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| LTC3446 Monolithic Buck Regulator with Dual VLDO Regulators FEATURES n n DESCRIPTION The LTC(R)3446 combines a synchronous buck DC/DC converter with two very low dropout (VLDO) linear regulators to provide up to three stepped-down output voltages from a single input voltage. The input voltage range is ideally suited for Li-Ion battery-powered applications, as well as powering low voltage logic from 5V or 3.3V rails. The output voltage range extends down to 0.4V for the VLDO regulators and 0.8V for the buck. The 1A synchronous buck converter provides the main output with high efficiency, typically 85%. The two 300mA VLDO regulators can run off the main output to provide two additional lower voltage outputs. A built-in supply monitor provides a power good indication. The buck converter switches at 2.25MHz, allowing the use of small surface mount inductors and capacitors. Constant frequency current mode operation produces controlled output spectrum and fast transient response. A modeselect pin allows automatic Burst Mode operation to be enabled for higher efficiency at light load, or disabled for lower noise operation down to very light loads. The two VLDO regulators are stable with ceramic output capacitors as small as 1F . L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. VLDO is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 6611131, 6304066, 6498466, 6580258. n n n n n n n n n n n n High Efficiency Triple Step-Down Outputs from a Single Input Supply 1A Synchronous Buck Regulator Provides Main Step-Down Output and Powers Two 300mA VLDOTM Linear Regulators Output Voltages as Low as 400mV (VLDO Outputs) Power Good Output Input Voltage Range: 2.7V to 5.5V Independent Internal Soft-Start for Each Supply Independent Enable Pin for Each Supply Low (140A Typ) No-Load Quiescent Current with all Outputs Enabled Constant Frequency Current Mode Operation 2.25MHz Switching Frequency Uses Small Inductors Defeatable Automatic Burst Mode(R) Operation for High Efficiency at Light Loads 1.5% Reference Accuracy Overtemperature Protection Thermally Enhanced 4mm x 3mm 14-Pin DFN Package APPLICATIONS n n Low Power Handheld Devices Low Voltage and Multivoltage Power for Digital Logic, I/O, FPGAs, CPLDs, ASICs and CPUs TYPICAL APPLICATION L1 1.8H VIN 2.9V TO 5.5V 22F X7R VIN SW 59k BUCKFB LTC3446 LVIN PGOOD LVOUT1 MODESEL ENBUCK ENLDO1 LVFB1 ENLDO2 3.3k ITH 1000pF LVFB2 GND 3446 TA01 22F X7R VOUT 1.8V 400mA MAX Buck Efficiency vs Buck Load Current 100 90 EFFICIENCY (%) 80 70 60 50 40 VIN = 2.7V VIN = 3.6V VIN = 4.2V 1 10 100 LOAD CURRENT (mA) 1000 3446 TA01b 47.5k VOUT 1.5V 300mA MAX Burst Mode OPERATION PWM MODE DIGITAL CONTROL 110k 2.2F X7R 40.2k VOUT 1.2V 300mA MAX LVOUT2 80.6k 2.2F X7R 40.2k L1: TOKO A960AW-1R8M 3446fd 1 LTC3446 ABSOLUTE MAXIMUM RATINGS (Note 1) PIN CONFIGURATION TOP VIEW MODESEL VIN ITH PGOOD LVOUT1 LVIN LVOUT2 1 2 3 4 5 6 7 15 14 SW 13 ENBUCK 12 BUCKFB 11 ENLDO1 10 LVFB1 9 LVFB2 8 ENLDO2 VIN, LVIN to GND ......................................... - 0.3V to 6V MODESEL, ENBUCK, ENLDO1, ENLDO2 to GND .......................................... -0.3V to 6V BUCKFB to GND .......................................... -0.3V to 6V LVFB1, LVFB2 to GND .................................... -0.3V to 6V ITH to GND ..... -0.3V to the Lesser of (VIN + 0.3V) or 3V SW to GND......-0.3V to the Lesser of (VIN + 0.3V) or 6V LVOUT1, LVOUT2 to GND .......... -0.3V to the Lesser of (LVIN + 0.3V) or 6V PGOOD to GND ............................................ -0.3V to 6V LVOUT1, LVOUT2 Short-Circuit to GND Duration............................................... Indefinite Operating Temperature Range (Note 2) LTC3446EDE ........................................ -40C to 85C LTC3446IDE ....................................... -40C to 125C Junction Temperature (Note 1) ........................... 125C Storage Temperature Range.................. -65C to 125C DE PACKAGE 14-LEAD (4mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 35C/W EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH LTC3446EDE#PBF LTC3446IDE#PBF TAPE AND REEL LTC3446EDE#TRPBF LTC3446IDE#TRPBF PART MARKING* 3446 3446 PACKAGE DESCRIPTION 14-Lead (4mm x 3mm) Plastic DFN 14-Lead (4mm x 3mm) Plastic DFN TEMPERATURE RANGE -40C to 85C -40C to 125C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. 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/ The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V unless otherwise specified. (Note 2) SYMBOL VIN VUVLO IQ PARAMETER Input Voltage Range VIN Undervoltage Lockout Threshold VIN Undervoltage Lockout Hysteresis VIN Quiescent Current (Note 4) Buck Enabled Only, Not Sleeping Buck Enabled Only, Sleeping One LDO Enabled Only All Three Outputs Enabled, Buck Not Sleeping All Three Outputs Enabled, Buck Sleeping Shutdown CONDITIONS (Note 3) VIN Rising ELECTRICAL CHARACTERISTICS MIN 2.7 TYP 2.37 10 310 50 75 400 140 MAX 5.5 2.5 30 500 75 100 600 210 1 UNITS V V mV A A A A A A 3446fd VBUCKFB = 0V, ISW = 0mA VBUCKFB = 1V, ISW = 0mA VLVIN = 1.5V, 10A LDO Output Load VBUCKFB = 0V, ISW = 0mA, VLVIN = 1.5V, 10A Output Load on Each LDO VBUCKFB = 1V, ISW = 0mA, VLVIN = 1.5V, 10A Load on Each LDO VENBUCK = 0V, VENLDO1 = 0V, VENLDO2 = 0V 2 LTC3446 ELECTRICAL CHARACTERISTICS SYMBOL RPGOOD IPGOOD IBUCKFB VBUCKFB VBUCKFB IMAXP IMAXN PARAMETER PGOOD Output Resistance PGOOD Hi-Z Leakage Current Feedback Current Regulated Feedback Voltage Feedback Voltage Line Regulation Maximum Peak Inductor Current NMOS Overcurrent Limit Feedback Voltage Load Regulation (with Respect to VITH) fOSC RPFET RNFET ILSW VENBUCK IENBUCK VMODESEL IMODESEL gm VLVIN ILVIN VLVFB ILVFB ILVOUT(MAX) VENLDOx IENLDOx Oscillator Frequency RDS(ON) of P-Channel FET RDS(ON) of N-Channel FET SW Leakage Buck Enable Pin Threshold Buck Enable Pin Leakage Current Mode Select Pin Threshold Mode Select Pin Leakage Current Error Amplifier Transconductance LVIN Pin Operating Voltage LVIN Pin Operating Current LVIN Shutdown Current Feedback Pin Regulation Voltage (Note 7) Feedback Pin Input Current Continuous Output Current Short-Circuit Output Current LDO Enable Pin Threshold LDO Enable Pin Leakage Current Output Voltage Load Regulation (Referred to the LVFB Pin) LVFB Line Regulation (with Respect to the LVIN Pin) LVFB Line Regulation (with Respect to the VIN Pin) VDO LVIN - LVOUT Dropout Voltage VENLDOx = 5.5V, All Other Pins Grounded IOUT = 1mA to 300mA VLVIN = 1.5V to 5.5V, VIN = 3.6V, VLVOUT = 1.2V, IOUT = 1mA VLVIN = 1.5V, VIN = 2.7V to 5.5V, VLVOUT = 1.2V, IOUT = 1mA VIN = 2.8V, VLVIN = 1.5V, VLVFB = 0.37V, IOUT = 300mA (Note 9) The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V unless otherwise specified. (Note 2) CONDITIONS MIN TYP 8 87 MAX 10 120 1 30 UNITS % A nA V mV/V A A mV/V VPG(THRESH) PGOOD Threshold (Note 8) PGOOD Low, Sinking 1mA VPGOOD = 6V (Note 5) (Note 5) VIN = 2.7V to 5.5V (Note 5) VBUCKFB = 0V, Duty Cycle < 35% VITH = 0.5V to 1V, VMODESEL = VIN (Note 5) Synchronous Buck Converter 0.788 1.2 0.800 0.3 1.55 1.8 0.5 0.812 0.5 2.0 1.8 2.25 0.13 0.14 2.7 MHz ISW = 500mA ISW = -500mA VENBUCK = 0V, VSW = 0V or 5.5V, VIN = 5.5V 1 0.3 0.3 450 A V A V A A/V V A A V V nA mA mA 0.65 0.65 700 1 1 1 1 950 5.5 VENBUCK = 5.5V, All Other Pins Grounded VMODESEL = 5.5V, All Other Pins Grounded VITH = 0.6V (Note 6) IOUT = 10A VENLDO = 0V 1mA IOUT 300mA, 1.5V VLVIN 5.5V VLVFB at Regulation Each VLDO: VIN = 3.6V, VLVIN = 1.5V, VLVOUT = 1.2V, Unless Otherwise Specified 0.9 3 1.5 20 2 0.405 0.408 10 0.395 0.392 300 0.400 0.400 2 760 0.3 0.65 -1 7.5 0.44 68 1 1 V A mV/A V/V mV/V 175 mV 3446fd 3 LTC3446 ELECTRICAL CHARACTERISTICS 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 LTC3446E is guaranteed to meet performance specifications from 0C to 85C. Specifications over the - 40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LTC3446I is guaranteed to meet performance specifications over the -40C to 125C operating temperature range. Note 3: Minimum operating VIN voltage required for the VLDO regulators to stay in regulation is: VIN LVOUT(MAX) + 1.4V and VIN 2.7V Note 4: Dynamic supply current is higher due to the internal gate charge being delivered at the switching frequency. Note 5: The LTC3446 is tested in a feedback loop that connects the BUCKFB pin to the output of the buck converter's error amplifier (i.e., the ITH pin). Note 6: Minimum operating LVIN voltage required for the VLDO regulators to stay in regulation is: LVIN LVOUT(MAX) + 100mV and LVIN 0.9V Note 7: Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, the output current range must be limited. When operating at maximum output current, the input voltage range must be limited. Note 8: PGOOD assertion indicates that the feedback voltages of all enabled supplies are within the specified percentage of their target values. Note 9: Dropout voltage in the DFN package is assured by design, characterization and statistical process control. 3446fd 4 LTC3446 TYPICAL PERFORMANCE CHARACTERISTICS Buck Regulated Feedback Voltage vs Temperature 808 806 804 VBUCKFB (mV) VLVFB1 (mV) VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V 802 800 798 796 794 408 406 404 402 400 398 396 394 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V LDO1 Regulated Feedback Voltage vs Temperature 792 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) 3446 G01 392 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) 3446 G02 LDO2 Regulated Feedback Voltage vs Temperature 408 406 404 VLVFB2 (mV) 402 400 398 396 394 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V 2.50 2.45 2.40 2.35 VIN (V) 2.30 2.25 2.20 2.15 2.10 2.05 Undervoltage Lockout Threshold vs Temperature UVLO RISING UVLO FALLING 392 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) 3446 G03 2.00 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) 3446 G04 Maximum Peak Inductor Current 2.5 2.4 2.3 2.2 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 -50 -30 2.50 2.45 OSCILLATOR FREQUENCY (MHz) 2.40 2.35 2.30 2.25 2.20 2.15 2.10 2.05 Oscillator Frequency vs Temperature CURRENT (A) VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V -10 10 30 50 70 90 110 130 TEMPERATURE (C) 3446 G05 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V 2.00 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C) 3446 G06 3446fd 5 LTC3446 TYPICAL PERFORMANCE CHARACTERISTICS Peak Inductor Current vs ITH Voltage 1.6 PEAK INDUCTOR CURRENT (A) VIN = 3.6V 1.4 VMODESEL = 3.6V VLDO CURRENT LIMIT (mA) 1800 1600 1400 1200 1000 800 600 400 200 0 0.25 0.5 0.75 1 1.25 1.5 1.75 ITH PIN VOLTAGE (V) 2 0 0.00 1.00 2.00 3.00 4.00 LVIN PIN VOLTAGE (V) 5.00 6.00 PULSED MEASUREMENT, TJ TA 27C VIN = 3.6V LVOUT = 0V VLDO Current Limit vs LVIN Voltage 1.2 1.0 0.8 0.6 0.4 0.2 0 3446 G07 3446 G08 VLDO Dropout Voltage vs Load Current 100 VIN = 2.8V 90 LVOUT = 1.2V -45C 80 27C 90C 70 130C 60 50 40 30 20 10 0 0 50 150 200 100 LOAD CURRENT (mA) 250 300 450 400 350 VIN CURRENT (A) 300 250 200 150 100 50 0 VIN Bias Current vs VLDO Load Current DROPOUT VOLTAGE (mV) VIN = 3.6V LVIN = 1.5V LVOUT = 1.2V ONLY ONE VLDO ENABLED -45C 27C 90C 130C 0 100 150 50 250 200 VLDO OUTPUT CURRENT (mA) 300 3446 G10 3446 G09 LVIN No-Load Operating Current 20 18 16 LVIN CURRENT (A) 14 12 10 8 6 4 2 0 0 1 3 4 LVIN PIN VOLTAGE (V) 2 -45C 27C 90C 130C 5 6 3446 G11 Enable/MODESEL Thresholds 1000 ENABLE/MODESEL THRESHOLD (mV) 900 800 700 600 500 400 300 200 100 0 2.5 3 3.5 4 VIN (V) 4.5 -45C 27C 90C 130C 5 5.5 3446 G12 VIN = 5V BOTH VLDOS ON AND REGULATING 0.8V 3446fd 6 LTC3446 TYPICAL PERFORMANCE CHARACTERISTICS Buck PMOS Switch On-Resistance 200 180 160 140 120 100 80 -45 -20 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V 55 30 80 5 TEMPERATURE (C) 105 130 NMOS RESISTANCE (m) PMOS RESISTANCE (m) 200 180 160 140 120 100 80 -45 -20 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5.5V 55 30 80 5 TEMPERATURE (C) 105 130 Buck NMOS Switch On-Resistance 3446 G17 3446 G18 Buck Transient Response with Burst Mode Defeated Buck Transient Response with Burst Mode Enabled BUCK OUTPUT VOLTAGE 50mV/DIV AC-COUPLED 500mA LOAD CURRENT 50mA 100s/DIV FRONT PAGE APPLICATION CIRCUIT 3446 G13 BUCK OUTPUT VOLTAGE 50mV/DIV AC-COUPLED 500mA LOAD CURRENT 50mA 100s/DIV FRONT PAGE APPLICATION CIRCUIT 3446 G14 VLDO Transient Response VLVIN = BUCK VOUT 20mV/DIV AC-COUPLED VLVOUT 10mV/DIV AC-COUPLED VLDO Rejection of Buck DC/DC Burst Mode Ripple VLDO OUTPUT VOLTAGE 20mV/DIV AC-COUPLED 300mA LOAD CURRENT 30mA 100s/DIV LVOUT = 1.5V OR 1.2V FRONT PAGE APPLICATION CIRCUIT 3446 G15 2s/DIV VLVIN = BUCK VOUT = 1.8V VIN = 4.2V VLVOUT = 1.5V ILVOUT = 50mA CLVOUT = 2.2F 3446 G16 3446fd 7 LTC3446 PIN FUNCTIONS MODESEL (Pin 1): Chooses Between Burst Mode Operation and Pulse Skipping Operation at Light Loads. Forcing this pin below 0.3V allows the buck converter to automatically enter Burst Mode operation at light loads. Forcing this pin above 1V disallows entering Burst Mode operation; the buck converter will cycle skip at light loads. Do not leave this pin floating. This is a MOS gate input. VIN (Pin 2): Input Supply to the LTC3446. Must be closely decoupled to GND with a 10F or greater ceramic capacitor. ITH (Pin 3): Buck Error Amplifier Output and Servo-Loop Compensation Point. PGOOD (Pin 4): Supply Monitor Output, Open-Drain NMOS. LVOUT1 (Pin 5): Output of the First VLDO Regulator. LVIN (Pin 6): Input Supply to the LTC3446's VLDO Circuits. Bypass LVIN to GND with at least a 1F low ESR ceramic capacitor. Typical LTC3446 application circuits will connect this pin to the output of the buck converter but this is not required. The VLDO regulators may be used independently of the buck converter. LVOUT2 (Pin 7): Output of the Second VLDO Regulator. LVFB2 (Pin 9): Feedback Pin for the Second VLDO Regulator. An output divider should be connected from LVOUT2 to LVFB2 to set the desired LVOUT2 regulated output voltage. LVFB1 (Pin 10): Feedback Pin for the First VLDO Regulator. An output divider should be connected from LVOUT1 to LVFB1 to set the desired LVOUT1 regulated output voltage. ENLDO1/ENLDO2 (Pin 11/Pin 8): Enable Pin for the First and Second VLDO Regulators, Respectively. Forcing this pin above 1V enables the corresponding VLDO regulator and forcing this pin below 0.3V shuts it down. Each VLDO regulator draws <1A of supply current in shutdown. Do not leave this pin floating. This is a MOS gate input. BUCKFB (Pin 12): Buck Converter's Feedback Pin. Receives the feedback voltage from an external resistive divider across the output. External resistance from this pin to ground should be equal to or less than 50k. ENBUCK (Pin 13): Enable Pin for the LTC3446's Buck Converter Circuit. Forcing this pin above 1V enables the buck converter and forcing this pin below 0.3V shuts down the converter. In shutdown, the buck converter draws <1A of supply current. Do not leave this pin floating. This is a MOS gate input. SW (Pin 14): Switch Node Connection to Inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. Exposed Pad (Pin 15): Ground. The Exposed Pad is the only ground and must connect to the PCB ground for electrical contact and rated thermal performance. 3446fd 8 LTC3446 BLOCK DIAGRAM 3 ITH ENBUCK 0.4V 0.8V SOFT-START VOLTAGE REFERENCE ERROR AMPLIFIER ITH PARK ITH LIMIT B BCLAMP PMOS CURRENT COMPARATOR 2 VIN + 12 BUCKFB + - - VB + BURST COMPARATOR OSCILLATOR SLOPE COMPENSATION SW 14 4 PGOOD LOGIC POWER GOOD NMOS OVERCURRENT COMPARATOR 13 1 ENBUCK MODESEL REVERSE CURRENT COMPARATOR VIN + SOFT-START VLDO1 - 6A 11 ENLDO1 VIN + SOFT-START VLDO2 - 6A 8 ENLDO2 - + + - + - GND EXPOSED PAD 15 LVIN 6 LVOUT1 LVFB1 5 10 LVOUT2 LVFB2 7 9 3446 BD 3446fd 9 LTC3446 OPERATION The LTC3446 combines a constant frequency, current mode synchronous buck converter with two very low dropout (VLDO) linear DC regulators to provide up to three high efficiency, low voltage outputs from a single higher voltage input source. Each output can be independently enabled and disabled, and has its own independent soft-start circuit to help reduce inrush current. A power good circuit monitors all three supplies. The LTC3446 incorporates an undervoltage lockout circuit that shuts down the IC when the input voltage drops below about 2.4V to prevent unstable operation. SYNCHRONOUS BUCK OPERATION A buck converter takes power from a high input voltage, VIN, and delivers it at a lower output voltage, VOUT. The buck converter inside the LTC3446 achieves over 80% efficient power conversion under a wide range of VIN, VOUT and load conditions, whereas a linear regulator is limited by physics to a maximum efficiency of (VOUT/VIN) x 100%. Main Control Loop During normal operation, the internal oscillator produces a constant frequency 2.25MHz clock. The top power switch (P-channel MOSFET) turns on at the beginning of a clock cycle. Inductor current increases to a peak value which is set by the voltage on the ITH pin. Then the top switch turns off and the energy stored in the inductor flows through the bottom switch (N-channel MOSFET) into the load until the next clock cycle. The peak inductor current is controlled by the voltage on the ITH pin, which is the output of the error amplifier. This amplifier compares the BUCKFB pin to the 0.8V reference. When the load current increases, the BUCKFB voltage decreases slightly below the reference. This decrease causes the error amplifier to increase the ITH voltage until the average inductor current matches the new load current. The main control loop is shut down by pulling the ENBUCK pin to ground. A soft-start is enabled whenever ENBUCK is brought high. Soft-start limits the peak inductor current from reaching maximum for the first millisecond after ENBUCK is brought high. Overcurrent Protection To help avert inductor current runaway in case the buck output is accidentally shorted to ground, the LTC3446 features a bottom switch NMOS overcurrent limit, which works as follows. When the buck output is shorted to ground, inductor current will rise to its maximum peak level, IMAXP, such that on every oscillator cycle the PMOS top switch will turn on for only its minimum duty cycle, and the bottom switch NMOS turns on for the remainder of the cycle. Temporarily ignoring inductor, switch and parasitic resistance drops, which in most applications are designed to be small in order to maximize buck converter efficiency, it is to first order true that when the PMOS is on, the VIN supply voltage is placed across the inductor, increasing the inductor current, but when the NMOS is on, there is no output voltage to be placed across the inductor to reduce its current. Inductor current ratchets up each cycle and could lead to the destruction of the buck IC. The NMOS overcurrent limit helps prevent this by sensing the current through the NMOS bottom switch, and for as long as this current exceeds the overcurrent limit level, IMAXN, it: 1. Keeps the NMOS on, allowing the tiny voltage drops from parasitic resistances to reduce the inductor current. 2. Refuses to allow the PMOS to turn on, preventing any additional energy from being fed into the system. Low Current Operation The MODESEL pin controls the buck converter's behavior at light load currents to help optimize efficiency, output ripple and noise. When the load is relatively light and MODESEL is grounded, the buck converter automatically switches into Burst Mode operation, which operates the PMOS switch intermittently based on load demand rather than at a constant frequency. Every switch cycle during Burst Mode operation delivers more energy than would occur in constant frequency operation, minimizing the switching loss per unit of energy delivered. Since the dominant power loss at light loads is gate charge switching loss in the power MOSFETs, operating in Burst Mode operation 3446fd 10 LTC3446 OPERATION can dramatically improve light load efficiency. The tradeoff is higher output ripple than in constant frequency operation, as well as the presence of noise below the 2.25MHz clock frequency. If MODESEL were instead tied to VIN, pulse skipping mode is selected. In this mode, the buck converter continues to switch at a constant frequency down to very light loads where it will eventually begin skipping pulses. Because constant frequency operation is extended down to light loads, low output ripple is maintained and any coupled or radiated noise is at or higher than the clock frequency. The tradeoff is lower efficiency compared to Burst Mode operation. Dropout Operation When the input supply voltage decreases toward the output voltage, the duty cycle increases to 100%, which is known as the dropout condition. In dropout, the PMOS switch is turned on continuously with the output voltage equal to the input voltage minus any voltage drop across the PMOS switch and the external inductor. VLDO LINEAR REGULATOR OPERATION The two micropower, VLDO (very low dropout) linear regulators in the LTC3446 operate from input voltages as low as 0.9V. Each VLDO regulator provides a high accuracy output that is capable of supplying 300mA of output current with a typical dropout voltage of only 70mV. A single ceramic capacitor as small as 1F is all that is required for output bypassing. A low reference voltage of 400mV allows the VLDO regulators to be programmed to much lower voltages than available in common LDOs. As shown in the Block Diagram, the VIN input supplies the internal reference and biases the VLDO circuitry while all output current comes directly from the LVIN input for high efficiency regulation. The low per-VLDO quiescent supply currents ILVIN = 4A, IVIN = 80A drop to ILVIN < 2A, IVIN < 1A in shutdown, are well-suited to batterypowered systems. Each VLDO includes current limit protection. The fast transient response of the follower output stage overcomes the traditional tradeoff between dropout voltage, quiescent current and load transient response inherent in most LDO regulator architectures. Overshoot detection circuitry is included to bring the output back into regulation when going from heavy to light output loads ("load-dump" handling). POWER GOOD CIRCUIT OPERATION The LTC3446 has a built-in supply monitor. The feedback voltage of each enabled supply is monitored by a window comparator to determine whether it is within 8% of its target value. If they all are, then the PGOOD pin becomes high impedance. If no supply is enabled, or if any enabled supply is more than 8% away from its target, then the PGOOD pin is driven to ground by an internal open-drain NMOS. The PGOOD pin may be connected through a pull-up resistor to a supply voltage of up to 5.5V, independent of the VIN pin voltage. 3446fd 11 LTC3446 APPLICATIONS INFORMATION A general LTC3446 application circuit is shown in Figure 1. External component selection is driven by output voltage and load requirements. The following text is divided into two sections: the first covers Buck regulator design and the second covers use of the linear VLDO regulators. BUCK REGULATOR DESIGN Buck regulator design begins with the selection of the L1 inductor based on desired ripple current. Once L1 is chosen, CIN and COUTB can be selected based on output voltage ripple requirements. Output voltage is programmed through R1 and R2, and loop response can be optimized by choice of RITH and CITH. Inductor Selection Although the inductor does not influence the operating frequency, the inductor value has a direct effect on ripple current. The inductor ripple current IL decreases with higher inductance and increases with higher VIN or VOUTB: IL = VOUTB V * 1 OUTB f O* L V IN Accepting larger values of IL allows the use of low inductances, but results in higher output voltage ripple, greater core losses, and lower output current capability. A reasonable starting point for setting ripple current is IL = 0.3 * IMAXP, where IMAXP is the peak switch current limit. The largest ripple current IL occurs at the maximum input voltage. To guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation: L= VOUTB VOUTB *1 f O* IL V IN(MAX) The inductor value will also have an effect on Burst Mode operation. The transition from low current operation begins when the peak inductor current falls below a level set by the burst clamp. Lower inductor values result in higher ripple current which causes this to occur at lower load currents. This causes a dip in efficiency in the upper range of low current operation. In Burst Mode operation, lower inductance values will cause the burst frequency to increase. VIN 2.7V TO 5.5V L1 VIN CIN BUCKFB LTC3446 LVIN PGOOD LVOUT1 MODESEL ENBUCK ENLDO1 LVFB1 ENLDO2 RTH ITH LVOUT2 R6 LVFB2 GND R5 3446 F01 SW D1 OPT R2 CF OPT VOUTB COUTB R1 VOUT1 R4 COUT1 DIGITAL CONTROL R3 VOUT2 COUT2 CITH Figure 1. General LTC3446 Application Circuit 3446fd 12 LTC3446 APPLICATIONS INFORMATION Inductor Core Selection 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. The choice of which style inductor to use often depends more on the price vs size requirements and any radiated field/EMI requirements than on what the LTC3446 requires to operate. Table 1 shows some typical surface mount inductors that work well in LTC3446 applications. Table 1. Representative Surface Mount Inductors MANUFACTURER PART NUMBER Toko Toko Coilcraft Coilcraft Sumida Sumida Taiyo Yuden Taiyo Yuden Murata Wurth A914BYW-2R2MD52LC A915AY-2ROMD53LC D01608C-222 LP01704-222M CDRH4D282R2 CDC5D232R2 N06DB2R2M N05DB2R2M LQN6C2R2M04 744042001 MAX DC VALUE CURRENT 2.2H 2H 2.2H 2.2H 2.2H 2.2H 2.2H 2.2H 2.2H 1H 2.05A 3.3A 2.3A 2.4A 2.04A 2.16A 3.2A 2.9A 3.2A 2.6A DCR 49m 22m 70m 120m 23m 30m 29m 32m 24m 20m HEIGHT 2mm 3mm 3mm 1mm 3mm 2.5mm 3.2mm 2.8mm 5mm 2mm current and average power dissipation so as not to exceed the diode ratings. The main problem with Schottky diodes is that their parasitic capacitance reduces the efficiency, usually negating the possible benefits for LTC3446 circuits. Another problem that a Schottky diode can introduce is higher leakage current at high temperatures, which could reduce the low current efficiency. Remember to keep lead lengths short and observe proper grounding to avoid ringing and increased dissipation when using a catch diode. Input Capacitor (CIN) Selection In continuous mode, the input current of the converter is a square wave with a duty cycle of approximately VOUTB /VIN. To prevent large voltage transients, a low equivalent series resistance (ESR) input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by: IRMS IMAX VOUTB (VIN VOUTB ) VIN where the maximum average output current IMAX equals the peak current minus half the peak-to-peak ripple current, IMAX = IMAXP - IL /2. This formula has a maximum at VIN = 2VOUTB, where IRMS = IOUT/2. This simple worst case is commonly used to design because even significant deviations do not offer much relief. Note that capacitor manufacturer's ripple current ratings are often based on only 2000 hours lifetime. This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet the size or height requirements of the design. An additional 0.1F to 1F ceramic capacitor is also recommended on VIN for high frequency decoupling, when not using an all ceramic capacitor solution. Catch Diode Selection Although unnecessary in most applications, a small improvement in efficiency can be obtained in a few applications by including the optional diode D1 shown in Figure 1, which conducts when the synchronous switch is off. When using Burst Mode operation or pulse skip mode, the synchronous switch is turned off at a low current and the remaining current will be carried by the optional diode. It is important to adequately specify the diode peak 3446fd 13 LTC3446 APPLICATIONS INFORMATION Output Capacitor (COUTB) Selection The selection of COUTB is driven by the required ESR to minimize voltage ripple and load step transients. Typically, once the ESR requirement is satisfied, the capacitance is adequate for filtering. The output ripple (VOUTB) is determined by: VOUTB IL ESR + 1 8fO COUTB with trace inductance can lead to significant ringing. Other capacitor types include the Panasonic specialty polymer (SP) capacitors. In most cases, 0.1F to 1F of ceramic capacitors should also be placed close to the LTC3446 in parallel with the main capacitors for high frequency decoupling. Ceramic Input and Output Capacitors Higher value, lower cost ceramic capacitors are now becoming available in smaller case sizes. These are tempting for switching regulator use because of their very low ESR. Unfortunately, the ESR is so low that it can cause loop stability problems. Solid tantalum capacitor ESR generates a loop "zero" at 5kHz to 50kHz that is instrumental in giving acceptable loop phase margin. Ceramic capacitors remain capacitive to beyond 300kHz and usually resonate with their ESL before ESR becomes effective. Also, ceramic caps are prone to temperature effects which requires the designer to check loop stability over the operating temperature range. To minimize their large temperature and voltage coefficients, only X5R or X7R ceramic capacitors should be used. A good selection of ceramic capacitors is available from Taiyo Yuden, TDK and Murata. Great care must be taken when using only ceramic input and output capacitors. When a ceramic capacitor is used at the input and the power is being supplied through long wires, such as from a wall adapter, a load step at the output can induce ringing at the VIN pin. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, the ringing at the input can be large enough to damage the part. Since the ESR of a ceramic capacitor is so low, the input and output capacitor must instead fulfill a charge storage requirement. During a load step, the output capacitor must instantaneously supply the current to support the load until the feedback loop raises the switch current enough to support the load. The time required for the feedback loop to respond is dependent on the compensation components and the output capacitor size. Typically, 3 to 4 cycles are required to respond to a load step, but only in where f = 2.25MHz, COUTB = output capacitance and IL = ripple current in the inductor. The output ripple is highest at maximum input voltage since IL increases with input voltage. Once the ESR requirements for COUTB have been met, the RMS current rating generally far exceeds the IRIPPLE(P-P) requirement, except for an all ceramic solution. In surface mount applications, multiple capacitors may have to be paralleled to meet the capacitance, ESR or RMS current handling requirement of the application. Aluminum electrolytic, special polymer, ceramic and dry tantulum capacitors are all available in surface mount packages. The OS-CON semiconductor dielectric capacitor available from Sanyo has the lowest ESR(size) product of any aluminum electrolytic at a somewhat higher price. Special polymer capacitors, such as Sanyo POSCAP offer very low ESR, , but have a lower capacitance density than other types. Tantalum capacitors have the highest capacitance density, but have a larger ESR and it is critical that the capacitors are surge tested for use in switching power supplies. An excellent choice is the AVX TPS series of surface mount tantalums, avalable in case heights ranging from 2mm to 4mm. Aluminum electrolytic capacitors have a significantly larger ESR, and are often used in extremely cost-sensitive applications provided that consideration is given to ripple current ratings and long-term reliability. Ceramic capacitors have the lowest ESR and cost but also have the lowest capacitance density, a high voltage and temperature coefficient and exhibit audible piezoelectric effects. In addition, the high Q of ceramic capacitors along 3446fd 14 LTC3446 APPLICATIONS INFORMATION the first cycle does the output drop linearly. The output droop, VDROOP, is usually about 2 to 3 times the linear drop of the first cycle. Thus, a good place to start is with the output capacitor size of approximately: COUTB 2.5 IOUT fO * VDROOP Checking Buck Converter Transient Response The OPTI-LOOP compensation allows the transient response to be optimized for a wide range of loads and output capacitors. The availability of the ITH pin not only allows optimization of the control loop behavior but also provides a DC coupled and AC filtered closed-loop response test point. The DC step, rise time and settling at this test point truly reflects the closed-loop response. Assuming a predominantly second order system, phase margin and/or damping factor can be estimated using the percentage of overshoot seen at this pin. The bandwidth can also be estimated by examining the rise time at the pin. The ITH external components shown in the front page Typical Application circuit will provide an adequate starting point for most applications. The series R-C filter sets the dominant pole-zero loop compensation. The values can be modified slightly (from 0.5 to 2 times their suggested values) to optimize transient response once the final PC layout is done and the particular output capacitor type and value have been determined. The output capacitors need to be selected because the various types and values determine the loop feedback factor gain and phase. An output current pulse of 20% to 100% of full load current having a rise time of 1s to 10s will produce output voltage and ITH pin waveforms that will give a sense of the overall loop stability without breaking the feedback loop. Switching regulators take several cycles to respond to a step in load current. When a load step occurs, VOUTB immediately shifts by an amount equal to ILOAD * ESR, where ESR is the effective series resistance of COUT. ILOAD also begins to charge or discharge COUTB generating a feedback error signal used by the regulator to return VOUTB to its steady-state value. During this recovery time, VOUTB can be monitored for overshoot or ringing that would indicate a stability problem. The initial output voltage step may not be within the bandwidth of the feedback loop, so the standard second order overshoot/DC ratio cannot be used to determine phase margin. The gain of the loop increases with R and the bandwidth of the loop increases with decreasing C. More capacitance may be required depending on the duty cycle and load step requirements. In most applications, the input capacitor is merely required to supply high frequency bypassing, since the impedance to the supply is very low. A 10F ceramic capacitor is usually enough for these conditions. Setting the Buck Converter's Output Voltage The buck develops a 0.8V reference voltage between the feedback pin, BUCKFB, and the signal ground as shown in Figure 1. The output voltage is set by a resistive divider according to the following formula: VOUTB 0.8V 1+ R2 R1 Keep R1 at or less than 50k. Great care should be taken to route the BUCKFB line away from noise sources, such as the inductor or the SW line. To improve high frequency loop response, a feed forward capacitor, CF, can be added as shown in Figure 1. Capacitor CF provides phase lead by creating a high frequency zero with R2, improving phase margin. Buck Converter Shutdown and Soft-Start The ENBUCK pin enables and shuts down the LTC3446's buck converter. Do not leave this pin floating! Tying ENBUCK to ground disables the buck converter. Bringing ENBUCK more than 1V above ground enables the buck. When the buck is brought out of shutdown, an internal soft-start clamp reduces surge currents from VIN by gradually increasing the internal peak inductor current limit over the course of a millisecond. 3446fd 15 LTC3446 APPLICATIONS INFORMATION If R is increased by the same factor that C is decreased, the zero frequency will be kept the same, thereby keeping the phase the same in the most critical frequency range of the feedback loop. The output voltage settling behavior is related to the stability of the closed-loop system and will demonstrate the actual overall supply performance. For a detailed explanation of optimizing the compensation components, including a review of control loop theory, refer to Linear Technology Application Note 76. Although a buck regulator is capable of providing the full output current in dropout, it should be noted that as the input voltage VIN drops toward VOUT, the load step capability does decrease due to the decreasing voltage across the inductor. Applications that require large load step capability near dropout should use a different topology such as SEPIC, Zeta or single inductor, positive buck/boost. In some applications, a more severe transient can be caused by switching in loads with large (>1F) input capacitors. The discharged input capacitors are effectively put in parallel with COUTB, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem, if the switch connecting the load has low resistance and is driven quickly. The solution is to limit the turn-on speed of the load switch driver. A Hot Swap controller is designed specifically for this purpose and usually incorporates current limiting, short-circuit protection, and soft-starting. Efficiency Considerations The percent efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: %Efficiency = 100% - (L1 + L2 + L3 + ...) where L1, L2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3446 circuits: 1) LTC3446 VIN current, 2) switching losses, 3) I2R losses, 4) other losses. 1) The VIN current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and control currents. VIN current results in a small (<0.1%) loss that increases with VIN, even at no load. 2) The switching current is the sum of the MOSFET driver and control currents. The MOSFET driver current results from switching the gate capacitance of the power MOSFETs. Each time a MOSFET gate is switched from low to high to low again, a packet of charge dQ moves from VIN to ground. The resulting dQ/dt is a current out of VIN that is typically much larger than the DC bias current. In continuous mode, IGATECHG = fO(QT + QB), where QT and QB are the gate charges of the internal top and bottom MOSFET switches. The gate charge losses are proportional to VIN and thus their effects will be more pronounced at higher supply voltages. 3) I2R Losses are calculated from the DC resistances of the internal switches, RSW, and external inductor, RL. In continuous mode, the average output current flowing through inductor L is "chopped" between the internal top and bottom switches. Thus, the series resistance looking into the SW pin is a function of both top and bottom MOSFET RDS(ON) and the duty cycle (DC) as follows: RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 - DC) 4) Other "hidden" losses such as copper trace and internal battery resistances can account for additional efficiency degradations in portable systems. It is very important to include these "system" level losses in the design of a system. The internal battery and fuse resistance losses can be minimized by making sure that CIN has adequate charge storage and very low ESR at the switching frequency. Other losses including diode conduction losses during dead-time and inductor core losses generally account for less than 2% total additional loss. Hot Swap is a trademark of Linear Technology Corporation. 3446fd 16 LTC3446 APPLICATIONS INFORMATION VLDO LINEAR REGULATOR DESIGN Adjustable Output Voltage Each VLDO regulator's output voltage is set by the ratio of two external resistors as shown in Figure 2. The VLDO regulator servos the output to maintain the LVFB pin voltage at 0.4V (referenced to ground). Thus the current in R1 is equal to 0.4V/R1. For good transient response, stability and accuracy, the current in R1 should be at least 8A, thus the value of R1 should be no greater than 50k. The current in R2 is the current in R1 plus the LVFB pin bias current. Since the LVFB pin bias current is typically <10nA, it can be ignored in the output voltage calculation. The output voltage can be calculated using the formula in Figure 2. Note that in shutdown, the output is turned off and the divider current will be zero once COUT is discharged. Each VLDO regulator operates at a relatively high gain of -0.7V/mA referred to its LVFB input. Thus a load current change of 1mA to 300mA produces a -0.2mV drop at the LVFB input. To calculate the change referred to the output, simply multiply by the gain of the feedback network (i.e., 1 + R2/R1). For example, to program the output for 1.2V, choose R2/R1 = 2. In this example, an output current change of 1mA to 300mA produces -0.2mV * (1 + 2) = 0.6mV drop at the output. Because the LVFB pins are relatively high impedance (depending on the resistor dividers used), stray capacitance at these pins should be minimized (<10pF) to prevent phase shift in the error amplifier loop. Additionally, special attention should be given to any stray capacitances that can couple external signals onto the LVFB pins producing undesirable output ripple. For optimum performance, connect each LVFB pin to its resistor divider with a short PCB trace and minimize all other stray capacitance to the LVFB pin. VLDO Regulator Output Capacitance and Transient Response The VLDO regulators are designed to be stable with a wide range of ceramic output capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 1F with an ESR of 0.05 or less is recommended to ensure stability. The VLDO regulators are micropower devices and output transient response will be a function of output capacitance. Larger values of output capacitance decrease the peak deviations and provide improved transient response for larger load current changes. Note that bypass capacitors used to decouple individual components powered by a VLDO regulator will increase the effective output capacitor value. High ESR tantalum and electrolytic capacitors may be used, but a low ESR ceramic capacitor must be in parallel at the output. There is no minimum ESR or maximum capacitor size requirements. Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across temperature and applied voltage. The most common dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high capacitances in a small package, but exhibit large voltage and temperature coefficients as shown in Figures 3 and 4. When used with a 2V regulator, a 1F Y5V capacitor can lose as much as 75% of its intial capacitance over the operating temperature range. The X5R and X7R dielectrics result VOUT = 0.4V 1+ R2 R1 COUT R1 GND 3446 F02 LVOUT LTC3446 LVFB R2 () Figure 2. Programming a VLDO Regulator's Output Voltage 3446fd 17 LTC3446 APPLICATIONS INFORMATION 20 0 CHANGE IN VALUE (%) X5R -20 -40 -60 -80 -100 CHANGE IN VALUE (%) BOTH CAPACITORS ARE 1F, 10V, 0603 CASE SIZE 20 0 X5R -20 Y5V -40 -60 -80 -100 -50 BOTH CAPACITORS ARE 1F, 10V, 0603 CASE SIZE -25 0 25 50 TEMPERATURE (C) 75 3446 F04 Y5V 0 2 6 4 DC BIAS VOLTAGE (V) 8 10 3446 F03 Figure 3. Ceramic Capacitor DC Bias Characteristics Figure 4. Ceramic Capacitor Temperature Characteristics in more stable characteristics and are usually more suitable for use as the output capacitor. The X7R type has better stability across temperature, while the X5R is less expensive and is available in higher values. In all cases, the output capacitance should never drop below 0.4F or , instability or degraded performance may occur. VLDO Output Short-Circuit Protection The VLDO regulators have built-in short-circuit limiting. During short-circuit conditions, internal circuitry automatically limits the output current to approximately 760mA. VLDO Regulator Soft-Start Each VLDO regulator includes a soft-start feature to prevent excessive current flow during start-up. When the VLDO regulator is enabled, the soft-start circuitry gradually increases the VLDO regulator reference voltage from 0V to 0.4V over a period of about 600s. There is a short 700s delay from the time the part is enabled until the LDO output starts to rise. Figure 5 shows the start-up output waveform. 1.5V VLDO OUTPUT 1.2V VLDO OUTPUT 0.5V/DIV BOTH VLDO ENABLES 5V/DIV VLVIN = 1.8V 200s/DIV VIN = 3.6V FRONT PAGE APPLICATION CIRCUIT WITH 10mA RESISTOR LOADS ON EACH VLDO OUTPUT 3446 F05 Figure 5. VLDO Regulator Output Start-Up 3446fd 18 LTC3446 PACKAGE DESCRIPTION DE Package 14-Lead Plastic DFN (4mm x 3mm) (Reference LTC DWG # 05-08-1708 Rev B) 0.70 0.05 3.60 0.05 2.20 0.05 3.30 0.05 1.70 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC 3.00 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 4.00 0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 8 14 0.40 0.10 3.00 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 3.30 0.10 1.70 0.10 PIN 1 NOTCH R = 0.20 OR 0.35 x 45 CHAMFER (DE14) DFN 0806 REV B 7 0.200 REF 0.75 0.05 3.00 REF 0.00 - 0.05 1 0.25 0.05 0.50 BSC BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC PACKAGE OUTLINE MO-229 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 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 3446fd 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. 19 LTC3446 TYPICAL APPLICATION L1 1.8H VIN 2.9V TO 5.5V 22F X7R VIN SW 59k BUCKFB LTC3446 LVIN PGOOD LVOUT1 MODESEL ENBUCK ENLDO1 LVFB1 ENLDO2 3.3k ITH 1000pF LVFB2 GND 3446 TA01 22F X7R VOUT 1.8V 400mA MAX 47.5k VOUT 1.5V 300mA MAX DIGITAL CONTROL 110k 2.2F X7R 40.2k VOUT 1.2V 300mA MAX LVOUT2 80.6k 2.2F X7R 40.2k L1: TOKO A960AW-1R8M RELATED PARTS PART NUMBER LT3023 DESCRIPTION Dual, 2x100mA, Low Noise Micropower LDO Dual, 100mA/500mA, Low Noise Micropower LDO 300mA, Micropower VLDO Linear Regulator Dual Synchronous 600mA Synchronous Step-Down DC/DC Regulator Dual Synchronous 800mA Synchronous Step-Down DC/DC Regulator, 2.25MHz I2C Controllable Buck Regulator with Two LDOs and and Backup Battery Input High Efficiency USB Power Manager Plus Triple Step-Down DC/DC COMMENTS VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, VDO = 0.30V, IQ = 40A, ISD < 1A, VOUT = ADJ, DFN, MS Packages, Low Noise < 20VRMS(P-P), Stable with 1F Ceramic Capacitors VIN: 1.8V to 20V, VOUT(MIN) = 1.22V, VDO = 0.30V, IQ = 60A, ISD < 1A, VOUT = ADJ, DFN, TSSOP Packages, Low Noise < 20VRMS(P-P), Stable with 1F Ceramic Capacitors VIN: 0.9V to 5.5V, VOUT(MIN) = 0.4V, 2.7V to 5.5V Bias Voltage Required, VDO = 45mV, IQ = 50A, ISD < 1A, VOUT = ADJ, DFN Packages, Stable with 1F Ceramic Capacitors 1.5MHz Constant Frequency Current Mode Operation, VIN from 2.5V to 5.5V, VOUT Down to 0.6V, DFN, MS Packages 2.25MHz Constant Frequency Current Mode Operation, VIN from 2.5V to 5.5V, VOUT Down to 0.6V, DFN, MS Packages 600mA, 1.5MHz Current Mode Buck Regulator, I2C Programmable VOUT from 0.85V to 1.55V, two 50mA LDOs, Backup Battery Input with PowerPathTM Control, QFN Package Maximizes Available Power from USB Port, Bat-TrackTM, "Instant On" Operation, 1.5A Maximum Charge Current, 180m Ideal Diode with <50 Option, 3.3V/25mA Always-On LDO, Three Synchronous Buck Regulators (400mA/400mA/1A), 4mm x 5mm QFN28 Package Complete Multifunction ASSP: Linear Power Manager and Three Buck Regulators, Charge Current Programmable Up to 1.5A from Wall Adapter Input, Thermal Regulation, Synchronous Buck Efficiency: >95%, ADJ Outputs: 0.8V to 3.6V at 400mA/400mA/600mA, Bat-Track Adaptive Output Control, 200m Ideal Diode, 4mm x 4mm QFN28 Package Charge Current Programmable Up to 950mA, USB Compatible, Dual Synchronous 400mA Buck Regulators, Efficiency >90%, 3mm x 3mm QFN16 Package >90% Efficiency, VIN: 2.9V to 5.5V, IQ = 260A, LTC3672B-1: Buck = 1.8V, LDO1 = 1.2V, LDO2 = 2.8V LTC3672B-2: Buck = 1.2V, LDO1 = 2.8V, LDO2 = 1.8V Consult LTC Factory for Other Voltage Combinations VIN from 2.65V to 9.8V, Constant Frequency 550kHz Operation LT3024 LTC3025 LTC3407 LTC3407-2 LTC3445 LTC3555 LTC3557 USB Power Manager with Li-Ion/Polymer Charger and Triple Synchrounous Buck Converter LTC3559 LTC3672B-1/ LTC3672B-2 Linear USB Li-Ion Battery Charger with Dual Buck Regulators Fixed-Output Monolithic 400mA Buck Regulator with Dual 150mA LDOs in a 2mm x 2mm DFN Step-Down DC/DC Controller with LDO Regulator LTC3700 PowerPath and Bat-Track is a trademark of Linear Technology Corporation. 3446fd LT 0108 REV D * PRINTED IN USA 20 Linear Technology Corporation (408) 432-1900 FAX: (408) 434-0507 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2006 |
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