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FEATURES
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LTC3670 Monolithic 400mA Buck Regulator with Dual 150mA LDOs in 3mm x 2mm DFN DESCRIPTION
The LTC(R)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 x 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.
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(R) Operation for High Efficiency at Light Loads; IQ = 70A, 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 x 2mm x 0.75mm DFN Package
APPLICATIONS
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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
TYPICAL APPLICATION
Triple Power Supply with Independent Enables
VIN 3.3V TO 5.5V
Demoboard
2.2F GND
VIN SW
4.7H 232k BUCKFB 464k 10pF 4.7F
VOUT1 1.2V 400mA
LTC3670 DIGITAL CONTROL ENBUCK ENLDO1 ENLDO2 PGOOD LDO1 806k LDO1_FB 324k LDO2 1.02M LDO2_FB 324k
3670 TA01a
9.3mm VOUT2 2.8V 150mA
1F
9.4mm ACTIVE AREA
1F
VOUT3 3.3V 150mA
3670 TA01b
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LTC3670 ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2, 3)
PIN CONFIGURATION
TOP VIEW SW 1 GND 2 ENLD01 3 ENLD02 4 ENBUCK 5 BUCKFB 6 13 12 VIN 11 LDO2 10 LDO1 9 LDO1_FB 8 LDO2_FB 7 PGOOD
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 ........................................... 125C Operating Temperature Range.................. -40C to 85C Storage Temperature Range................... -65C to 125C
DDB PACKAGE 12-LEAD (3mm x 2mm) PLASTIC DFN TJMAX = 125C, JA = 76C/W, JC = 13.5C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LTC3670EDDB#PBF TAPE AND REEL LTC3670EDDB#TRPBF PART MARKING LDBY PACKAGE DESCRIPTION 12-Lead (3mm x 2mm) Plastic DFN TEMPERATURE RANGE -40C to 85C 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
SYMBOL VIN VUVLO IQ PARAMETER Input Voltage Range Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis VIN Quiescent Current, No Load All Outputs Enabled Buck Enabled Only Buck Enabled Only, in Dropout One LDO Enabled Only Shutdown ENBUCK, ENLDO1, ENLDO2 Pin Thresholds Logic Low Voltage Logic High Voltage ENBUCK, ENLDO1, ENLDO2 Pin Pull-Down Resistance RPGOOD PGOOD Pin Logic Low Output Resistance PGOOD Pin Hi-Z Leakage PGOOD Threshold on Feedback Voltages of Enabled Regulators
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V, unless otherwise noted.
CONDITIONS
l
MIN 2.5
TYP 2.2 18
MAX 5.5 2.3 100 110 60 1100 35 1 0.4
UNITS V V mV A A A A A V V M
VIN Rising (Note 4) VBUCKFB = 0.9V VBUCKFB = 0.9V VBUCKFB = 0V VENBUCK = VENLDO1 = VENLDO2 = 0V
l l
70 38 700 22
VIL VIH
1.2 4 30
VPGOOD = 6V (Note 5) 92
1
A %
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LTC3670 ELECTRICAL CHARACTERISTICS
SYMBOL fOSC VBUCKFB IBUCKFB IMAXP RP(BUCK) RN(BUCK) RPD(BUCK) tSS(BUCK) VLDO PARAMETER Oscillator Frequency Buck Regulated Feedback Voltage Feedback Pin Input Bias Current PMOS Switch Maximum Peak Current (Note 6) PMOS Switch On-Resistance NMOS Switch On-Resistance SW Pin Pull-Down Resistance in Shutdown Soft-Start Time LDO Regulated Feedback Voltage LDO Line Regulation (Note 7) LDO Load Regulation (Note 7) ILDO_FB VDROP Feedback Pin Input Bias Current Short-Circuit Output Current (Note 6) Dropout Voltage (Note 8) ILDO = 150mA VIN = 3.6V VIN = 2.5V LDO Output, ILDO = 1mA to 150mA ILDO = 1mA, VIN = 2.5V to 5.5V ILDO = 1mA to 150mA
l l l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 3.6V, unless otherwise noted.
CONDITIONS MIN 1.91 0.78 600 TYP 2.25 0.8 800 0.6 0.7 10 0.6 0.78 0.8 0.25 -5 20 420 150 200 0.1 10 200 300 0.82 MAX 2.59 0.82 20 1100 UNITS MHz V nA mA k ms V mV/V V/mA nA mA mV mV ms k
Synchronous Buck Regulator
Each LDO Regulator
tSS(LDO) RPD(LDO)
Soft-Start Time Output Pull-Down Resistance in Shutdown
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 125C 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 0C to 85C. Specifications over the -40C to 85C 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
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LTC3670 TYPICAL PERFORMANCE CHARACTERISTICS
VIN Supply Current vs VIN
120 100 VIN SUPPLY CURRENT (A) 80 60 40 20 0 90C 25C -45C 820 REGULATED BUCKFB PIN VOLTAGE (mV) ALL THREE OUTPUTS ENABLED, NO LOAD 130C
(TA = 25C unless otherwise noted) Regulated LDO Feedback Pin Voltage vs Temperature
REGULATED LDO FEEDBACK PIN VOLTAGE (mV) 820 UNITY GAIN, V(OUT) = V(LDO_FB) 815 I(OUT) = 0.1mA 810 805 800 795 790 785 VIN = 2.5V VIN = 3.6V VIN = 4.2V VIN = 5.5V
Buck Regulated Feedback Voltage vs Temperature
UNITY GAIN, V(OUT) = V(BUCKFB) 815 I(OUT) = 100mA 810 805 800 VIN = 2.5V 795 790 785 780 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
3670 G02
VIN = 5.5V
VIN = 4.2V
VIN = 3.6V
2.5
3
3.5
4 VIN (V)
4.5
5
5.5
3670 G01
780 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
3670 G03
Buck Load Regulation
820 815 BUCKFB PIN VOLTAGE (mV) 810 805 800 795 790 785 780 0 50 100 150 200 250 300 350 400 LOAD CURRENT (mA)
3670 G04
LDO Load Regulation
820 LDO FEEDBACK PIN VOLTAGE (mV) 815 810 805 800 795 790 785 780 0 25 50 75 100 LOAD CURRENT (mA) 125 150 DROPOUT VOLTAGE (mV) VIN = 3.6V 300 250 200 150
LDO Dropout vs Load Current at VIN = 2.5V
VIN = 2.5V 130C
VIN = 3.6V
90C
- 45C 100 50 0 25C
0
25
50 75 100 LOAD CURRENT (mA)
125
150
3670 G05
3670 G06
LDO Dropout vs Load Current at VIN = 3.6V
300 250 DROPOUT VOLTAGE (mV) 200 150 100 50 0 90C - 45C 130C VIN = 3.6V SHORT-CIRCUIT CURRENT (mA) 500 450 400 350 300 250 200 150 100 50 125 150 0
LDO Short-Circuit Current vs VIN
2.35 2.30 OSCILLATOR FREQUENCY (MHz) 2.25 2.20 2.15 2.10 2.05 2.00 1.95 5.5
3670 G08
Buck Oscillator Frequency vs Temperature
VIN = 5.5V VIN = 4.2V
VIN = 3.6V VIN = 2.5V
25C 0 25 50 75 100 LOAD CURRENT (mA)
- 45C 25C 90C 2.5 3 3.5 4 VIN (V) 4.5 5
1.90 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
3670 G09
3670 G07
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LTC3670 TYPICAL PERFORMANCE CHARACTERISTICS
PMOS Switch Maximum Peak Current vs Temperature
900 PMOS MAXIMUM PEAK CURRENT (mA) 800 PMOS ON-RESISTANCE (m) 700 600 500 400 300 200 100 0 -50 -30 -10 10 30 50 70 90 110 130 TEMPERATURE (C)
3670 G1O
(TA = 25C unless otherwise noted) PGOOD Threshold at Any Feedback Pin
100 FRACTION OF REGULATION POINT (%) 99 98 97 96 95 94 93 92 91 90 2.5 3 3.5 25C 4 VIN (V) 4.5 -45C 5 5.5
3670 G12
Buck PMOS On-Resistance
1000 900 130C 25C -45C 90C
VIN = 5.5V VIN = 4.2V VIN = 3.6V VIN = 2.5V
800 700 600 500 400 300 200 100 0 2.5 3
90C 130C
3.5
4 VIN (V)
4.5
5
5.5
3670 G11
PGOOD Pin Pull-Down Resistance
80 PGOOD PIN PULL-DOWN RESISTANCE () 70 60 50 40 30 20 10 0 2.5 3 3.5 4 VIN (V) 4.5 5 5.5
3670 G13
Front Page Application Efficiency
100 95 90 FRONT PAGE APPLICATION CIRCUIT WITH ONLY THE BUCK ENABLED. INDUCTOR: COILCRAFT EPL2014-472ML VOUT = 1.2V VIN = 2.5V VIN = 3.6V
PGOOD PIN SINKING 2mA
130C 90C 25C
EFFICIENCY (%)
85 80 75 70 65 60 1
-45C
VIN = 5.5V
100 10 LOAD CURRENT (mA)
1000
3670 G14
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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 4M 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 4M pull-down. ENBUCK (Pin 5): Enables the Buck Converter When High. This is a MOS gate input. There is an internal 4M 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 1F or greater ceramic capacitor. LDO2 (Pin 11): Output of the Second Low Dropout Linear Regulator. This pin must be bypassed to ground with a 1F or greater ceramic capacitor. VIN (Pin 12): Input Supply. This pin should be bypassed to ground with a 2.2F 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
GND 2
ENABLE BUCK 7 PGOOD 2.25MHz OSC LDO2 LDO1
BUCKFB 6
ENLDO1 3 ENLDO2 4 ENBUCK 5 LOGIC
800mV REFERENCE
POWER GOOD COMPARATORS ENABLE_LDO2 ENABLE_LDO1 GND 13
9 LDO1_FB 8 LDO2_FB
3670 BD
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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 600s 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).
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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 1F 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.
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LTC3670 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 2.2H to 10H. A 4.7H 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. 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. 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 EPL2014-472ML LPS3015 DE2818C DE2812C CDRH3D16 CDRH2D11 SD3118 *Typical DCR L (H) 4.7 4.7 3.3 4.7 3.3 4.7 3.3 4.7 4.7 3.3 4.7 3.3 MAXIMUM IDC (A) 1.3 1.1 1.3 1.25 1.45 1.15 1.37 0.9 0.5 0.6 1.3 1.59 MAXIMUM DCR () 0.254 0.2 0.13 0.072 0.053 0.13* 0.105* 0.11 0.17 0.123 0.162 0.113 SIZE in mm (L x W x H) 1.8 x 2.0 x 1.4 3.0 x 3.0 x 1.5 3.0 x 3.0 x 1.5 3.0 x 2.8 x 1.8 3.0 x 2.8 x 1.8 3.0 x 2.8 x 1.2 3.0 x 2.8 x 1.2 4.0 x 4.0 x 1.8 3.2 x 3.2 x 1.2 3.2 x 3.2 x 1.2 3.1 x 3.1 x 1.8 3.1 x 3.1 x 1.8 Sumida www.sumida.com Cooper www.cooperet.com MANUFACTURER Coilcraft www.coilcraft.com
Toko www.toko.com
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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 10F 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 4F of capacitance over operating temperature and bias voltage. The VIN pin should be bypassed with a 2.2F capacitor. The LDO1 and LDO2 output pins should each be bypassed with a 1F 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 Murata Taiyo Yuden Vishay Siliconix TDK www.avxcorp.com www.murata.com www.t-yuden.com www.vishay.com www.tdk.com
The output voltage of the buck regulator is determined by R1 and R2, following the equation: R2 VOUT(BUCK ) = 1+ * 0.8 V R1 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 When laying out the printed circuit board, the following list should be followed to ensure proper operation of the LTC3670: 1) The Exposed Pad of the package should connect directly to a large ground plane to minimize thermal and electrical impedance. 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. 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.
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Output Voltage Programming Figure 1 shows how feedback resistor dividers are connected to the LTC3670 to set the output voltages of the buck and an LDO.
SW R2 BUCKFB R1 LTC3670 LDO R4 LDO_FB R3
3670 F01
VOUT(BUCK) CFB
VOUT(LDO)
Figure 1. Setting the Output Voltages of the LTC3670
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LTC3670 PACKAGE DESCRIPTION
DDB Package 12-Lead Plastic DFN (3mm x 2mm)
(Reference LTC DWG # 05-08-1723 Rev O)
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
PIN 1 BAR TOP MARK (SEE NOTE 6)
2.00 0.10 (2 SIDES) 0.64 0.10 (2 SIDES) 6 0.23 0.05 2.39 0.10 (2 SIDES) BOTTOM VIEW--EXPOSED PAD
1
PIN 1 R = 0.20 OR 0.25 45 CHAMFER
(DDB12) DFN 0106 REV O
0.200 REF
0.75 0.05
0.45 BSC
0 - 0.05
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
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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.
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LTC3670 TYPICAL APPLICATION
LTC3670 with More Output Capacitance for Improved Transient Response
VIN 2.5V TO 5.5V
OUTPUT VOLTAGES 500mV/DIV
Start-Up Transient
ALL ENABLE 1V PINS 0V VOUT3
VOUT2
10F GND
VIN SW
4.7H 232k BUCKFB 464k 10pF 10F
VOUT1 1.2V 400mA
VOUT1
LTC3670 DIGITAL CONTROL ENBUCK ENLDO1 ENLDO2 PGOOD LDO1 1.00M LDO1_FB 806k LDO2 590k LDO2_FB 280k
3670 TA02
50s/DIV
3670 TA03
4.7F
VOUT2 1.8V 150mA
VOUT1, VOUT2 AND VOUT3 LOAD CURRENT
VIN = 3.6V Li-Ion CELL, 10mA RESISTIVE LOAD ON EACH OUTPUT
Load Transient Response
100mA 10mA
4.7F
VOUT3 2.5V 150mA
VOUT1 50mV/DIV AC COUPLED
VOUT2
VOUT3 20s/DIV
3670 TA04
VIN = 3.6V Li-Ion CELL, SIMULTANEOUS LOAD TRANSIENT ALL OUTPUTS
RELATED PARTS
PART NUMBER LTC3405/LTC3405A LTC3406/LTC3406B LTC3407/LTC3407-2 LTC3410/LTC3410B LTC3411 LTC3445 LTC3446 LTC3448 DESCRIPTION 300mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converter 600mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converter Dual 600mA/800mA IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converter 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter 1.25A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter I2C Controllable 600mA Synchronous Buck Regulator with Two 50mA LDOs in a 4mm x 4mm QFN Synchronous 1A, 2.25MHz Step-Down DC/DC Regulator with Dual VLDOs 600A IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converter with LDO Mode COMMENTS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 20A, ISD <1A, ThinSOT Package 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20A, ISD <1A, ThinSOT Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, MS10E Package 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 26A, ISD <1A, SC70 Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60A, ISD <1A, MS10 Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.85V, IQ = 360A, ISD <27A, 4mm x 4mm QFN Package 95% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 0.4V, IQ = 140A, ISD <1A, 3mm x 4mm DFN Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 32A, ISD <1A, MS10, DFN Packages 95% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 0.4V, IQ = 85A, ISD <1A, 3mm x 3mm DFN Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, DFN-8 Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40A, ISD <1A, MS10, DFN Packages 95% Efficiency, VIN: 2.9V to 5.5V, IQ = 260A, LTC3672B-1: Buckout = 1.8V, LDO1 = 1.2V, LDO2 = 2.8V LTC3672B-2: Buckout = 1.2V, LDO1 = 2.8V, LDO2 = 1.8V
3670f LT 0108 * PRINTED IN USA
LTC3541/LTC3541-1/ Synchronous 500mA, 2.25MHz Step-Down DC/DC LTC3541-2/LTC3541-3 Regulator with a 300mA VLDO in a 3mm x 3mm DFN LTC3547 LTC3548/LTC3548-1/ LTC3548-2 LTC3672B-1/ LTC3672B-2 Dual 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter Dual 800mA/400mA IOUT, 2.25MHz, Synchronous StepDown DC/DC Converter Monolithic Fixed-Output 400mA Buck Regulator with Dual 150mA LDOs in a 2mm x 2mm DFN
12 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

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