Datasheet LTC3868 (Analog Devices)

LTC3868 Low IQ, Dual 2-Phase Synchronous Step-Down Controller
FEATURES DESCRIPTION
n
Low Operating IQ: 170µA (One Channel On)
The LTC®3868 is a high performance dual step-down n
Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 14V
switching regulator controller that drives all N-channel n
Wide VIN Range: 4V to 24V
synchronous power MOSFET stages. A constant frequency n
RSENSE or DCR Current Sensing
current mode architecture allows a phase-lockable fre- n Out-of-Phase Controllers Reduce Required Input quency of up to 850kHz. Power loss and noise due to the Capacitance and Power Supply Induced Noise input capacitor ESR are minimized by operating the two n OPTI-LOOP® Compensation Minimizes COUT controller outputs out of phase. n Phase-Lockable Frequency (75kHz to 850kHz) The 170μA no-load quiescent current extends operating life in n Programmable Fixed Frequency (50kHz to 900kHz) battery-powered systems. OPTI-LOOP compensation allows n Selectable Continuous, Pulse-Skipping or the transient response to be optimized over a wide range of Burst Mode® Operation at Light Loads output capacitance and ESR values. The LTC3868 features a n Very Low Dropout Operation: 99% Duty Cycle precision 0.8V reference and a power good output indicator. n Adjustable Output Voltage Soft-Start A wide 4V to 24V input supply range encompasses a wide n Power Good Output Voltage Monitor range of intermediate bus voltages and battery chemistries. n Output Overvoltage Protection Independent soft-start pins for each controller ramp the n Output Latchoff Protection During Short Circuit output voltages during start-up. Current foldback limits n Low Shutdown IQ: 8µA MOSFET heat dissipation during short-circuit conditions. n Internal LDO Powers Gate Drive from VIN or EXTVCC The output short-circuit latchoff feature further protects n No Current Foldback During Start-Up the circuit in short-circuit conditions. n Small 5mm × 5mm QFN Package
APPLICATIONS
For a leaded 28-lead SSOP package with a fixed current limit and one PGOOD output, without phase modulation n Notebook and Palmtop Computers or a clock output, see the LTC3868-1 data sheet. n Portable Instruments L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, PolyPhase, µModule, Linear Technology and the Linear n Battery Operated Digital Devices logo are registered trademarks and No RSENSE and UltraFast are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. n Distributed DC Power Systems Patents, including 5481178, 5705919, 5929620, 6100678, 6144194, 6177787, 6304066, 6580258.
TYPICAL APPLICATION High Efficiency Dual 8.5V/3.3V Step-Down Converter
VIN
Efficiency and Power Loss
9V TO 24V 22µF
vs Load Current
4.7µF 50V VIN INTVCC 100 10000 TG1 TG2 90 0.1µF 0.1µF 3.3µH BOOST1 BOOST2 7.2µH 80 1000 EFFICIENCY SW1 SW2 POWER LOSS (mW) 70 BG1 BG2 60 100 LTC3868 POWER LOSS PGND 50 SENSE1+ SENSE2+ 40 10 EFFICIENCY (%) 0.007Ω 0.01Ω 30 V SENSE1– SENSE2– V 20 1 OUT1 OUT2 VIN = 12V 3.3V 8.5V VFB1 VFB2 10 VOUT = 3.3V 5A 62.5k I 193k 3.5A TH1 ITH2 FIGURE 12 CIRCUIT 150µF 680pF 680pF 0 0.1 SS1 SGND SS2 150µF 20k 0.0001 0.001 0.01 0.1 1 10 20k 15k 15k 0.1µF 0.1µF OUTPUT CURRENT (A) 3868 TA01b 3868 TA01 3868fe For more information www.linear.com/LTC3868 1 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Typical Performance Characteristics Pin Functions Operation Package Description Typical Application Related Parts