80 75 70 65 Battery Charging Efficiency vs Battery Voltage with No External Load (PBAT/PVBUS) RCLPROG = 3.01k RPROG = 1k 1x MODE IVOUT 500mA/DIV 0mA VBUS = 5V VOUT = 3.65V CHARGER OFF 10x MODE 20μs/DIV 3576 G07 5x MODE 60 55 10 100 LOAD CURRENT (mA) 1000 3576 G08 40 30 50 2.7 3.0 3.9 3.6 3.3 BATTERY VOLTAGE (V) 4.2 3576 G09 3576f 7 LTC3576/LTC3576-1 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified. VBUS Quiescent Current vs VBUS Voltage (Suspend) 60 50 QUIESCENT CURRENT (μA) 40 VOUT (V) 4.0 30 20 10 0 0 1 2 3 BUS VOLTAGE (V) 4 5 3576 G10 VOUT Voltage vs Load Current in Suspend 5.0 HIGH POWER SUSPEND 4.5 VBUS CURRENT (mA) 2.0 2.5 VBUS Current vs Load Current in Suspend VBUS = 5V BAT = 3.3V RCLPROG = 3.01k 1.5 HIGH POWER SUSPEND 1.0 3.5 LOW POWER SUSPEND VBUS = 5V BAT = 3.3V RCLPROG = 3.01k 0 0.5 1.5 2.0 1.0 LOAD CURRENT (mA) 2.5 3576 G11 3.0 0.5 LOW POWER SUSPEND 2.5 0 0 0.5 1.5 2.0 1.0 LOAD CURRENT (mA) 2.5 3576 G12 Battery Charge Current vs VOUT Voltage 600 500 BATTERY CURRENT (mA) 400 VOUT (V) 300 200 100 0 3.40 3.45 3.50 3.55 3.60 3.65 3.70 3.75 3.80 VOUT (V) 3576 G13 VOUT Voltage vs Battery Voltage (Charger Overprogrammed) 4.7 4.5 4.3 4.1 3.9 3.7 3.5 3.3 3.1 2.9 2.7 2.7 3.0 3.6 3.9 3.3 BATTERY VOLTAGE (V) 4.2 3576 G14 Normalized Battery Charger Float Voltage vs Temperature 1.001 NORMALIZED FLOAT VOLTAGE RCLPROG = 3.01k RPROG = 2k 5x MODE VBUS = 5V IVOUT = 0V RCLPROG = 3.01k RPROG = 1k 1.000 0.999 5x MODE 0.998 1x MODE 0.997 0.996 –40 –15 35 10 TEMPERATURE (°C) 60 85 3576 G15 VBUS Quiescent Current vs Temperature 25 VBUS = 5V QUIESCENT CURRENT (mA) QUIESCENT CURRENT (μA) 20 5x MODE 15 50 60 VBUS Quiescent Current in Suspend vs Temperature VBUS = 5V 35 30 BATTERY CURRENT (μA) 25 20 15 10 5 Battery Drain Current vs Temperature 40 30 20 10 0 –40 10 1x MODE 5 0 –40 –15 35 10 TEMPERATURE (°C) 60 85 3576 G16 –15 10 35 TEMPERATURE (°C) 60 85 3576 G17 0 –40 BAT = 3.8V VBUS = 0V SWITCHING REGULATORS OFF –15 10 35 60 85 3576 G18 TEMPERATURE (°C) 3576f 8 LTC3576/LTC3576-1 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified. OTG Boost Quiescent Current vs VOUT Voltage 2.5 2.3 QUIESCENT CURRENT (mA) 2.1 1.9 VBUS (V) 1.7 1.5 1.3 1.1 0.9 0.7 0.5 2.90 3.55 4.20 VOUT (V) 4.85 5.50 3576 G19 OTG Boost VBUS Voltage vs Load Current 5.5 100 90 EFFICIENCY (%) VBUS = 4.75V 80 70 60 50 40 OTG Boost Efficiency vs Load Current 5.0 4.5 4.0 IVBUS = 500mA 3.5 VOUT = 5V VOUT = 4.4V VOUT = 3.8V VOUT = 3.2V 0 100 200 300 400 500 LOAD CURRENT (mA) 600 700 3.0 VOUT = 5V VOUT = 4.4V VOUT = 3.8V VOUT = 3.2V 1 10 100 LOAD CURRENT (mA) 1000 3576 G21 3576 G20 OTG Boost Efficiency vs VOUT Voltage 95 500mA LOAD 90 EFFICIENCY (%) 100mA LOAD 85 TIME (ms) 2.00 2.50 OTG Boost Start-Up Time into Current Source Load vs VOUT Voltage 400 OTG Boost Burst Mode Current Threshold vs VOUT Voltage LOAD CURRENT (mA) 2.25 22μF ON VBUS, 22μF AND LOAD THROUGH OVP 300 RISING THRESHOLD FALLING THRESHOLD 200 22μF ON VBUS, NO OVP 22μF ON VBUS, LOAD THROUGH OVP 80 1.75 75 100 70 2.90 1.50 3.55 4.20 VOUT (V) 3576 G22 4.85 5.50 2.9 3.4 3.9 4.4 VOUT (V) 4.9 5.4 3576 G23 0 2.90 3.55 4.20 VOUT (V) 4.85 5.50 3576 G24 OTG Boost Transient Response VBUS 50mV/DIV AC COUPLED OTG Boost Start-Up into Current Source Load VBUS 50mV/DIV AC COUPLED IVBUS 200mA/DIV 0mA VSW 1V/DIV OTG Boost Burst Mode Operation IVBUS 200mA/DIV 0mA VOUT = 3.8V 20μs/DIV 3576 G25 VBUS 2V/DIV 0V VOUT = 3.8V ILOAD = 500mA 200μs/DIV 3576 G26 0V VOUT = 3.8V ILOAD = 10mA 50μs/DIV 3576 G27 3576f 9 LTC3576/LTC3576-1 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified. Battery Charging from USB-HV BUCK-USB VOUT 1V/DIV AC COUPLED VBUS 100mV/DIV AC COUPLED VSW 5V/DIV 0V HVOK 5V/DIV 0V VBUS = 5V HVIN = 12V USING LT3653 500μs/DIV 3576 G28 USB OTG from BAT-HV BUCK-BAT 2.30 VOUT 1V/DIV AC COUPLED VBUS 200mV/DIV AC COUPLED IBAT 1A/DIV 0A HVOK 5V/DIV 0V VBAT = 3.8V IBUS = 285mA HVIN = 12V USING LT3653 500μs/DIV 3576 G29 Oscillator Frequency vs Temperature 2.25 FREQUENCY (MHz) 2.20 2.15 VOUT = 5V VOUT = 4.2V VOUT = 3.6V VOUT = 3V VOUT = 2.7V –15 35 10 TEMPERATURE (°C) 60 85 3576 G30 2.10 2.05 –40 OVP Connect Waveform VBUS 5V/DIV VBUS 5V/DIV OVP Disconnect Waveform 6.280 Rising OVP Threshold vs Temperature 6.275 OVP THRESHOLD (V) 500μs/DIV 3576 G32 OVGATE 5V/DIV OVGATE 5V/DIV OVP INPUT VOLTAGE 5V TO 10V STEP 5V/DIV 500μs/DIV 3576 G31 6.270 6.265 OVP INPUT VOLTAGE 0V TO 5V STEP 5V/DIV 6.260 6.255 –40 –15 35 10 TEMPERATURE (°C) 60 85 3576 G33 OVGATE vs OVSENS 12 OVSENS CONNECTED TO INPUT THROUGH 10 6.2k RESISTOR 8 OVGATE (V) 6 4 2 0 0 2 4 6 INPUT VOLTAGE (V) 8 3576 G34 OVGATE Quiescent Current vs Temperature 37 VOVSENS = 5V RST3, CHRG PIN CURRENT (mA) 100 RST3, CHRG Pin Current vs Voltage (Pull-Down State) VBUS = 5V BAT = 3.8V QUIESCENT CURRENT (μA) 35 80 33 60 31 40 29 20 27 –40 –15 35 10 TEMPERATURE (°C) 60 85 3576 G35 0 0 1 3 4 2 RST3, CHRG PIN VOLTAGE (V) 5 3576 G36 3576f 10 LTC3576/LTC3576-1 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified. 3.3V LDO Output Voltage vs Load Current, VBUS = 0V 3.4 BAT = 3.9V, 4.2V BAT = 3.4V BAT = 3.5V BATTERY CURRENT (μA) BAT = 3.6V ILDO3V3 5mA/DIV 0mA 3.0 VLDO3V3 20mV/DIV AC COUPLED 3576 G38 3.3V LDO Step Response (5mA to 15mA) 35 30 Battery Drain Current vs Battery Voltage IVOUT = 0mA VBUS = 0V 25 20 15 10 5 0 2.7 OUTPUT VOLTAGE (V) 3.2 2.8 BAT = 3V BAT = 3.1V BAT = 3.2V BAT = 3.3V 2.6 5 15 0 20 10 LOAD CURRENT (mA) BAT = 3.8V 20μs/DIV VBUS = 5V (SUSPEND MODE) 25 3576 G37 3.0 3.3 3.6 3.9 4.2 3576 G39 BATTERY VOLTAGE (V) Switching Regulator Soft-Start Waveform 2.0 Switching Regulator Current Limit vs Temperature 1.0 REGULATOR 3 RDS(ON) for Switching Regulator Power Switches vs Temperature REGULATORS 1, 2 VOUT 500mV/DIV ON-RESISTANCE (Ω) 1.5 CURRENT LIMIT (A) 0.8 NMOS SWITCH 0.6 PMOS SWITCH 0.4 NMOS SWITCH PMOS SWITCH 60 85 3576 G41 1.0 REGULATORS 1, 2 REGULATOR 3 0.5 50μs/DIV 3576 G40 0.2 VIN1,2,3 = 3.8V 0 –40 –15 35 10 TEMPERATURE (°C) 0 –40 –15 35 10 TEMPERATURE (°C) 60 85 3576 G42 Switching Regulator Low Power Quiescent Currents vs Temperature 100 90 QUIESCENT CURRENTS (μA) 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 –40 –15 Burst Mode OPERATION LDO MODE 35 10 TEMPERATURE (°C) 60 85 3576 G43 Switching Regulators 1, 2 Pulse-Skip Mode Efficiency 100 90 VIN3 = 3.8V 100 VOUT1,2 = 2.5V VOUT1,2 = 1.2V EFFICIENCY (%) VOUT1,2 = 1.8V 90 80 70 60 50 40 30 20 10 1 10 100 LOAD CURRENT (mA) 1000 3576 G44 Switching Regulators 1, 2 Burst Mode Efficiency VIN3 = 3.8V VOUT1,2 = 2.5V VOUT1,2 = 1.2V VOUT1,2 = 1.8V PULSE-SKIP MODE 80 70 60 50 40 30 20 10 0 0.1 0 0.1 1 10 100 LOAD CURRENT (mA) 1000 3576 G45 3576f 11 LTC3576/LTC3576-1 TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise specified. Switching Regulator Constant Frequency Quiescent Currents 8 7 QUIESCENT CURRENT (mA) 6 5 4 3 2 1 0 –40 –15 35 TEMPERATURE (°C) 10 60 85 3576 G46 Switching Regulator 3 Pulse-Skip Mode Efficiency 100 90 80 EFFICIENCY (%) EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.1 1 10 100 LOAD CURRENT (mA) 1000 3576 G47 Switching Regulator 3 Burst Mode Efficiency 100 90 80 VIN3 = 3.8V VOUT3 = 2.5V VIN3 = 3.8V VOUT3 = 2.5V SWITCHING REGULATOR 3 VOUT3 = 1.8V VOUT3 = 1.2V 70 60 50 40 30 20 10 0 0.1 1 VOUT3 = 1.2V VOUT3 = 1.8V SWITCHING REGULATORS 1, 2 10 100 LOAD CURRENT (mA) 1000 3576 G48 Switching Regulators 1, 2 Feedback Voltage vs Load Current 0.820 0.815 FEEDBACK VOLTAGE (V) 0.810 PULSE-SKIP MODE 0.805 0.800 0.795 0.790 0.1 IOUT2 200mA/DIV 0mA Burst Mode OPERATION VOUT2 50mV/DIV AC COUPLED Switching Regulators 1, 2 Transient Response VOUT3 50mV/DIV AC COUPLED Switching Regulator Mode Transition, Pulse Skip-LDOPulse Skip VSW3 1V/DIV 0V VIN2 = 3.8V VOUT2 = 3.4V 50μs/DIV 3576 G50 VIN3 = 3.8V VOUT3 = 1.8V IOUT3 = 50mA 50μs/DIV 3576 G51 1 10 100 LOAD CURRENT (mA) 1000 3576 G49 Switching Regulator 3 Feedback Voltage vs Load Current 0.810 VOUT3 50mV/DIV AC COUPLED Switching Regulator 3 Transient Response Switching Regulator Mode Transition, Pulse Skip–Burst Mode Operation–Pulse Skip FEEDBACK VOLTAGE (V) 0.805 Burst Mode OPERATION VOUT3 50mV/DIV AC COUPLED 0.800 PULSE SKIP MODE 0.795 IOUT3 500mA/DIV 0mA VIN3 = 3.8V VOUT3 = 1.8V 50μs/DIV 3576 G53 VSW3 1V/DIV 0V VIN3 = 3.8V VOUT3 = 1.8V IOUT3 = 100mA 50μs/DIV 3576 G54 0.790 0.1 1 10 100 LOAD CURRENT (mA) 1000 3576 G52 3576f 12 LTC3576/LTC3576-1 PIN FUNCTIONS CLPROG (Pin 1): USB Current Limit Program and Monitor Pin. A 1% resistor from CLPROG to ground determines the upper limit of the current drawn or sourced from the VBUS pins. A precise fraction, hCLPROG, of the VBUS current is sent to the CLPROG pin when the PMOS switch of the PowerPath switching regulator is on. The switching regulator delivers power until the CLPROG pin reaches 1.18V in step-down mode and 1.15V in step-up mode. When the switching regulator is in step-down mode, CLPROG is used to regulate the average input current. Several VBUS current limit settings are available via user input which will typically correspond to the 500mA and 100mA USB specifications. When the switching regulator is in step-up mode (USB on-the-go), CLPROG is used to limit the average output current to 680mA. A multilayer ceramic averaging capacitor or R-C network is required at CLPROG for filtering. LDO3V3 (Pin 2): 3.3V LDO Output Pin. This pin provides a regulated always-on 3.3V supply voltage. LDO3V3 gets its power from VOUT. It may be used for light loads such as a watchdog microprocessor or real time clock. A 1μF capacitor is required from LDO3V3 to ground. If the LDO3V3 output is not used it should be disabled by connecting it to VOUT. NTCBIAS (Pin 3): NTC Thermistor Bias Output. If NTC operation is desired, connect a bias resistor between NTCBIAS and NTC, and an NTC thermistor between NTC and GND. To disable NTC operation, connect NTC to GND and leave NTCBIAS open. NTC (Pin 4): Input to the Thermistor Monitoring Circuits. The NTC pin connects to a negative temperature coefficient thermistor, which is typically co-packaged with the battery, to determine if the battery is too hot or too cold to charge. If the battery’s temperature is out of range, charging is paused until it re-enters the valid range. A low drift bias resistor is required from NTCBIAS to NTC and a thermistor is required from NTC to ground. To disable NTC operation, connect NTC to GND and leave NTCBIAS open. OVGATE (Pin 5): Overvoltage Protection Gate Output. Connect OVGATE to the gate pin of an external N-channel MOS pass transistor. The source of the transistor should be connected to VBUS and the drain should be connected to the product’s DC input connector. In the absence of an overvoltage condition, this pin is connected to an internal charge pump capable of creating sufficient overdrive to fully enhance the pass transistor. If an overvoltage condition is detected, OVGATE is brought rapidly to GND to prevent damage to the LTC3576/LTC3576-1. OVGATE works in conjunction with OVSENS to provide this protection. OVSENS (Pin 6): Overvoltage Protection Sense Input. OVSENS should be connected through a 6.2k resistor to the input power connector and the drain of an external N-channel MOS pass transistor. When the voltage on this pin exceeds VOVCUTOFF, the OVGATE pin will be pulled to GND to disable the pass transistor and protect the LTC3576/LTC3576-1. The OVSENS pin shunts current during an overvoltage transient in order to keep the pin voltage at 6V. FB1 (Pin 7): Feedback Input for Switching Regulator 1. When regulator 1’s control loop is complete, this pin servos to 1 of 16 possible set points based on the commanded value from the I2C serial port. See Table 4. VIN1 (Pin 8): Power Input for Switching Regulator 1. This pin will generally be connected to VOUT. A 1μF MLCC capacitor is recommended on this pin. SW1 (Pin 9): Power Transmission Pin for Switching Regulator 1. EN1 (Pin 10): Logic Input. This logic input pin independently enables switching regulator 1. Active high. This pin is logically ORed with its corresponding bit in the I2C serial port. See Table 3. Has a 2μA internal pull-down current source. ENOTG (Pin 11): Logic Input. This logic input pin independently enables the bidirectional switching regulator to step up the voltage on VOUT and provide a 5V output on VBUS for USB on-the-go applications. Active high. This pin is logically ORed with its corresponding bit in the I2C serial port. See Table 3. Has a 2μA internal pull-down current source. 3576f 13 LTC3576/LTC3576-1 PIN FUNCTIONS DVCC (Pin 12): Logic Supply for the I2C Serial Port. If the serial port is not needed, it can be disabled by grounding DVCC. When DVCC is grounded, the I2C bits are set to their default values. See Table 3. SCL (Pin 13): Clock Input Pin for the I2C Serial Port. The I2C logic levels are scaled with respect to DVCC. If DVCC is grounded, the SCL pin is equivalent to the C2, C4 and C6 bits in the I2C serial port. SCL in conjunction with SDA determine the operating modes of switching regulators 1, 2 and 3 when DVCC is grounded. See Tables 3 and 5. Has a 2μA internal pull-down current source. SDA (Pin 14): Data Input Pin for the I2C Serial Port. The I2C logic levels are scaled with respect to DVCC. If DVCC is grounded, the SDA pin is equivalent to the C3, C5 and C7 bits in the I2C serial port. SDA in conjunction with SCL determine the operating modes of switching regulators 1, 2 and 3 when DVCC is grounded. See Tables 3 and 5. Has a 2μA internal pull-down current source. NC (Pin 15): Unconnected Pin. This pin is not connected internally to the part. It is permissible to tie this pin to VIN3 in order to make the VIN3 PCB trace wider. VIN3 (Pin 16): Power Input for Switching Regulator 3. This pin will generally be connected to VOUT. A 1μF MLCC capacitor is recommended on this pin. SW3 (Pin 17): Power Transmission Pin for Switching Regulator 3. NC (Pin 18): Unconnected Pin. This pin is not connected internally to the part. It is permissible to tie this pin to SW3 in order to make the SW3 PCB trace wider. EN3 (Pin 19): Logic Input. This logic input pin independently enables switching regulator 3. Active high. This pin is logically ORed with its corresponding bit in the I2C serial port. See Table 3. Has a 2μA internal pull-down current source. FB3 (Pin 20): Feedback Input for Switching Regulator 3. When regulator 3’s control loop is complete, this pin servos to 1 of 16 possible set points based on the commanded value from the I2C serial port. See Table 4. RST3 (Pin 21): Logic Output. This in an open-drain output which indicates that switching regulator 3 has settled to its final value. It can be used as a power-on reset for the primary microprocessor or to enable the other switching regulators for supply sequencing. EN2 (Pin 22): Logic Input. This logic input pin independently enables switching regulator 2. Active high. This pin is logically ORed with its corresponding bit in the I2C serial port. See Table 3. Has a 2μA internal pull-down current source. SW2 (Pin 23): Power Transmission Pin for Switching Regulator 2. VIN2 (Pin 24): Power Input for Switching Regulator 2. This pin will generally be connected to VOUT. A 1μF MLCC capacitor is recommended on this pin. FB2 (Pin 25): Feedback Input for Switching Regulator 2. When regulator 2’s control loop is complete, this pin servos to 1 of 16 possible set points based on the commanded value from the I2C serial port. See Table 4. VC (Pin 26): Bat-Track External Switching Regulator Control Output. This pin drives the VC pin of an external Linear Technology step-down switching regulator. An external Pchannel MOSFET is sometimes required to provide power to VOUT with its gate tied to the ACPR pin (see Applications Information). In concert with WALL and ACPR, it will regulate VOUT to maximize battery charger efficiency WALL (Pin 27): External Power Source Sense Input. WALL should be connected to the output of the external high voltage switching regulator and to the drain of an external P-channel MOSFET if used. It is used to determine when power is applied to the external regulator. When power is detected, ACPR is driven low and the USB input is automatically disabled. Pulling this pin above 4.3V enables the VC pin. 3576f 14 LTC3576/LTC3576-1 PIN FUNCTIONS ACPR (Pin 28): External Power Source Present Output (Active Low). ACPR indicates that the output of the external high voltage step-down switching regulator is suitable for use by the LTC3576/LTC3576-1. It should be connected to the gate of an external P-channel MOSFET whose source is connected to VOUT and whose drain is connected to WALL. ACPR has a high level of VOUT and a low level of GND. The USB bidirectional switcher is disabled when ACPR is low. PROG (Pin 29): Charge Current Program and Charge Current Monitor Pin. Connecting a 1% resistor from PROG to ground programs the charge current. If sufficient input power is available in constant-current mode, this pin servos to 1V. The voltage on this pin always represents the actual charge current by using the following formula: IBAT = VPROG • 1030 RPROG BAT (Pin 32): Single Cell Li-Ion Battery Pin. Depending on available VBUS power, a Li-Ion battery on BAT will either deliver power to VOUT through the ideal diode or be charged from VOUT via the battery charger. VOUT (Pin 33): Output Voltage of the Bidirectional PowerPath Switching Regulator in step-down mode and Input Voltage of the Battery Charger. The majority of the portable product should be powered from VOUT. The LTC3576/LTC3576-1 will partition the available power between the external load on VOUT and the internal battery charger. Priority is given to the external load and any extra power is used to charge the battery. An ideal diode from BAT to VOUT ensures that VOUT is powered even if the load exceeds the allotted power from VBUS or if the VBUS power source is removed. In on-the-go mode, this pin delivers power to VBUS via the SW pin. VOUT should be bypassed with a low impedance ceramic capacitor. VBUS (Pins 34, 35): Power Pins. These pins deliver power to VOUT via the SW pin by drawing controlled current from a DC source such as a USB port or DC output wall adapter. In on-the-go mode these pins provide power to external loads. Tie the two VBUS pins together at the part and bypass with a low impedance multilayer ceramic capacitor. SW (Pin 36): The SW pin transfers power between VBUS and VOUT via the bidirectional switching regulator. See the Applications Information section for a discussion of inductance value and current rating. ILIM0, ILIM1 (Pins 37, 38): ILIM0 and ILIM1 control the current limit of the PowerPath switching regulator. See Table 1. Both the ILIM0 and ILIM1 pins are logically ORed with their corresponding bits in the I2C serial port. See Tables 3 and 6. Each has a 2μA internal pull-down current source. Exposed Pad (Pin 39): Ground. The Exposed Pad should be connected to a continuous ground plane on the second layer of the printed circuit board by several vias directly under the LTC3576/LTC3576-1. CHRG (Pin 30): Open-Drain Charge Status Output. The CHRG pin indicates the status of the battery charger. Four possible charger states are represented by CHRG: charging, not charging, unresponsive battery and battery temperature out of range. In addition, CHRG is used to indicate whether there is a short-circuit condition on VBUS when the bidirectional switching regulator is in step-up mode (on-the-go). CHRG is modulated at 35kHz and switches between a low and a high duty cycle for easy recognition by either humans or microprocessors. See Table 1. CHRG requires a pull-up resistor and/or LED to provide indication. IDGATE (Pin 31): Ideal Diode Amplifier Output. This pin controls the gate of an optional external P-channel MOSFET used as an ideal diode between VOUT and BAT. The external ideal diode operates in parallel with the internal ideal diode. The source of the P-channel MOSFET should be connected to VOUT and the drain should be connected to BAT. If the external ideal diode MOSFET is not used, IDGATE should be left floating. 3576f 15 LTC3576/LTC3576-1 BLOCK DIAGRAM VC 26 OVSENS 6 OVP OVGATE 5 VBUS 35 VBUS 34 2.25MHz BIDIRECTIONAL PowerPath SWITCHING REGULATOR 3.3V LDO SUSPEND LDO 500μA/2.5mA 33 VOUT VC CONTROL WALL DETECT 27 WALL 28 ACPR 36 SW 2 LDO3V3 + CLPROG 1 NTCBIAS 3 NTC 4 CHRG 30 CHARGE STATUS BATTERY TEMPERATURE MONITOR 5.1V CC/CV CHARGER 0.3V 3.6V 29 PROG IDEAL – + – 15mV 31 IDGATE 1.18V OR 1.15V D/A 4 24 VIN2 ENABLE D/A 400mA 2.25MHz BUCK REGULATOR 23 SW2 ILIM DECODE LOGIC 4 D/A ILIM0 37 ILIM1 38 ENOTG 11 EN1 10 EN2 22 EN3 19 DVCC 12 SDA 14 SCL 13 I2C PORT 4 16 –+ ENABLE 400mA 2.25MHz BUCK REGULATOR ENABLE 1A 2.25MHz BUCK REGULATOR 39 GND + + – + – + – 32 BAT 8 VIN1 9 SW1 7 FB1 25 FB2 16 VIN3 17 SW3 20 FB3 21 RST3 3576 BD 3576f LTC3576/LTC3576-1 TIMING DIAGRAM SDA tSU,DAT tLOW SCL tHD,STA START CONDITION tr tHIGH tf REPEATED START CONDITION tSP STOP CONDITION START CONDITION tHD,DAT tSU,STA tHD,STA tBUF tSU,STO 3208 F05 I2C WRITE PROTOCOL WRITE ADDRESS 0 START SDA 0 0 0 1 0 0 1 0 ACK ACK ACK 0 0 1 0 0 1 R/W 0 A7 A6 A5 SUB-ADDRESS A4 A3 A2 A1 A0 B7 B6 INPUT DATA BYTE B5 B4 B3 B2 B1 B0 STOP SCL 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 3576 I2C 3576f 17 LTC3576/LTC3576-1 OPERATION Introduction The LTC3576/LTC3576-1 are highly integrated power management ICs designed to make optimal use of the power available from a variety of sources, while minimizing power dissipation and easing thermal budgeting constraints. They include a high efficiency bidirectional PowerPath switching regulator, a controller for an external high voltage step-down switching regulator, a battery charger, an ideal diode, an always-on LDO, an overvoltage protection circuit and three general purpose step-down switching regulators. The entire chip is controlled by either direct digital control or by an I2C serial port or both. The innovative PowerPath architecture ensures that the application is powered immediately after external voltage is applied, even with a completely dead battery, by prioritizing power to the application. When acting as a step-down converter, the LTC3576/ LTC3576-1’s bidirectional switching regulator takes power from USB, wall adapters, or other 5V sources and provides power to the application and efficiently charges the battery using Bat-Track. Because power is conserved the LTC3576/LTC3576-1 allow the load current on VOUT to exceed the current drawn by the USB port making maximum use of the allowable USB power for battery charging. For USB compatibility the switching regulator includes a precision average input current limit. The PowerPath switching regulator and battery charger communicate to ensure that the average input current never exceeds the USB specifications. Additionally, the bidirectional switching regulator can also operate as a 5V synchronous step-up converter taking power from VOUT and delivering up to 500mA to VBUS without the need for any additional external components. This enables systems with USB dual-role transceivers to function as USB on-the-go dual-role devices. True output disconnect and average output current limit features are included for short-circuit protection. For automotive, firewire, and other high voltage applications, the LTC3576/LTC3576-1 provide Bat-Track control of an external LTC step-down switching regulator to maximize battery charger efficiency and minimize heat production. When power is available from both the USB and an auxiliary input, the auxiliary input is given priority. The LTC3576/LTC3576-1 contain both an internal 180mΩ ideal diode as well as an ideal diode controller for use with an optional external P-channel MOSFET. The ideal diode(s) from BAT to VOUT guarantee that ample power is always available to VOUT even if there is insufficient or absent power at VBUS or WALL. An “always-on” LDO provides a regulated 3.3V from available power at VOUT. Drawing very little quiescent current, this LDO will be on at all times and can be used to supply 20mA. The LTC3576/LTC3576-1 feature an overvoltage protection circuit which is designed to work with an external N-channel MOSFET to prevent damage to their inputs caused by accidental application of high voltage. To prevent battery drain when a device is connected to a suspended USB port, an LDO from VBUS to VOUT provides either low power or high power USB suspend current to the application. The three general purpose switching regulators can be independently enabled either by direct digital control or by operating the I2C serial port. Under I2C control, all three switching regulators have adjustable set points so that voltages can be reduced when high processor performance is not needed. Along with constant frequency PWM mode, all three switching regulators have automatic Burst Mode operation and LDO modes for significantly reduced quiescent current under light load conditions. 3576f 18 LTC3576/LTC3576-1 OPERATION Bidirectional PowerPath Switching Regulator— Step-Down Mode The power delivered from VBUS to VOUT is controlled by a 2.25MHz constant frequency bidirectional switching regulator operating in step-down mode. VOUT drives the combination of the external load (step-down switching regulators 1, 2 and 3) and the battery charger. To meet the maximum USB load specification, the switching regulator contains a measurement and control system that ensures that the average input current remains below the level programmed at CLPROG. If the combined load does not cause the switching regulator to reach the programmed input current limit, VOUT will track approximately 0.3V above the battery voltage. By keeping the voltage across the battery charger at this low level, power lost to the battery charger is minimized. Figure 1 shows the power flow in step-down mode. If the combined external load plus battery charge current is large enough to cause the switching regulator to reach the programmed input current limit, the battery charger will reduce its charge current by precisely the amount necessary to enable the external load to be satisfied. Even if the battery charge current is programmed to exceed the allowable USB current, the USB specification for average input current will not be violated; the battery charger will reduce its current as needed. Furthermore, if the load current at VOUT exceeds the programmed power from VBUS, load current will be drawn from the battery via the ideal diode(s) even when the battery charger is enabled. The current out of CLPROG is a precise fraction of the VBUS current. When a programming resistor and an averaging capacitor are connected from CLPROG to GND, the voltage on CLPROG represents the average input current of the switching regulator. As the input current approaches the programmed limit, CLPROG reaches 1.18V and power delivered by the switching regulator is held constant. TO AUTOMOTIVE, FIREWIRE, ETC. VIN VC HIGH VOLTAGE STEP-DOWN SWITCHING REGULATOR SW FB 26 6 5 OVSENS OVGATE OVERVOLTAGE PROTECTION VC 27 WALL 6V 2 VOUT 3.6V BAT + 0.3V 4.3V Bat-Track HV CONTROL +– TO USB OR WALL ADAPTER 35 34 VBUS VBUS PWM AND GATE DRIVE VBUS VOLTAGE CONTROLLER IDEAL DIODE CONSTANT CURRENT CONSTANT VOLTAGE BATTERY CHARGER OmV 5V 15mV 0.3V 3.6V 1 1.18V AVERAGE VBUS INPUT CURRENT LIMIT CONTROLLER VOUT VOLTAGE CONTROLLER 3576 F01 Figure 1. PowerPath Block Diagram—Power Available from USB/Wall Adapter 3576f + + – + – CLPROG +– + – + – ISWITCH/N + – + – + + – ACPR 28 + – SW 36 3.5V TO (BAT + 0.3V) TO SYSTEM LOAD VOUT 33 IDGATE 31 OPTIONAL EXTERNAL IDEAL DIODE PMOS BAT 32 + USB INPUT BATTERY POWER HV INPUT SINGLE CELL Li-Ion 19 LTC3576/LTC3576-1 OPERATION The input current limit is programmed by the ILIM0 and ILIM1 pins or by the I2C serial port. The input current limit has five possible settings ranging from the USB suspend limit of 500μA up to 1A for wall adapter applications. Two of these settings are specifically intended for use in the 100mA and 500mA USB applications. Refer to Table 1 for current limit settings using the ILIM0 and ILIM1 pins and Table 6 for current limit settings using the I2C port. Table 1. USB Current Limit Settings Using ILIM0 and ILIM1 ILIM1 0 0 1 1 ILIM0 0 1 0 1 USB SETTING 1× Mode (USB 100mA Limit) 10× Mode (Wall 1A Limit) Low Power Suspend (USB 500μA Limit) 5× Mode (USB 500mA Limit) 4.5 4.2 3.9 VOUT (V) NO LOAD 3.6 300mV 3.3 3.0 2.7 2.4 2.4 2.7 3.0 3.6 3.3 BAT (V) 3.9 4.2 3576 F02 Figure 2. VOUT vs BAT When the switching regulator is activated, the average input current will be limited by the CLPROG programming resistor according to the following expression: IVBUS = IVBUSQ + VCLPROG • hCLPROG + 1 RCLPROG ( ) where IVBUSQ is the quiescent current of the LTC3576/ LTC3576-1, VCLPROG is the CLPROG servo voltage in current limit, RCLPROG is the value of the programming resistor and hCLPROG is the ratio of the measured current at VBUS to the sample current delivered to CLPROG. Refer to the Electrical Characteristics table for values of hCLPROG, VCLPROG and IVBUSQ. Given worst-case circuit tolerances, the USB specification for the average input current in 100mA or 500mA mode will not be violated, provided that RCLPROG is 3.01k or greater. While not in current limit, the switching regulator’s BatTrack feature will set VOUT to approximately 300mV above the voltage at BAT. However, if the voltage at BAT is below 3.3V, and the load requirement does not cause the switching regulator to exceed its current limit, VOUT will regulate at a fixed 3.6V as shown in Figure 2. This “instant-on” operation will allow a portable product to run immediately when power is applied without waiting for the battery to charge. If the load does exceed the current limit at VBUS, VOUT will range between the no-load voltage and slightly below the battery voltage, indicated by the shaded region of Figure 2. For very low-battery voltages, the battery charger acts like a load and, due to limited input power, its current will tend to pull VOUT below the 3.6V “Instant On” voltage. To prevent VOUT from falling below this level, an undervoltage circuit automatically detects that VOUT is falling and reduces the battery charge current as needed. This reduction ensures that load current and voltage are always prioritized while allowing as much battery charge current as possible. See Over Programming the Battery Charger in the Applications Information section. The voltage regulation loop is compensated by the capacitance on VOUT. A 10μF MLCC capacitor is required for loop stability. Additional capacitance beyond this value will improve transient response. An internal undervoltage lockout circuit monitors VBUS and keeps the switching regulator off until VBUS rises above 4.30V and is about 200mV above the battery voltage. Hysteresis on the UVLO turns off the regulator if VBUS falls below 4V or to within 50mV of the battery voltage. When this happens, system power at VOUT will be drawn from the battery via the ideal diode(s). Bidirectional PowerPath Switching Regulator— Step-Up Mode For USB on-the-go applications, the bidirectional PowerPath switching regulator acts as a step-up converter to deliver power from VOUT to VBUS. The power from VOUT can come from the battery or the output of the external 3576f 20 LTC3576/LTC3576-1 OPERATION TO AUTOMOTIVE, FIREWIRE, ETC. VIN VC HIGH VOLTAGE SW STEP-DOWN SWITCHING REGULATOR FB 26 6 5 OVSENS OVGATE OVERVOLTAGE PROTECTION VC 27 WALL 6V 2 VOUT 3.6V BAT + 0.3V 4.3V +– Bat-Track HV CONTROL TO USB CABLE 35 34 VBUS VBUS PWM AND GATE DRIVE VBUS VOLTAGE CONTROLLER IDEAL DIODE CONSTANT CURRENT CONSTANT VOLTAGE BATTERY CHARGER OmV 5V 15mV 0.3V 3.6V 1 1.15V AVERAGE VBUS OUTPUT CURRENT LIMIT CONTROLLER VOUT VOLTAGE CONTROLLER 3576 F03 Figure 3. PowerPath Block Diagram—USB On-the-Go high voltage switching regulator. As a step-up converter, the bidirectional switching regulator produces 5V on VBUS and is capable of delivering at least 500mA. USB on-the-go can be enabled by either the external control pin, ENOTG, or via I2C. Figure 3 shows the power flow in step-up mode. An undervoltage lockout circuit monitors VOUT and prevents step-up conversion until VOUT rises above 2.8V. To prevent backdriving of VBUS when input power is available, the VBUS undervoltage lockout circuit prevents step-up conversion if VBUS is greater than 4.3V at the time step-up mode is enabled. The switching regulator is also designed to allow true output disconnect by eliminating body diode conduction of the internal PMOS switch. This allows VBUS to go to zero volts during a short-circuit condition or while shut down, drawing zero current from VOUT . The voltage regulation loop is compensated by the capacitance on VBUS. A 4.7μF MLCC is required for loop stability. Additional capacitance beyond this value will improve + + – + – CLPROG +– transient response. The VBUS voltage has approximately 3% load regulation up to an output current of 500mA. At light loads, the switching regulator goes into Burst Mode operation. The regulator will deliver power to VBUS until it reaches 5.1V after which the NMOS and PMOS switches shut off. The regulator delivers power again to VBUS once it falls below 5.1V. The switching regulator features both peak inductor and average output current limit. The peak current mode architecture limits peak inductor current on a cycle-bycycle basis. The peak current limit is equal to VBUS/2Ω to a maximum of 1.8A so that in the event of a sudden short circuit, the current limit will fold back to a lower value. In step-up mode, the voltage on CLPROG represents the average output current of the switching regulator when a programming resistor and an averaging capacitor are connected from CLPROG to GND. With a 3.01k resistor on CLPROG, the bidirectional switching regulator has an output current limit of 680mA. As the output current approaches this limit CLPROG servos to 1.15V and VBUS falls 3576f + – + – ISWITCH/N + – + – + + – ACPR 28 + – SW 36 3.5V TO (BAT + 0.3V) TO SYSTEM LOAD VOUT 33 IDGATE 31 OPTIONAL EXTERNAL IDEAL DIODE PMOS BAT 32 + BATTERY POWER HV INPUT SINGLE CELL Li-Ion 21 LTC3576/LTC3576-1 OPERATION rapidly to VOUT . When VBUS is close to VOUT there may not be sufficient negative slope on the inductor current when the PMOS switch is on to balance the rise in the inductor current when the NMOS switch is on. This will cause the inductor current to run away and the voltage on CLPROG to rise. When CLPROG reaches 1.2V the switching of the synchronous PMOS is terminated and VOUT is applied statically to its gate. This ensures that the inductor current will have sufficient negative slope during the time current is flowing to the output. The PMOS will resume switching when CLPROG drops down to 1.15V. The LTC3576/LTC3576-1 maintain voltage regulation even if VOUT is above VBUS. This is achieved by disabling the PMOS switch. The PMOS switch is enabled when VBUS rises above VOUT + 180mV and is disabled when it falls below VOUT + 70mV to prevent the inductor current from running away when not in current limit. Since the PMOS no longer acts as a low impedance switch in this mode, there will be more power dissipation within the IC. This will cause a sharp drop in efficiency. If VBUS is less than 4V and the PMOS switch is disabled for more than 7.2ms a short-circuit fault will be declared and the part will shut off. The CHRG pin will blink at 35kHz with a duty cycle that varies between 12% and 88% at a 4Hz rate. See Table 2. To re-enable step-up mode, the ENOTG pin or, with ENOTG grounded, the B0 bit in the I2C port must be cycled low and then high. Bat-Track Auxiliary High Voltage Switching Regulator Control The WALL, ACPR and VC pins can be used in conjunction with an external high voltage step-down switching regulator such as the LT®3480 or the LT3653 to minimize heat production when operating from higher voltage sources, as shown in Figures 1 and 3. Bat-Track control circuitry regulates the external switching regulator’s output voltage to the larger of (BAT + 300mV) or 3.6V. This maximizes battery charger efficiency while still allowing instant-on operation when the battery is deeply discharged. The feedback network of the high voltage regulator should be set to generate an output voltage between 4.5V and 5.5V. When high voltage is applied to the external regulator, WALL will rise toward this programmed output voltage. When WALL exceeds approximately 4.3V, ACPR is brought low and the Bat-Track control of the LTC3576/ LTC3576-1 overdrives the local VC control of the external high voltage step-down switching regulator. Therefore, once the Bat-Track control is enabled, the output voltage is set independent of the switching regulator feedback network. Bat-Track control provides a significant efficiency advantage over the simple use of a 5V switching regulator output to drive the battery charger. With a 5V output driving VOUT, battery charger efficiency is approximately: ηTOTAL = ηBUCK • VBAT 5V where ηBUCK is the efficiency of the high voltage switching regulator and 5V is the output voltage of the switching regulator. With a typical switching regulator efficiency of 87% and a typical battery voltage of 3.8V, the total battery charger efficiency is approximately 66%. Assuming a 1A charge current, 1.7W of power is dissipated just to charge the battery! With Bat-Track, battery charger efficiency is approximately: ηTOTAL = ηBUCK • VBAT VBAT + 0.3V With the same assumptions as above, the total battery charger efficiency is approximately 81%. This example works out to less than 1W of power dissipation, or almost 60% less heat. See the Typical Applications section for complete circuits using the LT3480 and the LT3653 with Bat-Track control. Ideal Diode(s) from BAT to VOUT The LTC3576/LTC3576-1 each have an internal ideal diode as well as a controller for an optional external ideal diode. Both the internal and the external ideal diodes are always on and will respond quickly whenever VOUT drops below BAT. If the load current increases beyond the power allowed from the switching regulator, additional power will be pulled from the battery via the ideal diode(s). Further3576f 22 LTC3576/LTC3576-1 OPERATION 2200 2000 1800 1600 CURRENT (mA) 1400 1200 1000 800 600 400 200 0 0 60 120 180 240 300 360 420 480 FORWARD VOLTAGE (mV) (BAT – VOUT) 3576 F04 VISHAY Si2333 OPTIONAL EXTERNAL IDEAL DIODE LTC3576/ LTC3576-1 IDEAL DIODE ON SEMICONDUCTOR MBRM120LT3 this LDO only becomes active when the switching converter is disabled (suspended). The suspend LDO sends a scaled copy of the VBUS current to the CLPROG pin, which will servo to approximately 100mV in this mode. To remain compliant with the USB specification, the input to the LDO is current limited so that it will not exceed the low power or high power suspend specification. If the load on VOUT exceeds the suspend current limit, the additional current will come from the battery via the ideal diode(s). 3.3V Always-On LDO Supply The LTC3576/LTC3576-1 include a low quiescent current low dropout regulator that is always powered. This LDO can be used to provide power to a system pushbutton controller, standby microcontroller or real time clock. Designed to deliver up to 20mA, the always-on LDO requires at least a 1μF low impedance ceramic bypass capacitor for compensation. The LDO is powered from VOUT, and therefore will enter dropout at loads less than 20mA as VOUT falls near 3.3V. If the LDO3V3 output is not used, it should be disabled by connecting it to VOUT. Battery Charger The LTC3576/LTC3576-1 include a constant-current/constant-voltage battery charger with automatic recharge, automatic termination by safety timer, low voltage trickle charging, bad cell detection and thermistor sensor input for out-of-temperature charge pausing. Battery Preconditioning When a battery charge cycle begins, the battery charger first determines if the battery is deeply discharged. If the battery voltage is below VTRKL, typically 2.85V, an automatic trickle charge feature sets the battery charge current to 10% of the programmed value. If the low voltage persists for more than 1/2 hour, the battery charger automatically terminates and indicates via the CHRG pin that the battery was unresponsive. Once the battery voltage is above 2.85V, the charger begins charging in full power constant-current mode. The current delivered to the battery will try to reach 1030/RPROG. Depending on available input power and external load conditions, the battery charger may or may not be able 3576f Figure 4. Ideal Diode V-I Characteristics more, if power to VBUS (USB or wall adapter) is removed, then all of the application power will be provided by the battery via the ideal diodes. The ideal diode(s) will be fast enough to keep VOUT from drooping with only the storage capacitance required for the switching regulator. The internal ideal diode consists of a precision amplifier that activates a large on-chip P-channel MOSFET whenever the voltage at VOUT is approximately 15mV (VFWD) below the voltage at BAT. Within the amplifier’s linear range, the small-signal resistance of the ideal diode will be quite low, keeping the forward drop near 15mV. At higher current levels, the MOSFET will be in full conduction. To supplement the internal ideal diode, an external P-channel MOSFET may be added from BAT to VOUT. The IDGATE pin of the LTC3576/LTC3576-1 drives the gate of the external P-channel MOSFET for automatic ideal diode control. The source of the external P-channel MOSFET should be connected to VOUT and the drain should be connected to BAT. Capable of driving a 1nF load, the IDGATE pin can control an external P-channel MOSFET transistor having an on-resistance of 30mΩ or lower. Suspend LDO If the LTC3576/LTC3576-1 are configured for USB suspend mode, the bidirectional switching regulator is disabled and the suspend LDO provides power to the VOUT pin (presuming there is power available to VBUS). This LDO will prevent the battery from running down when the portable product has access to a suspended USB port. Regulating at 4.6V, 23 LTC3576/LTC3576-1 OPERATION to charge at the full programmed rate. The external load will always be prioritized over the battery charge current. Likewise, the USB current limit programming will always be observed and only additional power will be available to charge the battery. When system loads are light, battery charge current will be maximized. Charge Termination The battery charger has a built-in safety timer. When the voltage on the battery reaches the pre-programmed float voltage, the battery charger will regulate the battery voltage and the charge current will decrease naturally. Once the battery charger detects that the battery has reached the float voltage, the four hour safety timer is started. After the safety timer expires, charging of the battery will discontinue and no more current will be delivered. Automatic Recharge After the battery charger terminates, it will remain off drawing only microamperes of current from the battery. If the portable product remains in this state long enough, the battery will eventually self discharge. To ensure that the battery is always topped off, a charge cycle will automatically begin when the battery voltage falls below the recharge threshold which is typically 100mV less than the charger’s float voltage. In the event that the safety timer is running when the battery voltage falls below the recharge threshold, it will reset back to zero. To prevent brief excursions below the recharge threshold from resetting the safety timer, the battery voltage must be below the recharge threshold for more than 1ms. The charge cycle and safety timer will also restart if the VBUS UVLO cycles low and then high (e.g., VBUS is removed and then replaced), or if the battery charger is cycled on and off by the I2C port. Charge Current The charge current is programmed using a single resistor from PROG to ground. 1/1030th of the battery charge current is sent to PROG which will attempt to servo to 1.000V. Thus, the battery charge current will try to reach 1030 times the current in the PROG pin. The program resistor and the charge current are calculated using the following equation: ICHG = VPROG • 1030 RPROG In either the constant-current or constant-voltage charging modes, the voltage at the PROG pin will be proportional to the actual charge current delivered to the battery. Therefore, the actual charge current can be determined at any time by monitoring the PROG pin voltage and using the following equation: IBAT = VPROG •1030 RPROG In many cases, the actual battery charge current, IBAT, will be lower than ICHG due to limited input power available and prioritization with the system load drawn from VOUT. The Battery Charger Flow Chart illustrates the battery charger’s algorithm. Charge Status Indication The CHRG pin indicates the status of the battery charger. Four possible states are represented by CHRG which include charging, not charging, unresponsive battery and battery temperature out of range. The signal at the CHRG pin can be easily recognized as one of the above four states by either a human or a microprocessor. An open-drain output, the CHRG pin can drive an indicator LED through a current limiting resistor for human interfacing or simply a pull-up resistor for microprocessor interfacing. To make the CHRG pin easily recognized by both humans and microprocessors, the pin is either low for charging, high for not charging, or it is switched at high frequency (35kHz) to indicate the two possible faults, unresponsive battery and battery temperature out of range. When charging begins, CHRG is pulled low and remains low for the duration of a normal charge cycle. When charging is complete, i.e., the BAT pin reaches the float voltage and the charge current has dropped to one-tenth of the programmed value, the CHRG pin is released (Hi-Z). If a fault occurs, the pin is switched at 35kHz. While 3576f 24 LTC3576/LTC3576-1 OPERATION Battery Charger Flow Chart POWER ON/ ENABLE CHARGER CLEAR EVENT TIMER ASSERT CHRG LOW NTC OUT OF RANGE YES INHIBIT CHARGING NO PAUSE EVENT TIMER BAT < 2.85V BATTERY STATE BAT > VFLOAT – 2.85V < BAT < VFLOAT – CHARGE AT 100V/RPROG (C/10 RATE) CHARGE AT 1030V/RPROG RATE CHARGE WITH FIXED VOLTAGE (VFLOAT) CHRG CURRENTLY HIGH-Z YES NO RUN EVENT TIMER PAUSE EVENT TIMER RUN EVENT TIMER INDICATE NTC FAULT AT CHRG NO TIMER > 30 MINUTES TIMER > 4 HOURS NO YES YES NO INHIBIT CHARGING STOP CHARGING IBAT < C/10 YES INDICATE BATTERY FAULT AT CHRG BAT RISING THROUGH VRECHRG YES CHRG HIGH-Z CHRG HIGH-Z NO NO BAT > 2.85V BAT FALLING THROUGH VRECHRG YES NO BAT < VRECHRG YES NO YES 3576 FLOW 3576f 25 LTC3576/LTC3576-1 OPERATION switching, its duty cycle is modulated between a high and low value at a very low frequency. The low and high duty cycles are disparate enough to make an LED appear to be on or off thus giving the appearance of “blinking”. Each of the two faults has its own unique “blink” rate for human recognition as well as two unique duty cycles for machine recognition. The CHRG pin does not respond to the C/10 threshold if the LTC3576/LTC3576-1 is in VBUS current limit. This prevents false end of charge indications due to insufficient power available to the battery charger. Table 2 illustrates the four possible states of the CHRG pin when the battery charger is active. Table 2. CHRG Signal STATUS Charging Not Charging NTC Fault Bad Battery or On-The-Go Short-Circuit Fault MODULATION FREQUENCY (BLINK) FREQUENCY 0Hz 0Hz 35kHz 35kHz 0Hz (Low-Z) 0Hz (Hi-Z) 1Hz at 50% 4Hz at 50% DUTY CYCLES 100% 0% 6%, 94% 12%, 88% In addition to charge status, the CHRG pin is also used to indicate whether there is a short-circuit condition on VBUS when the bidirectional switching regulator is in onthe-go mode. When a short-circuit condition is detected, CHRG will blink with the same modulation frequency and duty cycle as a bad battery fault. If the charger is on at the same time that on-the-go is enabled, a 4Hz modulation of 12% and 88% duty cycles on CHRG could indicate a bad battery or a short-circuit fault on VBUS. System software should turn off the charger or on-the-go to determine which fault has occurred. Although very improbable, it is possible that a duty cycle reading could be taken at the bright-dim transition (low duty cycle to high duty cycle). When this happens the duty cycle reading will be precisely 50%. If the duty cycle reading is 50%, system software should disqualify it and take a new duty cycle reading. NTC Thermistor The battery temperature is measured by placing a negative temperature coefficient (NTC) thermistor close to the battery pack. To use this feature connect the NTC thermistor, RNTC, between the NTC pin and ground and a bias resistor, RNOM, from NTCBIAS to NTC. RNOM should be a 1% 200ppm resistor with a value equal to the value of the chosen NTC thermistor at 25°C (R25). The LTC3576/LTC3576-1 pauses charging when the resistance of the NTC thermistor drops to 0.54 times the value of R25 or approximately 54k for a 100k thermistor. For a Vishay Curve 1 thermistor, this corresponds to approximately 40°C. If the battery charger is in constant voltage (float) mode, the safety timer also pauses until the thermistor indicates a return to a valid temperature. As the temperature drops, the resistance of the NTC thermistor rises. The LTC3576/LTC3576-1 are also designed to pause charging when the value of the NTC thermistor increases to 3.25 times the value of R25. For a Vishay Curve 1 100k thermistor, this resistance, 325k, corresponds to approximately 0°C. The hot and cold comparators each have approximately 3°C of hysteresis to prevent oscillation about the trip point. Grounding the NTC pin disables all NTC functionality. 3576f An NTC fault is represented by a 35kHz pulse train whose duty cycle alternates between 6% and 94% at a 1Hz rate. A human will easily recognize the 1Hz rate as a “slow” blinking which indicates the out-of-range battery temperature while a microprocessor will be able to decode either the 6% or 94% duty cycles as an NTC fault. If a battery is found to be unresponsive to charging (i.e., its voltage remains below 2.85V for 1/2 hour), the CHRG pin gives the bad battery fault indication. For this fault, a human would easily recognize the 4Hz “fast” blink of the LED while a microprocessor would be able to decode either the 12% or 88% duty cycles as a bad battery fault. Note that the LTC3576/LTC3576-1 are 3-terminal PowerPath products where system load is always prioritized over battery charging. Due to excessive system load, there may not be sufficient power to charge the battery beyond the trickle charge threshold voltage within the bad battery timeout period. In this case, the battery charger will falsely indicate a bad battery. System software may then reduce the load and reset the battery charger to try again. 26 LTC3576/LTC3576-1 OPERATION Thermal Regulation To prevent thermal damage to the LTC3576/LTC3576-1 or surrounding components, an internal thermal feedback loop will automatically decrease the programmed charge current if the die temperature rises to 105°C. This thermal regulation technique protects the LTC3576/LTC3576-1 from excessive temperature due to high power operation or high ambient thermal conditions, and allows the user to push the limits of the power handling capability with a given circuit board design. The benefit of the LTC3576/ LTC3576-1 thermal regulation loop is that charge current can be set according to actual conditions rather than worst-case conditions for a given application with the assurance that the charger will automatically reduce the current in worst-case conditions. Overvoltage Protection The LTC3576/LTC3576-1 can protect itself from the inadvertent application of excessive voltage to VBUS or WALL with just two external components: an N-channel MOSFET and a 6.2k resistor. The maximum safe overvoltage magnitude will be determined by the choice of the external MOSFET and its associated drain breakdown voltage. The overvoltage protection module consists of two pins. The first, OVSENS, is used to measure the externally applied voltage through an external resistor. The second, OVGATE, is an output used to drive the gate pin of the external MOSFET. When OVSENS is below 6V, an internal charge pump will drive OVGATE to approximately 1.88 × OVSENS. This will enhance the N-channel MOSFET and provide a low impedance connection to VBUS or WALL which will, in turn, power the LTC3576/LTC3576-1. If OVSENS should rise above 6V due to a fault or use of an incorrect wall adapter, OVGATE will be pulled to GND disabling the external MOSFET and therefore protecting downstream circuitry. When the voltage drops below 6V again, the external MOSFET will be re-enabled. When USB on-the-go is enabled, the bidirectional switching regulator powers up the overvoltage protection circuit through the body diode of the external MOSFET, thus providing protection to the part even when VBUS is sourcing power. When high voltage is applied to the drain of the external MOSFET, VBUS will remain at 5V. Once the high voltage is removed, the drain of the external MOSFET will return to 5V. The charge pump output on OVGATE has limited output drive capability. Care must be taken to avoid leakage on this pin as it may adversely affect operation. See the Applications Information section for resistor power dissipation rating calculations, a table of recommended components, and examples of dual-input and reverse input protection. I2C Interface The LTC3576/LTC3576-1 may receive commands from a host (master) using the standard 2-wire I2C interface. The Timing Diagram shows the timing relationship of the signals on the bus. The two bus lines, SDA and SCL, must be HIGH when the bus is not in use. External pull-up resistors or current sources, such as the LTC1694 I2C accelerator, are required on these lines. The LTC3576/LTC3576-1are receive-only slave devices. The I2C control signals, SDA and SCL are scaled internally to the DVCC supply. DVCC should be connected to the same power supply as the microcontroller generating the I2C signals. The I2C port has an undervoltage lockout on the DVCC pin. When DVCC is below approximately 1V, the I2C serial port is cleared and switching regulators 1, 2 and 3 are set to full scale. Bus Speed The I2C port is designed to be operated at speeds of up to 400kHz. It has built-in timing delays to ensure correct operation when addressed from an I2C compliant master device. It also contains input filters designed to suppress glitches should the bus become corrupted. Start and Stop Conditions A bus master signals the beginning of a communication to a slave device by transmitting a START condition. A START condition is generated by transitioning SDA from high to LOW while SCL is HIGH. When the master has finished communicating with the slave, it issues a STOP condition by transitioning SDA from LOW to HIGH while SCL is high. The bus is then free for communication with another I2C device. 3576f 27 LTC3576/LTC3576-1 OPERATION Byte Format Each byte sent to the LTC3576/LTC3576-1 must be eight bits long followed by an extra clock cycle for the acknowledge bit. The data should be sent to the LTC3576/LTC3576-1 with the most significant bit (MSB) first. Acknowledge The acknowledge signal is used for handshaking between the master and the slave. An acknowledge (active low) generated by the slave (LTC3576/LTC3576-1) lets the master know that the latest byte of information was received. The acknowledge related clock pulse is generated by the master. The master releases the SDA line (HIGH) during the acknowledge clock cycle. The slave-receiver must pull down the SDA line during the acknowledge clock pulse so that it remains a stable LOW during the HIGH period of this clock pulse. Slave Address The address byte consists of the 7-bit address and the read/write (R/W) bit. The LTC3576/LTC3576-1 respond to only one 7-bit address which has been factory programmed to 0001001. The R/W bit is the least significant bit of the address byte. It must be 0 for the LTC3576/LTC3576-1 to recognize the address since they are write only devices. Thus the address byte is 0x12. If the correct seven bit address is given but the R/W bit is 1, the LTC3576/LTC3576-1 will not respond. Sub-Addressed Writing The LTC3576/LTC3576-1 have four command registers for control input. They are accessed by the I2C port via a sub-addressed writing system. Each write to the LTC3576/LTC3576-1 consists of three bytes. The first byte is always the LTC3576/LTC3576-1’s write address. The second byte represents the LTC3576/ LTC3576-1’s sub-address. The sub-address acts as pointer to direct the subsequent data byte within the LTC3576/LTC3576-1. The third byte consists of the data to be written to the location pointed to by the sub-address. The LTC3576/LTC3576-1 contain four sub-addresses at locations 0x00, 0x01, 0x02 and 0x03. Bus Write Operation The master initiates communication with the LTC3576/ LTC3576-1 with a START condition and a 7-bit address followed by the R/W bit = 0. If the address matches that of the LTC3576/LTC3576-1, the LTC3576/LTC3576-1 return an acknowledge. The master should then deliver the subaddress. Again the LTC3576/LTC3576-1 acknowledge and the cycle is repeated for the data byte. The data byte is transferred to an internal holding latch upon the return of its acknowledge by the LTC3576/LTC3576-1. This procedure must be repeated for each sub-address that requires new data. After one or more data bytes have been transferred to the LTC3576/LTC3576-1, the master may terminate the communication with a STOP condition. Alternatively, a repeated START condition can be initiated by the master and another chip on the I2C bus can be addressed. This cycle can continue indefinitely and the LTC3576/LTC3576-1 remembers the last input of valid data that it received. Once all chips on the bus have been addressed and sent valid data, a global STOP condition can be sent and the LTC3576/LTC3576-1 will update their command latches with the data that they have received. In certain circumstances the data on the I2C bus may become corrupted. In these cases, the LTC3576/LTC35761 respond appropriately by preserving only the last set of complete data that they have received. For example, assume the LTC3576/LTC3576-1 have been successfully addressed and are receiving data when a STOP condition mistakenly occurs. The LTC3576/LTC3576-1 will ignore this STOP condition and will not respond until a new START condition, correct address and sub-address, new set of data and STOP condition are transmitted. Likewise, with only one exception, if the LTC3576/ LTC3576-1 were previously addressed and sent valid data but not updated with a STOP they will respond to any , STOP that appears on the bus, independent of the number of repeated STARTs that have occurred. If a repeated START is given and the LTC3576/LTC3576-1 successfully acknowledge their address and sub-address, they will not respond to a STOP until a full byte of the new data has been received and acknowledged. 3576f 28 LTC3576/LTC3576-1 OPERATION Input Data Table 3 illustrates the four data bytes that may be written to the LTC3576/LTC3576-1. The first byte at sub-address 0 controls the servo voltage for switching regulators 1 and 2. The second byte at Table 3. I2C Serial Port Mapping* A7 A6 A5 A4 A3 A2 A1 A0 B7 B6 B5 B4 B3 ENABLE 3 B2 ENABLE 2 B1 ENABLE 1 0 D1 0 B0 ENABLE OTG 0 D0 0 3576f sub-address 1 controls the servo voltage of switching regulator 3 and the enable signals for all three switching regulators, as well as the enable signal for the PowerPath switching regulator to power up VBUS for USB on-the-go. The servo voltages are decoded in Table 4. The default servo voltage is 0.8V. Switching Regulator 1 Voltage (See Table 4) Switching Regulator 2 Voltage (See Table 4) Switching Regulator 3 Voltage (See Table 4) Reset Value 1 C7 1 C6 1 C5 1 C4 1 C3 1 C2 1 C1 1 C0 0 D7 DISABLE BATTERY CHARGER 0 D6 HIGH POWER SUSPEND 0 D5 0 D4 0 D3 0 D2 Switching Regulator 1 Modes (See Table 5) Switching Regulator 2 Modes (See Table 5) Switching Regulator 3 Modes (See Table 5) Input Current Limit (See Table 6) Unused Reset Value 0 0 0 0 0 0 0 0 0 0 0 0 0 0 *The A7-A0 and B7-B4 bits default to 1 and all other bits default to 0 when the chip is powered and DVCC = 0. Table 4. Switching Regulator Servo Voltage A7 A3 B7 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 A6 A2 B6 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 A5 A1 B5 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 A4 A0 B4 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Switching Regulator 1 Servo Voltage Switching Regulator 2 Servo Voltage Switching Regulator 3 Servo Voltage 0.425 0.450 0.475 0.500 0.525 0.550 0.575 0.600 0.625 0.650 0.675 0.700 0.725 0.750 0.775 0.800 29 LTC3576/LTC3576-1 OPERATION The third data byte at sub-address 2 controls the operating modes of each switching regulator as well as the input current limit settings. Each switching regulator can be independently set to one of three operating modes listed in Table 5. The input current limit settings are decoded according to Table 6. This table indicates the maximum current that will be drawn from the VBUS pin in the event that the load at VOUT (battery charger plus system load) exceeds the power available. Any additional power will be drawn from the battery. The start-up state for the input current limit setting is 00 representing the low power 100mA USB setting. The fourth and final byte of input data at sub-address 3 provides bits for disabling the battery charger and enabling the high power suspend mode current limit of 2.5mA. Table 5. General Purpose Switching Regulator Modes C7 (SDA)* C5 (SDA)* C3 (SDA)* 0 1 1 C6 (SCL)* C4 (SCL)* C2 (SCL)* X 0 1 Switching Regulator 1 Mode Switching Regulator 2 Mode Switching Regulator 3 Mode Pulse Skip Mode LDO Mode Burst Mode Operation Disabling the I2C Port The I2C serial port can be disabled by grounding the DVCC pin. In this mode, the LTC3576/LTC3576-1 are controlled through the individual logic input pins EN1, EN2, EN3, ENOTG, ILIM0, ILIM1, SDA and SCL. Some functionality is not available in this mode such as the programmability of switching regulators 1, 2 and 3’s output voltage, the battery charger disable feature and the high power suspend mode. In this mode, the programmable switching regulators have a fixed servo voltage of 0.8V. Because the SDA and SCL pins have no other context when DVCC is grounded, these pins are re-mapped to control the switching regulator mode bits C2 to C7. SCL maps to C2, C4 and C6 while SDA maps to C3, C5 and C7. RST3 Pin The RST3 pin is an open-drain output used to indicate that switching regulator 3 has been enabled and has reached its final voltage. RST3 remains low impedance until regulator 3 reaches 92% of its regulation value. A 230ms delay is included to allow a system microcontroller ample time to reset itself. RST3 may be used as a poweron reset to the microprocessor powered by regulator 3 or may be used to enable regulators 1 and/or 2 for supply sequencing. RST3 is an open-drain output and requires a pull-up resistor to the output voltage of regulator 3 or another appropriate power source. Shutdown Mode The bidirectional USB switching regulator in step-down mode is enabled whenever VBUS is above VUVLO and the LTC3576/LTC3576-1are not in one of the two USB suspend modes (500μA or 2.5mA). When power is available from both the USB and auxiliary inputs, the auxiliary input is given priority and the USB switching regulator is disabled. The ideal diode(s) are enabled at all times and cannot be disabled. *SDA and SCL take on this context only when DVCC = 0V. Table 6. USB Current Limit Settings D6 X X 0 1 X C1 (ILIM1)* 0 0 1 1 1 C0 (ILIM0)* 0 1 0 0 1 USB SETTING 1x Mode (USB 100mA Limit) 10x Mode (Wall 1A Limit) Low Power Suspend (USB 500μA Limit) High Power Suspend (USB 2.5mA Limit) 5x Mode (USB 500mA Limit) *ILIM1 and ILIM0 can only be used to enable the low power suspend mode and are logically ORed with C1 and C0, respectively. 3576f 30 LTC3576/LTC3576-1 OPERATION Step-Down Switching Regulators The LTC3576/LTC3576-1 contain three general purpose 2.25MHz step-down constant-frequency current mode switching regulators. Two regulators provide up to 400mA and a third switching regulator can provide up to 1A. All three switching regulators can be programmed for a minimum start-up output voltage of 0.8V and can be used to power a microcontroller core, microcontroller I/O, memory, disk drive or other logic circuitry. All three switching regulators have I2C programmable set points for on-the-fly power savings. They also support 100% duty cycle operation (low dropout mode) when their input voltage drops very close to their output voltage. To suit a variety of applications, selectable mode functions can be used to trade off noise for efficiency. Three modes are available to control the operation of the LTC3576/LTC3576-1’s general purpose switching regulators. At moderate to heavy loads, the pulse skip mode provides the lowest noise switching solution. At lighter loads, Burst Mode operation or LDO mode may be selected. The switching regulators include soft-start to limit inrush current when powering on, shortcircuit current protection and switch node slew limiting circuitry to reduce radiated EMI. No external compensation components are required. The operating mode of the regulators may be set by either I2C control or by manual control of the SDA and SCL pins if the I2C port is not used. Each converter may be individually enabled by either their external control pins EN1, EN2, EN3 or by the I2C port. All three switching regulators have individual programmable feedback servo voltages via I2C control. The switching regulator input supplies VIN1, VIN2 and VIN3 will generally be connected to the system load pin VOUT. Step-Down Switching Regulator Operating Modes The LTC3576/LTC3576-1’s general purpose switching regulators include three possible operating modes to meet the noise/power needs of a variety of applications. In pulse skip mode, an internal latch is set at the start of every cycle which turns on the main P-channel MOSFET switch. During each cycle, a current comparator compares the peak inductor current to the output of an error amplifier. The output of the current comparator resets the internal latch which causes the main P-channel MOSFET switch to turn off and the N-channel MOSFET synchronous rectifier to turn on. The N-channel MOSFET synchronous rectifier turns off at the end of the 2.25MHz cycle or if the current through the N-channel MOSFET synchronous rectifier drops to zero. Using this method of operation, the error amplifier adjusts the peak inductor current to deliver the required output power. All necessary compensation is internal to the switching regulator requiring only a single ceramic output capacitor for stability. At light loads in PWM mode, the inductor current may reach zero on each pulse which will turn off the N-channel MOSFET synchronous rectifier. In this case, the switch node (SW) goes high impedance and the switch node voltage will “ring”. This is discontinuous mode operation, and is normal behavior for a switching regulator. At very light loads in pulse skip mode, the switching regulators will automatically skip pulses as needed to maintain output regulation. At high duty cycles (VOUTx > VINx /2) it is possible for the inductor current to reverse, causing the regulator to operate continuously at light loads. This is normal and regulation is maintained, but the supply current will increase to several mA due to continuous switching. 3576f 31 LTC3576/LTC3576-1 OPERATION In Burst Mode operation, the switching regulator automatically switches between fixed frequency PWM operation and hysteretic control as a function of the load current. At light loads, the regulator operates in hysteretic mode and uses a constant current algorithm to control the inductor current. While in Burst Mode operation, the output capacitor is charged to a voltage slightly higher than the regulation point. The step-down switching regulator then goes into sleep mode, during which the output capacitor provides the load current. In sleep mode, most of the regulator’s circuitry is powered down, conserving battery power. When the output voltage drops below a pre-determined value, the switching regulator circuitry is powered on and another burst cycle begins. The duration for which the regulator operates in sleep mode depends on the load current. The sleep time decreases as the load current increases. Burst Mode operation provides a significant improvement in efficiency at light loads at the expense of higher output ripple when compared to pulse skip mode. At heavy loads Burst Mode operation functions in the same manner as pulse skip mode. Finally, the switching regulators have an LDO mode that gives a DC option for regulating their output voltages. In LDO mode, the switching regulators are converted to linear regulators and deliver continuous power from their SWx pins through their respective inductors. This mode gives the lowest possible output noise as well as low quiescent current at light loads. The step-down switching regulators allow on-the-fly mode transitions, providing seamless transition between modes even under load. This allows the user to switch back and forth between modes to reduce output ripple or increase low current efficiency as needed. Step-Down Switching Regulator Dropout Operation It is possible for a switching regulator’s input voltage, VINx, to approach its programmed output voltage (e.g., a battery voltage of 3.4V with a programmed output voltage of 3.3V). When this happens, the PMOS switch duty cycle increases until it is turned on continuously at 100%. In this dropout condition, the respective output voltage equals the regulator’s input voltage minus the voltage drops across the internal P-channel MOSFET and the inductor. Step-Down Switching Regulator Low Supply Operation The LTC3576/LTC3576-1 incorporate an undervoltage lockout circuit on VOUT which shuts down the general purpose switching regulators when VOUT drops below VOUT(UVLO). This UVLO prevents unstable operation. Step-Down Switching Regulator Soft-Start Operation Soft-start is accomplished by gradually increasing the peak inductor current for each switching regulator over a 500μs period. This allows each output to rise slowly, helping minimize the battery surge current. A soft-start cycle occurs whenever a given switching regulator is enabled, or after a fault condition has occurred (thermal shutdown or UVLO). A soft-start cycle is not triggered by changing operating modes. This allows seamless output operation when transitioning between Burst Mode operation, pulse skip mode or LDO mode. Step-Down Switching Regulator Switching Slew Rate Control The step-down switching regulators contain new patent pending circuitry to limit the slew rate of the switch node (SWx). This new circuitry is designed to transition the switch node over a period of a couple of nanoseconds, significantly reducing radiated EMI and conducted supply noise. Step-Down Switching Regulator in Shutdown The step-down switching regulators are in shutdown when not enabled for operation. In shutdown, all circuitry in the step-down switching regulator is disconnected from the switching regulator input supply leaving only a few nanoamperes of leakage current. The step-down switching regulator outputs are individually pulled to ground through a 10k resistor on their SWx pins when in shutdown. 3576f 32 LTC3576/LTC3576-1 APPLICATIONS INFORMATION Bidirectional PowerPath Switching Regulator CLPROG Resistor and Capacitor Selection As described in the Bidirectional Switching Regulator— Step-Down Mode section, the resistor on the CLPROG pin determines the average VBUS input current limit when the switching regulator is set to either the 1x mode (USB 100mA), the 5x mode (USB 500mA) or the 10x mode. The VBUS input current will be comprised of two components, the current that is used to drive VOUT and the quiescent current of the switching regulator. To ensure that the USB specification is strictly met, both components of the input current should be considered. The Electrical Characteristics table gives the typical values for quiescent currents in all settings as well as current limit programming accuracy. To get as close to the 500mA or 100mA specifications as possible, a precision resistor should be used. Recall that: IVBUS = IVBUSQ + VCLPROG/RCLPPROG • (hCLPROG +1). An averaging capacitor is required in parallel with the resistor so that the switching regulator can determine the average input current. This capacitor also provides the dominant pole for the feedback loop when current limit is reached. To ensure stability, the capacitor on CLPROG should be 0.1μF or larger. Bidirectional PowerPath Switching Regulator Inductor Selection Because the input voltage range and output voltage range of the PowerPath switching regulator are both fairly narrow, the LTC3576/LTC3576-1 were designed for a specific inductance value of 3.3μH. Some inductors which may be suitable for this application are listed in Table 7. Table 7. Recommended PowerPath Inductors for the LTC3576 INDUCTOR TYPE LPS4018 D53LC DB318C WE-TPC Type M1 CDRH6D12 CDRH6D38 L (μH) 3.3 3.3 3.3 3.3 3.3 3.3 MAX IDC (A) 2.2 MAX DCR (Ω) SIZE IN mm (L × W × H) MANUFACTURER Bidirectional PowerPath Switching Regulator VBUS and VOUT Bypass Capacitor Selection The type and value of capacitors used with the LTC3576/ LTC3576-1 determine several important parameters such as regulator control-loop stability and input voltage ripple. Because the LTC3576/LTC3576-1 use a bidirectional switching regulator between VBUS and VOUT, the VBUS current waveform contains high frequency components. It is strongly recommended that a low equivalent series resistance (ESR) multilayer ceramic capacitor (MLCC) be used to bypass VBUS. Tantalum and aluminum capacitors are not recommended because of their high ESR. The value of the capacitor on VBUS directly controls the amount of input ripple for a given load current. Increasing the size of this capacitor will reduce the input ripple. The inrush current limit specification for USB devices is calculated in terms of the total number of Coulombs needed to charge the VBUS bypass capacitor to 5V. The maximum inrush charge for USB on-the-go devices is 33μC. This places a limit of 6.5μF of capacitance on VBUS assuming a linear capacitor. However, most ceramic capacitors have a capacitance that varies with bias voltage. The average capacitance needs to be less than 6.5μF over a 0V to 5V bias voltage range to meet the inrush current limit specification. A 10μF capacitor in a 0805 package, such as the Murata GRM21BR71A106KE51L would be a suitable VBUS bypass capacitor. If more capacitance is required for better noise performance and stability it should be connected directly to the VBUS pin when using the overvoltage protection circuit. This extra capacitance will be soft-connected over several milliseconds to limit inrush current and avoid excessive transient voltage drops on VBUS. To prevent large VOUT voltage steps during transient load conditions, it is also recommended that an MLCC be used to bypass VOUT. The output capacitor is used in the compensation of the switching regulator. At least 10μF with low ESR are required on VOUT. Additional capacitance will improve load transient performance and stability. MLCCs typically have exceptional ESR performance. MLCCs combined with a tight board layout and an unbroken ground plane will yield very good performance and low EMI emissions. 3576f 0.08 3.9 × 3.9 × 1.7 Coilcraft www.coilcraft.com 2.26 0.034 Toko 5×5×3 1.55 0.070 3.8 × 3.8 × 1.8 www.toko.com 1.95 0.065 4.8 × 4.8 × 1.8 Wurth Electronik www.we-online.com 2.2 3.5 0.063 6.7 × 6.7 × 1.5 Sumida 0.020 www.sumida.com 7×7×4 33 LTC3576/LTC3576-1 APPLICATIONS INFORMATION There are MLCCs available with several types of dielectrics each having considerably different characteristics. For example, X7R MLCCs have the best voltage and temperature stability. X5R MLCCs have apparently higher packing density but poorer performance over their rated voltage and temperature ranges. Y5V MLCCs have the highest packing density, but must be used with caution, because of their extreme nonlinear characteristic of capacitance versus voltage. The actual in-circuit capacitance of a ceramic capacitor should be measured with a small AC signal and DC bias as is expected in-circuit. Many vendors specify the capacitance versus voltage with a 1VRMS AC test signal and, as a result, over state the capacitance that the capacitor will present in the application. Using similar operating conditions as the application, the user must measure or request from the vendor the actual capacitance to determine if the selected capacitor meets the minimum capacitance that the application requires. Step-Down Switching Regulator Output Voltage Programming All three switching regulators have I2C programmable set points and can be programmed for start-up output voltages of at least 0.8V. The full-scale output voltage for each switching regulator is programmed using a resistor divider from the switching regulator output connected to the FBx pins such that: VOUTx = VFBx R1 +1 R2 to improve transient response for output voltages much greater than 0.8V. A variety of capacitor sizes can be used for CFB but a value of 10pF is recommended for most applications. Experimentation with capacitor sizes between 2pF and 22pF may yield improved transient response. Step-Down Switching Regulator Inductor Selection Many different sizes and shapes of inductors are available from numerous manufacturers. Choosing the right inductor from such a large selection of devices can be overwhelming, but following a few basic guidelines will make the selection process much simpler. The general purpose step-down converters are designed to work with inductors in the range of 2μH to 10μH. For most applications a 4.7μH inductor is suggested for the lower current switching regulators 1 and 2 and 2μH is recommended for the higher current switching regulator 3. Larger value inductors reduce ripple current which improves output ripple voltage. Lower value inductors result in higher ripple current and improved transient response time. To maximize efficiency, choose an inductor with a low DC resistance. For a 1.2V output, efficiency is reduced about 2% for 100mΩ series resistance at 400mA load current, and about 2% for 300mΩ series resistance at 100mA load current. Choose an inductor with a DC current rating at least 1.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. If output short circuit is a possible condition, the inductor should be rated to handle the maximum peak current specified for the step-down converters. Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or Permalloy materials are small and don’t radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. Inductors that are very thin or have a very small volume typically have much higher core and DCR losses, and will not give the best efficiency. The choice of which style inductor to use often depends more on the price vs size, performance and any radiated EMI requirements than on what the LTC3576/LTC3576-1 require to operate. where VFBx ranges from 0.425V to 0.8V. See Figure 5. Typical values for R1 are in the range of 40k to 1M. The capacitor CFB cancels the pole created by feedback resistors and the input capacitance of the FBx pin and also helps VINx SWx LTC3576/ LTC3576-1 FBx L VOUTx CFB R1 COUT R2 GND 3576 F05 Figure 5. Buck Converter Application Circuit 3576f 34 LTC3576/LTC3576-1 APPLICATIONS INFORMATION The inductor value also has an effect on Burst Mode operation. Lower inductor values will cause the Burst Mode switching frequency to increase. Table 8 shows several inductors that work well with the LTC3576/LTC3576-1’s general purpose regulators. These inductors offer a good compromise in current rating, DCR and physical size. Consult each manufacturer for detailed information on their entire selection of inductors. Table 8. Recommended Inductors INDUCTOR TYPE DE2818C D312C DE2812C L (μH) 4.7 3.3 4.7 3.3 2.2 4.7 3.3 2.0 4.7 3.3 2.2 4.7 3.3 2.2 4.7 4.7 3.3 2.2 4.7 3.3 2.2 4.7 3.3 2.2 4.7 3.3 2.2 4.7 3.3 2.2 MAX IDC (A) 1.25 1.45 0.79 0.90 1.14 1.2 1.4 1.8 0.9 1.1 1.2 0.5 0.6 0.78 0.75 1.3 1.59 2.0 0.8 0.97 1.12 1.29 1.42 1.80 1.08 1.31 1.65 1.1 1.3 1.5 MAX DCR (Ω) 0.072 0.053 0.24 0.20 0.14 1.13* 0.10* 0.067* 0.11 0.085 0.072 0.17 0.123 0.098 0.19 0.162 0.113 0.074 0.246 0.165 0.14 0.117* 0.104* 0.075* 0.153* 0.108* 0.091* 0.2 0.13 0.11 SIZE IN mm (L × W × H) 3.0 × 2.8 × 1.8 3.0 × 2.8 × 1.8 3.6 × 3.6 × 1.2 3.6 × 3.6 × 1.2 3.6 × 3.6 × 1.2 3.0 × 2.8 × 1.2 3.0 × 2.8 × 1.2 3.0 × 2.8 × 1.2 4.0 × 4.0 × 1.8 4.0 × 4.0 × 1.8 4.0 × 4.0 × 1.8 3.2 × 3.2 × 1.2 3.2 × 3.2 × 1.2 3.2 × 3.2 × 1.2 4.9 × 4.9 × 1.0 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.2 3.1 × 3.1 × 1.2 3.1 × 3.1 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.0 5.2 × 5.2 × 1.0 5.2 × 5.2 × 1.0 3.0 × 3.0 × 1.5 3.0 × 3.0 × 1.5 3.0 × 3.0 × 1.5 MANUFACTURER Toko www.toko.comm ranges than other ceramic types. A 10μF output capacitor is sufficient for most applications. For good transient response and stability the output capacitor should retain at least 4μF of capacitance over operating temperature and bias voltage. Each switching regulator input supply should be bypassed with a 1μF capacitor. Consult with capacitor manufacturers for detailed information on their selection and specifications of ceramic capacitors. Many manufacturers now offer very thin (