LTC3544EUD

LTC3544 Quad Synchronous Step-Down Regulator: 2.25MHz, 300mA, 200mA, 200mA, 100mA FEATURES ■ ■ DESCRIPTION The LTC ®3544 is a quad, high efficiency, monolithic synchronous buck regulator using a constant-frequency, current mode architecture. The four regulators operate independently with separate run pins. The 2.25V to 5.5V input voltage range makes the LTC3544 well suited for single Li-Ion/polymer battery-powered applications. 100% duty cycle provides low dropout operation, extending battery runtime in portable systems. Low ripple Burst Mode® operation increases efficiency at light loads, further extending battery runtime with typically only 20mV of ripple. Switching frequency is internally set to 2.25MHz, allowing the use of small surface mount inductors and capacitors. The internal synchronous switches increase efficiency and eliminate the need for external Schottky diodes. Low output voltages are easily supported with the 0.8V feedback reference voltage. The LTC3544 is available in a low profile (0.75mm) (3mm × 3mm) QFN package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark 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, 5994885. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ High Efficiency: Up to 95% Four Independent Regulators Provide Up to 300mA, 200mA, 200mA and 100mA Output Current 2.25V to 5.5V Input Voltage Range 2.25MHz Constant-Frequency Operation No Schottky Diodes Required Extremely Low Channel-to-Channel Transient Crosstalk Low Ripple (20mVP-P) Burst Mode Operation: IQ = 70μA (All Channels On) 0.8V Reference Allows Low Output Voltages Shutdown Mode Draws 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 charging to 3.3V would require a 250μs rise time, limiting the charging current to about 130mA. 3544fa 12 LTC3544 APPLICATIONS INFORMATION PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3544. These items are also illustrated graphically in Figures 3 and 4. Check the following in your layout: 1. The power traces, consisting of the PGND trace, the GNDA trace, the SW traces, the PVIN trace and the VCC trace should be kept short, direct and wide. 2. Does each of the VFBx pins connect directly to the respective feedback resistors? The resistive dividers must be connected between the (+) plate of the corresponding output filter capacitor (e.g., C13) and GNDA. If the circuit being powered is at such a distance from the part where voltage drops along circuit traces are large, consider a Kelvin connection from the powered circuit back to the resistive dividers. 3. Keep C8 and C9 as close to the part as possible. 4. Keep the switching nodes (SWx) away from the sensitive VFBx nodes. 5. Keep the ground connected plates of the input and output capacitors as close as possible. 6. Care should be taken to provide enough space between unshielded inductors in order to minimize any transformer coupling. Design Example As a design example, consider using the LTC3544 as a portable application with a Li-Ion battery. The battery provides VIN ranging from 2.8V to 4.2V. The demand at 2.5V is 250mA necessitating the use of the 300mA output for this requirement. L4 VOUT1 R15 C13 R16 RUN100 C15 VCC 2.25V TO 5.5V C8 GNDA SW1000 RUN100 VFB100 VCC GNDA VFB200A VFB200B VFB300 VFB300 C1 GND C4 VFB100 L1 L4 LTC3544 RUN200A L2 VOUT3 R5 C4 R6 VFB200A L3 VOUT2 R8 C10 R11 C12 VFB200B 3544 F03 3544 F04 RUN200A SW200A SW200B SW200B PGND C9 RUN300 RUN200B PVIN SW300 SW300 RUN300 RUN200B VCC C9 L1 VOUT4 R2 C3 C2 C3 R3 PGND L2 L3 C10 SW200A C6 PGND PVIN 2.25V TO 5.5V C1 Figure 3. LTC3544 Layout Diagram Figure 4. LTC3544 Suggested Layout 3544fa 13 LTC3544 APPLICATIONS INFORMATION Beginning with this channel, first calculate the inductor value for about 35% ripple current (100mA in this example) at maximum VIN. Using a form of Equation 1: L4 = 2.5V ⎛ 2.5V ⎞ 1– = 4.5µH ⎝ ⎠ 2.25MHz • 100mA ⎜ 4.2V ⎟ 200k are a good compromise between efficiency and immunity to any adverse effects of PCB parasitic capacitance on the feedback pins. Choosing 10μA with 0.8V feedback voltage makes R7 = 80k. A close standard 1% resistor is 76.8k. Using: ⎛V ⎞ R8 = ⎜ OUT – 1 • R7 = 163.2k ⎟ ⎝ 0.8 ⎠ The closest standard 1% resistor is 162k. An optional 20pF feedback capacitor may be used to improve transient response. The component values for the other channels are chosen in a similar fashion. Figure 5 shows the complete schematic for this example, along with the efficiency curve and transient response for the 300mA channel. C10 4.7μF 15 L2 4.7μH R3 93.1k R4 107k L3 4.7μH C3 4.7μF R6 100k 3 5 2 RUN200A SW200A C6 20pF 16 4 1 RUN200B SW200B VFB200B LTC3544 RUN300 SW300 9 8 10 L4 4.7μH C8 20pF R7 162k R8 76.8k VCC 7 PVIN RUN100 SW100 VFB100 12 13 11 L1 10μH C5 20pF R1 59k R2 118k For the inductor, use the closest standard value of 4.7μH. A 4.7μF capacitor should be sufficient for the output capacitor. A larger output capacitor will attenuate the load transient response, but increase the settling time. A value for CIN = 4.7μF should suffice as the source impedance of a Li-Ion battery is very low. The feedback resistors program the output voltage. Minimizing the current in these resistors will maximize efficiency at very light loads, but totals on the order of VSUPPLY 3.6V C9 4.7μF VOUT2 1.5V C2 4.7μF VOUT1 1.2V C1 4.7μF VOUT3 0.8V VOUT2 2.5V C4 10μF VFB200A GNDA 14 PGND 6 VFB300 3544 F05a Figure 5. Design Example Efficiency vs Output Current—300mA Channel, All Other Channels Off 100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 VOUT = 2.5V TA = 25°C VIN = 2.7V VIN = 3.6V VIN = 4.2V 1 3544B F05b Transient Response VOUT300 50mV/DIV AC COUPLED IL 250mA/DIV ILOAD 250mA/DIV VIN = 3.6V 20μs/DIV VOUT = 2.5V TA = 25°C LOAD STEP = 300μA TO 300mA 3544B F05c 0 0.0001 0.001 0.01 0.1 LOAD CURRENT (A) 3544fa 14 LTC3544 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) 0.70 ± 0.05 3.50 ± 0.05 1.45 ± 0.05 2.10 ± 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.75 ± 0.05 BOTTOM VIEW—EXPOSED PAD R = 0.115 TYP 15 16 0.40 ± 0.10 1 1.45 ± 0.10 (4-SIDES) 2 PIN 1 NOTCH R = 0.20 TYP OR 0.25 × 45° CHAMFER 3.00 ± 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) (UD16) QFN 0904 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 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 0.25 ± 0.05 0.50 BSC 3544fa 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. 15 LTC3544 RELATED PARTS PART NUMBER LTC3405/LTC3405A LTC3406/LTC3406B LTC3407/LTC3407-2 LTC3409 LTC3410/LTC3410B LTC3411 LTC3412 LTC3441/LTC3442 LTC3443 LTC3446 LTC3531/LTC3531-3 LTC3531-3.3 LTC3532 LTC3544B LTC3547/LTC3547B LTC3548/LTC3548-1 LTC3548-2 LTC3561 DESCRIPTION 300mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converters 600mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converters Dual 600mA/800mA IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converters 600mA IOUT, 1.7MHz/2.6MHz, Synchronous Step-Down DC/DC Converter 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converters 1.25A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter 2.5A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter 1.2A IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converters Monolithic Synchronous Buck Regulator with Dual VLDOTM Requlators 200mA IOUT, 1.5MHz, Synchronous Buck-Boost DC/DC Converters 500mA IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converter 300mA, 2 × 200mA, 100mA Quad 2.25MHz Synchronous Buck DC/DC Converter Dual 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter Dual 400mA/800mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converters 1.25A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter COMMENTS 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 20μA, ISD < 1μA, ThinSOTTM Package 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD < 1μA, ThinSOT Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, 10-Lead MSE, DFN Packages 96% Efficiency, VIN: 1.6V to 5.5V, VOUT(MIN) = 0.6V, IQ = 65μA, ISD < 1μA, DFN Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 26μA, ISD < 1μA, SC70 Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD < 1μA, 10-Lead MSE, DFN Packages 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD < 1μA, 16-Lead TSSOPE Package 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN): 2.4V to 5.25V, IQ = 50μA, ISD < 1μA, DFN Package 92% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN) = 0.4V, IQ = 140μA, ISD < 1μA, 3mm × 4mm DFN Package 95% Efficiency, VIN: 1.8V to 5.5V, VOUT(MIN): 2V to 5V, IQ = 16μA, ISD < 1μA, ThinSOT, DFN Packages 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN): 2.4V to 5.25V, IQ = 35μA, ISD < 1μA, 10-Lead MSE, DFN Packages 95% Efficiency, VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, IQ = 825μA, ISD < 1mA, 3mm × 3mm QFN Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, 8-Lead DFN Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, 10-Lead MSE, DFN Packages 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 240μA, ISD < 1μA, DFN Package ThinSOT and VLDO are trademarks of Linear Technology Corporation 3544fa 16 Linear Technology Corporation (408) 432-1900 ● LT 0308 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007