LTC3822EMSE#TRPBF

LTC3822 No RSENSE™, Low Input Voltage, Synchronous Step-Down DC/DC Controller FEATURES DESCRIPTION n The LTC®3822 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. n n n n n n n n n n n n n 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 × 3mm) DFN or 10-Lead MSOP Package 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. L, 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. APPLICATIONS n n 3.3VIN Systems Li-Ion Battery Systems TYPICAL APPLICATION 1.8V/8A High Efficiency, 550kHz Step-Down Converter IPRG Efficiency and Power Loss vs Load Current 100 VIN 2.75V TO 4.5V VIN 90 47μF FDS6898A SW 0.47μH 80 FREQ ITH LTC3822 0.22μF BOOST 5.1k 100μF 680pF 70 BG 1 60 50 40 30 GND POWER LOSS 0.1 20 VFB 59k VOUT 1.8V 8A EFFICIENCY POWER LOSS (W) TG EFFICIENCY (%) RUN 10 VIN = 3.3V 10 118k 3822 TA01 0 100 1000 LOAD CURRENT (mA) 0.01 10000 3822 TA01b 3822fa 1 LTC3822 ABSOLUTE MAXIMUM RATINGS (Note 1) 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 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 ΔVSENSE(MAX) will be approximately 120mV and the switching frequency will be 550kHz. Duty Cycle = VOUT = 36.4% VIN From Figure 1, SF = 96%. RDS(ON)MAX = ΔVSENSE(MAX) 5 • 0.9 • SF • = 0.011Ω IOUT(MAX) • ρT 6 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: L MIN = ⎛ 1.2V ⎞ 1.2V • ⎜1– ⎟ = 0.35μH 550kHz • 4A ⎝ 3.3V ⎠ 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. 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. • 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. 3822fa 15 LTC3822 APPLICATIONS INFORMATION VIN CIN M1 GND L1 SW M2 VOUT COUT GND U1 AND OTHER SMALL-SIGNAL COMPONENTS GND SENSE TRACE 3822 F05 Figure 5. LTC3822 Suggested PCB Floorplan 5V SECONDARY SUPPLY IPRG VIN 2.75V TO 4.5V VIN RUN FDS6898A TG IHLP-2525CZ-01 0.47μH FREQ ITH LTC3822 22μF 2x SW 0.22μF BOOST 5.1k 47μF 2x D OPTIONAL 680pF GND VOUT 1.8V 8A BG VFB 59k 118k 3822 F06 Figure 6. Nominal 3.3VIN 1.8V/8A High Efficiency 550kHz Step-Down Converter with 5V Gate Drive IPRG VIN 3.3V VIN RUN Si4866 TG IHLP-2525CZ-01 0.22μH FREQ ITH LTC3822 SW 47μF 2x 0.22μF BOOST 27k 100μF 2x Si4866 680pF GND VOUT 1.8V 12A BG VFB 59k 118k 3822 F07 Figure 7. 3.3VIN 1.8V/12A High Efficiency, High Current 550kHz Step-Down Converter 3822fa 16 LTC3822 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699 Rev C) 0.70 ±0.05 3.55 ±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 3.00 ±0.10 (4 SIDES) R = 0.125 TYP 6 0.40 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.35 × 45° CHAMFER PIN 1 TOP MARK (SEE NOTE 6) (DD) DFN REV C 0310 5 0.200 REF 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD 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 3822fa 17 LTC3822 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 10-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1664 Rev H) BOTTOM VIEW OF EXPOSED PAD OPTION 1.88 ± 0.102 (.074 ± .004) 5.23 (.206) MIN 0.889 ± 0.127 (.035 ± .005) 1 0.05 REF 10 0.305 ± 0.038 (.0120 ± .0015) TYP RECOMMENDED SOLDER PAD LAYOUT DETAIL “B” CORNER TAIL IS PART OF DETAIL “B” THE LEADFRAME FEATURE. FOR REFERENCE ONLY NO MEASUREMENT PURPOSE 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 10 9 8 7 6 DETAIL “A” 0° – 6° TYP 1 2 3 4 5 GAUGE PLANE 0.53 ± 0.152 (.021 ± .006) DETAIL “A” 0.18 (.007) 0.497 ± 0.076 (.0196 ± .003) REF 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 4.90 ± 0.152 (.193 ± .006) 0.254 (.010) 0.29 REF 1.68 (.066) 1.68 ± 0.102 3.20 – 3.45 (.066 ± .004) (.126 – .136) 0.50 (.0197) BSC 1.88 (.074) SEATING PLANE 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) TYP 0.50 (.0197) NOTE: BSC 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 6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL NOT EXCEED 0.254mm (.010") PER SIDE. 0.86 (.034) REF 0.1016 ± 0.0508 (.004 ± .002) MSOP (MSE) 0911 REV H 3822fa 18 LTC3822 REVISION HISTORY REV DATE DESCRIPTION A 12/11 Changed P-channel to N-channel in the Peak Current Sense Voltage Selection and Slope Compensation (IPRG Pin) section. PAGE NUMBER 9 3822fa 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. 19 LTC3822 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1628/LTC3728 Dual High Efficiency, 2-Phase Synchronous Step Down Controllers Constant Frequency, Standby, 5V and 3.3V LDOs, VIN to 36V, 28-Lead SSOP LTC1735 High Efficiency Synchronous Step-Down Controller Burst Mode Operation, 16-Pin Narrow SSOP, Fault Protection, 3.5V ≤ VIN ≤ 36V LTC1778 No RSENSE, Synchronous Step-Down Controller Current Mode Operation Without Sense Resistor, Fast Transient Response, 4V ≤ VIN ≤ 36V LTC3411 1.25A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT ≥ 0.8V, IQ = 60μA, ISD =