LTC3544B Quad Synchronous Step-Down Regulator: 2.25MHz, 300mA, 200mA, 200mA, 100mA FEATURES
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DESCRIPTION
The LTC®3544B 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 LTC3544B well suited for single Li-Ion/polymer battery-powered applications. 100% duty cycle provides low dropout operation, extending battery runtime in portable systems. At moderate and low output load levels PWM pulse skip mode operation provides very low output ripple voltage for noise sensitive applications. 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 LTC3544B is available in a low profile (0.75mm) (3mm × 3mm) QFN package.
, LT, LTC and LTM 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, 5994885.
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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 Low Dropout Operation: 100% Duty Cycle Pulse Skipping at Low Load for Minimum Ripple 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. PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3544B. 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.
VCC 2.25V TO 5.5V
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.
L4 VOUT1 R15 C13 R16 RUN100 C15
C8
GNDA
SW1000 RUN100 VFB100
VCC
GNDA
VFB200A VFB200B VFB300 VFB300
VFB100
LTC3544B RUN200A L2 VOUT3 R5 C4 R6 VFB200A L3 VOUT2 R8 C10 R11 C12 VFB200B
3544B F03
RUN200A SW200A SW200B SW200B PGND C9
RUN300 RUN200B PVIN SW300 SW300
RUN300 RUN200B
SW200A
C6
L1 VOUT4 R2 C3
PGND PVIN 2.25V TO 5.5V
C1 R3
Figure 3. LTC3544B Layout Diagram
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LTC3544B APPLICATIONS INFORMATION
C1 GND C4
L1
L4
VCC C9 L2 L3
C10
C2 C3
PGND
3544B F04
Figure 4
Design Example As a design example, consider using the LTC3544B 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. 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: L4 = 2.5V ⎛ 2.5V ⎞ = 4.5µH 1– ⎠ ⎝ 2.25MHz • 100mA ⎜ 4.2V ⎟
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 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.
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.
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LTC3544B APPLICATIONS INFORMATION
VSUPPLY 3.6V C9 4.7μF 15 L2 4.7μH R3 93.1k R4 107k L3 4.7μH R5 0Ω R6 100k C7 20pF 3 5 2 RUN200A SW200A C6 20pF 16 4 1 RUN200B SW200B VFB200B LTC3544B 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 C10 4.7μF
VOUT2 1.5V C2 4.7μF
VOUT1 1.2V C1 4.7μF
VOUT3 0.8V C3 4.7μF
VOUT2 2.5V C4 4.7μF
VFB200A GNDA 14 PGND 6
VFB300
3544B F05a
Figure 5
Efficiency vs Output Current—300mA Channel, All Other Channels Off
100 VOUT = 2.5V 90 TA = 25°C 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0.0001 VIN = 2.7V VIN = 3.6V VIN = 4.2V 0.01 0.1 0.001 LOAD CURRENT (A) 1
3544B F05b
Transient Response
VOUT300 100mV/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
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LTC3544B 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
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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.
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LTC3544B RELATED PARTS
PART NUMBER LTC3405/LTC3405A LTC3406/LTC3406B LTC3407/LTC3407-2 LTC3409 LTC3410/LTC3410B LTC3411 LTC3412 LTC3441/LTC3442 LTC3443 LTC3531/LTC3531-3 LTC3531-3.3 LTC3532 LTC3547 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 200mA IOUT, 1.5MHz, Synchronous Buck-Boost DC/DC Converters 500mA IOUT, 2MHz, Synchronous Buck-Boost 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 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: 2.5V 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
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