LTC3670 Monolithic 400mA Buck Regulator with Dual 150mA LDOs in 3mm × 2mm DFN DESCRIPTION FEATURES n n n n n n n n n n Triple Output Supply from a Single 2.5V to 5.5V Input 400mA Buck DC/DC Plus Dual 150mA LDOs in One IC Outputs Regulate Down to 0.8V ±2.5% Reference Accuracy Constant-Frequency 2.25MHz Operation Burst Mode® Operation for High Efficiency at Light Loads; IQ = 70μA, All Outputs Enabled Independent Enable Pin for Each Output Current Mode Operation for Excellent Line and Load Transient Response Internal Soft-Start for Each Output Tiny 12-Lead 3mm × 2mm × 0.75mm DFN Package APPLICATIONS n n n n n Handheld Products Portable Instruments Single-Cell Li-Ion/Li-Polymer Powered Devices DMB/DVB-H Multimedia Cell Phones Multivoltage Power for Digital Logic, I/O, FPGAs, CPLDs, ASICs, SoCs, CPUs and RF Chipsets The LTC®3670 is a triple power supply composed of a 400mA synchronous buck regulator and two 150mA low dropout linear regulators (LDOs). The input supply range of 2.5V to 5.5V is especially well-suited for single-cell Lithium-Ion and Lithium-Ion/Polymer applications, and for powering low voltage ASICs and SoCs from 3V, 3.3V or 5V rails. Regulated output voltages are programmed via external resistors. Each output has its own enable pin for maximum flexibility. The 400mA buck regulator features constant-frequency 2.25MHz operation, allowing small surface mount inductors and capacitors to be used. Burst Mode operation maintains high efficiency in light-load and no-load conditions. Internal control-loop compensation simplifies application design. The LTC3670 is available in a 0.75mm profile, 3mm × 2mm 12-lead DFN package. L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents pending. TYPICAL APPLICATION Triple Power Supply with Independent Enables Demoboard VIN 3.3V TO 5.5V 2.2μF VIN 4.7μH GND SW 232k 10pF 4.7μF VOUT1 1.2V 400mA BUCKFB 464k 9.3mm LTC3670 DIGITAL CONTROL ENBUCK ENLDO1 ENLDO2 PGOOD LDO1 806k 1μF VOUT2 2.8V 150mA LDO1_FB 9.4mm ACTIVE AREA 324k LDO2 1.02M 1μF VOUT3 3.3V 150mA 3670 TA01b LDO2_FB 324k 3670 TA01a 3670f 1 LTC3670 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Notes 1, 2, 3) VIN, ENBUCK, ENLDO1, ENLDO2, PGOOD .................................................... –0.3V to 6V SW, BUCKFB, LDO1_FB, LDO2_FB, LDO1, LDO2...............................–0.3V to (VIN + 0.3V) ISW .......................................................................600mA ILDO1, ILDO2 ..........................................................250mA IPGOOD ....................................................................40mA Junction Temperature ........................................... 125°C Operating Temperature Range.................. –40°C to 85°C Storage Temperature Range................... –65°C to 125°C TOP VIEW SW 1 12 VIN GND 2 ENLD01 3 ENLD02 4 11 LDO2 10 LDO1 13 9 LDO1_FB ENBUCK 5 8 LDO2_FB BUCKFB 6 7 PGOOD DDB PACKAGE 12-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 76°C/W, θJC = 13.5°C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3670EDDB#PBF LTC3670EDDB#TRPBF LDBY 12-Lead (3mm × 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 = 3.6V, unless otherwise noted. SYMBOL PARAMETER VIN Input Voltage Range VUVLO Undervoltage Lockout Threshold CONDITIONS MIN l 2.5 VIN Rising Undervoltage Lockout Hysteresis IQ VIL VIH RPGOOD VIN Quiescent Current, No Load All Outputs Enabled Buck Enabled Only Buck Enabled Only, in Dropout One LDO Enabled Only Shutdown TYP (Note 4) VBUCKFB = 0.9V VBUCKFB = 0.9V VBUCKFB = 0V l l UNITS 5.5 V 2.2 2.3 V 18 100 mV 70 38 700 22 110 60 1100 35 1 μA μA μA μA μA 0.4 V V VENBUCK = VENLDO1 = VENLDO2 = 0V ENBUCK, ENLDO1, ENLDO2 Pin Thresholds Logic Low Voltage Logic High Voltage MAX 1.2 ENBUCK, ENLDO1, ENLDO2 Pin Pull-Down Resistance 4 MΩ PGOOD Pin Logic Low Output Resistance 30 Ω PGOOD Pin Hi-Z Leakage VPGOOD = 6V PGOOD Threshold on Feedback Voltages of Enabled Regulators (Note 5) 1 92 μA % 3670f 2 LTC3670 ELECTRICAL CHARACTERISTICS The l 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 MIN TYP MAX UNITS 1.91 2.25 2.59 MHz 0.78 0.8 0.82 V ±20 nA 1100 mA Synchronous Buck Regulator fOSC Oscillator Frequency VBUCKFB Buck Regulated Feedback Voltage l IBUCKFB Feedback Pin Input Bias Current l IMAXP PMOS Switch Maximum Peak Current (Note 6) RP(BUCK) PMOS Switch On-Resistance 0.6 Ω RN(BUCK) NMOS Switch On-Resistance 0.7 Ω RPD(BUCK) SW Pin Pull-Down Resistance in Shutdown 10 kΩ tSS(BUCK) Soft-Start Time 0.6 ms 600 800 Each LDO Regulator VLDO ILDO_FB LDO Regulated Feedback Voltage LDO Output, ILDO = 1mA to 150mA LDO Line Regulation (Note 7) ILDO = 1mA, VIN = 2.5V to 5.5V LDO Load Regulation (Note 7) ILDO = 1mA to 150mA Dropout Voltage (Note 8) 0.78 0.8 0.82 0.25 μV/mA ±20 420 ILDO = 150mA VIN = 3.6V VIN = 2.5V 150 200 V mV/V –5 l Feedback Pin Input Bias Current Short-Circuit Output Current (Note 6) VDROP l nA mA 200 300 mV mV tSS(LDO) Soft-Start Time 0.1 ms RPD(LDO) Output Pull-Down 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: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperatures will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 3: The LTC3670 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 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: PGOOD threshold is expressed as a percentage of the feedback regulation voltage. The threshold is measured for the feedback pin voltage rising. Note 6: The current limit features are intended to protect the IC from short term or intermittent fault conditions. Prolonged operation above the specified Absolute Maximum pin current rating may result in device degradation or failure. Note 7: Measured with the LDO running unity gain, with output tied to feedback pin. Note 8: Dropout voltage is the minimum input to output voltage differential needed for an LDO to maintain regulation at a specified output current. When an LDO is in dropout, its output voltage will be equal to: VIN – VDROP 3670f 3 LTC3670 TYPICAL PERFORMANCE CHARACTERISTICS 130°C 90°C 80 25°C –45°C 60 40 20 2.5 3.5 3 4 VIN (V) 4.5 5 810 VIN = 5.5V 805 VIN = 4.2V 800 VIN = 2.5V 795 VIN = 3.6V 790 785 780 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (˚C) 5.5 820 LDO FEEDBACK PIN VOLTAGE (mV) BUCKFB PIN VOLTAGE (mV) 810 805 800 795 790 785 50 0 90°C – 45°C 25°C 0 25 50 75 100 LOAD CURRENT (mA) 780 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (˚C) 300 130°C 805 800 795 790 200 150 3670 G07 90°C 150 – 45°C 100 25°C 50 785 0 25 50 75 100 LOAD CURRENT (mA) 125 150 0 25 50 75 100 LOAD CURRENT (mA) 2.35 2.30 400 350 300 250 200 150 – 45°C 25°C 90°C 3 3.5 4 VIN (V) 4.5 5 2.25 VIN = 5.5V VIN = 4.2V VIN = 3.6V 2.20 2.15 VIN = 2.5V 2.10 2.05 2.00 1.95 0 2.5 150 Buck Oscillator Frequency vs Temperature 450 100 125 3670 G06 500 50 125 VIN = 2.5V 3670 G05 SHORT-CIRCUIT CURRENT (mA) DROPOUT VOLTAGE (mV) 130°C 50 785 LDO Short-Circuit Current vs VIN 250 VIN = 2.5V VIN = 3.6V VIN = 4.2V VIN = 5.5V 250 0 VIN = 3.6V 100 790 VIN = 3.6V 810 LDO Dropout vs Load Current at VIN = 3.6V 150 795 815 100 150 200 250 300 350 400 LOAD CURRENT (mA) 200 800 LDO Dropout vs Load Current at VIN = 2.5V 3670 G04 300 805 3670 G03 780 0 810 DROPOUT VOLTAGE (mV) VIN = 3.6V 815 780 UNITY GAIN, V(OUT) = V(LDO_FB) 815 I(OUT) = 0.1mA LDO Load Regulation Buck Load Regulation 820 820 3670 G02 3670 G01 OSCILLATOR FREQUENCY (MHz) VIN SUPPLY CURRENT (μA) 100 UNITY GAIN, V(OUT) = V(BUCKFB) 815 I(OUT) = 100mA REGULATED BUCKFB PIN VOLTAGE (mV) ALL THREE OUTPUTS ENABLED, NO LOAD REGULATED LDO FEEDBACK PIN VOLTAGE (mV) 820 120 Regulated LDO Feedback Pin Voltage vs Temperature Buck Regulated Feedback Voltage vs Temperature VIN Supply Current vs VIN 0 (TA = 25°C unless otherwise noted) 5.5 3670 G08 1.90 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (˚C) 3670 G09 3670f 4 LTC3670 TYPICAL PERFORMANCE CHARACTERISTICS PMOS Switch Maximum Peak Current vs Temperature 100 FRACTION OF REGULATION POINT (%) 1000 900 PMOS ON-RESISTANCE (mΩ) 800 VIN = 4.2V 700 VIN = 3.6V VIN = 2.5V 500 400 300 200 100 130°C 800 700 90°C 25°C 600 500 –45°C 400 300 200 100 2.5 3.5 3 4 VIN (V) 5 4.5 3670 G1O PGOOD PIN SINKING 2mA 90 60 130°C 90°C 25°C 30 20 96 95 94 90°C 93 130°C 92 91 –45°C 25°C 2.5 5.5 3 3.5 4 VIN (V) 5 5.5 3670 G12 VIN = 2.5V 85 80 VIN = 3.6V 75 VIN = 5.5V 70 –45°C 4.5 FRONT PAGE APPLICATION CIRCUIT WITH ONLY THE BUCK ENABLED. INDUCTOR: COILCRAFT EPL2014-472ML VOUT = 1.2V 95 40 97 Front Page Application Efficiency 100 70 50 98 3670 G11 PGOOD Pin Pull-Down Resistance 80 99 90 0 0 –50 –30 –10 10 30 50 70 90 110 130 TEMPERATURE (˚C) EFFICIENCY (%) 600 PGOOD Threshold at Any Feedback Pin Buck PMOS On-Resistance VIN = 5.5V PGOOD PIN PULL-DOWN RESISTANCE (Ω) PMOS MAXIMUM PEAK CURRENT (mA) 900 (TA = 25°C unless otherwise noted) 65 10 60 0 2.5 3 3.5 4 VIN (V) 4.5 5 5.5 3670 G13 1 100 10 LOAD CURRENT (mA) 1000 3670 G14 3670f 5 LTC3670 PIN FUNCTIONS SW (Pin 1): Buck Regulator Switch Node Connection to Inductor. This pin connects to the drains of the buck regulator’s main PMOS and synchronous NMOS switches. GND (Pin 2): Ground. ENLDO1 (Pin 3): Enables the First Low Dropout Linear Regulator (LDO1) When High. This is a MOS gate input. There is an internal 4MΩ pull-down. ENLDO2 (Pin 4): Enables the Second Low Dropout Linear Regulator (LDO2) When High. This is a MOS gate input. There is an internal 4MΩ pull-down. ENBUCK (Pin 5): Enables the Buck Converter When High. This is a MOS gate input. There is an internal 4MΩ pulldown. BUCKFB (Pin 6): Feedback Voltage Input for the Buck Regulator. Typically, an external resistor divider feeds a fraction of the buck output voltage to this pin. PGOOD (Pin 7): Power Good Open-Drain NMOS Output. The PGOOD pin goes Hi-Z when all enabled outputs are within 8% of final value. LDO2_FB (Pin 8): Feedback Voltage Input for the Second Low Dropout Linear Regulator (LDO2). Typically, an external resistor divider feeds a fraction of the LDO2 output voltage to this pin. LDO1_FB (Pin 9): Feedback Voltage Input for the First Low Dropout Linear Regulator (LDO1). Typically, an external resistor divider feeds a fraction of the LDO1 output voltage to this pin. LDO1 (Pin 10): Output of the First Low Dropout Linear Regulator. This pin must be bypassed to ground with a 1μF or greater ceramic capacitor. LDO2 (Pin 11): Output of the Second Low Dropout Linear Regulator. This pin must be bypassed to ground with a 1μF or greater ceramic capacitor. VIN (Pin 12): Input Supply. This pin should be bypassed to ground with a 2.2μF or greater ceramic capacitor. Exposed Pad (Pin 13): Ground. This pin must be soldered to the PCB. BLOCK DIAGRAM VIN 12 10 LDO1 11 LDO2 SW 1 400mA BUCK ENABLE BUCK GND 2 7 PGOOD 2.25MHz OSC BUCKFB 6 LDO2 800mV REFERENCE ENLDO1 3 ENLDO2 4 LDO1 LOGIC 9 LDO1_FB POWER GOOD COMPARATORS ENBUCK 5 8 LDO2_FB ENABLE_LDO2 ENABLE_LDO1 GND 13 3670 BD 3670f 6 LTC3670 OPERATION INTRODUCTION The LTC3670 combines a synchronous buck converter with two low dropout linear regulators (LDOs) to provide three low voltage outputs from a higher voltage input source. The input supply range of 2.5V to 5.5V spans the single-cell Li-Ion operating range. Each output can be independently enabled or shut down via the three enable pins. The output regulation voltages are programmed by external resistor dividers. SYNCHRONOUS BUCK REGULATOR The synchronous buck includes many features: It uses a Constant-frequency current mode architecture, switching at 2.25MHz down to light loads. Automatic Burst Mode operation maintains efficiency in light load and no-load situations. Should the input voltage ever fall below the target output voltage, the buck enters 100% duty cycle operation. Also known as operating in dropout, this can extend operating life in battery-powered systems. 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 BUCKFB pin. When the BUCKFB voltage is below the reference, the error amplifier output voltage increases. When the BUCKFB 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 BUCKFB pin. All necessary control-loop compensation is internal to the step-down switching regulator requiring only a single ceramic output capacitor for stability. 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. Burst Mode Operation At light load and no-load conditions, the buck automatically switches to a power-saving hysteretic control algorithm that operates the switches intermittently to minimize switching losses. Known as Burst Mode operation, the buck cycles the power switches enough times to charge the output capacitor to a voltage slightly higher than the regulation point. The buck then goes into a reduced quiescent current sleep mode. In this state, power loss is minimized while the load current is supplied by the output capacitor. Whenever the output voltage drops below a pre-determined value, the buck wakes from sleep and cycles the switches again until the output capacitor voltage is once again slightly above the regulation point. Sleep time thus depends on load current, because the load current determines the discharge rate of the output capacitor. Should load current increase above roughly 1/4 of the rated output load current, the buck resumes constant-frequency operation. Soft-Start Soft-start in the buck regulator is accomplished by gradually increasing the maximum allowed peak inductor current over a 600μs 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 LTC3670 is enabled, or after a fault condition has occurred (thermal shutdown or UVLO). 3670f 7 LTC3670 OPERATION 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 DROPOUT LINEAR REGULATORS (LDOs) The LTC3670 contains two independent LDO regulators, each supporting a load of up to 150mA. Each LDO takes power from the VIN pin and drives its output pin with the goal of bringing its feedback pin voltage to 0.8V. In the usual case, a resistor divider is connected between the LDO’s output pin, feedback pin and ground, in order to close the control loop and program the output voltage. For stability, each LDO output must be bypassed to ground with a minimum 1μF ceramic capacitor. Each LDO can be enabled or disabled via its own enable pin. When disabled with VIN still applied, an internal pull-down resistor is switched in to help bring the output to ground. When an LDO is enabled, a soft-start circuit ramps its regulation point from zero to final value over a period of roughly 0.1ms, reducing the required VIN inrush current. LOW VIN SUPPLY UNDERVOLTAGE LOCKOUT An undervoltage lockout (UVLO) circuit shuts down the LTC3670 when VIN drops below about 2.2V. POWER GOOD DETECTION The LTC3670 has a built-in supply monitor. If the feedback voltage of every enabled regulator is above 92% of its regulation value, the PGOOD pin becomes high impedance. Otherwise, or if no regulators are enabled, 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. 3670f 8 LTC3670 APPLICATIONS INFORMATION Buck Regulator Inductor 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 do not 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. 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 buck regulator. 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. Table 1. Recommended Inductors for the Buck Regulator INDUCTOR TYPE L (μH) MAXIMUM IDC (A) MAXIMUM DCR (Ω) SIZE in mm (L × W × H) EPL2014-472ML 4.7 1.3 0.254 1.8 × 2.0 × 1.4 LPS3015 4.7 3.3 1.1 1.3 0.2 0.13 3.0 × 3.0 × 1.5 3.0 × 3.0 × 1.5 DE2818C 4.7 3.3 1.25 1.45 0.072 0.053 3.0 × 2.8 × 1.8 3.0 × 2.8 × 1.8 DE2812C 4.7 3.3 1.15 1.37 0.13* 0.105* 3.0 × 2.8 × 1.2 3.0 × 2.8 × 1.2 CDRH3D16 4.7 0.9 0.11 4.0 × 4.0 × 1.8 CDRH2D11 4.7 3.3 0.5 0.6 0.17 0.123 3.2 × 3.2 × 1.2 3.2 × 3.2 × 1.2 SD3118 4.7 3.3 1.3 1.59 0.162 0.113 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.8 MANUFACTURER Coilcraft www.coilcraft.com Toko www.toko.com Sumida www.sumida.com Cooper www.cooperet.com *Typical DCR 3670f 9 LTC3670 APPLICATIONS INFORMATION Input/Output Capacitor Selection Low ESR (equivalent series resistance) ceramic capacitors should be used to bypass the following pins to ground: VIN, 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 each be bypassed with a 1μF capacitor or greater. Larger values yield improved transient response. Consult with capacitor manufacturers for detailed information and specifications on their selection 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 VOUT(BUCK) CFB BUCKFB R1 LTC3670 VOUT(LDO) LDO R4 LDO_FB An LDO’s output voltage is similarly determined by R3 and R4, following: ⎛ R4 ⎞ VOUT(LDO) = ⎜ 1+ ⎟ • 0.8 V ⎝ R3 ⎠ Typical values for R2 and R4 are in the range from 40k to 1M. For improved buck regulator transient response, the capacitor CFB cancels the pole created by the feedback resistors and the input capacitance of the BUCKFB pin. A variety of capacitor sizes can be used for CFB, but a value of 10pF is recommended for most applications. Experimentation with capacitor sizes between 2pF and 22pF may yield improved transient response. Printed Circuit Board Layout Considerations 1) The Exposed Pad of the package should connect directly to a large ground plane to minimize thermal and electrical impedance. Figure 1 shows how feedback resistor dividers are connected to the LTC3670 to set the output voltages of the buck and an LDO. R2 ⎛ R2 ⎞ VOUT(BUCK ) = ⎜ 1+ ⎟ • 0.8 V ⎝ R1⎠ When laying out the printed circuit board, the following list should be followed to ensure proper operation of the LTC3670: Output Voltage Programming SW The output voltage of the buck regulator is determined by R1 and R2, following the equation: 2) The connection from the input supply pin (VIN) to its decoupling capacitor should be kept as short as possible. The GND side of this capacitor 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 LTC3670. 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. 3670 F01 R3 Figure 1. Setting the Output Voltages of the LTC3670 4) The LDO output capacitors should be placed as close to the IC as possible, and connected to the LDO outputs and the GND pin as directly as possible. 3670f 10 LTC3670 PACKAGE DESCRIPTION DDB Package 12-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1723 Rev Ø) 0.64 ±0.05 (2 SIDES) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 2.39 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 3.00 ±0.10 (2 SIDES) R = 0.05 TYP R = 0.115 TYP 7 0.40 ± 0.10 12 2.00 ±0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF 0.75 ±0.05 0.64 ± 0.10 (2 SIDES) 6 0.23 ± 0.05 0 – 0.05 PIN 1 R = 0.20 OR 0.25 s 45° CHAMFER 1 (DDB12) DFN 0106 REV Ø 0.45 BSC 2.39 ±0.10 (2 SIDES) 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 3670f 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 LTC3670 TYPICAL APPLICATION Start-Up Transient LTC3670 with More Output Capacitance for Improved Transient Response ALL ENABLE 1V PINS 0V VIN 2.5V TO 5.5V 10μF VOUT3 VIN 4.7μH GND SW 232k 10pF 10μF VOUT1 1.2V 400mA VOUT2 OUTPUT VOLTAGES 500mV/DIV VOUT1 BUCKFB 464k 50μs/DIV LTC3670 ENBUCK ENLDO1 ENLDO2 PGOOD DIGITAL CONTROL LDO1 1.00M 4.7μF VOUT2 1.8V 150mA Load Transient Response LDO1_FB 806k LDO2 590k 4.7μF VOUT3 2.5V 150mA 3670 TA03 VIN = 3.6V Li-Ion CELL, 10mA RESISTIVE LOAD ON EACH OUTPUT VOUT1, VOUT2 AND VOUT3 LOAD CURRENT 100mA 10mA VOUT1 LDO2_FB 50mV/DIV AC COUPLED 280k VOUT2 3670 TA02 VOUT3 20μs/DIV 3670 TA04 VIN = 3.6V Li-Ion CELL, SIMULTANEOUS LOAD TRANSIENT ALL OUTPUTS 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 LTC3672B-1/ LTC3672B-2 Monolithic Fixed-Output 400mA Buck Regulator with Dual 150mA LDOs in a 2mm × 2mm DFN 95% Efficiency, VIN: 2.9V to 5.5V, IQ = 260μA, LTC3672B-1: Buckout = 1.8V, LDO1 = 1.2V, LDO2 = 2.8V LTC3672B-2: Buckout = 1.2V, LDO1 = 2.8V, LDO2 = 1.8V 3670f 12 Linear Technology Corporation LT 0108 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008