Datasheet LTC3858 (Analog Devices)

LTC3858 Low IQ, Dual 2-Phase Synchronous Step-Down Controller
FEATURES DESCRIPTION
n
Low Operating IQ: 170μA (One Channel On)
The LTC®3858 is a high performance dual step-down n
Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
switching regulator controller that drives all N-channel n
Wide VIN Range: 4V to 38V
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-850kHz) The 170μA no-load quiescent current extends operating n Programmable Fixed Frequency (50kHz-900kHz) life in battery-powered systems. OPTI-LOOP compensa- n Selectable Continuous, Pulse-Skipping or tion allows the transient response to be optimized over Burst Mode® Operation at Light Loads a wide range of output capacitance and ESR values. The n Very Low Dropout Operation: 99% Duty Cycle LTC3858 features a precision 0.8V reference and a power n Adjustable Output Voltage Soft-Start good output indicator. A wide 4V to 38V input supply range n Power Good Output Voltage Monitor encompasses a wide range of intermediate bus voltages n Output Overvoltage Protection and battery chemistries. n Output Latch-Off Protection During Short Circuit n Low Shutdown I Independent soft-start pins for each controller ramp the Q: 8μA n Internal LDO Powers Gate Drive from V output voltages during start-up. The output latch-off feature IN or EXTVCC n No Current Foldback During Start-Up protects the circuit in short-circuit conditions. n Small 5mm × 5mm QFN Package For a leaded 28-lead SSOP package with a fi xed current
APPLICATIONS
limit and one PGOOD output, without phase modulation or a clock output, see the LTC3858-1 data sheet. n Automotive Systems L, LT, LTC, LTM, Burst Mode, OPTI-LOOP, μModule, PolyPhase, 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 Effi ciency Dual 8.5V/3.3V Step-Down Converter
VIN
Effi ciency and Power Loss
9V TO 38V 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 LTC3858 POWER LOSS PGND 50 SENSE1+ SENSE2+ 40 10 EFFICIENCY (%) 0.007Ω 0.01Ω 30 20 1 V V OUT1 SENSE1– SENSE2– 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 0 0.1 150μF 680pF 680pF SS1 SS2 150μF SGND 20k 0.0001 0.001 0.01 0.1 1 10 20k 15k 15k OUTPUT CURRENT (A) 0.1μF 0.1μF 3858 TA01b 3858 TA01 3858fc 1