LTC3822

LTC3822 No RSENSETM, Low Input Voltage, Synchronous Step-Down DC/DC Controller FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO No Current Sense Resistor Required All N-Channel MOSFET Synchronous Drive High Current Outputs Possible Constant Frequency Current Mode Operation for Excellent Line and Load Transient Response VIN: 2.75V to 4.5V ±1% 0.6V Reference Low Dropout Operation: 99% Duty Cycle Selectable Frequency (300kHz/550kHz/750kHz) Internal Soft-Start Circuitry Selectable Maximum Peak Current Sense Threshold Digital RUN Control Pin Output Overvoltage Protection Micropower Shutdown: IQ = 7.5µA Tiny Thermally Enhanced Leadless (3mm x 3mm) DFN or 10-Lead MSOP Package The LTC3822 is a synchronous step-down switching regulator controller that drives external N-channel power MOSFETs using few external components. The constant frequency current mode architecture with MOSFET VDS sensing eliminates the need for sense resistors and improves efficiency. A maximum duty cycle of 99% provides low dropout operation. The switching frequency can be programmed up to 750kHz, allowing the use of small surface mount inductors and capacitors. The LTC3822 is available in thermally enhanced DFN and 10-lead MSOP packages. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. No RSENSE is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 5929620, 6580258, 6304066, 5847554, 6611131, 6498466. APPLICATIO S ■ ■ 3.3VIN Systems Li-Ion Battery Systems TYPICAL APPLICATIO 1.8V/8A High Efficiency, 550kHz Step-Down Converter 100 IPRG RUN FREQ ITH 5.1k 680pF GND VFB 59k 118k 3822 TA01 VIN 47µF TG LTC3822 SW FDS6898A 0.47µH VIN 2.75V TO 4.5V 90 80 EFFICIENCY EFFICIENCY (%) 70 60 50 40 30 POWER LOSS 0.22µF BOOST VOUT 1.8V 100µF 8A BG 20 10 0 100 1000 LOAD CURRENT (mA) 0.01 10000 3822 TA01b U Efficiency and Power Loss vs Load Current VIN = 3.3V 10 U U POWER LOSS (W) 1 0.1 3822f 1 LTC3822 ABSOLUTE MAXIMUM RATINGS Input Supply Voltage (VIN)....................... – 0.3V to 4.5V BOOST Voltage ..........................................– 0.3V to 10V FREQ, RUN, IPRG Voltages .......... –0.3V to (VIN + 0.3V) VFB, ITH Voltages...................................... –0.3V to 2.4V SW Voltage .......................................... – 2V to VIN + 1V TG, BG Peak Output Current (1µF) supply bypass capacitors. The U discharged bypass capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem if the load switch resistance is low and it is driven quickly. The only solution is to limit the rise time of the switch drive so that the load rise time is limited to approximately (25) • (CLOAD). Thus a 10µF capacitor would be require a 250µs rise time, limiting the charging current to about 200mA. Design Example For a design example, VIN will be a 3.3V power supply. Output voltage is 1.2V with a load current requirement of 10A. The IPRG and FREQ pins will be left floating, so the maximum current sense threshold ∆VSENSE(MAX) will be approximately 120mV and the switching frequency will be 550kHz. W UU Duty Cycle = VOUT = 36.4% VIN From Figure 1, SF = 96%. RDS(ON)MAX = ∆VSENSE(MAX) 5 • 0.9 • SF • = 0.011Ω 6 IOUT(MAX) • ρT The Si4486DY has an RDS(ON) of 9mΩ. To prevent inductor saturation during a short circuit, the inductor current rating should be higher than 20A. For 4A IRIPPLE, the required minimum inductor value is: LMIN = 1.2 V 1.2 V = 0. 35 µH • 1– 3.3 V 550kHz • 4A A 22A 0.39µH inductor works well for this application. CIN will require an RMS current rating of at least 5A at temperature. A COUT with 25mΩ ESR will cause approximately 100mV output ripple. Figure 7 shows a 12A, 3.3VIN/1.8VOUT application. 3822f 15 LTC3822 APPLICATIO S I FOR ATIO PC Board Layout Checklist When laying out the printed circuit board, use the following checklist to ensure proper operation of the LTC3822. Figure 5 shows a suggested PCB floorplan. • The power loop (input capacitor, MOSFET, inductor, output capacitor) and high di/dt loop (VIN, through both MOSFETs to power GND and back through CIN to VIN) should be as small as possible and located on one layer. Excess inductance here can cause increased stress on the MOSFETs and increased high frequency ringing on the output. • Put the feedback resistors close to the VFB pins. The ITH compensation components should also be very close to the LTC3822. All small-signal circuitry should be isolated from the main switching loop with ground Kelvin connected to the output capacitor ground. VIN CIN GND SW M2 GND U1 AND OTHER SMALL-SIGNAL COMPONENTS GND SENSE TRACE M1 L1 VOUT COUT Figure 5. LTC3822 Suggested PCB Floorplan 16 U • The current sense traces (VIN and SW) should be Kelvin connected right at the top-side MOSFET source and drain. The positive current sense pin is shared with the VIN pin. This must not be locally decoupled with a capacitor. • Keep the switch node (SW) and the gate driver nodes (TG, BG) away from the small-signal components, especially the feedback resistors, and ITH compensation components. • Place CB as close as possible to the SW and BOOST pins. This capacitor carries high di/dt MOSFET gate drive currents. The charging current to the boost diode should be provided from a separate VIN trace than that to the VIN pin. • Beware of ground loops in multiple layer PC boards. Try to maintain one central signal ground node on the board. If the ground plane must be used for high DC currents, keep that path away from small signal components. 3822 F05 W UU 3822f LTC3822 APPLICATIO S I FOR ATIO IPRG RUN FREQ ITH 5.1k 680pF GND VFB 59k 118k LTC3822 VIN TG SW FDS6898A IHLP-2525CZ-01 0.47µH 47µF 2x D OPTIONAL 22µF 2x BOOST BG Figure 6. Nominal 3.3VIN 1.8V/8A High Efficiency 550kHz Step-Down Converter with 5V Gate Drive IPRG RUN FREQ ITH 27k 680pF GND VFB 59k 118k LTC3822 BOOST Si4866 BG Figure 7. 3.3VIN 1.8V/12A High Efficiency, High Current 550kHz Step-Down Converter U 5V SECONDARY SUPPLY VIN 2.75V TO 4.5V 0.22µF VOUT 1.8V 8A 3822 F06 W UU VIN TG SW Si4866 IHLP-2525CZ-01 0.22µH 47µF 2x VIN 3.3V 0.22µF VOUT 1.8V 100µF 12A 2x 3822 F07 3822f 17 LTC3822 PACKAGE DESCRIPTIO 3.50 ± 0.05 1.65 ± 0.05 2.15 ± 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ± 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 6 10 0.38 ± 0.10 PIN 1 TOP MARK (SEE NOTE 6) 5 0.200 REF 0.75 ± 0.05 2.38 ± 0.10 (2 SIDES) 1 NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 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 18 U DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 ± 0.05 3.00 ± 0.10 (4 SIDES) 1.65 ± 0.10 (2 SIDES) (DD10) DFN 1103 0.25 ± 0.05 0.50 BSC 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD 3822f LTC3822 PACKAGE DESCRIPTIO 2.794 ± 0.102 (.110 ± .004) 5.23 (.206) MIN 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 0.254 (.010) GAUGE PLANE 0.18 (.007) NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 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. U MSE Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1663) BOTTOM VIEW OF EXPOSED PAD OPTION 0.889 ± 0.127 (.035 ± .005) 1 2.06 ± 0.102 (.081 ± .004) 1.83 ± 0.102 (.072 ± .004) 2.083 ± 0.102 3.20 – 3.45 (.082 ± .004) (.126 – .136) 10 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 10 9 8 7 6 0.497 ± 0.076 (.0196 ± .003) REF 4.90 ± 0.152 (.193 ± .006) DETAIL “A” 0° – 6° TYP 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 12345 0.53 ± 0.152 (.021 ± .006) DETAIL “A” SEATING PLANE 1.10 (.043) MAX 0.86 (.034) REF 0.17 – 0.27 (.007 – .011) TYP 0.50 (.0197) BSC 0.127 ± 0.076 (.005 ± .003) MSOP (MSE) 0603 3822f 19 LTC3822 RELATED PARTS PART NUMBER LTC1628/LTC3728 LTC1735 LTC1778 LTC3411 LTC3412 LTC3416 LTC3418 LTC3708 DESCRIPTION Dual High Efficiency, 2-Phase Synchronous Step Down Controllers High Efficiency Synchronous Step-Down Controller No RSENSE, Synchronous Step-Down Controller 1.25A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 2.5A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 4A, 4MHz, Monolithic Synchronous Step-Down Regulator 8A, 4MHz, Synchronous Step-Down Regulator 2-Phase, No RSENSE, Dual Synchronous Controller with Output Tracking COMMENTS Constant Frequency, Standby, 5V and 3.3V LDOs, VIN to 36V, 28-Lead SSOP Burst Mode Operation, 16-Pin Narrow SSOP, Fault Protection, 3.5V ≤ VIN ≤ 36V Current Mode Operation Without Sense Resistor, Fast Transient Response, 4V ≤ VIN ≤ 36V 95% Efficiency, VIN: 2.5V to 5.5V, VOUT ≥ 0.8V, IQ = 60µA, ISD =