LTC3672B-1 Monolithic Fixed-Output 400mA Buck Regulator with Dual 150mA LDOs in 2mm × 2mm DFN FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION Triple Output Supply From a Single 2.9V to 5.5V Input Buck DC/DC: Fixed 1.8V Output, Up to 400mA LDO1: Fixed 1.2V Output, Up to 150mA LDO2: Fixed 2.8V Output, Up to 150mA ±2.5% Reference Accuracy Constant Frequency 2.25MHz Operation Minimum External Component Count Current Mode Operation for Excellent Line and Load Transient Response Internal Soft-Start for Each Output Single Enable Pin Turns On/Shuts Down All Three Outputs Tiny 2mm × 2mm × 0.75mm DFN Package APPLICATIONS ■ ■ ■ DMB Cellphones Handheld Products (PDA, PMP, GPS) Multivoltage Power for Digital Logic, I/O, FPGAs, CPLDs, ASICs, CPUs, and RF Chipsets The LTC®3672B-1 is a triple power supply composed of a 400mA synchronous buck regulator and two 150mA lowdropout linear regulators (LDOs), where one of the LDOs can be powered from the buck output to improve efficiency. Constant-frequency 2.25MHz operation is maintained down to very light loads. The input supply range of 2.9V to 5.5V is especially well-suited for single-cell Lithium-Ion and Lithium-Polymer applications, and for powering low voltage ASICs from 3.3V or 5V rails. The LTC3672B-1 regulates 1.8V at the buck output, 1.2V at the LDO1 output, and 2.8V at the LDO2 output. External component count is minimal—all that is needed is a single inductor, an input capacitor, and output capacitors for each of the three outputs. Control loop compensation is internal to the LTC3672B-1. The LTC3672B-1 is available in a 2mm × 2mm × 0.75mm 8-Lead DFN package. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION Buck DC/DC Efficiency vs Load 100 VIN 2.9V TO 5.5V VIN GND 4.7MH SW BUCKOUT 10MF VIN1 ENABLE INPUT ENALL LDO1 1MF LTC3672B-1 LDO2 3672b1 TA01 1MF VOUT1 1.8V 400mA (250mA IF LDO1 FULLY-LOADED) VOUT2 1.2V 150mA VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS) VIN = 2.9V 90 EFFICIENCY (%) 2.2MF 95 VIN = 3.6V 85 VIN = 5.5V 80 75 70 65 60 0 50 100 150 200 250 300 350 400 ILOAD (mA) 3672b1 TA01b 3672B1f 1 LTC3672B-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2, 3) TOP VIEW VIN ............................................................... –0.3V to 6V VIN1, BUCKOUT, ENALL, SW, LDO2 ...........–0.3V to the lesser of (VIN + 0.3V) or 6V LDO1 ............. –0.3V to the lesser of (VIN1 + 0.3V) or 6V Junction Temperature ........................................... 125°C Operating Temperature Range...................... –40 to 85°C Storage Temperature Range....................... –65 to 125°C 8 VIN SW 1 GND 2 ENALL 3 9 BUCKOUT 4 7 LDO2 6 LDO1 5 VIN1 DC PACKAGE 8-LEAD (2mm s 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 102°C/W, θJC = 20°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3672BEDC-1#PBF LTC3672BEDC-1#TRPBF LCWH 8-Lead (2mm × 2mm) Plastic DFN –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. *For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, unless otherwise noted. SYMBOL PARAMETER VIN Input Voltage Range VUVLO VIN Undervoltage Lockout Threshold CONDITIONS MIN ● 2.9 VIN Rising Undervoltage Lockout Hysteresis IQ,VIN IQ,VIN1 VIN Quiescent Current All Outputs Enabled, No Load Shutdown (Note 4) VBUCKOUT = 1.9V VENALL = 0V VIN1 Quiescent Current All Outputs Enabled, No Load Shutdown VIN1 = 1.8V TYP ENALL Pin Logic Low Voltage ● VIH ENALL Pin Logic High Voltage ● RENALL ENALL Pin Pulldown Resistance UNITS 5.5 V 1.7 2 V 12 100 mV 260 400 1 μA μA 2.3 5 1 μA μA VENALL = 0V VIL MAX 0.4 1.2 V V 5.5 MΩ Synchronous Buck Regulator fOSC Oscillator Frequency VBUCKOUT Regulated Output Voltage IMAXP 1.8 2.25 2.7 1.755 1.8 1.845 V PMOS Switch Maximum Peak Current (Note 5) 550 800 1100 mA IOUT,BUCK Available Output Current 400 RP,BUCK PMOS Switch On-Resistance 0.6 Ω RN,BUCK NMOS Switch On-Resistance 0.7 Ω ● MHz mA 3672B1f 2 LTC3672B-1 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS RPD,BUCKOUT BUCKOUT Pulldown Resistance in Shutdown VENALL = 0V MIN TYP 10 MAX UNITS kΩ RPD,SW SW Pulldown Resistance in Shutdown VENALL = 0V 10 kΩ tSS,BUCK Soft-Start Time 0.2 ms LDO Regulator 1: VIN1 = 1.8V Unless Otherwise Noted VLDO1 ● Regulated Output Voltage LDO1 Output, ILDO1 = 1mA Line Regulation with Respect to VIN with Respect to VIN1 ILDO1 = 1mA VIN = 3V to 5.5V, VIN1 = 1.8V VIN = 3.6V, VIN1 = 1.7V to 1.9V 0.05 1 mV/V mV/V Load Regulation ILDO1 = 1mA to 150mA –0.05 mV/mA Available Output Current 1.17 1.2 1.23 150 Short-Circuit Output Current mA 347 ILDO1 = 150mA V 484 mA VDROP1 Dropout Voltage (Note 6) 570 mV tSS,LDO1 Soft-Start Time 0.3 ms RPD,LDO1 Output Pulldown Resistance in Shutdown 10 kΩ LDO Regulator 2 VLDO2 Regulated Output Voltage LDO2 Output, ILDO2 = 1mA Line Regulation with Respect to VIN ILDO2 = 1mA, VIN = 3V to 5.5V Load Regulation ILDO2 = 1mA to 150mA Available Output Current ● 2.73 2.8 2.87 1 mV/V 0.1 mV/mA 150 Short-Circuit Output Current mA 453 ILDO2 = 150mA V VDROP2 Dropout Voltage (Note 6) tSS,LDO2 Soft-Start Time 0.1 ms RPD,LDO2 Output Pulldown Resistance in Shutdown 10 kΩ 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 LTC3672B-1 is guaranteed to meet performance specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. 188 mA 250 mV Note 4: Dynamic supply current is higher due to the gate charge delivered to the buck regulator’s internal MOSFET switches at the switching frequency. Note 5: The current limit features of this part are intended to protect the IC from short term or intermittent fault conditions. Continuous operation above the specified maximum specified pin current rating may result in device degradation or failure. Note 6: Dropout voltage is the minimum input to output voltage differential needed to maintain regulation at a specified output current. When LDO1 is in dropout, its output voltage will be equal to: VIN1 – VDROP1. When LDO2 is in dropout, its output voltage will be equal to: VIN – VDROP2. 3672B1f 3 LTC3672B-1 TYPICAL PERFORMANCE CHARACTERISTICS VIN Quiescent Current vs VIN Voltage 5 SW PIN NOT SWITCHING 130°C 2 3.5 4.0 VIN (V) 4.5 5.0 LDO1 REGULATED OUTPUT (V) BUCK REGULATED OUTPUT (V) 1.23 BUCK AT NO LOAD 1.800 BUCK AT 400mA LOAD 1.770 0 1.22 1.19 BUCK AT NO LOAD 1.80 BUCK AT 400mA LOAD 1.78 1.77 1.76 3.0 3.5 4.0 4.5 5.0 VIN INPUT VOLTAGE (V) 2.85 5.5 3672b1 G07 VIN = 3.6V VIN1 = 1.8V 2.83 2.81 LDO2 AT NO LOAD 2.79 LDO2 AT 150mA LOAD 2.77 2.75 2.73 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 3672b1 G05 LDO1 REGULATED OUTPUT (V) BUCK REGULATED OUTPUT (V) 1.82 1.75 2.5 3672b1 G03 2.87 1.18 1.23 1.22 1.20 ILDO1 = 150mA 1.18 1.17 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN1 INPUT VOLTAGE (V) 3672b1 G08 25 50 75 100 125 150 TEMPERATURE (°C) LDO2 Regulated Output Voltage vs VIN Input Voltage 2.86 ILDO1 = 0mA 0 3672b1 G06 BUCK AND LDO2 UNLOADED VIN = 3.6V 1.21 1.19 25 50 75 100 125 150 TEMPERATURE (°C) LDO2 Regulated Output vs Temperature LDO1 AT 150mA LOAD 0 0 3672b1 G02 LDO1 Regulated Output vs VIN1 Input Voltage 1.83 1.79 0 –50 –25 5.5 LDO1 AT NO LOAD 1.17 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) BOTH LDOs UNLOADED 1.81 5.0 1.20 Buck Regulated Output vs VIN Input Voltage 1.84 4.0 4.5 VIN1 (V) VIN = 3.6V VIN1 = 1.8V 1.21 3672b1 G04 1.85 3.5 LDO1 Regulated Output vs Temperature 1.815 1.755 –50 –25 3.0 3672b1 G01 VIN = 3.6V VIN1 = 1.8V 1.785 1.0 0.5 0 2.5 5.5 1.5 25°C LDO2 REGULATED OUTPUT (V) 3.0 Buck Regulated Output vs Temperature 1.830 –45°C 1 0 2.5 VIN = 2.8V TO 5.5V VIN1 = 1.8V 2.0 130°C 3 IVIN1 (μA) –45°C 100 1.845 2.5 90°C 25°C 200 3.0 VIN = VIN1 4 90°C 300 VIN1 Quiescent Current vs Temperature LDO2 REGULATED OUTPUT (V) 400 IVIN (μA) VIN1 Quiescent Current vs VIN1 Voltage IVIN1 (μA) 500 TA = 25°C unless otherwise specified. BUCK AND LDO1 UNLOADED 2.84 2.82 ILDO2 = 0mA 2.80 ILDO2 = 150mA 2.78 2.76 2.74 2.5 3.0 3.5 4.0 4.5 5.0 VIN INPUT VOLTAGE (V) 5.5 3672b1 G09 3672B1f 4 LTC3672B-1 TYPICAL PERFORMANCE CHARACTERISTICS VIN1-LDO1 Dropout Voltage vs Load VIN-LDO2 Dropout Voltage vs Load 250 DROPOUT VOLTAGE (mV) 25°C 400 300 –45°C 200 130°C 100 200 –45°C 100 50 25 0 50 75 100 LDO1 LOAD (mA) 125 0 150 VIN1 = 1.8V 400 300 200 100 0 2.5 –45°C 25°C 90°C 3.0 3.5 4.0 VIN (V) 4.5 25 0 50 75 100 LDO2 LOAD (mA) 3672b1 G10 5.0 3672b1 G16 150 100 0 200 –45°C 25°C 90°C 3.0 3.5 4.0 VIN (V) 4.5 0 PMOS ON-RESISTANCE (mΩ) 600 500 5.0 5.5 3672b1 G14 2.4 2.2 2.1 5 6 3672b1 G12 VIN = 5.5V VIN = 4.2V VIN = 3.6V VIN = 2.9V 1.9 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) 3672b1 G15 Startup Transient –45°C 0V ENALL 300 4 2.0 OUTPUT VOLTAGES 500mV/DIV 25°C 3 VIN1 (V) 2.3 130°C 90°C 400 1V 0V VOUT3 VOUT1 VOUT1 VOUT2 50μs/DIV 3672b1 G18 FRONT PAGE APPLICATION VIN = 3.6V 10mA RESISTIVE LOAD ON EACH OUTPUT 200 100 0 2.5 2 Buck Oscillator Frequency vs Temperature Buck PMOS Switch On-Resistance 700 1 3672b1 G11 300 100 –45°C 25°C 90°C 50 150 400 800 600 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) 200 2.5 900 1000 VIN = 2.9V VIN = 3.6V VIN = 5.5V 250 500 PMOS Switch Maximum Peak Current 700 300 2.6 3672b1 G13 800 350 600 0 2.5 5.5 900 125 400 LDO2 Short Circuit Current vs VIN LDO2 SHORT CIRCUIT CURRENT (mA) LDO1 SHORT CIRCUIT CURRENT (mA) 25°C 150 LDO1 Short Circuit Current vs VIN PMOS SWITCH MAX PEAK CURRENT (mA) 130°C VIN = 5.5V 450 FREQUENCY (MHz) DROPOUT VOLTAGE (mV) 500 500 LDO1 Short Circuit Current vs VIN1 500 300 LDO1 SHORT CIRCUIT CURRENT (mA) 600 0 TA = 25°C unless otherwise specified. 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 3672b1 G17 3672B1f 5 LTC3672B-1 PIN FUNCTIONS SW (Pin 1): Switch Node Connection to Inductor. This pin connects to the drains of the buck regulator’s main PMOS and synchronous NMOS switches. LDO1 (Pin 6): Output of the First Low Dropout Linear Regulator. This pin must be bypassed to ground with a 1μF or greater ceramic capacitor. GND (Pin 2): Ground. LDO2 (Pin 7): Output of the Second Low Dropout Linear Regulator. This pin must be bypassed to ground with a 1μF or greater ceramic capacitor. ENALL (Pin 3): Enables all three outputs when high, shuts down the IC when low. This is a MOS gate input. An internal 5.5MΩ resistor pulls this pin to ground. BUCKOUT (Pin 4): Output Voltage Sense Connection for the Buck Regulator. VIN1 (Pin 5): Power Input for the First Low Dropout Linear Regulator, LDO1. This pin may be connected to the buck regulator’s output, VIN, or a voltage not exceeding VIN. VIN (Pin 8): Input Bias Supply for the IC, and Power Input for the Buck Regulator and LDO2. This pin should be bypassed to ground with a 2.2μF or greater ceramic capacitor. Exposed Pad (Pin 9): Ground. The Exposed Pad must be soldered to PCB. BLOCK DIAGRAM 4 8 BUCKOUT LDO1 VIN1 6 LDO2 + 400mA BUCK SW 5 VIN 1 7 1M 400k 2M 800k 800k 800k – GND 2 ENABLE BUCK LOGIC LDO2 LDO1 2.25MHz OSC 800mV REFERENCE ENALL 3 5.5M ENABLE LDO2 ENABLE LDO1 EXPOSED PAD (GND) 9 3672b1 BD 3672B1f 6 LTC3672B-1 OPERATION INTRODUCTION The LTC3672B-1 combines a synchronous buck converter with two low dropout linear DC regulators (LDOs) to provide three low voltage outputs from a higher voltage input source. All outputs are enabled and disabled together through the ENALL pin. The output regulation voltages are set during manufacturing to 1.8V nominal for the buck, 1.2V nominal for LDO1, and 2.8V nominal for LDO2. LDO1 may be powered off of the buck output for higher overall efficiency. For versions of the IC with different output regulation voltages, consult the LTC factory. SYNCHRONOUS BUCK REGULATOR The synchronous buck uses a constant-frequency current mode architecture, switching at 2.25MHz down to very light loads, and supports no-load operation by skipping cycles. When the input voltage drops very close to or falls below the target output voltage, the buck supports 100% duty cycle operation (low dropout mode). Soft-start circuitry limits inrush current when powering on. Output current is limited in the event of an output short-circuit. The switch node is slew-rate limited to reduce EMI radiation. The buck regulation control-loop compensation is internal to the IC, and requires no external components. Main Control Loop An error amplifier monitors the difference between an internal reference voltage and the voltage on the BUCKOUT pin. When the BUCKOUT voltage is below the reference, the error amplifier output voltage increases. When the BUCKOUT voltage exceeds the reference, the error amplifier output voltage decreases. The error amplifier output controls the peak inductor current through the following mechanism: Paced by a free-running 2.25MHz oscillator, the main P-channel MOSFET switch is turned on at the start of the oscillator cycle. Current flows from the VIN supply through this PMOS switch, through the inductor via the SW pin, and into the output capacitor and load. When the current reaches the level programmed by the output of the error amplifier, the PMOS is shut off, and the N-channel MOSFET synchronous rectifier turns on. Energy stored in the inductor discharges into the load through this NMOS. The NMOS turns off at the end of the 2.25MHz cycle, or sooner, if the current through it drops to zero before the end of the cycle. Through these mechanisms, the error amplifier adjusts the peak inductor current to deliver the required output power to regulate the output voltage as sensed by the BUCKOUT pin. All necessary control-loop compensation is internal to the step-down switching regulator, requiring only a single ceramic output capacitor for stability. Light Load/No-Load Cycle-Skipping At light loads, the inductor current may reach zero before the end of the oscillator cycle, which will turn off the NMOS synchronous rectifier. In this case, the SW pin goes high impedance and will show damped “ringing”. This is known as discontinuous operation, and is normal behavior for a switching regulator. At very light load and no-load conditions, the buck will automatically skip cycles as needed to maintain output regulation. Soft-Start Soft-start in the buck regulator is accomplished by gradually increasing the maximum allowed peak inductor current over a 200μs period. This allows the output to rise slowly, controlling the inrush current required to charge up the output capacitor. A soft-start cycle occurs whenever the LTC3672B-1 is enabled, or after a fault condition has occurred (thermal shutdown or UVLO). Switch Slew-Rate Control The buck regulator contains new patent pending circuitry to limit the slew rate of the switch node (SW pin). This new circuitry is designed to transition the switch node over a period of a couple nanoseconds, significantly reducing radiated EMI and conducted supply noise while maintaining high efficiency. LOW VIN SUPPLY UNDERVOLTAGE LOCKOUT An undervoltage lockout (UVLO) circuit shuts down the LTC3672B-1 when VIN drops below about 1.7V. 3672B1f 7 LTC3672B-1 OPERATION LOW DROPOUT LINEAR REGULATORS (LDOS) The LTC3672B-1 contains two 150mA fixed-output LDO regulators. LDO1 takes power from the VIN1 pin and regulates a 1.2V output at the LDO1 pin. By connecting VIN1 to the buck regulator’s 1.8V output, overall conversion efficiency can be improved, because the bulk of the stepdown will be done by the buck regulator at higher efficiency than what the LDO can do on its own. For example, for the case of deriving a 1.2V output from a 3.6V input (e.g. Lithium-Ion battery nominal voltage), using an LDO to do all of the step-down results in an efficiency of at most 1.2V/3.6V = 33.3%, using the fact that the upper-bound on any linear regulator’s efficiency is output voltage divided by input voltage. Feeding the LDO from the output of the buck regulator, with a typical buck efficiency of 85%, raises the ceiling on overall efficiency to 85% • 1.2V/1.8V = 56.6%. This can increase battery life by up to 70%! LDO2 takes power straight from VIN and regulates a 2.8V output at the LDO2 pin. For stability, each LDO output must be bypassed to ground with a minimum 1μF ceramic capacitor. APPLICATIONS INFORMATION BUCK REGULATOR INDUCTOR SELECTION Many different sizes and shapes of inductors are available from numerous manufacturers. Choosing the right inductor from such a large selection of devices can be overwhelming, but following a few basic guidelines will make the selection process much simpler. The buck regulator is designed to work with inductors in the range of 2.2μH to 10μH. A 4.7μH inductor is a good starting point. Larger value inductors reduce ripple current, which improves output ripple voltage. Lower value inductors result in higher ripple current and improved transient response time. To maximize efficiency, choose an inductor with a low DC resistance. Choose an inductor with a DC current rating at least 1.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. If output short circuit is a possible condition, the inductor should be rated to handle the maximum peak current specified for the stepdown converters. Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or Permalloy™ materials are small and don’t radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. Inductors that are very thin or have a very small volume typically have much higher core and DCR losses, and will not give the best efficiency. The choice of which style inductor to use often depends more on the price vs size, performance, and any radiated EMI requirements than on what the buck regulator needs to operate. Table 1 shows several inductors that work well with the buck regulator. These inductors offer a good compromise in current rating, DCR and physical size. Consult each manufacturer for detailed information on their entire selection of inductors. 3672B1f 8 LTC3672B-1 APPLICATIONS INFORMATION Table 1. Recommended Inductors for the Buck Regulator INDUCTOR TYPE L (μH) MAX IDC (A) MAX DCR (Ω) SIZE IN mm (L × W × H) MANUFACTURER DB318C 4.7 3.3 4.7 3.3 4.7 3.3 1.07 1.2 0.79 0.9 1.15 1.37 0.1 0.07 0.24 0.2 0.13* 0.105* 3.8 × 3.8 × 1.8 3.8 × 3.8 × 1.8 3.6 × 3.6 × 1.2 3.6 × 3.6 × 1.2 3 × 2.8 × 1.2 3 × 2.8 × 1.2 Toko www.toko.com 4.7 3.3 4.7 3.3 4.7 0.9 1.1 0.5 0.6 0.75 0.11 0.085 0.17 0.123 0.19 4 × 4 × 1.8 4 × 4 × 1.8 3.2 × 3.2 × 1.2 3.2 × 3.2 × 1.2 4.9 × 4.9 × 1 Sumida www.sumida.com 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 1.3 1.59 0.8 0.97 1.29 1.42 1.08 1.31 0.162 0.113 0.246 0.165 0.117* 0.104* 0.153* 0.108* 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.2 3.1 × 3.1 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1 5.2 × 5.2 × 1 Cooper www.cooperet.com 4.7 3.3 1.1 1.3 0.2 0.13 3 × 3 × 1.5 3 × 3 × 1.5 Coil Craft www.coilcraft.com D312C DE2812C CDRH3D16 CDRH2D11 CLS4D09 SD3118 SD3112 SD12 SD10 LPS3015 * = Typical DCR INPUT/OUTPUT CAPACITOR SELECTION Low ESR (equivalent series resistance) ceramic capacitors should be used to bypass the following pins to ground: VIN, VIN1, the buck output, LDO1, and LDO2. Only X5R or X7R ceramic capacitors should be used because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. A 10μF output capacitor is sufficient for the buck regulator output. For good transient response and stability the output capacitor for the buck regulator should retain at least 4μF of capacitance over operating temperature and bias voltage. The VIN pin should be bypassed with a 2.2μF capacitor. The LDO1 and LDO2 output pins should be bypassed with a 1μF capacitor or greater. VIN1 should be bypassed with a 1μF capacitor, which may be omitted if VIN1 is tied to the buck regulator’s output capacitor. Consult with capacitor manufacturers for detailed information on their selection and specifications of ceramic capacitors. Many manufacturers now offer very thin (<1mm tall) ceramic capacitors ideal for use in height-restricted designs. Table 2 shows a list of several ceramic capacitor manufacturers. Table 2. Ceramic Capacitor Manufacturers AVX www.avxcorp.com Murata www.murata.com Taiyo Yuden www.t-yuden.com Vishay Siliconix www.vishay.com TDK www.tdk.com 3672B1f 9 LTC3672B-1 APPLICATIONS INFORMATION PRINTED CIRCUIT BOARD LAYOUT CONSIDERATIONS When laying out the printed circuit board, the following list should be followed to ensure proper operation of the LTC3672B-1: 1) The Exposed Pad of the package should connect directly to a large ground plane to minimize thermal and electrical impedance. 2) The connections from the input supply pins (VIN and VIN1) to their respective decoupling capacitors should be kept as short as possible. The GND side of these capacitors should connect directly to the ground plane of the part. The VIN capacitor provides the AC current to the buck regulator’s power MOSFETs and their drivers. It is especially important to minimize PCB trace inductance from this capacitor to the VIN and GND pins of the LTC3672B-1. 3) The switching power trace connecting the SW pin to the inductor should be kept as short as possible to reduce radiated EMI and parasitic coupling. 4) The LDO output capacitors should be placed as close to the IC as possible, and connect to the LDO outputs and the GND pin as directly as possible. 3672B1f 10 LTC3672B-1 PACKAGE DESCRIPTION DC Package 8-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1719 Rev Ø) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 0.64 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 1.37 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.05 TYP 2.00 ±0.10 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) R = 0.115 TYP 5 8 0.40 ± 0.10 0.64 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER (DC8) DFN 0106 REVØ 4 0.200 REF 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 1.37 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 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 3672B1f 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. 11 LTC3672B-1 TYPICAL APPLICATION LTC3672B-1 with VIN1 Tied to VIN, VOUT1 Capable of 400mA Even with VOUT2 and VOUT3 Fully Loaded LTC3672B-1 with VIN1 Tied to an Independent Supply, VOUT1 Capable of 400mA Even with VOUT2 and VOUT3 Fully Loaded VIN 2.9V TO 5.5V VIN 2.9V TO 5.5V 4.7MH VIN VIN1 SW 2.2MF GND ENABLE INPUT BUCKOUT 10MF VOUT1 1.8V 400mA 1MF VOUT2 1.2V 150mA LDO1 ENALL LTC3672B-1 LDO2 1MF 3672b1 TA02 VIN 2.2MF GND 1MF VOUT1 1.8V 400mA (250mA IF LDO1 FULLY-LOADED) BUCKOUT 10MF LTC3672B-1 VIN1 1.8V TO VIN VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS) 4.7MH SW VIN1 ENABLE INPUT VOUT2 1.2V 150mA LDO1 1MF ENALL VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS) LDO2 3672b1 TA03 1MF LTC3672B-1 with VIN1 Tied to Buckout with More LDO Output Capacitance for Improved Transient Response VIN 2.9V TO 5.5V 4.7MH VIN 10MF GND Load Transient Response SW BUCKOUT 10MF VIN1 LDO1 ENABLE INPUT ENALL 4.7MF LTC3672B-1 LDO2 3672b1 TA04 4.7MF VOUT1 1.8V 400mA (250mA IF LDO1 FULLY-LOADED) VOUT2 1.2V 150mA VOUT3 2.8V UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS) VOUT2 50mV/DIV AC-COUPLED VOUT3 VOUT1 VOUT2 AND VOUT3 100mA LOAD CURRENT 10mA 3672b1 TA04b 20μs/DIV VIN = 3.6V SIMULTANEOUS LOAD TRANSIENT ON BOTH LDOs VOUT1 FLOATING RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3405/LTC3405A 300mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 20μA, ISD <1μA, ThinSOT Package LTC3406/LTC3406B 600mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converter 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD <1μA, ThinSOT Package LTC3407/LTC3407-2 Dual 600mA/800mA IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD <1μA, MS10E Package LTC3410/LTC3410B 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 26μA, ISD <1μA, SC70 Package LTC3411 1.25A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD <1μA, MS10 Package LTC3445 I2C Controllable 600mA Synchronous Buck Regulator with Two 50mA LDOs in a 4mm × 4mm QFN 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.85V, IQ = 360μA, ISD <27μA, 4mm × 4mm QFN Package LTC3446 Synchronous 1A, 2.25MHz Step-Down DC/DC Regulator with Dual VLDOs 95% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 0.4V, IQ = 140μA, ISD <1μA, 3mm × 4mm DFN Package LTC3448 600A IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converter with LDO Mode 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 32μA, ISD <1μA, MS10, DFN Packages LTC3541/LTC3541-1/ Synchronous 500mA, 2.25MHz Step-Down DC/DC LTC3541-2/LTC3541-3 Regulator with a 300mA VLDO in a 3mm × 3mm DFN 95% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 0.4V, IQ = 85μA, ISD <1μA, 3mm × 3mm DFN Package LTC3547 Dual 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD <1μA, DFN-8 Package LTC3548/LTC3548-1/ LTC3548-2 Dual 800mA/400mA IOUT, 2.25MHz, Synchronous StepDown DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD <1μA, MS10, DFN Packages 3672B1f 12 Linear Technology Corporation LT 0607 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007