PDF LTC3606B Data sheet ( Hoja de datos )

Número de pieza	LTC3606B
Descripción	800mA Synchronous Step-Down DC/DC
Fabricantes	Linear Technology Corporation
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No Preview Available ! LTC3606B 800mA Synchronous Step-Down DC/DC with Average Input Current Limit FEATURES DESCRIPTION n Programmable Average Input Current Limit: ±5% Accuracy n Step-Down Output: Up to 96% Efﬁciency n Low Noise Pulse-Skipping Operation at Light Loads n Input Voltage Range: 2.5V to 5.5V n Output Voltage Range: 0.6V to 5V n 2.25MHz Constant-Frequency Operation n Power Good Output Voltage Monitor n Low Dropout Operation: 100% Duty Cycle n Internal Soft-Start n Current Mode Operation for Excellent Line and Load Transient Response n ±2% Output Voltage Accuracy n Short-Circuit Protected n Shutdown Current ≤ 1μA n Available in Small Thermally Enhanced 8-Lead 3mm × 3mm DFN Package APPLICATIONS n High Peak Load Current Applications n USB Powered Devices n Supercapacitor Charging wwwn.DaRtaaSdhieoetT4rUa.ncosmmitters and Other Handheld Devices The LTC®3606B is an 800mA monolithic synchronous buck regulator using a constant frequency current mode architecture. The input supply voltage range is 2.5V to 5.5V, making it ideal for Li-Ion and USB powered applications. 100% duty cycle capability provides low dropout operation, extending the run time in battery-operated systems. Low output voltages are supported with the 0.6V feedback reference voltage. The LTC3606B can supply 800mA output current. The LTC3606B’s programmable average input current limit is ideal for USB applications and for point-of-load power supplies because the LTC3606B’s limited input current will still allow its output to deliver high peak load currents without collapsing the input supply. The operating frequency is internally set at 2.25MHz allowing the use of small surface mount inductors. Internal soft-start reduces in-rush current during start-up. The LTC3606B is available in an 8-Lead 3mm × 3mm DFN package. L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S.Patents, including 5481178, 6127815, 6304066, 6498466, 6580258, 6611131. TYPICAL APPLICATION Monolithic Buck Regulator with Input Current Limit VIN 3.4V TO 5.5V PGOOD CIN 10μF 499k VIN SW LTC3606B RUN PGOOD RLIM VFB GND 1000pF 116k ILIM = 475mA 1.5μH 1210k 255k VOUT 3.4V AT 800mA + 2.2mF s2 SuperCap 3606B TA01 GSM Pulse Load VOUT 200mV/DIV VIN AC-COUPLED 1V/DIV IOUT 500mA/DIV IIN 500mA/DIV 1ms/DIV VIN = 5V, 500mA COMPLIANT ILOAD = 0A to 2.2A 3606B TA01b 3606bf 1 1 page LTC3606B TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, VIN = 5V, unless otherwise noted. Efﬁciency vs Load Current 100 VOUT = 1.2V 90 80 70 60 50 40 30 20 10 0 0.0001 VIN = 2.7V VIN = 3.6V VIN = 4.2V VIN = 5V 0.001 0.01 0.1 OUTPUT CURRENT (A) 1 3606B G13 Load Regulation 3.0 2.5 2.0 1.5 1.0 0.5 0 –0.5 –1.0 0 VOUT = 1.8V VOUT = 2.5V VOUT = 3.3V 100 200 300 400 500 600 700 800 LOAD CURRENT (mA) 3606B G15 Line Regulation 0.6 VOUT = 1.8V ILOAD = 100mA 0.4 0.2 0 –0.2 –0.4 –0.6 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VIN (V) 3606B G16 Start-Up from Shutdown RUN 2V/DIV VOUT 1V/DIV IL 250mA/DIV 200μs/DIV www.DataSheeVt4INU=.c5Vo,mVOUT = 3.3V RLOAD = 7Ω CLOAD = 4.7μF Start-Up from Shutdown RUN 2V/DIV VOUT 2V/DIV RLIM 1V/DIV IIN 500mA/DIV 3606B G17 2ms/DIV VIN = 5V, VOUT = 3.4V RL = NO LOAD, CL = 4.4mF CLIM = 2200pF, ILIM = 500mA 3606B G18 VRLIM vs Input Current 1.2 ILIM = 475mA RLIM = 116k 1.0 0.8 0.6 0.4 0.2 0 0 100 200 300 400 500 600 IIN (mA) 3606B G18b Average Input Current Limit vs Temperature 8 VIN = 5V 6 ILIM = 475mA 4 Load Step VOUT 200mV/DIV AC-COUPLED 2 IL 0 1A/DIV –2 ILOAD –4 1A/DIV –6 –8 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 3606B G19 20μs/DIV VIN = 5V, VOUT = 3.3V ILOAD = 0A TO 800mA COUT = 100μF, CF = 20pF Load Step VOUT 200mV/DIV AC-COUPLED 3606B G20 IL 1A/DIV ILOAD 1A/DIV 20μs/DIV VIN = 5V, VOUT = 1.8V ILOAD = 80mA TO 800mA COUT = 100μF, CF = 20pF 3606B G21 3606bf 5 5 Page LTC3606B APPLICATIONS INFORMATION A general LTC3606B application circuit is shown in Figure 2. External component selection is driven by the load require- ment, and begins with the selection of the inductor L. Once the inductor is chosen, CIN and COUT can be selected. Inductor Selection Although the inductor does not inﬂuence the operat- ing frequency, the inductor value has a direct effect on ripple current. The inductor ripple current ΔIL decreases with higher inductance and increases with higher VIN or VOUT : ΔIL = VOUT fO • L • ⎛ ⎝⎜ 1− VOUT VIN ⎞ ⎠⎟ (1) Accepting larger values of ΔIL allows the use of low inductances, but results in higher output voltage ripple, greater core losses, and lower output current capability. A reasonable starting point for setting ripple current is 40% of the maximum output load current. So, for a 800mA regulator, ΔIL = 320mA (40% of 800mA). The inductor value will also have an effect on Burst Mode operation. The transition to low current operation begins when the peak inductor current falls below a level set by the internal burst clamp. Lower inductor values result in higher ripple current which causes the transition to occur wwwa.DtaltoawSheeretl4oUa.dcocmurrents. This causes a dip in efﬁciency in the upper range of low current operation. Furthermore, lower inductance values will cause the bursts to occur with increased frequency. VIN 2.5V TO 5.5V PGOOD RPGD CIN VIN SW LTC3606B RUN PGOOD RLIM VFB GND RLIM CLIM L1 CF R2 R1 3606B F02 VOUT COUT Figure 2. LTC3606B General Schematic Inductor Core Selection Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and do not radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. The choice of which style inductor to use often depends more on the price versus size requirements, and any radiated ﬁeld/EMI requirements, than on what the LTC3606B requires to operate. Table 1 shows some typical surface mount inductors that work well in LTC3606B applications. Table 1. Representative Surface Mount Inductors MANU- MAX DC FACTURER PART NUMBER VALUE CURRENT DCR HEIGHT Coilcraft LPS4012-152ML LPS4012-222ML LPS4012-332ML LPS4012-472ML LPS4018-222ML LPS4018-332ML LPS4018-472ML 1.5μH 2.2μH 3.3μH 4.7μH 2.2μH 3.3μH 4.7μH 2200mA 1750mA 1450mA 1450mA 2300mA 2000mA 1800mA 0.070Ω 0.100Ω 0.100Ω 0.170Ω 0.070Ω 0.080Ω 0.125Ω 1.2mm 1.2mm 1.2mm 1.2mm 1.8mm 1.8mm 1.8mm FDK FDKMIPF2520D 4.7μH 1100mA 0.11Ω 1mm FDKMIPF2520D 3.3μH 1200mA 0.1Ω 1mm FDKMIPF2520D 2.2μH 1300mA 0.08Ω 1mm Murata LQH32CN4R7M23 4.7μH 450mA 0.2Ω 2mm Panasonic ELT5KT4R7M 4.7μH 950mA 0.2Ω 1.2mm Sumida CDRH2D18/LD CDH38D11SNP- 3R3M CDH38D11SNP- 2R2M 4.7μH 3.3μH 2.2μH 630mA 1560mA 1900mA 0.086Ω 0.115Ω 0.082Ω 2mm 1.2mm 1.2mm Taiyo Yuden CB2016T2R2M CB2012T2R2M CB2016T3R3M NR30102R2M NR30104R7M 2.2μH 2.2μH 3.3μH 2.2μH 4.7μH 510mA 530mA 410mA 1100mA 750mA 0.13Ω 0.33Ω 0.27Ω 0.1Ω 0.19Ω 1.6mm 1.25mm 1.6mm 1mm 1mm TDK VLF3010AT4R7- 4.7μH 700mA 0.28Ω 1mm MR70 VLF3010AT3R3- 3.3μH 870mA 0.17Ω 1mm MR87 VLF3010AT2R2- 2.2μH 1000mA 0.12Ω 1mm M1R0 VLF4012AT-2R2 2.2μH 1500mA 0.076Ω 1.2mm M1R5 VLF5012ST-3R3 3.3μH 1700mA 0.095Ω 1.2mm M1R7 VLF5014ST-2R2 2.2μH 2300mA 0.059Ω 1.4mm M2R3 3606bf 11 11 Page

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