Datasheet LTC3855 (Analog Devices)

LTC3855 Dual, Multiphase Synchronous DC/DC Controller with Differential Remote Sense FeaTures DescripTion n
Dual, 180
°
Phased Controllers Reduce Required
The LTC®3855 is a dual PolyPhase® current mode synchro-
Input Capacitance and Power Supply Induced Noise
nous step-down switching regulator controller that drives n
High Efficiency: Up to 95%
all N-channel power MOSFET stages. It includes a high n
RSENSE or DCR Current Sensing
speed differential remote sense amplifier. The maximum n
Programmable DCR Temperature Compensation
current sense voltage is programmable for either 30mV, n
±0.75% 0.6V Output Voltage Accuracy
50mV or 75mV, allowing the use of either the inductor DCR n
Phase-Lockable Fixed Frequency 250kHz to 770kHz
or a discrete sense resistor as the sensing element. n
True Remote Sensing Differential Amplifier
The LTC3855 features a precision 0.6V reference and can n Dual N-Channel MOSFET Synchronous Drive produce output voltages up to 12.5V. A wide 4.5V to 38V n Wide VIN Range: 4.5V to 38V input supply range encompasses most intermediate bus n VOUT Range: 0.6V to 12.5V without Dif erential Amplifier voltages and battery chemistries. Power loss and supply n VOUT Range: 0.6V to 3.3V with Differential Amplifier noise are minimized by operating the two controller output n Clock Input and Output for Up to 12-Phase Operation stages out of phase. Burst Mode® operation, continuous n Adjustable Soft-Start or VOUT Tracking or pulse-skipping modes are supported. n Foldback Output Current Limiting n Output Overvoltage Protection The LTC3855 can be configured for up to 12-phase op- n 40-Pin (6mm × 6mm) QFN and 38-Lead FE Packages eration, has DCR temperature compensation, two power good signals and two current limit set pins. The LTC3855 applicaTions is available in low profile 40-pin 6mm × 6mm QFN and 38-lead exposed pad FE packages. n Computer Systems L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode and PolyPhase are registered n Telecom Systems trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 5481178, 5705919, 5929620, 6100678, n Industrial and Medical Instruments 6144194, 6177787, 6304066, 6580258. n DC Power Distribution Systems Typical applicaTion
High Efficiency Dual 1.8V/1.2V Step-Down Converter
VIN 4.5V TO
Load Step
+ 4.7µF 1µF 22µF 20V
(Forced Continuous Mode)
VIN INTVCC TG1 TG2 0.1µF 0.1µF ILOAD 0.56µH BOOST1 BOOST2 0.4µH 5A/DIV SW1 SW2 300mA TO 5A BG1 BG2 IL PGND1 PGND2 LTC3855 5A/DIV FREQ SENSE1+ SENSE2+ SENSE1– SENSE2– VOUT V 20k OUT1 DIFFOUT VOUT2 100mV/DIV 1.8V VFB1 V 1.2V AC-COUPLED 15A FB2 40.2k 15A ITH1 ITH2 470pF 470pF + TK/SS1 DIFFP SGND DIFFN TK/SS2 + 330µF 20k 330µF 100k 7.5k ×2 15k 0.1µF 0.1µF ×2 50µs/DIV 3855 TA01a 20k VIN = 12V VOUT = 1.8V 3855 TA01 3855f Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order information Electrical Characteristics Typical Performance Characteristics Pin Functions Functional Block Diagram Operation Applications Information Typical Applications Package Description Related Parts