LTC3406BES5-1.2#TRMPBF

LTC3406B-1.2 1.5MHz, 600mA Synchronous Step-Down Regulator in ThinSOT U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC ®3406B-1.2 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. Supply current with no load is 300µA dropping to 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. 3. Keep the (–) plates of CIN and COUT as close as possible. Design Example As a design example, assume the LTC3406B-1.2 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 0.6A but most of the time it will be in standby mode, requiring only 2mA. Efficiency at both low and high load currents is important. With this information we can calculate L using equation (1), L= 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 (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 1 (3) Substituting VIN = 4.2V, ∆IL = 240mA and f = 1.5MHz in equation (3) gives: PC Board Layout Checklist When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the LTC3406B-1.2. These items are also illustrated graphically in Figures 3 and 4. Check the following in your layout: ⎛ 1.2V ⎞ 1 1.2V⎜ 1 − ( f)(∆IL ) ⎝ VIN ⎟⎠ L= 1.2V ⎛ 1.2V ⎞ ⎜1 − ⎟ = 2.38 µH 1.5MHz(240mA) ⎝ 4.2V ⎠ A 2.2µH inductor works well for this application. For best efficiency choose a 720mA or greater inductor with less than 0.2Ω series resistance. CIN will require an RMS current rating of at least 0.3A ≅ ILOAD(MAX)/2 at temperature and COUT will require an ESR of less than 0.25Ω. In most cases, a ceramic capacitor will satisfy this requirement. VIA TO VOUT VIA TO VIN RUN VIN LTC3406B-1.2 2 – GND VOUT 5 PIN 1 COUT VOUT + 3 L1 SW VIN LTC3406B-1.2 VOUT 4 L1 CIN SW VIN 3406B12 F03 BOLD LINES INDICATE HIGH CURRENT PATHS COUT CIN GND 3406B12 F04 Figure 3. LTC3406B-1.2 Layout Diagram Figure 4. LTC3406B-1.2 Suggested Layout sn3406b12 3406b12fs 10 LTC3406B-1.2 U TYPICAL APPLICATIO S Single Li-Ion 1.2V/600mA Regulator for Lowest Profile, ≤1mm High VIN 2.7V TO 4.2V 4 CIN** 4.7µF CER VIN SW 3 2.2µH† COUT1* 10µF CER LTC3406B-1.2 1 RUN VOUT GND VOUT 1.2V 5 3406B12 TA02 2 *MURATA GRM219R60JI06KE19B **AVX06036D475MAT † FDK MIPW3226D2R2M Efficiency vs Output Current Load Step Load Step 100 90 EFFICIENCY (%) 80 70 VOUT 100mV/DIV AC COUPLED VOUT 100mV/DIV AC COUPLED IL 500mA/DIV IL 500mA/DIV ILOAD 500mA/DIV ILOAD 500mA/DIV VIN = 2.7V 60 50 VIN = 4.2V 40 30 20 10 0.1 3406B12 TA04 20µs/DIV VIN = 3.6V ILOAD = 0mA TO 600mA VIN = 3.6V 1 10 100 OUTPUT CURRENT (mA) 20µs/DIV VIN = 3.6V ILOAD = 200mA TO 600mA 3406B12 TA05 1000 3406B12 TA03 U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.09 – 0.20 (NOTE 3) 0.20 BSC 0.01 – 0.10 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 1.90 BSC S5 TSOT-23 0302 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 sn3406b12 3406b12fs 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. 11 LTC3406B-1.2 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1616 500mA (IOUT), 1.4MHz, High Efficiency Step-Down DC/DC Converter 90% Efficiency, VIN = 3.6V to 25V, VOUT = 1.25V, IQ = 1.9mA, ISD =