LTC3672BEDC-2#TRMPBF

LTC3672B-2 Monolithic Fixed-Output 400mA Buck Regulator with Dual 150mA LDOs in 2mm × 2mm DFN FEATURES DESCRIPTION n The LTC®3672B-2 is a triple power supply composed of a 400mA synchronous buck regulator and two 150mA low-dropout linear regulators (LDOs). Constant-frequency 2.25MHz operation is maintained down to very light loads. The input supply range of 2.9V to 5.5V is especially wellsuited for single-cell Lithium-Ion and Lithium-Polymer applications, and for powering low voltage ASICs from 3.3V or 5V rails. n n n n n n n n n n Triple Output Supply From a Single 2.9V to 5.5V Input Buck DC/DC: Fixed 1.2V Output, Up to 400mA LDO1: Fixed 2.8V Output, Up to 150mA LDO2: Fixed 1.8V 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 n n n DMB and DVB-H Cellphones Handheld Products (PDA, PMP, GPS) Multivoltage Power for Digital Logic, I/O, FPGAs, CPLDs, ASICs, CPUs, and RF Chipsets The LTC3672B-2 regulates 1.2V at the buck output, 2.8V at the LDO1 output, and 1.8V 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-2. The LTC3672B-2 is available in a 2mm × 2mm × 0.75mm 8-Lead DFN package. , 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 Buck Load VIN 2.9V TO 5.5V 100 95 VIN VIN1 SW 4.7μF GND BUCKOUT LTC3672B-2 ENABLE INPUT ENALL VOUT1 1.2V 400mA LDO1 1μF LDO2 3672B2 TA01 1μF VOUT2 2.8V, UP TO 150mA (SUBJECT TO DROPOUT LIMITATIONS) VOUT3 1.8V 150mA 90 EFFICIENCY (%) 4.7μH 2.2μF VIN = 2.9V 85 VIN = 3.6V 80 75 VIN = 5.5V 70 65 60 0 50 100 150 200 250 300 350 400 ILOAD (mA) 3672B2 TA01b 3672b2fa 1 LTC3672B-2 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 3) 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 (Note 2)........ –40 to 85°C Storage Temperature Range....................... –65 to 125°C TOP VIEW 8 VIN SW 1 GND 2 9 ENALL 3 7 LDO2 6 LDO1 BUCKOUT 4 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-2#PBF LTC3672BEDC-2#TRPBF LDBH 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 l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = VIN1 = 3.6V, unless otherwise noted. SYMBOL PARAMETER VIN Input Voltage Range VUVLO VIN Undervoltage Lockout Threshold CONDITIONS MIN l 2.9 VIN Rising Undervoltage Lockout Hysteresis IQ,VIN IQ,VIN1 VIN Quiescent Current All Outputs Enabled, No Load Shutdown (Note 4) VBUCKOUT = 1.3V VENALL = 0V VIN1 Quiescent Current All Outputs Enabled, No Load Shutdown VENALL = 0V VIL ENALL Pin Logic Low Voltage l VIH ENALL Pin Logic High Voltage l RENALL ENALL Pin Pulldown Resistance TYP MAX UNITS 5.5 V 1.7 2 V 12 100 mV 260 400 1 μA μA 2.3 5 1 μA μA 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 MHz 1.17 1.2 1.23 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 l mA 3672b2fa 2 LTC3672B-2 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = VIN1 = 3.6V, unless otherwise noted. SYMBOL PARAMETER RPD,BUCKOUT BUCKOUT Pulldown Resistance in Shutdown VENALL = 0V CONDITIONS MIN 10 kΩ RPD,SW SW Pulldown Resistance in Shutdown 10 kΩ tSS,BUCK Soft-Start Time 0.2 ms VENALL = 0V TYP MAX UNITS LDO Regulator 1 VLDO1 Regulated Output Voltage LDO1 Output, ILDO1 = 1mA Line Regulation with Respect to VIN ILDO1 = 1mA, VIN = VIN1 = 2.9V to 5.5V Load Regulation ILDO1 = 1mA to 150mA l 2.73 2.8 2.87 1 Available Output Current mV/V –0.1 mV/mA 440 mA 150 Short-Circuit Output Current ILDO1 = 150mA V mA VDROP1 Dropout Voltage (Note 6) 135 250 mV tSS,LDO1 Soft-Start Time 0.1 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 = 2.9V to 5.5V Load Regulation ILDO2 = 1mA to 150mA Available Output Current l 1.755 1.8 1.845 0.6 mV/V –0.1 mV/mA 150 Short-Circuit Output Current mA 450 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-2 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. 290 mA 400 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. 3672b2fa 3 LTC3672B-2 TYPICAL PERFORMANCE CHARACTERISTICS 500 VIN1 Quiescent Current vs VIN1 Voltage 5 SW PIN NOT SWITCHING 130°C 400 Buck Regulated Output vs Temperature 1.23 VIN = VIN1 BUCK REGULATED OUTPUT (V) VIN Quiescent Current vs VIN Voltage TA = 25°C unless otherwise specified. 4 90°C 25°C 200 –45°C IVIN1 (μA) IVIN (μA) 90°C 300 130°C 3 2 –45°C 25°C 100 1 3.0 3.5 4.0 VIN (V) 4.5 5.0 0 2.5 5.5 3.5 3672B2 G01 LDO1 Regulated Output vs Temperature 4.0 4.5 VIN1 (V) 5.0 2.87 V = VIN1 = 3.6V 2.86 IN 2.85 2.84 2.83 2.82 LDO1 AT NO LOAD 2.81 2.80 LDO1 AT 150mA LOAD 2.79 2.78 2.77 2.76 2.75 2.74 2.73 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (oC) 1.21 BUCK AT NO LOAD 1.20 1.845 BUCK AT 400mA LOAD 1.19 1.18 1.17 –50 –25 5.5 0 25 50 75 100 125 150 TEMPERATURE (°C) 3672B2 G03 3672B2 G02 Buck Regulated Output vs VIN Input Voltage 1.23 VIN = 3.6V 1.830 BOTH LDOs UNLOADED 1.22 1.815 LDO2 AT NO LOAD 1.800 LDO2 AT 150mA LOAD 1.785 1.770 1.21 BUCK AT NO LOAD 1.20 BUCK AT 400mA LOAD 1.19 1.18 1.755 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1.17 2.5 3672B2 G05 3672B2 G04 LDO1 Regulated Output vs VIN1 Input Voltage 3.0 3.5 4.0 4.5 5.0 VIN INPUT VOLTAGE (V) 5.5 3672B2 G06 LDO2 Regulated Output Voltage vs VIN Input Voltage 2.87 BUCK AND LDO2 UNLOADED 2.86 VIN = VIN1 2.85 2.84 2.83 2.82 2.81 ILDO1 = 0mA 2.80 2.79 ILDO1 = 150mA 2.78 2.77 2.76 2.75 2.74 2.73 2.5 3.0 3.5 4.0 4.5 5.0 VIN1 INPUT VOLTAGE (V) 1.85 BUCK AND LDO1 UNLOADED 1.84 1.83 LDO2 OUTPUT (V) LDO1 OUTPUT (V) 1.22 LDO2 Regulated Output vs Temperature LDO2 REGULATED OUTPUT (V) LD01 REGULATED OUTPUT (V) 3.0 BUCK OUTPUT (V) 0 2.5 VIN = 3.6V 1.82 1.81 ILDO2 = 0mA 1.80 1.79 ILDO2 = 150mA 1.78 1.77 1.76 5.5 3672b2 G07 1.75 2.5 3.0 3.5 4.0 4.5 5.0 VIN INPUT VOLTAGE (V) 5.5 3672B2 G08 3672b2fa 4 LTC3672B-2 TYPICAL PERFORMANCE CHARACTERISTICS VIN1 – LDO1 Dropout Voltage vs Load VIN – LDO2 Dropout Voltage vs Load VIN = VIN1 90oC 150 DROPOUT VOLTAGE (mV) 300 90oC 25oC 100 –45oC 50 25oC 250 200 150 –45oC 100 50 400 50 75 100 LDO1 LOAD (mA) 125 0 150 25 50 75 100 LDO2 LOAD (mA) 125 25oC 200 100 VIN = VIN1 0 2.5 3.0 2.6 500 2.5 FREQUENCY (MHz) 600 400 300 200 100 3.5 4.0 VIN (V) 3.5 4.0 4.5 VIN1 (V) 4.5 5.0 5.0 5.5 3672B2 G11 2.4 VIN = 5.5V VIN = 4.2V 2.3 VIN = 3.6V 2.2 2.1 VIN = 2.9V –45°C 25°C 90°C 3.0 150 Buck Oscillator Frequency vs Temperature LDO2 Short-Circuit Current vs VIN 0 2.5 –45oC 3672B2 G10 3672B2 G09 2.0 1.9 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) 5.5 3672B2 G12 3672B2 G13 PMOS Switch Maximum Peak Current vs Temperature Buck PMOS Switch On-Resistance vs Temperature 900 1000 130°C 800 PMOS ON-RESISTANCE (mΩ) 25 LDO2 SHORT CIRCUIT CURRENT (mA) 0 90oC 300 0 0 PMOS SWITCH MAX PEAK CURRENT (mA) DROPOUT VOLTAGE (mV) LDO1 Short-Circuit Current vs VIN1 500 350 LDO1 SHORT-CIRCUIT CURRENT (mA) 200 TA = 25°C unless otherwise specified. 900 800 700 VIN = 2.9V VIN = 3.6V VIN = 5.5V 600 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (°C) 3672B2 G14 700 600 500 90°C 25°C –45°C 400 300 200 100 0 2.5 3.0 3.5 4.0 VIN (V) 4.5 5.0 5.5 3672B2 G15 3672b2fa 5 LTC3672B-2 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 VIN (Pin 8), or to a voltage never 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 ground. BLOCK DIAGRAM 4 8 BUCKOUT 5 VIN LDO1 VIN1 6 LDO2 + 400mA BUCK SW 1 7 400k 2M 1M 800k 800k 800k – GND 2 LDO2 ENABLE BUCK LOGIC LDO1 2.25MHz OSC 800mV REFERENCE ENALL 3 5.5M ENABLE LDO2 ENABLE LDO1 EXPOSED PAD (GND) 9 3672B2 BD 3672b2fa 6 LTC3672B-2 OPERATION INTRODUCTION The LTC3672B-2 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 1.2V nominal for the buck, 2.8V nominal for LDO1, and 1.8V nominal for LDO2. 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-2 is enabled, or after a fault condition has occurred (thermal shutdown or UVLO). 3672b2fa 7 LTC3672B-2 OPERATION Switch Slew-Rate Control LOW DROPOUT LINEAR REGULATORS (LDOs) 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. The LTC3672B-2 contains two 150mA fixed-output LDO regulators. LDO1 takes power from the VIN1 pin and regulates a 2.8V output at the LDO1 pin. LDO2 takes power straight from VIN and regulates a 1.8V output at the LDO2 pin. For stability, each LDO output must be bypassed to ground with a minimum 1μF ceramic capacitor. LOW VIN SUPPLY UNDERVOLTAGE LOCKOUT An undervoltage lockout (UVLO) circuit shuts down the LTC3672B-2 when VIN drops below about 1.7V. 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. 3672b2fa 8 LTC3672B-2 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 DE2818C 4.7 3.3 4.7 3.3 4.7 3.3 1.25 1.45 0.79 0.9 1.15 1.37 0.072 0.053 0.24 0.2 0.13* 0.105* 3 × 2.8 × 1.8 3 × 2.8 × 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 VIN pin. Consult with capacitor manufacturers for detailed information on their selection and specifications of ceramic capacitors. Many manufacturers now offer very thin (