LTC3409AEDD#TRPBF

LTC3409A 600mA Low VIN Buck Regulator in 3mm × 3mm DFN FEATURES DESCRIPTION n The LTC®3409A is a high efficiency, monolithic synchronous buck regulator using a constant frequency, current mode architecture. The LTC3409A improves upon the LTC3409’s light load regulation in Burst Mode operation. The output voltage is adjusted via an external resistor divider. n n n n n n n n n n n n n n n n 1.6V to 5.5V Input Voltage Range 0.62V to 5.5V Output Voltage Range Internal Soft-Start Selectable 1.7MHz or 2.6MHz Constant Frequency Operation Internal Oscillator Can Be Synchronized to an External Clock, 1MHz to 3MHz Range High Efficiency: Up to 95% 65μA Quiescent Current, Burst Mode® Operation 600mA Output Current (VIN = 1.8V, VOUT = 1.2V) 750mA Peak Inductor Current No Schottky Diode Required Low Dropout Operation: 100% Duty Cycle 0.612V Reference Voltage Stable with Ceramic Capacitors 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. 4. The SW trace should be kept as small as possible. Keep sensitive components away from the SW pins. The input capacitor CIN and the resistors R1 and R2 should be routed away from the SW traces and the inductors. 5. A ground plane is preferred, but if not available, keep the signal and power grounds segregated with small signal components returning to the GND pin at one point. They should not share the high current path of CIN or COUT. 6. Flood all unused areas on all layers with copper. Flooding with copper will reduce the temperature rise of power components. These copper areas should be connected to VIN or GND (preferably). VIN CIN VIN Board Layout Considerations When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3409A. These items are also illustrated graphically in the layout diagram of Figure 3. Check the following in your layout. 1. Does the capacitor CIN connect to the power VIN (Pins 3, 4) and GND (Exposed Pad) as close as possible? This capacitor provides the AC current to the internal power MOSFETs and their drivers. VIN LTC3409A RUN SYNC VFB MODE L1 VOUT SW SGND GND C1 COUT R2 R1 3409A F03 Figure 3 3409af 13 LTC3409A APPLICATIONS INFORMATION Design Example As a design example, assume the LTC3409A is used in a 2-alkaline cell battery-powered application. The VIN will be operating from a maximum of 3.2V down to about 1.8V. The load current requirement is a maximum of 600mA but most of the time it will be in standby mode, requiring only 2mA. Efficiency at both low and high load currents is important, so the minimum frequency setting of 1.7MHz is chosen. Output voltage is 1.5V. With this information we can calculate L using Equation 3: ⎛ V ⎞ 1 L= VOUT ⎜ 1– OUT ⎟ f • ΔIL VIN ⎠ ⎝ For best efficiency choose a 750mA or greater inductor with less than 0.3Ω series resistance. CIN will require an RMS current rating of at least 0.3A ≅ ILOAD(MAX) /2 at temperature. For the feedback resistors, choose R2 = 137k. R1 is then calculated to be 200k from Equation 2. Figure 4 shows the complete circuit along with its efficiency curve. Table 2 below gives 1% resistor values for selected output voltages. (3) Substituting VOUT = 1.5V, VIN = 3.2V, ΔIL = 240mA and f = 1.7MHz in Equation 2 gives: L= VOUT R1 R2 0.85V 53.6k 137k 1.2V 137k 143k 1.5V 200k 137k 1.8V 267k 137k 1 ⎛ 1.5V ⎞ 1.5V ⎜ 1– ≅ 2.2µH ⎝ 3.2V ⎟⎠ 1.7MHz • 240mA Burst Mode Efficiency, 1.5VOUT 100 CIN 4.7μF R2 137k 90 LTC3409A VFB SYNC GND RUN VIN SW VIN R1 200k 1.8VIN 3.2VIN 80 L1 2.2μH COUT 22μF s2 MODE 3409A F04 VOUT 1.5V 0.6A EFFICIENCY (%) VIN 1.8V TO 3.2V 70 60 2.5VIN 50 40 30 20 L1: SUMIDA CDRH2D18/LD 10 0 0.1 C1 10pF 1 10 100 LOAD CURRENT (mA) 1000 3409A F04b Figure 4 3409af 14 LTC3409A PACKAGE DESCRIPTION DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) 0.675 ±0.05 3.5 ±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 = 0.115 TYP 5 0.38 ± 0.10 8 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (NOTE 6) (DD) DFN 1203 0.200 REF 0.75 ±0.05 0.00 – 0.05 4 0.25 ± 0.05 1 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-1) 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 TOP AND BOTTOM OF PACKAGE 3409af 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 LTC3409A RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3409 600mA (IOUT) Low VIN Step-Down DC/DC Converter 95% Efficiency, VIN: 1.6V to 5.5V, VOUT(MIN) = 0.61V, IQ = 65μA, ISD < 1μA, 8-Lead DFN Package LTC3549 250mA Low VIN Step-Down DC/DC Converter 93% Efficiency, VIN: 1.6V to 5.5V, VOUT(MIN) = 0.61V, IQ = 50μA, ISD < 1μA, 6-Lead DFN Package LTC3417A-2 Dual 1.5A/1A 4MHz Step-Down DC/DC Regulator 95% Efficiency, Low Ripple, VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, DFN and TSSOP Packages LTC3410 300mA, 2.25MHz, Synchronous Step-Down Regulator in SC-70 96% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 0.8V, IQ = 26μA LTC1878 600mA (IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 96% Efficiency, VIN: 2.7V to 6V, VOUT(MIN) = 0.8V, IQ = 10μA, ISD