LTC3545EUD-1#PBF

LTC3545/LTC3545-1 Triple 800mA Synchronous Step-Down Regulator–2.25MHz FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION Three 800mA Outputs High Efficiency: Up to 95% 2.25V to 5.5V Input Voltage Range Low Ripple (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. Design Example As a design example, consider using the LTC3545/LTC35451 in a portable application with a Li-Ion battery. The battery provides VIN ranging from 2.8V to 4.2V. The demand on one channel at 2.5V is 600mA. Using this channel as an example, first calculate the inductor value for 40% ripple current (240mA in this example) at maximum VIN. Using a form of Equation 1: L1= 2.5V ⎛ 2.5V ⎞ 1– = 1.41µH (2.25MHz )(240mA ) ⎜⎝ 3.6V ⎟⎠ Use the closest standard value of 1.5μH. For low ripple applications, 10μF is a good choice for the output capacitor. A smaller output capacitor will shorten transient response settling time, but also increase the load transient ripple. A value for C5 = 4.7μF should suffice as the source impedance of a Li-Ion battery is very low. C5 and C1 both provide switching current to the output power switches. They should be placed as close a possible to the chip between VIN/GNDA and PVIN/PGND respectively. PVIN and PGND are the supply and return power paths for both channels 2 and 3, so a value of 10μF for C1 is appropriate. 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 200k are a good compromise between efficiency and immunity to any adverse effects of PCB parasitic capacitance on the feedback pins. Choosing 10μA as the feedback current with 0.6V feedback voltage makes R4 = 60k. A close standard 1% resistor is 60.4k. Using: ⎛ 2.5V ⎞ R3 = ⎜ – 1 • R4 = 191.1k ⎝ 0.6 V ⎟⎠ The closest standard 1% resistor is 191k. A 20pF feedforward capacitor is recommended to improve transient response. The component values for the other channels are chosen in a similar fashion. Figure 4 shows the complete schematic for this example, along with the efficiency curve and burst mode ripple at an output current for the 2.5V output. 35451fb 15 LTC3545/LTC3545-1 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 LTC3545/LTC3545-1. These items are also illustrated graphically in Figures 3 and 4. Figure 3 shows the power path components and traces. In this figure the feedback networks are not shown since they reside on the bottom side of the board. Check the following in your layout: 1. The power traces consisting of the PGND trace, the SW trace, the PVIN trace, the VIN and GNDA traces, 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 cor- responding output filter capacitor (e.g. C2) 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 C1 and C5 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. VOUT3 (VIA TO FEEDBACK NETWORK) L3 C4 SW3 VIN C1 PVIN PGND C5 GNDA SW1 SW2 C3 C2 L1 L2 VOUT2 (VIA TO FEEDBACK NETWORK) 3545 F03 (VIA TO FEEDBACK NETWORK) VOUT1 Figure 3. Layout Diagram 35451fb 16 LTC3545/LTC3545-1 TYPICAL APPLICATIONS L1 1.5μH C6 20pF R2 511k E2 PGOOD2 C5 4.7μF R1 511k 1 2 E1 PGOOD1 3 4 5 6 7 VIN 2.7V TO 5.5V C1 10μF 10V 8 SW1 LTC3545 PGOOD1 GNDA VIN RUN2 RUN1 PGOOD2 VFB1 SW2 VFB2 PGND VFB3 PVIN RUN3 SW3 SYNC/MODE R3 191k E3 VOUT1 C2 10μF 6.3V 2.5V AT 0.8A E4 GND R4 60.4k 16 15 14 L2 1.5μH 13 12 C7 20pF 11 R5 100k 10 E7 VOUT2 C3 10μF 6.3V 1.2V AT 0.8A E6 GND R6 100k 9 GND L3 1.5μH 17 C8 20pF R7 165k E5 VOUT3 C4 10μF 6.3V 1.5V AT 0.8A E8 GND R8 110k 3545 TA02 Overall Efficiency vs Channel 1 Load Current Burst Mode Ripple 100 VOUT3 AC COUPLED 20mV/DIV OVERALL EFFICIENCY (%) 90 80 70 IL3 250mA/DIV 60 50 40 30 20 10 0 0.1 SW3 2V/DIV TA = 25°C VIN = 3.6V VOUT = 2.5V fOSC = 2.25MHz CHANNEL 2 = 1.2V, ILOAD = 400mA CHANNEL 3 = 1.5V, ILOAD = 400mA 1 10 100 CHANNEL 1 LOAD CURRENT (mA) 1000 TA = 25°C VIN = 3.6V VOUT = 1.5V ILOAD = 50mA fOSC = 2.25MHz 1μs/DIV 3545 TA04 3545 TA03 Figure 4. LTC3545 Low Ripple Burst Mode Operation 35451fb 17 LTC3545/LTC3545-1 TYPICAL APPLICATIONS L1 1.5μH C6 20pF R9 511k E9 PGOOD3 E2 PGOOD2 R2 511k R1 511k 1 2 E1 PGOOD1 3 4 5 6 VIN 2.5V TO 5.5V 7 C1 4.7μF 8 SW1 LTC3545-1 GNDA PGOOD1 VIN RUN1 RUN2 PGOOD2 VFB1 SW2 VFB2 PGND VFB3 PVIN RUN3 SW3 PGOOD3 C2 10μF E3 VOUT1 1.2V AT 0.8A E4 GND R4 100k C5 10μF 16 R3 100k 15 14 L2 1.5μH 13 12 C7 20pF 11 R5 165k C3 10μF 10 R6 110k 9 E7 VOUT2 1.5V AT 0.8A E6 GND GND L3 1.5μH 17 C8 20pF R7 133k C4 10μF E5 VOUT3 1.8V AT 0.8A E8 GND R8 66.5k 3545 TA05 3-Channel Power Sequencing RUN1 VOUT1 VOUT2 VOUT3 PGOOD3 TA = 25°C VIN = 3.6V 400μs/DIV 3545 TA06 Figure 5. LTC3545-1 Three PGOODs and Power Sequencing 35451fb 18 LTC3545/LTC3545-1 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm s 3mm) (Reference LTC DWG # 05-08-1700 Rev A) Exposed Pad Variation AA 0.70 p0.05 3.50 p 0.05 1.65 p 0.05 2.10 p 0.05 (4 SIDES) PACKAGE OUTLINE 0.25 p0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 p 0.10 (4 SIDES) BOTTOM VIEW—EXPOSED PAD PIN 1 NOTCH R = 0.20 TYP OR 0.25 s 45o CHAMFER R = 0.115 TYP 0.75 p 0.05 15 16 PIN 1 TOP MARK (NOTE 6) 0.40 p 0.10 1 1.65 p 0.10 (4-SIDES) 2 (UD16 VAR A) QFN 1207 REV A 0.200 REF 0.00 – 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-4) 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 p 0.05 0.50 BSC 35451fb 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 LTC3545/LTC3545-1 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3405/LTC3405A 300mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converters 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 20μA, ISD < 1μA, ThinSOT™ Package LTC3406/LTC3406B 600mA IOUT, 1.5MHz, Synchronous Step-Down DC/DC Converters 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 20μA, ISD < 1μA, ThinSOT Package LTC3407/LTC3407-2 Dual 600mA/800mA IOUT, 1.5MHz/2.25MHz, Synchronous Step-Down DC/DC Converters 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, 10-Lead MSE, DFN Packages LTC3409 600mA IOUT, 1.7MHz/2.6MHz, Synchronous Step-Down DC/DC Converter 96% Efficiency, VIN: 1.6V to 5.5V, VOUT(MIN) = 0.6V, IQ = 65μA, ISD < 1μA, DFN Package LTC3410/LTC3410B 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converters 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 26μA, ISD < 1μA, SC70 Package LTC3411 1.25A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD < 1μA, 10-Lead MSE, DFN Packages LTC3412 2.5A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD < 1μA, 16-Lead TSSOPE Package LTC3419 Dual 600mA, 2.25MHz, Synchronous Step-Down DC/DC 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 35μA, ISD < 1μA, MS10, 3mm × 3mm DFN Package Converter LTC3441/LTC3442 LTC3443 1.2A IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converters 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN): 2.4V to 5.25V, IQ = 50μA, ISD < 1μA, DFN Package LTC3531/LTC3531-3 LTC3531-3.3 200mA IOUT, 1.5MHz, Synchronous Buck-Boost DC/DC Converters 95% Efficiency, VIN: 1.8V to 5.5V, VOUT(MIN): 2V to 5V, IQ = 16μA, ISD < 1μA, ThinSOT, DFN Packages LTC3532 500mA IOUT, 2MHz, Synchronous Buck-Boost DC/DC Converter 95% Efficiency, VIN: 2.4V to 5.5V, VOUT(MIN): 2.4V to 5.25V, IQ = 35μA, ISD < 1μA, 10-Lead MSE, DFN Packages LTC3544/LTC3544B 300mA, 2 × 200mA, 100mA, 2.25MHz Quad Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 60μA, ISD < 1μA, 3mm × 3mm QFN Package LTC3547 Dual 300mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, 8-Lead DFN Package LTC3548/LTC3548-1 LTC3548-2 Dual 400mA/800mA IOUT, 2.25MHz, Synchronous Step-Down DC/DC Converters 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.6V, IQ = 40μA, ISD < 1μA, 10-Lead MSE, DFN Packages LTC3561 1.25A IOUT, 4MHz, Synchronous Step-Down DC/DC Converter 95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 240μA, ISD < 1μA, DFN Package ThinSOT is a Trademark of Linear Technology Corporation. 35451fb 20 Linear Technology Corporation LT 0908 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008