LTC3418

LTC3418 8A, 4MHz, Monolithic Synchronous Step-Down Regulator DESCRIPTIO The LTC®3418 is a high efficiency, monolithic synchronous step-down DC/DC converter utilizing a constant frequency, current mode architecture. It operates from an input voltage range of 2.25V to 5.5V and provides a regulated output voltage from 0.8V to 5V while delivering up to 8A of output current. The internal synchronous power switch increases efficiency and eliminates the need for an external Schottky diode. Switching frequency is set by an external resistor or can be synchronized to an external clock. OPTI-LOOP® compensation allows the transient response to be optimized over a wide range of loads and output capacitors. The LTC3418 can be configured for either Burst Mode operation or forced continuous operation. Forced continuous operation reduces noise and RF interference while Burst Mode operation provides high efficiency by reducing gate charge losses at light loads. In Burst Mode operation, external control of the burst clamp level allows the output voltage ripple to be adjusted according to the requirements of the application. A tracking input in the LTC3418 allows for proper sequencing with respect to another power supply. , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815, 6498466, 6611131, 6724174. FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency: Up to 95% 8A Output Current 2.25V to 5.5V Input Voltage Range Low RDS(ON) Internal Switch: 35mΩ Tracking Input to Provide Easy Supply Sequencing Programmable Frequency: 300kHz to 4MHz 0.8V ±1% Reference Allows Low Output Voltage Quiescent Current: 380µA Selectable Forced Continuous/Burst Mode® Operation with Adjustable Burst Clamp Synchronizable Switching Frequency Low Dropout Operation: 100% Duty Cycle Power Good Output Voltage Monitor Overtemperature Protected 38-Lead Low Profile (0.75mm) Thermally Enhanced QFN (5mm × 7mm) Package APPLICATIO S ■ ■ ■ ■ ■ Microprocessor, DSP and Memory Supplies Distributed 2.5V, 3.3V and 5V Power Systems Automotive Applications Point of Load Regulation Notebook Computers TYPICAL APPLICATIO VIN 2.8V TO 5.5V Efficiency and Power Loss vs Load Current 100 90 EFFICIENCY 100000 2.5V/8A Step-Down Regulator CIN 100µF 0.2µH COUT 100µF ×2 SVIN TRACK PVIN RT 2.2M 30.1k SW LTC3418 PGOOD RUN/SS ITH 4.99k 820pF PGND SGND EFFICIENCY (%) VOUT 2.5V 8A 80 70 60 50 40 POWER LOSS 1000pF SYNC/MODE VFB 332Ω 1.69k 4.32k 3418 TA01a 30 20 0.01 0.1 1 LOAD CURRENT (A) U U U 10000 POWER LOSS (mW) 1000 100 10 VIN = 3.3V VOUT = 2.5V 10 3418 TA01b 1 3418f 1 LTC3418 ABSOLUTE MAXIMUM RATINGS (Note 1) PACKAGE/ORDER INFORMATION TOP VIEW TRACK PGND PGND PGND PGND PGND PGND Input Supply Voltage .................................. – 0.3V to 6V ITH, RUN/SS, VFB Voltages ......................... – 0.3V to VIN SYNC/MODE Voltages ............................... – 0.3V to VIN TRACK Voltage .......................................... –0.3V to VIN SW Voltage .................................. – 0.3V to (VIN + 0.3V) Operating Ambient Temperature Range (Note 2) .............................................. – 40°C to 85°C Junction Temperature (Note 5) ............................. 125°C Storage Temperature Range ................. –65°C to 125°C 38 37 36 35 34 33 32 SW 1 SW 2 PVIN 3 PVIN 4 PGOOD 5 RT 6 RUN/SS 7 SGND 8 PVIN 9 PVIN 10 SW 11 SW 12 13 14 15 16 17 18 19 PGND PGND PGND VREF PGND PGND PGND 39 31 SW 30 SW 29 PVIN 28 PVIN 27 SYNC/MODE 26 ITH 25 VFB 24 SVIN 23 PVIN 22 PVIN 21 SW 20 SW UHF PACKAGE 38-LEAD (7mm × 5mm) PLASTIC QFN TJMAX = 125°C, θJA = 34°C/W, θJC = 1°C/W EXPOSED PAD (PIN 39) IS PGND AND MUST BE SOLDERED TO PCB ORDER PART NUMBER UH PART MARKING LTC3418EUHF 3418 Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS SYMBOL VIN VFB IFB ∆VFB VLOADREG VTRACK ITRACK ∆VPGOOD RPGOOD IQ PARAMETER Input Voltage Range Regulated Feedback Voltage Feedback Input Current Reference Voltage Line Regulation Output Voltage Load Regulation Tracking Voltage Offset Tracking Voltage Range TRACK Input Current Power Good Range Power Good Resistance Input DC Bias Current Active Current Shutdown The ● indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V. (Note 2) CONDITIONS 0°C ≤ TA ≤ 85°C (Note 3) VIN = 2.5V to 5.5V (Note 3) Measured in Servo Loop, VITH = 0.36V Measured in Servo Loop, VITH = 0.84V VTRACK = 0.4V 0 100 ±7.5 100 (Note 4) VFB = 0.7V, VITH = 1V VRUN = 0V 380 0.03 ● ● MIN 2.25 ● TYP 0.800 0.800 100 0.04 0.02 –0.02 MAX 5.5 0.808 0.816 200 0.2 0.2 –0.2 15 0.8 200 ±9 150 450 1.5 UNITS V V V nA %/V % % mV V nA % Ω µA µA 3418f 0.792 0.784 2 U W U U WW W LTC3418 ELECTRICAL CHARACTERISTICS SYMBOL fOSC fSYNC RPFET RNFET ILIMIT VUVLO VREF ILSW VRUN PARAMETER Switching Frequency Switching Frequency Range SYNC Capture Range RDS(ON) of P-Channel FET RDS(ON) of N-Channel FET Peak Current Limit Undervoltage Lockout Threshold Reference Output SW Leakage Current RUN Threshold The ● indicates specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.3V. (Note 2) CONDITIONS ROSC = 69.8kΩ (Note 6) (Note 6) ISW = 600mA ISW = – 600mA 12 1.75 1.219 VRUN = 0V, VIN = 5.5V 0.5 MIN 0.88 0.3 0.3 35 25 17 2 1.250 0.1 0.65 2.25 1.281 1 0.8 TYP 1 MAX 1.12 4 4 50 35 UNITS MHz MHz MHz mΩ mΩ A V V µA V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC3418 is guaranteed to meet performance specifications from 0oC to 70oC. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: The LTC3418 is tested in a feedback loop that adjusts VFB to achieve a specified error amplifier output voltage (ITH). Note 4: Dynamic supply current is higher due to the internal gate charge being delivered at the switching frequency. Note 5: TJ is calculated from the ambient temperature TA and power dissipation PD as follows: LTC3418: TJ = TA + (PD)(34°C/W) Note 6: This parameter is guaranteed by design and characterization. TYPICAL PERFOR A CE CHARACTERISTICS Internal Reference Voltage vs Temperature 0.8000 0.7995 VIN = 3.3V 45 40 REFERENCE VOLTAGE (V) ON-RESISTANCE (mΩ) PFET 30 NFET 25 20 15 10 5 ON-RESISTANCE (mΩ) 0.7990 0.7985 0.7980 0.7975 0.7970 0.7965 0.7960 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 3418 G07 UW TA = 25°C unless otherwise noted. Switch On-Resistance vs Input Voltage 50 45 40 35 30 25 20 15 10 5 2.75 3.25 3.75 4.25 4.75 INPUT VOLTAGE (V) 5.25 3418 G01 On-Resistance vs Temperature VIN = 3.3V 35 PFET NFET 0 2.25 0 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 3418 G02 3418f 3 LTC3418 TYPICAL PERFOR A CE CHARACTERISTICS Switch Leakage vs Input Voltage 5.0 4.5 QUIESCENT CURRENT (µA) 500 450 400 FREQUENCY (kHz) 350 300 250 200 150 100 50 4.0 LEAKAGE CURRENT (nA) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 2.25 2.75 3.25 3.75 4.25 4.75 INPUT VOLTAGE (V) 5.25 3418 G03 NFET PFET Frequency vs Temperature 1100 1080 1060 FREQUENCY (kHz) FREQUENCY (kHz) 1040 1020 1000 980 960 940 920 900 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 100 120 3418 G06 VIN = 3.3V EFFICIENCY (%) Efficiency vs Load Current 100 90 80 EFFICIENCY (%) Burst Mode OPERATION 70 EFFICIENCY (%) 60 50 40 30 20 10 VIN = 3.3V VOUT = 2.5V FORCED CONTINUOUS 60 50 40 30 20 10 FORCED CONTINUOUS VOUT = 2.5V 0.1 1 LOAD CURRENT (A) 10 3418 G11 EFFICIENCY (%) 0 0.01 0.1 1 LOAD CURRENT (A) 4 UW 3418 G10 TA = 25°C unless otherwise noted. Quiescent Current vs Input Voltage 4500 4000 3500 3000 2500 2000 1500 1000 500 0 Frequency vs ROSC VIN = 3.3V 0 2.5 3 4 4.5 3.5 INPUT VOLTAGE (V) 5 5.5 3418 G04 10 50 90 130 170 ROSC (kΩ) 210 250 3418 G08 Frequency vs Input Voltage 1100 1080 1060 1040 1020 1000 980 960 940 920 900 2.25 2.75 3.25 3.75 4.25 4.75 INPUT VOLTAGE (V) 5.25 3418 G05 Efficiency and Power Loss vs Load Current 100 90 80 70 60 50 40 30 20 0.01 0.1 1 LOAD CURRENT (A) VIN = 3.3V VOUT = 2.5V 10 3418 TA01b 100000 EFFICIENCY 10000 POWER LOSS (mW) 1000 POWER LOSS 100 10 1 Efficiency vs Load Current 100 90 3.3V 80 70 5V 80 70 60 50 40 30 20 10 100 90 Efficiency vs Load Current 3.3V 5V 10 0 0.01 0 0.01 Burst Mode OPERATION VOUT = 2.5V 0.1 1 LOAD CURRENT (A) 10 3418 G12 3418f LTC3418 TYPICAL PERFOR A CE CHARACTERISTICS Peak Inductor Current vs Burst Clamp Voltage 12 PEAK INDUCTOR CURRENT (A) 10 ∆VOUT/VOUT (%) 8 6 4 2 0 0 0.1 0.2 5V 3.3V 0.3 0.4 0.5 VBCLAMP (V) 0.6 0.7 0.8 –0.30 0 1 2 6 5 4 3 LOAD CURRENT (A) 7 8 Load Step Transient OUTPUT VOLTAGE 100mV/DIV INDUCTOR CURRENT 5A/DIV VIN = 3.3V 40µs/DIV VOUT = 2.5V LOAD STEP: 3A TO 8A PI FU CTIO S SW (Pins 1, 2, 11, 12, 20, 21, 30, 31): Switch Node Connection to Inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. PVIN (Pins 3, 4, 9, 10, 22, 23, 28, 29): Power Input Supply. Decouple this pin to PGND with a capacitor. PGOOD (Pin 5): Power Good Output. Open-drain logic output that is pulled to ground when the output voltage is not within ±7.5% of regulation point. RT (Pin 6): Oscillator Resistor Input. Connecting a resistor to ground from this pin sets the switching frequency. RUN/SS (Pin 7): Run Control and Soft-Start Input. Forcing this pin below 0.5V shuts down the LTC3418. In shutdown all functions are disabled drawing