LTC3456 2-Cell, Multi-Output DC/DC Converter with USB Power Manager U FEATURES DESCRIPTIO ■ The LTC®3456 is a complete power management system IC optimized for a variety of portable applications. The device generates two separate power rails: a 3.3V (fixed) Main supply and a 1.8V (adjustable) Core supply. In addition, the LTC3456 contains a USB power manager, a Hot Swap output, a low-battery indicator and an alwaysalive VMAX output. The LTC3456 takes power from one of three sources: a Wall adapter, a USB port or a 2-cell Alkaline/NiCd/NiMH battery, in that order of priority. Current drawn from the USB port is accurately limited to 100mA or 500mA based on the state of the USBHP pin. ■ ■ ■ ■ ■ ■ ■ ■ ■ Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter Input Power Sources Main Output: Fixed 3.3V Output Core Output: Adjustable from 0.8V to VBATT(MIN) Hot SwapTM Output for Memory Cards All Outputs Discharged to Ground During Shutdown Power Supply Sequencing: Main and Hot Swap Outputs Come Up After Core Output Accurate USB Current Limiting High Frequency Operation: 1MHz High Efficiency: Up to 92% Small (4mm × 4mm × 0.75mm) 24-Pin QFN Package U APPLICATIO S ■ ■ ■ ■ GPS Portable Navigators MP3 Players Digital Cameras Handheld Computers The Main and Core switchers are all high efficiency, 1MHz fixed frequency PWM converters. Availability in a small (4mm × 4mm × 0.75mm) 24-pin QFN package makes the LTC3456 ideal for space-sensitive portable devices. , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. U TYPICAL APPLICATIO + 4.7µF L2 4.7µH 100k VBATT 22µF L3 10µH SW2_BST SW2_BK AIN VINT 80.6k AO 4.7µF USB CONTROLLER 1Ω HSO L1 10µH SUSPEND LTC3456 USB SW1 1k AC WALL ADAPTER (5V ±10%) 220pF VEXT 11.3k FB1 10µF WALLFB VMAX PWRKEY PBSTAT RESET MODE PWRON PGND AGND 250 VBATT = 2.4V 90 MODE = 0V 200 80 1.8V OUTPUT 70 60 3.3V OUTPUT 40 POWER LOSS 30 3.3V OUTPUT 1.8V OUTPUT 10 VMAX (POWERS 1µF REAL-TIME CLOCK) 150 EFFICIENCY 50 20 80.6k 1Ω 4.32k CORE OUTPUT 1.8V 10µF 200mA 100k EXT_PWR 4.7µF Hot Swap OUTPUT 3.3V 1µF 50mA 100 0 1 10 100 LOAD CURRENT (mA) 100 POWER LOSS (mW) USB POWER (4.35V TO 5.5V) Efficiency and Power Loss vs Load Current (Battery Powered) MAIN OUTPUT 3.3V 1µF 150mA VMAIN USBHP VINT 3.3V EFFICIENCY (%) 2 AA CELLS 50 0 1000 3456 TA01b µP 3456 TA01 3456f 1 LTC3456 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART NUMBER PWRKEY PBSTAT PWRON MODE FB1 RESET TOP VIEW VBATT, VMAX Voltages ................................. – 0.3V to 6V VINT, VMAIN, VEXT, HSO Voltages ................ – 0.3V to 6V SW1, SW2_BK, SW2_BST Voltages ........... – 0.3V to 6V USB, USBHP, SUSPEND Voltages .............. –0.3V to 6V PWRKEY, PBSTAT, PWRON Voltages ........ –0.3V to 6V MODE, AO, EXT_PWR, RESET Voltages ..... –0.3V to 6V FB1, AIN, WALLFB Voltages ....................... –0.3V to 2V Junction Temperature .......................................... 125°C Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C LTC3456EUF 24 23 22 21 20 19 AIN 1 18 SUSPEND AO 2 17 HSO AGND 3 16 VMAIN 25 VBATT 4 15 VINT UF PART MARKING USBHP 9 10 11 12 VMAX 8 USB 7 VEXT 13 SW2_BK WALLFB 14 SW2_BST PGND 6 EXT_PWR SW1 5 3456 UF PACKAGE 24-LEAD (4mm × 4mm) PLASTIC QFN TJMAX = 125°C, θJA = 37°C/ W, θJC = 2°C/ W EXPOSED PAD (PIN 25) IS PGND MUST BE SOLDERED TO PCB Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBATT = 2.4V, VINT = 3.3V, VPWRON = 2V, PWRKEY is open, VUSB = 0V, VWALLFB = 0V, unless otherwise specified. PARAMETER CONDITIONS MIN Battery Voltage Range Quiescent Current (Battery Powered) Burst Mode® Operation PWM Operation Shutdown TYP 1.8 (Note 3) VMODE = 2V, VFB1 = 1V, VINT = 3.4V VMODE = 0V, VFB1 = 1V, VINT = 3.4V VPWRON = 0V, VINT = 0V 180 380 0.1 MAX UNITS 3.2 V 250 450 1 µA µA µA VBATT Pin Current (Wall Powered) VWALLFB = 1.5V, VEXT = 5V (Note 4) 1 2 µA VBATT Pin Current (USB Powered) VUSB = 5V, VEXT = 5V (Note 4) 1 2 µA Switching Frequency Battery Powered USB or Wall Powered VBATT = 2.4V VEXT = 5V, VWALLFB = 1.5V 1 1 1.2 1.2 3.3 3.38 V 0.1 0.5 %/V 0.8 0.8 MHz MHz Main Output ● VINT Voltage Regulation VINT Voltage Line Regulation VBATT = 1.8V to 3.2V ● Max Duty Cycle 3.22 ● 80 87 Switch Leakage (Battery Powered) SW2_BST PMOS Switch SW2_BST NMOS Switch VSW2_BST = 0V VSW2_BST = 3.3V 0.1 0.1 Switch On-Resistance (Battery Powered) SW2_BST PMOS Switch SW2_BST NMOS Switch ISW2_BST = 150mA ISW2_BST = –150mA 0.8 0.5 % 1 1 µA µA Ω Ω Burst Mode is a registered trademark of Linear Technology 3456f 2 LTC3456 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBATT = 2.4V, VINT = 3.3V, VPWRON = 2V, PWRKEY is open, VUSB = 0V, VWALLFB = 0V, unless otherwise specified. PARAMETER CONDITIONS Switch Leakage (USB/Wall Powered) SW2_BK PMOS Switch SW2_BK NMOS Switch MIN TYP MAX VEXT = 5V, VWALLFB = 1.5V VSW2_BK = 0V VSW2_BK = 5V 0.1 0.1 1 1 Switch On-Resistance (USB/Wall Powered) SW2_BK PMOS Switch SW2_BK NMOS Switch VEXT = 5V, VWALLFB = 1.5V ISW2_BK = 150mA ISW2_BK = –150mA 0.9 0.4 Ω Ω Switch Current Limit Battery Powered (SW2_BST NMOS Current) Wall/USB Powered (SW2_BK PMOS Current) VBATT = 2.4V VEXT = 5V, VWALLFB = 1.5V 900 500 mA mA VMAIN PMOS Switch On-Resistance Measured Between VINT and VMAIN Pins 0.4 Ω VMAIN Turn-On Delay Battery Powered USB or Wall Powered After FB1 and VINT in Regulation VBATT = 2.4V VEXT = 5V, VWALLFB = 1.5V 700 400 ● ● 0.8 1.5 2 2 UNITS µA µA ms ms Hot Swap Output HSO PMOS Switch On-Resistance Measured Between VINT and HSO Pins HSO PMOS Switch Current Limit VINT = 3.3V, VHSO = 2.5V HSO Turn-On Delay Battery Powered USB or Wall Powered After FB1 and VINT in Regulation VBATT = 2.4V VEXT = 5V, VWALLFB = 1.5V 90 ● ● 0.8 Ω 120 mA 0.5 0.5 1 1 ms ms VMAX Output VMAX Output Voltage Shutdown Battery Powered USB/Wall Powered VMAX Output Unloaded VPWRON = 0V VPWRON = 2V, VBATT = 2.4V VPWRON = 2V, VEXT = 5V, VWALLFB = 1.5V Maximum VMAX Output Current VMAX Output < 12.5% Below Nominal Value VBATT 3.3 5 ● 1 ● 0.784 V V V mA Core Output FB1 Voltage 0.800 0.816 V FB1 Voltage Line Regulation VBATT = 1.8V to 3.2V ● 0.1 0.5 %/V FB1 Pin Input Bias Current VFB1 = 0.8V ● ±2 ±20 nA Duty Cycle Range Buck Switchers ● 100 % SW1 PMOS Switch Current Limit Battery Powered Wall/USB Powered VBATT = 2.4V VEXT = 5V SW1 Leakage Current VSW1 = 0V, VEXT = 5V or VBATT = 5V 0.1 SW1 PMOS Switch On-Resistance Battery Powered Wall/USB Powered ISW1 = 150mA VBATT = 2.4V VEXT = 5V, VWALLFB = 1.5V 0.5 0.5 Ω Ω SW1 NMOS Switch On-Resistance Battery Powered Wall/USB Powered ISW1 = –150mA VBATT = 2.4V VEXT = 5V, VWALLFB = 1.5V 0.4 0.4 Ω Ω 0 400 350 550 450 mA mA 1 µA 3456f 3 LTC3456 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VBATT = 2.4V, VINT = 3.3V, VPWRON = 2V, PWRKEY is open, VUSB = 0V, VWALLFB = 0V, unless otherwise specified. PARAMETER CONDITIONS MIN TYP MAX UNITS Rising Edge 3.9 4 4.1 V USB USB Turn-On Voltage Threshold USB Turn-On Voltage Hysteresis 75 mV USB PMOS Switch On-Resistance VUSB = 5V USB Current Limit VUSBHP = 2V (500mA Mode), VUSB = 5V VUSBHP = 0V (100mA Mode), VUSB = 5V 0.5 SUSPEND Pin Threshold VUSB = 5V 0.3 USBHP Pin Threshold VUSB = 5V 0.3 SUSPEND Pin Pull-Down Current VUSB = 5V, VSUSPEND = 2V USBHP Pin Pull-Down Current VUSB = 5V, VUSBHP = 2V 2.5 USB Pin Bias Current (Suspend Mode) VUSB = 5V, VSUSPEND = 2V 100 150 1.25 1.3 ● Ω 420 85 500 100 mA mA 0.8 1.2 V 0.8 1.2 2.5 V µA µA µA AC Adapter WALLFB Pin Threshold ● Rising Edge 1.2 WALLFB Pin Hysteresis 20 WALLFB Pin Input Bias Current VWALLFB = 1.25V, VEXT = 5V VEXT UVLO Voltage Rising Edge ● 3.9 VEXT UVLO Hysteresis EXT_PWR Pin Low Voltage ±2 ±20 4 4.1 150 VUSB > 4V and VSUSPEND = 0V or WALLFB > 1.25V, IEXT_PWR = 1mA V mV nA V mV 0.25 0.5 V 0.800 0.83 V ±2 ±20 nA 0.25 0.5 V Gain Block AIN Pin Reference Voltage 0.78 ● AIN Pin Input Bias Current VAIN = 0.8V AO Pin Low Voltage VAIN = 0V, IAO = 1mA Logic Inputs PWRKEY Pin Input High Voltage 0.7VMAX V PWRKEY Pin Input Low Voltage 0.3VMAX PWRKEY Pin Pull-Up Resistor to VMAX PBSTAT Pin Low Voltage 400 VPWRKEY = 0V, IPBSTAT = 100µA PWRON Pin Threshold PWRON Pin Pull-Down Current 0.3 VPWRON = 2V 0.05 0.1 V 0.8 1.2 V 1 MODE Pin Threshold 0.3 0.8 MODE Pin Pull-Down Current VMODE = 2V RESET Pin Low Voltage IRESET = 100µA 0.05 RESET Pulse Duration After VFB1 and VINT in Regulation 262 Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC3456 is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. V kΩ µA 1.2 1 V µA 0.1 V ms Note 3: Quiescent current is pulled from the VINT pin when neither USB nor wall power is present. Multiply this value by VINT/VBATT to get the equivalent input (battery) current. Note 4: Quiescent current is pulled from the VEXT pin when either USB or wall power is present. Note 5: Specification is guaranteed by design and not 100% tested in production. 3456f 4 LTC3456 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified. Main Converter Efficiency (Battery Powered) 100 100 90 90 90 80 80 70 70 60 50 40 60 50 40 30 30 20 20 PWM MODE Burst Mode OPERATION VBATT = 2.4V VCORE = 1.8V 0 10 100 LOAD CURRENT (mA) 1 EFFICIENCY (%) 80 70 10 0 10 100 LOAD CURRENT (mA) 1 50 40 20 0 1000 Oscillator Frequency vs Temperature 1150 1150 1150 1100 1100 1100 FREQUENCY (kHz) 1200 FREQUENCY (kHz) 1200 950 1050 1000 950 1000 950 900 900 850 850 850 1.8 2.0 2.2 2.4 2.6 VBATT (V) 2.8 3.0 800 3.2 4 4.25 4.5 4.75 VEXT (V) 5 3456 G04 800 –50 5.5 PWM MODE 3 2 1 Burst Mode OPERATION 1.8 2 2.2 2.4 2.6 2.8 3 3.2 VBATT (V) 3456 G07 3.0 2.5 FB1 = 1V (CORE CONVERTER NOT SWITCHING) 2.0 1.5 1.0 0.5 0 – 50 – 25 125 VBATT = 2.4V PWM MODE Burst Mode OPERATION 0 50 75 25 TEMPERATURE (°C) 100 125 3456 G08 SHUTDOWN CURRENT (µA) 4 BATTERY SUPPLY CURRENT (mA) 5 3.5 100 Shutdown Current vs Temperature 5 4.0 FB1 = 1V (CORE CONVERTER NOT SWITCHING) 50 75 0 25 TEMPERATURE (°C) 3456 G06 No Load Battery Supply Currrent vs Temperature 7 6 –25 3456 G05 No Load Battery Supply Current vs Battery Voltage 0 1.6 5.25 VBATT = 2.4V 1050 900 800 1.6 1000 3456 G02 1200 1000 10 100 LOAD CURRENT (mA) 1 Oscillator Frequency vs VEXT Voltage 1050 1.8V OUTPUT 3.3V OUTPUT 10 3456 G02 Oscillator Frequency vs Battery Voltage FREQUENCY (kHz) 60 PWM MODE Burst Mode OPERATION VBATT = 2.4V VMAIN = 3.3V 10 1000 VUSB = 5V VUSBHP = 2V 30 3456 G01 BATTERY SUPPLY CURRENT (mA) Efficiency (USB Powered) 100 EFFICIENCY (%) EFFICIENCY (%) Core Converter Efficiency (Battery Powered) 4 3 2 1 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 3456 G09 3456f 5 LTC3456 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified. VBATT Pin Current when USB or Wall Powered 2.0 3 2 1 0 –50 –25 75 0 25 50 TEMPERATURE (°C) 100 800 FB1 = 1V CORE CONVERTER NOT SWITCHING 1.6 700 1.2 0.8 0.4 0 125 4 4.25 4.5 4.75 VEXT (V) 5 5.25 850 825 800 775 100 VEXT = 5V 550 525 500 475 450 700 0 50 75 25 TEMPERATURE (°C) 100 150 125 100 75 50 2.2 2.4 2.6 VBATT (V) 2.8 100 75 50 3 3.2 3456 G16 0 50 75 25 TEMPERATURE (°C) 100 3456 G15 600 L = 4.7µH (BATTERY POWERED) 600 500 400 300 100 1.8 125 Maximum VCORE Load Current Capability (Output 4% Below Regulation) L = 10µH (BATTERY POWERED) 500 VCORE = 1.5V VCORE = 1.8V 400 300 200 100 200 25 2 125 0 – 50 – 25 125 VCORE LOAD CURRENT (mA) PWM MODE OPERATION Burst Mode OPERATION (RESISTOR LOAD) 0 1.8 150 Maximum VMAIN Load Current Capability (Output 4% Below Regulation) VMAIN LOAD CURRENT (mA) VINT LOAD CURRENT (mA) 175 VBATT = 2.4V 3456 G14 VINT Load Current vs Start-Up Battery Voltage 125 25 400 – 50 – 25 125 100 175 3456 G13 200 50 25 75 0 TEMPERATURE (°C) Hot Swap (HSO) Current Limit 200 425 50 75 25 TEMPERATURE (°C) 400 3456 G12 HSO CURRENT LIMIT (mA) 875 VBATT = 2.4V 200 –50 –25 5.5 575 SW2_BK CURRENT LIMIT (mA) SW2_BST CURRENT LIMIT (mA) VBATT = 2.4V 925 0 500 SW2_BK Current Limit 600 900 VEXT = 5V 3456 G11 SW2_BST Current Limit 750 – 50 – 25 600 300 3456 G10 950 SW1 Current Limit SW1 CURRENT LIMIT (mA) VEXT = 5V VEXT SUPPLY CURRENT (mA) VBATT PIN CURRENT (µA) 4 No Load VEXT Suppy Current when USB or Wall Powered 2 2.2 2.4 2.6 VBATT (V) 2.8 3 3.2 3456 G17 0 1.8 2 2.2 2.4 2.6 VBATT (V) 2.8 3 3.2 3456 G18 3456f 6 LTC3456 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified. Maximum VCORE Load Current Capability (Output 4% Below Regulation) 500 500 400 300 USB Undervoltage Lockout 4.10 L = 10µH (USB/WALL POWERED) 4.05 400 USB VOTLAGE (V) L = 10µH (USB/WALL POWERED) VMAIN LOAD CURRENT (mA) VCORE LOAD CURRENT (mA) 600 Maximum VMAIN Load Current Capability (Output 4% Below Regulation) 300 RISING 4.00 3.95 FALLING 3.90 200 3.85 100 200 4 4.25 4.5 4.75 VEXT (V) 5 5.25 4 5.5 4.25 4.5 4.75 VEXT (V) 5 5.25 USB Current Limit 125 WALLFB Trip Point 1.28 0.820 450 0.815 USBHP = 2V 400 0.805 AIN (V) 300 250 200 WALLFB VOLTAGE (V) 0.810 350 VEXT = 5V 0.800 0.795 VBATT = 2.4V 150 0.790 USBHP = 0V 1.26 RISING 1.24 FALLING 1.22 0.785 50 VUSB = 5V 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 0.780 – 50 – 25 0 50 75 25 TEMPERATURE (°C) 100 3456 G22 1.20 –50 125 –25 75 0 25 50 TEMPERATURE (°C) 4.50 3.5 VMAX Output Voltage (USB/Wall Powered) 6 PWRON = 2V 3.0 VMAX OUTPUT CURRENT = 0.5mA 5 4.25 PWRON = 0V, 2V 2.5 4 FALLING VMAX (V) VMAX (V) PWRON = 0V RISING 125 3456 G24 VMAX Output Voltage (Battery Powered) 4.00 100 3456 G23 VEXT Undervoltage Lockout VEXT (V) 100 3456 G21 AIN Pin Reference Voltage 500 100 50 25 75 0 TEMPERATURE (°C) 3456 G20 3456 G19 USB CURRENT LIMIT (mA) 3.80 –50 –25 5.5 2.0 1.5 3 2 1.0 3.75 1 0.5 3.50 –50 –25 75 0 25 50 TEMPERATURE (°C) 100 125 3456 G25 VMAX OUTPUT CURRENT = 0.5mA 0 1.6 1.8 2 2.2 2.4 2.6 2.8 VBATT (V) 0 3 3.2 3456 G26 4 4.25 4.5 4.75 VEXT (V) 5 5.25 5.5 3456 G27 3456f 7 LTC3456 U W TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified. Switching Waveforms (Battery Powered) Switching Waveforms (Wall/USB Powered) IL1 50mA/DIV IL1 200mA/DIV VSW1 5V/DIV VSW1 5V/DIV IL2 200mA/DIV VSW2_BST 5V/DIV IL3 100mA/DIV VSW2_BK 5V/DIV VBATT = 2.4V VPWRON = 2V ICORE = 100mA IMAIN = 100mA 0.5µs/DIV VEXT = 5V VPWRON = 2V ICORE = 100mA IMAIN = 100mA 3456 G28 USB ↔ Battery Switchover (Main Converter Transient Waveforms) 0.5µs/DIV 3456 G29 USB ↔ Battery Switchover (Core Converter Transient Waveforms) VCORE 100mV/DIV (AC COUPLED) VMAIN 100mV/DIV (AC COUPLED) IL2 200mA/DIV IL1 100mA/DIV IL3 100mA/DIV SUSPEND 5V/DIV SUSPEND 5V/DIV VUSB = 5V VUSBHP = 5V VBATT = 2.4V ICORE = 100mA IMAIN = 100mA 200µs/DIV VUSB = 5V VUSBHP = 5V VBATT = 2.4V ICORE = 100mA IMAIN = 100mA 3456 G30 200µs/DIV 3456 G31 Power Supply Sequencing (Battery Powered) Power Up/Power Down Sequencing (Battery Powered) VPWRON 5V/DIV VMAIN 5V/DIV VPWRON 5V/DIV VCORE 2V/DIV VCORE 2V/DIV RESET 5V/DIV VMAIN 5V/DIV VINT 5V/DIV VBATT = 2.4V ICORE = 10mA IMAIN = 10mA 100ms/DIV 3456 G32 VBATT = 2.4V ICORE = 5mA 200µs/DIV 3456 G33 3456f 8 LTC3456 U U U PI FU CTIO S AIN (Pin 1): Low-Battery Detector Input Pin. The detector compares the voltage on this pin to an 800mV reference. Connect the resistor divider tap to this pin to set the lowbattery trip point. AO (Pin 2): Open-Drain Digital Output. This open-drain logic output is pulled to GND whenever the AIN pin voltage falls lower than 0.8V. AGND (Pin 3): Analog Ground. All resistor dividers should be connected to this pin. VBATT (Pin 4): Battery Input Supply. The input voltage at this pin can range from 1.8V to 3.2V. Must be locally bypassed with a 1µF (or greater) X5R or X7R type ceramic capacitor. SW1 (Pin 5): Switch Pin for Core Regulator. Connect the inductor between SW1 and the output capacitor. Keep these PCB trace lengths as short and wide as possible to reduce EMI. PGND (Pin 6): Power Ground. This is the ground pin for all internal drivers and switches. Provide a short PCB path between PGND and PCB system ground. WALLFB (Pin 7): Wall Feedback Pin. This pin receives the feedback voltage from an external resistor divider across the AC wall adapter input. When the pin voltage is higher than 1.25V, the chip is powered from the VEXT pin and the USB switch is turned off. Ensure that the resistor ratio is set so that the wall adapter voltage (min) is still high enough to make VEXT > 4V. Connect to ground if not used. EXT_PWR (Pin 8): External Power Good Pin. This opendrain logic output is pulled to GND whenever the WALLFB pin is pulled higher than 1.25V or the USB pin voltage is greater than 4V and SUSPEND is low. Essentially this pin is pulled low whenever the AC adapter or the USB power is present. When pulled low, this pin is capable of sinking 5mA suitable for driving an external LED. VEXT (Pin 9): External Power Pin. This pin is connected to the USB pin via an internal 0.5Ω (typ) PMOS switch. The AC wall adapter can be connected to this pin through a Schottky diode. An onboard voltage detector prevents the IC from drawing power from this pin until the pin voltage rises above 4V. The voltage detector for VEXT has built-in 150mV hysteresis. Connect a 10µF X5R or X7R type ceramic capacitor from this pin to ground. USB (Pin 10): USB Input Supply. Input current into this pin is limited to either 100mA or 500mA based on the state of the USBHP pin. When the USB pin voltage is greater than 4V and SUSPEND is low, and WALLFB is less than 1.25V, USB is connected to the VEXT pin via an internal 0.5Ω current limited PMOS Switch. Connect a 4.7µF (X5R or X7R type) ceramic capacitor in series with a 1Ω resistor from this pin to ground. VMAX (Pin 11): Maximum Supply Voltage Pin. A special internal PowerPathTM controller monitors the VBATT, VINT, VEXT and USB voltages and passes the highest available supply voltage to the VMAX pin. This pin is used to power some of the internal circuitry of the IC. Connect a 1µF bypass capacitor from this pin to ground. It can be used to supply a maximum of 1mA output load. The VMAX output voltage stays alive even when the IC is in shutdown. USBHP (Pin 12): USB High Power Select Pin. This pin is used to set the USB current limit. Pull high to select 500mA current limit (High Power mode); low to select 100mA current limit (Low Power mode). This pin has a weak pulldown current source to ensure that Low Power mode is in effect during start-up. SW2_BK (Pin 13): Switch Pin for Main Regulator (USB or Wall Powered). Connect the inductor between SW2_BK and the output voltage. Keep these PCB trace lengths as short and wide as possible to reduce EMI. SW2_BST (Pin 14): Switch Pin for Main Regulator (Battery Powered). Connect the inductor between SW2_BST and VBATT. Keep these PCB trace lengths as short and wide as possible to reduce EMI. VINT (Pin 15): Internal Supply Voltage Pin. The VINT voltage is regulated to 3.3V. This pin is used to power most of the internal circuitry of the IC. Do not load this output. Connect an output capacitor from this pin to ground. VMAIN (Pin 16): Main Regulator Output Voltage. An internal 0.4Ω PMOS switch connects this pin to the VINT pin 0.8ms (typ) after the Core voltage comes into regulation. This ensures that VMAIN will always power up after Core output during start-up. Connect an output capacitor from this pin to ground. PowerPath is a trademark of Linear Technology Corporation. 3456f 9 LTC3456 U U U PI FU CTIO S HSO (Pin 17): Hot Swap Output. An internal 0.8Ω current limited PMOS switch connects this pin to the VINT pin 0.5ms after the core voltage comes into regulation. The nominal voltage at this pin is 3.3V. It is short-circuit protected and the current out of this pin is limited to 120mA (typ). SUSPEND (Pin 18): USB Suspend Pin. Pull this pin high to disable all USB functionality. The USB switch connected between USB and VEXT behaves like a back-to-back diode whenever SUSPEND is pulled high. In Suspend mode the device limits the current drawn from the USB port to 100µA (typ). PWRKEY (Pin 19): Power ON/OFF Key. Connecting this pin to GND will turn on the IC. This pin is typically used with a momentary-on pushbutton switch to turn on the LTC3456. This pin must be held low until the PWRON pin is pulled high (usually from a microprocessor) in order to keep the IC turned on. This pin has a 400k pull-up resistor to VMAX. PBSTAT (Pin 20): Power ON/OFF Key Status Pin. This open-drain output pin indicates the state of the PWRKEY pin to the microcontroller. The pin output follows the state of the PWRKEY pin (PBSTAT goes low when PWRKEY is pulled low). PWRON (Pin 21): Power On Pin. When pulled high this microprocessor controlled pin turns on the IC. This pin has a weak 1µA pull-down current source. MODE (Pin 22): Burst Mode Select Pin. Tie this pin high to allow automatic Burst Mode operation. Burst Mode operation will provide superior efficiency when any of the outputs are operating with very low output currents. Tie this pin low to force PWM operation under all load current conditions. The device operates in forced PWM mode when powered from USB or wall input (irrespective of the state of the MODE pin). Furthermore, at initial power-up, the device operates in forced PWM mode during the 262ms internal delay timeout. This pin has a weak 1µA pull-down current source. RESET (Pin 23): Fault Indicator Output Pin. This opendrain output is active both at power-up and power-down. RESET is held low at initial power up. When both the Core and Main outputs come into regulation, an internal reset delay timer is activated. RESET is released at the end of the 262ms timeout. If either Main or Core outputs fall out of regulation during normal operation, RESET is pulled low. Also, RESET is pulled low at power-off to prevent spurious turn-on of the microprocessor. FB1 (Pin 24): Feedback Pin for the Core Regulator. The regulator drives the voltage at this pin to 0.8V. Connect the resistor divider tap to this pin. The output voltage of the core regulator can be adjusted from 0.8V to VBATT(MIN). Exposed Pad (Pin 25): The Exposed Pad must be soldered to the PCB system ground. 3456f 10 LTC3456 W BLOCK DIAGRA USB VEXT VINT VBATT R USB – +VOS 4V 4.7µF + – 1Ω EN USB CONTROLLER 18 12 11.3k AC ADAPTER 7 SUSPEND WALLFB 1.25V 4.32k USB CONTROL LOGIC USBHP 4V + – PowerPath CONTROLLER VMAX 1µF PWRKEY VEXT_RDY PBSTAT USB_RDY + – PWRON START-UP LOGIC MODE D1 RESET 1k 8 EXT_PWR TURN-ON SWITCHERS D2 VEXT 9 VEXT HSO 80.6k 1 100k 4 VBATT R AO – + 2 0.8V 19 20 21 22 23 262ms TIMER 10µF AO 11 VEXT AIN 1µF – VOS + PSWITCH VMAIN VBATT VMAIN 16 1µF 200k L1 10µH VCORE 5 SW1 625k VINT SW2_BST DRV 100k 24 10µF HSO 17 4.7µF 220pF MICROCONTROLLER 10 USB 0.8V FB1 80.6k 0.8V – + – + VINT 15 L2 4.7µH 22µF VBATT 14 DRV 4.7µF SW2_BK L3 10µH 13 AGND 3 PGND 6 3456 F01 Figure 1. LTC3456 Block Diagram 3456f 11 LTC3456 U OPERATIO INTRODUCTION OPERATING MODES The LTC3456 is a complete system-level power supply IC used to power GPS portable navigators and other portable systems. It takes power from one of three sources: battery, USB or wall adapter. The device provides an integrated standard solution resulting in a reduced parts count and higher efficiency. The LTC3456 is powered from an AC wall adapter, USB or battery, in that order of priority. It has onboard voltage detectors to monitor the status of the wall adapter and USB voltages. The unique control scheme of the LTC3456 allows seamless transition between battery, USB and wall adapter input power sources. The LTC3456 generates two separate power supplies: a Core supply for the processor and a Main supply for the peripheral circuitry. The Main supply is a fixed 3.3V output and the Core supply voltage can be adjusted from 0.8V to VBATT(MIN). In addition, the LTC3456 provides a Hot Swap output which can be used for powering flash memory cards. Both regulators utilize a 1MHz constant frequency current mode architecture. Battery Powered The LTC3456 is designed to accept an input battery voltage range from 1.8V to 3.2V. This range is ideal for 2-cell Alkaline, NiCd or NiMH designs. Figure 2 shows an LTC3456 being powered from two AA cells. When enabled, the internal supply voltage VINT (3.3V) is generated via the boost regulator. VINT is used to power the bandgap reference, drivers and other internal circuitry. Core output (1.8V) comes up next via the buck regulator. Main output and the Hot Swap output are powered up with a delay after the core output is in regulation. The device also incorporates a low-battery detector (configurable as a low dropout regulator), USB power manager and several protection features in a single package. The LTC3456’s control scheme allows 100% duty cycle operation for the core output. It provides low dropout operation when the core output is powered from the battery, thereby extending battery life. LTC3456 VBATT 2 AA CELLS 1.8V TO 3.2V 4 VBATT BUCK SW1 L1 10µH 5 + 10µF L2 4.7µH 14 SW2_BST BOOST VINT 15 22µF VMAIN R HSO VINT 3.3V 1µF MAIN OUTPUT 3.3V 150mA 1µF Hot Swap OUTPUT 3.3V 50mA 16 17 – +VOS CORE OUTPUT 1.8V 200mA 3456 F02 Figure 2. Battery-Powered LTC3456 3456f 12 LTC3456 U OPERATIO AC Wall Adapter Powered will draw all its power from the AC adapter via the VEXT pin. The WALLFB voltage should always be kept below 2V. The LTC3456 can be powered off the AC wall adapter as shown in Figure 3. The wall adapter is connected to the VEXT pin via the diode D1. When enabled, the onboard voltage detector checks the status of the VEXT voltage. If the VEXT pin voltage is greater than 4V, the VINT, Core output, Main output and Hot Swap outputs power-up in that sequence. The status of the AC wall adapter power is monitored through the WALLFB pin. The nominal voltage at this pin is 1.25V. When the pin voltage is higher than 1.25V, the IC 4V VEXT 9 – + LTC3456 L1 10µH EN VEXT BUCK 1 SW1 5 10µF 10µF BUCK 2 D1 SW2_BK VINT AC ADAPTER 5V ±5% WALL_RDY 11.3k 7 4.32k L3 10µH 13 22µF VINT 3.3V 15 1µF MAIN OUTPUT 3.3V 150mA 1µF Hot Swap OUTPUT 3.3V 50mA 16 + – VMAIN CORE OUTPUT 1.8V 200mA WALLFB 1.25V R HSO 17 – +VOS 3456 F03 Figure 3. AC Adapter-Powered LTC3456 3456f 13 LTC3456 U OPERATIO USB Powered Pulling the SUSPEND pin logic high disables all USB functionality. The USB switch connected between USB and VEXT behaves like a back-to-back diode whenever SUSPEND is pulled high. In Suspend mode the device limits the current drawn from the USB pin to 100µA (typ). The LTC3456 is designed to be powered from the USB as shown in Figure 4. The LTC3456 has an internal currentlimited 0.5Ω (typ) PMOS switch with preset 0.1A and 0.5A current limits. The LTC3456 interfaces with the USB controller bus via logic pins USBHP and SUSPEND. The minimum voltage to a USB-powered device may drop as low as 4.35V due to cable and connector drops. The LTC3456 has an internal voltage monitor that checks the USB supply voltage and cuts off the USB power if the USB voltage falls below 4V. There is 75mV of hysteresis builtin the USB voltage monitor. The USBHP pin is used to set the USB current limit to either 100mA or 500mA. This pin has a weak 2.5µA pull-down current source to ensure that Low Power mode is in effect during start-up. If the USBHP pin is held low, it limits the input power drawn from the USB port. The USB port can supply the Core output (1.8V at 200mA) effortlessly in Low Power mode (USBHP = 0V). However, the loading on the 3.3V output must be held below 100mA (typ) when the USB is in low power mode. If the loading on 3.3V output is increased beyond 100mA (typ), the USB port is unable to supply the load current and the LTC3456 will switch between the battery and the USB port. This results in undesirable switching noise and increased voltage ripple at the 3.3V output. 4V VEXT 9 – + When the IC is enabled, the USB pin is connected to the VEXT pin via the PMOS switch. The VEXT pin gets charged by the preset 0.1A or 0.5A current limit determined by the state of the USBHP pin. As the VEXT pin voltage rises above 4V, the VINT, Core output, Main output and Hot Swap outputs power-up in that sequence. LTC3456 EN VEXT SW1 BUCK 1 L1 10µH 5 10µF 10µF BUCK 2 500mA 100mA USBHP 12 SUSPEND 18 USB 4.35V TO 5.5V 10 VINT USBHP VMAIN SUSPEND USB 4.7µF 1Ω SW2_BK 4V R + – USB_RDY HSO L3 10µH 13 22µF CORE OUTPUT 1.8V 200mA VINT 3.3V 15 1µF MAIN OUTPUT 3.3V 150mA 1µF Hot Swap OUTPUT 3.3V 50mA 16 17 – +VOS 3456 F04 Figure 4. USB-Powered LTC3456 3456f 14 LTC3456 U OPERATIO MAIN REGULATOR PWRON 5V/DIV VINT Output The main regulator produces a fixed 3.3V output from a 1.8V to 3.2V input (2-cell battery), USB port or AC adapter input supply. The main regulator output, VINT, is used to power most of the internal circuitry of the IC. It is the first one to power-up. Connect a 22µF or higher X5R or X7R type ceramic capacitor from this pin to ground. The loading on this output should be limited to 20mA. Refer to the Minimum Start-Up Battery Voltage vs VINT Output Current graph in the Typical Performance Characteristics. When the IC is turned off, the VINT output voltage is discharged to ground. Output Disconnect and Inrush Limiting The LTC3456 allows true output disconnect when powered off the battery (boost topology). It achieves this by disconnecting the body diode of the synchronous PMOS switch from the output. This allows the VINT to go to ground during shutdown. Do not connect a Schottky diode from SW2_BST to VINT; doing so will defeat the output disconnect feature. The LTC3456 also features inrush current limiting at power-up (battery powered). Inrush current in boost converters is important when powering from input sources with high input impedance like alkaline cells. The LTC3456 incorporates an inrush current limiting scheme that regulates the inrush current to 600mA (typ) during power-up. Figure 5 shows inrush current when the device is powered up from the battery. Short-Circuit Protection The LTC3456 features short-circuit protection for the main regulator output. When the main regulator is powered from the USB or wall input, it operates in a buck topology. VINT 2V/DIV IL2 500mA/DIV VBATT = 2.4V IVINT = 10mA 100µs/DIV 3456 F05 Figure 5. Inrush Current at Power-Up (Battery Powered) If the main regulator outputs (VINT or VMAIN) are shorted to ground, the LTC3456 unique control scheme prevents inductor current runaway. When the device is powered from the battery, it operates in a boost topology. Most boost converters do not allow their outputs to be shorted to ground. However, the LTC3456 allows the output of its main regulator (VINT or VMAIN) to be short-circuited due to its unique inrush current limiting. In the event of a short-circuit, the input current is well regulated. VMAIN Output The LTC3456 is designed to supply power to the microprocessor peripheral circuitry in a controlled manner. The peripheral circuitry should be connected to the VMAIN output. VMAIN is connected to VINT via a 0.4Ω (typ) PMOS switch 0.8ms (typ) after the Core output comes into regulation. This ensures that the peripheral circuitry always powers up after the microprocessor. The VMAIN output is discharged to ground through internal pull-down resistors at shutdown. This ensures that the peripheral circuitry gets turned-off completely during shutdown. Connect a 1µF (X5R or X7R) bypass capacitor from this pin to ground. 3456f 15 LTC3456 U OPERATIO Hot Swap Output CORE REGULATOR The LTC3456 is designed to supply power to flash memory cards. It has a built-in Hot Swap output, HSO, which allows memory cards to be hot swapped into and out of the system. The Hot Swap output features short-circuit and reverse-voltage blocking protection. Connect a 1µF (X5R or X7R) bypass capacitor from this pin to ground. The core regulator produces a 0.8V to 1.8V adjustable output from a 1.8V to 3.2V input (2-cell battery), USB port or AC adapter supply. The core regulator utilizes a synchronous N-channel MOSFET, improving efficiency and eliminating the need for an external Schottky diode. The core output voltage is measured at the FB1 pin through a resistive divider network. The nominal voltage at the FB1 pin is 0.8V. The divider can be adjusted to set the output voltage level. The FB1 voltage should always be kept below 2V. After the VINT and Core output voltages come into regulation, the HSO pin is connected to VINT via a 0.8Ω (typ) PMOS switch after a delay of 0.5ms. The PMOS switch has a 120mA built-in current limit. When a flash memory card is plugged into the system, the input bypass capacitors are slowly charged up to 3.3V with the preset 120mA current limit. Figure 6 shows the switching waveforms with Hot Swap output short-circuited. As seen in the figure, the shortcircuited current out of the HSO pin is well regulated. The LTC3456 also features reverse-voltage blocking capability for the HSO pin. In the event the HSO pin voltage rises greater than 3.3V (VINT pin voltage), the internal PMOS switch is turned off and behaves like a back-to-back diode. During shutdown, the Hot Swap output is discharged to ground via internal pull-down resistors. VINT 100mV/DIV (AC COUPLED) The LTC3456 internal soft-start circuitry limits current drawn at start-up. Soft-start is essential for input sources with high input impedance like alkaline cells. Soft-start is implemented by ramping up the current limit. At start-up, the current limit is set to 25% and increased by 25% every 256µs. The final inductor current limit is reached after 1ms. When the core regulator is turned off, the output voltage VCORE is discharged to ground. This is accomplished by pulling the switching node, SW1, to ground through the internal pull-down resistors. IL2 500mA/DIV VHSO 5V/DIV VINT 100mV/DIV (AC COUPLED) IL3 500mA/DIV VHSO 5V/DIV IHSO 200mA/DIV IHSO 200mA/DIV VBATT = 2.4V VPWRON = 2V 2ms/DIV 3456 F06a Figure 6a. Short-Circuit at the Hot Swap Output (Battery Powered) VEXT = 5V VPWRON = 2V 2ms/DIV 3456 F06b Figure 6b. Short-Circuit at the Hot Swap Output (Wall/USB Powered) 3456f 16 LTC3456 U OPERATIO The LTC3456 incorporates additional features like output short-circuit protection and thermal regulation. When the core regulator output (VCORE) is shorted to ground, the LTC3456’s unique control scheme prevents inductor current runaway. Dropout Operation The LTC3456 is capable of operating at 100% duty cycle when powered from the battery. If the input supply voltage decreases to a value close to the output voltage, the core regulator will run at 100% duty cycle. The output voltage is then determined by the input voltage minus the voltage drop across the PMOS switch and the inductor. When running off the USB or the AC adapter, this situation never arises (there is plenty of voltage headroom). When the LTC3456 operates with low input supply voltage, say 1.8V (fully discharged two AA cells) the maximum allowable output current gets reduced. Figure 7 shows the reduction in the maximum output current as a function of input voltage for various output voltages. VCORE LOAD CURRENT (mA) 600 L = 10µH (BATTERY POWERED) 500 VCORE = 1.5V VCORE = 1.8V 400 300 200 100 0 1.8 2 2.2 2.4 2.6 VBATT (V) 2.8 3 3.2 3456 G18 Figure 7. Maximum Output Current vs Battery Voltage VMAX OUTPUT A special internal PowerPath controller monitors the VBATT, VINT, VEXT and USB voltages and passes the highest available supply voltage to the VMAX pin. This pin is used to power some of the internal circuitry of the IC. Connect a 1µF bypass capacitor from this pin to ground. It can be used to supply a maximum of 1mA output load. The VMAX output voltage stays alive even when the IC is in shutdown. During shutdown, the VMAX output will be the highest of VBATT, VEXT and USB voltages. VMAX output can be used to supply power to a critical block like the real-time clock, which needs to stay alive even during shutdown. POWER SEQUENCING Power On/Off The LTC3456 can turned on in two different ways: • Pulling the PWRKEY pin low • Pulling the PWRON pin high Pulling the PWRKEY pin low is usually the first step in turning on the LTC3456. When PWRKEY is pulled low, it powers on the bandgap reference. Onboard voltage monitors check the status of the AC adapter and USB supply. The IC is powered from either the AC adapter, USB or the battery, in that order of preference. The VINT voltage powers up, followed by the Core, Main and Hot Swap outputs. At initial power up, the RESET pin is held low. When the Core output comes into regulation, the RESET timer is started. After a 262ms timeout, the RESET pin is released. This allows the microprocessor to turn on. The microprocessor in turn pulls PWRON high. After the PWRON pin is pulled high, the PWRKEY pin can be released. There is a 400kΩ pull-up resistor on the PWRKEY pin. The PWRKEY pin serves the dual purpose of turning on and off the IC. During regular operation, if PWRKEY is pressed low, the microprocessor detects this by monitoring the status of PBSTAT pin. The PBSTAT pin goes low whenever the PWRKEY pin is pulled low. The microprocessor then goes into shutdown mode and pulls the PWRON pin low. This results in powering off the LTC3456. Figure 8 shows the device power-on/power-off sequence. 3456f 17 LTC3456 U OPERATIO PWRKEY PWRKEY PULLED LOW PWRKEY RELEASED VCORE RESET 262ms TIMEOUT PWRON PBSTAT 3456 F08 POWER-ON SEQUENCE POWER-OFF SEQUENCE Figure 8. Power-On/Power-Off Sequence RESET The LTC3456 contains a RESET circuitry that is active during both power-up and shutdown. The RESET pin is held low during initial power-up. When both the VINT and Core outputs come into regulation, a reset delay timer gets activated. There is a full 262ms timeout before RESET is released. During power-off mode RESET is pulled low. This prevents the microprocessor from entering into any spurious operating mode. MODE The LTC3456 has a user selectable MODE pin. When the MODE pin is pulled logic high and the LTC3456 is battery powered, the device will automatically enter into Burst Mode operation under light load current situations. If the load current in either of the regulators falls below a predetermined value, the regulator will enter into Burst Mode operation independent of the other regulator. When the MODE pin is connected to ground, continuous PWM operation is selected. It provides the lowest output voltage ripple and current ripple, albeit at the cost of lower efficiency under light load conditions. The Burst Mode operation is disabled when the device is USB or wall powered. The device operates in forced PWM mode when powered from USB or wall input (irrespective of the state of the MODE pin). Also, at initial power up, the device operates in forced PWM mode during the 262ms initial delay timeout. Figure 9 shows the Main and Core converters in Burst Mode operation. VMAIN 100mV/DIV (AC COUPLED) IL2 500mA/DIV VCORE 100mV/DIV (AC COUPLED) IL1 100mA/DIV VBATT = 2.4V IMAIN = 37.5mA ICORE = 6.2mA 20µs/DIV 3456 F09 Figure 9. The LTC3456 in Burst Mode Operation 3456f 18 LTC3456 U OPERATIO VOLTAGE MONITORS Low-Battery Detection The LTC3456 has an on-chip gain block that can be used for low-battery detection. The low-battery trip point can be set by two resistors (Figure 10). The nominal voltage at AIN is 0.8V. If the voltage at AIN falls below 0.8V, AO sinks current to ground. The battery minimum voltage can be set according to the formula: The gain block can be configured to drive an external PNP transistor and generate an auxiliary voltage as shown in Figure 11. An auxiliary output voltage 2.5V/20mA is generated from the VMAIN (3.3V) power supply. VMAIN 3.3V 100k LTC3456 AIN Q1 PHILIPS MMBT3906 AO 43.2k ⎛ R2 ⎞ VBATT(MIN) = 0.8 V⎜ 1 + ⎟ ⎝ R1⎠ The AIN input bias current is quite low, on the order of 2nA (typ). Large resistor values (R2 ~ 100k) can be used in the divider network. This helps in minimizing the loading on the battery. AO is an open-drain logic output. The voltage at AIN must always be kept less than 2V. If the gain block is not used then connect AIN to ground. There is no built-in hysteresis in the gain block. Hysteresis can be added by connecting resistor R4 from AIN to AO as shown in Figure 10. Ensure that R4 ≅ 10R3 for correct operation. With the values shown in Figure 10b, the circuit has 180mV of hysteresis. VBATT 1.8V TO 3.2V R2 100k VCORE LTC3456 AIN R3 100k AO R1 80.6k (10a) VBATT R2 100k VCORE LTC3456 AIN R3 100k VAUX 2.5V 20mA 2.2µF 20.5k 3456 F11 Figure 11. Generating Auxiliary Voltage Supply External Power Detection The LTC3456 has an EXT_PWR output pin to indicate the presence of USB or wall power. Whenever the WALLFB pin is pulled higher than 1.25V (AC adapter present), or the USB input is greater than 4V and the SUSPEND pin is low (USB power available), the EXT_PWR pin is pulled to ground. When pulled low, this pin is capable of sinking 5mA suitable for driving an external LED. Otherwise, this pin is in a high impedance state. Overtemperature Protection The maximum allowable junction temperature for LTC3456 is 125°C. In normal operation, the IC does not dissipate much heat and its junction temperature stays well below 125°C at an ambient temperature of 85°C or less. If the junction temperature exceeds 150°C, the Core, Main and Hot Swap outputs are turned off and RESET is pulled low. AO R1 80.6k R4 1M 3456 F10 (10b) The VINT output stays alive in this state. The Core and Main outputs will remain off until the die temperature falls below 150°C, regardless of the state of the PWRKEY and PWRON inputs. Figure 10. Low-Battery Detector (10a) and Low-Battery Detector with Hysteresis (10b) 3456f 19 LTC3456 U W U U APPLICATIO S I FOR ATIO COMPONENT SELECTION Inductor Selection The high frequency operation of LTC3456 allows the use of small surface mount inductors. For most applications, the inductance value will be between 2.2µH and 10µH. The desired value of inductance is determined by the amount of ripple current, ∆IL, in the converter. The inductor current ripple, ∆IL, for Boost mode operation neglecting the voltage drop across the switches is given by: ∆IL = VIN • ( VOUT – VIN ) VOUT • f • L The inductor current ripple, ∆IL, for Buck mode operation neglecting the voltage drop across the switches is given by: ∆IL1 = VOUT • ( VIN – VOUT ) VIN • f • L where L = Inductor f = Operating Frequency VIN = Input Voltage VOUT = Output Voltage The ∆IL is typically set to 20% to 40% of the maximum inductor current. The inductor should have a saturation current rating greater than the peak inductor current required for the application. Also, ensure that the inductor has a low DCR (copper wire resistance) to minimize I2R power losses. Several inductors that work well with the LT3456 are listed in Table 1. Consult each manufacturer for more detailed information and for their entire selection of related parts. Table 1. Recommended Inductors PART L (µH) MAX DCR (Ω) CURRENT RATING (mA) ELT5KT-4R7 ELT5KT-100 4.7 10 0.2 0.36 950 680 Panasonic (714) 373-7939 www.panasonic.com CDRH4D18-4R7 CDRH4D18-100 4.7 10 0.16 0.2 840 610 Sumida (847) 956-0666 www.sumida.com LQH32CN4R7 LQH32CN100 4.7 10 0.15 0.3 650 450 Murata (814) 237-1431 www.murata.com 1002AS-4R7M 1002AS-100M 4.7 10 0.19 0.32 910 620 Toko (800) 745-8656 www.toko.com VENDOR Output Capacitor Selection Low ESR (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. Multilayer ceramic capacitors are an excellent choice, as they have an extremely low ESR and are available in very small packages. Use only X7R or X5R dielectrics, as these materials retain their capacitance over wider voltage and temperature ranges than other dielectrics. A 1µF to 22µF output capacitor is sufficient for most applications. Solid tantalum or OS-CON capacitors can be used, but they will occupy more board area than a ceramic and will have a higher ESR for the same device footprint. Always use a capacitor with a sufficient voltage rating. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information on their entire selection of ceramic parts. Table 2. Ceramic Capacitor Manufacturers Taiyo Yuden (408) 573-4150 www.t-yuden.com AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com TDK (847) 803-6100 www.component.tdk.com 3456f 20 LTC3456 U W U U APPLICATIO S I FOR ATIO 0.8V ≤ VCORE ≤ VBATT(MIN) Input Capacitor Selection R2 The LTC3456 can be powered from three different power sources: battery, USB or the AC wall adapter. Choose a 4.7µF or higher X5R or X7R type ceramic capacitor for bypassing the input of LTC3456. FB1 R1 LTC3456 AGND 3456 F13 However, special care must be taken when bypassing the USB and AC wall adapter inputs with ceramic capacitors. Ceramic capacitors with their low ESR can form a resonant tank circuit with the stray wiring inductance of the power leads. This can cause large voltage transients at the input of the device when the power is applied quickly (for example, plugging the AC adapter output into the portable device). This voltage spike can be large enough to damage the LTC3456. A possible solution is to clamp the input voltage or insert a small resistor in series with the ceramic capacitor as shown in Figure 12. Please refer to Linear Technology Application Note AN88 for more details. USB INPUT USB 1Ω 4.7µF AC ADAPTER LTC3456 VEXT 1Ω 10µF 3456 F12 4.7µF Figure 13. Setting the Core Output Voltage AC Adapter UVLO Voltage Programming The AC wall adapter UVLO voltage can be set by a resistor divider connected across the AC wall adapter as shown in Figure 14. The AC wall adapter UVLO voltage can be set by a resistor divider according to the formula: ⎛ R2 ⎞ VADAPTER(MIN) = 1.25V⎜ 1 + ⎟ ⎝ R1⎠ Choose 1% resistors for better accuracy. When the WALLFB pin voltage is higher than 1.25V, the LTC3456 will be powered from the VEXT pin. The internal USB power switch is turned off and the power is derived from the AC adapter through the diode D1. Ensure that the AC adapter UVLO voltage is set high enough to make VEXT > 4V during regular operation. Figure 12. Bypassing USB and AC Wall Adapter Inputs Output Voltage Programming The output of the core converter can be set by a resistor divider according to the formula: ⎛ R2 ⎞ VCORE = 0.8 V⎜ 1 + ⎟ ⎝ R1⎠ The external resistor divider is connected at the output as shown in Figure 13. Choose 1% resistors for better accuracy. R1 should be 80.6k or smaller for better noise immunity. LTC3456 USB USB POWER 1Ω EN 4.7µF D1 VEXT AC ADAPTER R2 10µF WALLFB R1 3456 F14 Figure 14. Setting the Wall Adapter UVLO Voltage 3456f 21 LTC3456 U W U U APPLICATIO S I FOR ATIO When the device is powered from the USB input (AC adapter is not present), the VEXT pin is charged close to the USB voltage. The reverse leakage current of the diode D1 flows through R1 and R2 as shown in Figure 15. If the leakage current is large enough to pull the WALLFB pin above 1.25V, then the USB power is switched off. The LTC3456 will then enter into a hiccup mode with USB power being turned on and off in a periodic fashion. A 4.32k or smaller resistor should be chosen for R1 to prevent this behavior. When the power is being delivered from the wall adapter, efficiency is not a big concern and choosing small value R1 and R2 resistors should be acceptable. Connect the WALLFB pin to ground if the wall adapter is not used. Rectifier Diode Selection The diode, D1, shown in Figures 14 and 15 is used to connect the VEXT pin to the AC adapter input. The IC is powered through the diode D1 when running off the AC adapter. A Schottky diode is recommended to minimize the voltage drop from the AC adapter to the VEXT pin. Always ensure that VEXT > 4V during regular operation. Choose a diode with a current rating high enough to handle the input current. Choose a Schottky diode with low reverse leakage current (as explained in previous section). ON Semiconductor MBRM120E (20V/1A) is a good choice for a low leakage Schottky rectifier. The Zetex ZLLS400 (40V/0.5A) Schottky diode is available in a small surface mount package and is also a good fit for this application. BOARD LAYOUT CONSIDERATION As with all switching regulators, careful attention must be paid to the PCB board layout and component placement. To prevent electromagnetic interference (EMI) problems, proper layout of high frequency switching paths is essential. Minimize the length and area of all traces connected to the switching node pins (SW1, SW2_BK, SW2_BST). Keep the feedback pins FB1 and AIN away from the switching nodes. The power traces shown as bold lines in Figure 16 should be kept short, direct and wide. VEXT(MIN) = VADAPTER(MIN) – VDIODE(MAX) LTC3456 USB USB POWER 1Ω EN 4.7µF D1 AC ADAPTER NOT PRESENT R2 ILKG 10µF VEXT WALLFB R1 3456 F15 Figure 15. Diode D1 Leakage Current Flow in USB Powered Mode 3456f 22 LTC3456 U W U U APPLICATIO S I FOR ATIO 2 AA + CELLS 4.7µF L2 4.7µH 100k VBATT 22µF L3 10µH SW2_BST SW2_BK AIN VINT 1µF MAIN OUTPUT 3.3V 150mA 1µF Hot Swap OUTPUT 3.3V 50mA 10µF CORE OUTPUT 1.8V 200mA 1µF VMAX (POWERS REAL-TIME CLOCK) VMAIN 80.6k AO USB POWER (4.35V TO 5.5V) 4.7µF HSO USBHP USB CONTROLLER L1 10µH SUSPEND 1Ω SW1 LTC3456 USB 1k 100k EXT_PWR AC ADAPTER (5V ±10%) 11.3k 220pF FB1 VEXT 4.7µF 80.6k 10µF 1Ω WALLFB 4.32k VINT 3.3V VMAX PWRKEY PBSTAT RESET MODE PWRON PGND AGND µP 3456 TA01 BOLD LINES INDICATE HIGH CURRENT PATHS Figure 16. Layout Diagram The QFN package has an exposed paddle and it must be connected to the system ground. The ground connection for the feedback resistors should be tied directly to the ground plane and not shared with any other component, ensuring a clean, noise-free connection. DESIGN EXAMPLE As a design example, we target a 2 AA cell powered GPS navigator application. Figure 17 shows LTC3456 being used to provide power to the core and I/O peripherals. The flash memory card is powered from the Hot Swap output. Core output needs to be 1.8V and the maximum load current is 200mA. The inductor current ripple, ∆IL, for buck mode of operation is given by: ∆IL1 = VOUT • ( VIN – VOUT ) VIN • f(L1) The maximum inductor current in L1 is set by the core converter current limit; i.e., 400mA (minimum). Choosing ∆IL = 100mA (~25% of peak inductor current) is a reasonable starting value. Substituting VOUT = 1.8V, VIN(MAX) = 3.2V, ∆IL1 = 100mA, f = 1MHz in above equation gives: L1 = 1.8 V • (3.2V – 1.8 V ) = 7.8µH 3.2V • 100mA • 1MHz We can choose a low resistance 7.8µH or slightly higher value inductor. We can choose a 450mA, 10µH inductor (Murata LQH32CN100). We need to check the ripple current when the core output is powered from the AC adapter or the USB. L1 is used to power the output in this case too. 3456f 23 LTC3456 U W U U APPLICATIO S I FOR ATIO Substituting VOUT = 1.8V, VIN(MAX) = 5.5V , L1 = 10µH, f = 1MHz in above equation gives: ∆IL1 = 1.8 V • (5.5V – 1.8 V ) = 120mA 5.5V • 10µH • 1MHz L1 gives a reasonable value of ripple current when powered from both battery and USB or AC adapter. The main output needs to be 3.3V and the maximum load current is 200mA. Hot Swap current is derived from the same main converter. When powered from the 2 AA cell, the 3.3V output is generated via the L2 boost inductor. The inductor current ripple, ∆IL2, for Boost mode operation is given by: ∆IL2 = VIN • ( VOUT – VIN ) VOUT • f(L2) A reasonable starting value of inductor ripple current is ∆IL2 = 150mA. Substituting VOUT = 3.3V, VIN(MIN) = 1.8V, ∆IL2 = 150mA, f = 1MHz in above equation gives: 1.8 V • (3.3V – 1.8 V ) L2 = = 5.4µH 3.3V • 150mA • 1MHz We can choose a low resistance 4.7µH, 650mA inductor (Murata LQH32CN4R7M53). When powered from the AC adapter or the USB, the 3.3V output is generated via the L3 buck inductor. The inductor current ripple (∆IL3) for Buck mode operation is given by: ∆IL3 = VOUT • ( VIN – VOUT ) VIN • f(L3) A reasonable starting value of inductor ripple current is ∆IL3 = 100mA. Substituting VOUT = 3.3V, VIN(MAX) = 5.5V, ∆IL3 = 100mA, f = 1MHz in above equation gives: L3 = 3.3V • (5.5V – 3.3V ) = 13.2µH 5.5V • 100mA • 1MHz We can choose a 450mA, 10µH inductor (Murata LQH32CN100K53). A 4.7µF to 22µF (X5R or X7R) ceramic output capacitor is sufficient for most applications. They have a low ESR and result in a low output ripple. Figure 17 shows the complete circuit along with the efficiency curves. 3456f 24 LTC3456 U W U U APPLICATIO S I FOR ATIO 2 AA CELLS + C1 4.7µF L3 10µH L2 4.7µH 100k VBATT C9 22µF SW2_BST SW2_BK VINT AIN VMAIN C8 1µF 80.6k AO USB POWER (4.35V TO 5.5V) C2 4.7µF 1Ω HSO USBHP USB CONTROLLER SW1 LTC3456 USB 1k D1 AC ADAPTER (5V ±10%) C3 4.7µF 1Ω C6 10µF 220pF 100k EXT_PWR MAIN OUTPUT 3.3V 150mA Hot Swap OUTPUT 3.3V 50mA CORE OUTPUT 1.8V 200mA FB1 VEXT C4 10µF 11.3k C7 1µF L1 10µH SUSPEND VINT 3.3V 80.6k WALLFB VMAX PWRKEY 4.32k C5 1µF PBSTAT RESET MODE PWRON PGND AGND µP C2 TO C5: X5R OR X7R, 6.3V C1, C6 TO C9: X5R OR X7R, 4V D1: ON SEMICONDUCTOR MBRM120E VMAX (POWERS REAL-TIME CLOCK) 3456 F17 L1, L3: MURATA LQH32CN100K53 L2: MURATA LQH32CN4R7M53 Figure 17. 2 AA Cells to 1.8V/200mA and 3.3V/200mA Outputs Using All Ceramic Capacitors with Lowest Parts Count Efficiency (USB Powered) Efficiency (Battery Powered) 100 VBATT = 2.4V 90 MODE = 0V POWER LOSS 20 3.3V OUTPUT 1.8V OUTPUT 10 0 1 10 100 LOAD CURRENT (mA) 100 50 0 1000 3456 TA01b VWALL = 5V 90 80 80 70 70 EFFICIENCY (%) EFFICIENCY 40 30 150 POWER LOSS (mW) 50 3.3V OUTPUT EFFICIENCY (%) 200 1.8V 70 OUTPUT 60 Efficiency (Wall Powered) 100 VUSB = 5V VUSBHP = 2V 90 80 EFFICIENCY (%) 100 250 60 50 40 60 50 40 30 30 20 20 1.8V OUTPUT 3.3V OUTPUT 10 0 1 10 100 LOAD CURRENT (mA) 1000 3456 G02 1.8V OUTPUT 3.3V OUTPUT 10 0 1 10 100 LOAD CURRENT (mA) 1000 3456 F17d 3456f 25 LTC3456 U TYPICAL APPLICATIO 2 AA Cells Power Complete Power Supply for Handheld Devices 2 AA CELLS + C1 4.7µF L2 4.7µH SW2_BST SW2_BK VINT VMAIN VBATT USBHP USB CONTROLLER C10 22µF L3 10µH C9 1µF MAIN OUTPUT 3.3V 100mA 100k Q1 A0 SUSPEND 49.9k USB POWER (4.35V TO 5.5V) C2 4.7µF 20k 1Ω LTC3456 EXT_PWR C4 10µF D1 AC ADAPTER (5V ±10%) HSO C7 1µF L1 10µH 1k VEXT C8 2.2µF AIN USB LCD LOGIC BIAS 2.8V 10mA SW1 VEXT 100k 220pF C6 10µF FLASH MEMORY CARD 3.3V 50mA CORE OUTPUT 1.8V 200mA FB1 80.6k 11.3k WALLFB C3 4.32k 4.7µF 1Ω PWRKEY VMAX PBSTAT RESET MODE PWRON PGND AGND C5 1µF VMAX (TO REAL-TIME CLOCK) 3456 TA02a MICROCONTROLLER L1, L3: MURATA LQH32CN100K53 C1, C6 TO C10: X5R OR X7R, 4V L2: MURATA LQH32CN4R7M53 C2 TO C5: X5R OR X7R, 6.3V D1: ON SEMICONDUCTOR MBRM120E Q1: PHILIPS MMBT3906 Load Transient (USB/Wall Powered) Load Transient (Battery Powered) VCORE 100mV/DIV (AC COUPLED) IL1 200mA/DIV VMAIN 200mV/DIV (AC COUPLED) VCORE 100mV/DIV (AC COUPLED) IL1 200mA/DIV VMAIN 200mV/DIV (AC COUPLED) IL2 200mA/DIV IL3 200mA/DIV VBATT = 2.4V 100µs/DIV IMAIN = 20mA TO 100mA ICORE = 20mA TO 150mA 3456 TA02b VEXT = 5V 200µs/DIV IMAIN = 20mA TO 100mA ICORE = 5mA TO 150mA 3456 TA02c 3456f 26 LTC3456 U PACKAGE DESCRIPTIO UF Package 24-Lead Plastic QFN (4mm × 4mm) (Reference LTC DWG # 05-08-1697) 0.70 ±0.05 4.50 ± 0.05 2.45 ± 0.05 3.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ±0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 4.00 ± 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD 0.23 TYP R = 0.115 (4 SIDES) TYP 23 24 0.75 ± 0.05 PIN 1 TOP MARK (NOTE 6) 0.38 ± 0.10 1 2 2.45 ± 0.10 (4-SIDES) (UF24) QFN 1103 0.200 REF 0.00 – 0.05 0.25 ± 0.05 0.50 BSC NOTE: 1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)—TO BE APPROVED 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE, IF PRESENT 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3456f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 27 LTC3456 U TYPICAL APPLICATIO Quad-Output Converter Runs Off 2 AA Cells, USB or Wall Adapter 2 AA CELLS + C1 4.7µF L2 4.7µH SW2_BST SW2_BK VINT VMAIN VBATT USBHP USB CONTROLLER C10 22µF L3 10µH C9 1µF Q2 A0 SUSPEND LCD LOGIC BIAS 2.8V C8 2.2µF 10mA 49.9k USB POWER (4.35V TO 5.5V) C2 4.7µF AIN USB 20k 1Ω LTC3456 EXT_PWR C3 10µF D1 AC ADAPTER (5V ±10%) HSO L1 10µH 1k VEXT MAIN OUTPUT 3.3V 100mA 100k D2 C7 1µF FLASH MEMORY CARD 3.3V 50mA CORE OUTPUT 2.5V 100mA SW1 Q1 VEXT 10µF 43.2k 330pF FB1 20.5k 11.3k WALLFB C4 4.32k 4.7µF PWRKEY VMAX PBSTAT RESET MODE PWRON PGND AGND 1Ω C5 1µF VMAX TO REAL-TIME CLOCK (ALIVE OR SHUT DOWN) 3456 TA03 MICROCONTROLLER L1, L3: MURATA LQH32CN100K53 C1, C6 TO C10: X5R OR X7R, 4V L2: MURATA LQH32CN4R7M53 C2 TO C5: X5R OR X7R, 6.3V D1, D2: ON SEMICONDUCTOR MBRM120E Q1: FAIRCHILD FDG327N Q2: PHILIPS MMBT3906 RELATED PARTS PART NUMBER LT1616 LTC1879 LTC3405/LTC3405A LTC3406/LTC3406B LTC3407 LTC3412 LTC3414 LTC3440/LTC3441 LTC3455 DESCRIPTION 500mA (IOUT), 1.4MHz, High Efficiency Step-Down DC/DC Converter 1.2A (IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 300mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter Dual 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 2.5A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 4A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 600mA/1A (IOUT), 2MHz/1MHz, Synchronous Buck-Boost DC/DC Converter Dual DC/DC Converter with USB Power Manager and Li-Ion Battery COMMENTS 90% Efficiency, VIN: 3.6V to 25V, VOUT(MIN) = 1.25V, IQ = 1.9mA, ISD < 1µA, ThinSOT 95% Efficiency, VIN: 2.7V to 10V, VOUT(MIN) = 0.8V, IQ = 15µA, ISD < 1µA, TSSOP16 95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 20µA, ISD < 1µA, ThinSOT 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20µA, ISD < 1µA, ThinSOT 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40µA, ISD < 1µA, MS10E 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60µA, ISD < 1µA, TSSOP16E 95% Efficiency, VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, IQ = 64µA, ISD < 1µA, TSSOP16E 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25µA/50µA, ISD < 1µA, MS/DFN 96% Efficiency, Seamless Transition Between Inputs, IQ = 110µA, ISD < 2µA, QFN 3456f 28 Linear Technology Corporation LT/TP 1204 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2004