LTC3560ES6TRPBF

LTC3560 2.25MHz, 800mA Synchronous Step-Down Regulator in ThinSOT FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO High Efficiency: Up to 95% Low Output 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. PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3560. These items are also illustrated graphically in Figures 4 and 5. Check the following in your layout: 1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide. 2. Does the VFB pin connect directly to the feedback resistors? The resistive divider R1/R2 must be connected between the (+) plate of COUT and ground. 3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 4. Keep the (–) plates of CIN and COUT as close as possible. 5. Keep the switching node, SW, away from the sensitive VFB node. Design Example As a design example, assume the LTC3560 is used in a single lithium-ion battery-powered cellular phone application. The VIN will be operating from a maximum of 4.2V down to about 2.7V. The load current requirement is a maximum of 0.8A but most of the time it will be in 3560f W UU 11 LTC3560 APPLICATIO S I FOR ATIO – VOUT COUT + L1 BOLD LINES INDICATE HIGH CURRENT PATHS Figure 4. LTC3560 Layout Diagram VOUT PIN 1 L1 LTC3560 SW Figure 5. LTC3560 Suggested Layout standby mode, requiring only 2mA. Efficiency at both low and high load currents is important. Output voltage is 2.5V. With this information we can calculate L using equation (1), L= ⎛V⎞ 1 VOUT ⎜ 1 − OUT ⎟ ( f)(∆IL ) ⎝ VIN ⎠ Substituting VOUT = 2.5V, VIN = 4.2V, ∆IL = 320mA and f = 2.25MHz in equation (3) gives: L= 2.5V ⎛ 2.5V ⎞ 1− ≅ 1.4µH ⎝ ⎠ 2.25MHz(320mA) ⎜ 4.2V ⎟ A 1.5µH inductor works well for this application. For best efficiency choose a 960mA or greater inductor with less than 0.2Ω series resistance. 3560f 12 U 1 RUN SYNC/MODE LTC3560 2 GND VFB VIN CIN VIN 5 R2 3 SW 4 CFWD R1 6 3560 F04 W UU VIA TO GND R1 VIA TO VIN R2 CFWD VIN VIA TO VOUT COUT GND CIN 3560 F05 CIN will require an RMS current rating of at least 0.4A ≅ ILOAD(MAX)/2 at temperature and COUT will require an ESR of less than 0.1Ω. In most cases, a ceramic capacitor will satisfy this requirement. For the feedback resistors, choose R1 = 309k. R2 can then be calculated from equation (2) to be: ⎛V ⎞ R2 = ⎜ OUT − 1⎟ R1= 978.5k ; use 976k ⎝ 0.6 ⎠ Figure 6 shows the complete circuit along with its efficiency curve. (3) LTC3560 APPLICATIO S I FOR ATIO VIN 2.7V TO 4.2V 4 CIN* 10µF CER VIN LTC3560 RUN SW 3 1.5µH** 10pF EFFICIENCY (%) 1 6 SYNC/MODE VFB GND 2 5 976k 309k 3560 F06a * TDK C2012X5R0J106M **TDK VLF3010AT-1R5N1R2 Figure 6a VOUT 200mV/DIV AC COUPLED IL 1A/DIV ILOAD 1A/DIV VIN = 3.6V 20µs/DIV VOUT = 2.5V ILOAD = 100mA TO 800mA Burst Mode OPERATION 3560 F06c Figure 6c U 100 90 80 70 VOUT 2.5V COUT* 10µF CER W UU VOUT = 2.5V Burst Mode OPERATION PULSE SKIPPING 60 50 40 30 20 10 0 0.1 VIN = 3.6V VIN = 4.2V 1 10 100 OUTPUT CURRENT (mA) 1000 3560 F06b Figure 6b VOUT 200mV/DIV AC COUPLED IL 1A/DIV ILOAD 1A/DIV 20µs/DIV VIN = 3.6V VOUT = 2.5V ILOAD = 100mA TO 800mA PULSE SKIPPING MODE 3560 F06d Figure 6d 3560f 13 LTC3560 APPLICATIO S I FOR ATIO EFFICIENCY (%) VIN 2.7V TO 4.2V 4 CIN* 10µF CER VIN LTC3560 RUN SW 3 1µH** 10pF 1 6 3MHz CLK SYNC/MODE VFB GND 2 5 301k 301k 3560 F07a *TDK C2012X5R0J106M **MURATA LQH32CN1R0M33 Figure 7a VOUT 100mV/DIV AC COUPLED IL 500mA/DIV ILOAD 500mA/DIV VIN = 3.6V 20µs/DIV VOUT = 1.2V ILOAD = 300A TO 800mA 3560 F07c Figure 7c 14 U 100 90 80 70 60 50 40 30 20 10 0 1 10 100 LOAD CURRENT (mA) VIN = 2.7V VIN = 3.6V VIN = 4.2V 1000 3560 F07b W UU VOUT 1.2V COUT* 10µF CER Figure 7b VOUT 100mV/DIV AC COUPLED IL 500mA/DIV ILOAD 500mA/DIV 20µs/DIV VIN = 3.6V VOUT = 1.2V ILOAD = 0mA TO 500mA 3560 F07d Figure 7d 3560f LTC3560 PACKAGE DESCRIPTIO 0.62 MAX 0.95 REF 3.85 MAX 2.62 REF RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.20 BSC 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 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. U S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID 0.95 BSC 0.30 – 0.45 6 PLCS (NOTE 3) 0.80 – 0.90 0.01 – 0.10 0.09 – 0.20 (NOTE 3) 1.90 BSC S6 TSOT-23 0302 3560f 15 LTC3560 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 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 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 =