Datasheet LTC3778 (Analog Devices)

LTC3778 Wide Operating Range, No R TM SENSE Step-Down Controller
U FEATURES DESCRIPTIO
■
Wide VIN Range: 4V to 36V
The LTC®3778 is a synchronous step-down switching ■
Sense Resistor Optional
regulator controller for computer memory, automobile ■
True Current Mode Control
and other DC/DC power supplies. The controller uses a ■
2% to 90% Duty Cycle at 200kHz
valley current control architecture to deliver very low duty ■
tON(MIN)
≤
100ns
cycles without requiring a sense resistor. Operating fre- ■
Stable with Ceramic COUT
quency is selected by an external resistor and is compen- ■ Dual N-Channel MOSFET Synchronous Drive sated for variations in VIN and VOUT. ■ Power Good Output Voltage Monitor Discontinuous mode operation provides high efficiency ■ ±1% 0.6V Reference operation at light loads. A forced continuous control pin ■ Adjustable Current Limit reduces noise and RF interference, and can assist second- ■ Adjustable Switching Frequency ary winding regulation when the main output is lightly ■ Programmable Soft-Start loaded. SENSE+ and SENSE– pins provide true Kelvin ■ Output Overvoltage Protection sensing across the optional sense resistor or the ■ Optional Short-Circuit Shutdown Timer sychronous MOSFET. ■ Micropower Shutdown: IQ ≤ 30µA ■ Available in a 1mm 20-Lead TSSOP Package Fault protection is provided by internal foldback current
U
limiting, an output overvoltage comparator, optional short-
APPLICATIO S
circuit shutdown timer and input undervoltage lockout. Soft-start capability for supply sequencing is accom- ■ Notebook and Palmtop Computers, PDAs plished using an external timing capacitor. The regulator ■ Battery Chargers current limit level is user programmable. Wide supply ■ Distributed Power Systems range allows operation from 4V to 36V at the input and ■ DDR Memory Power Supply from 0.6V up to (0.9)VIN at the output. ■ Automobile DC Power Supply , LTC and LT are registered trademarks of Linear Technology Corporation. No RSENSE is a trademark of Linear Technology Corporation.
U TYPICAL APPLICATIO
RON 1.4M ION
Efficiency vs Load Current
CSS VIN 0.1µF VIN 100 C 5V TO 28V IN M1 RUN/SS TG 10µF V Si4884 L1 IN = 5V 35V CC 1.8µH SW ×3 VOUT 500pF 90 C 2.5V B 0.22µF ITH BOOST 10A + COUT V D 180 IN = 25V R B µF C LTC3778 CMDSH-3 4V 20k SGND INTVCC ×2 80 M2 DRV D1 CC Si4874 B340A BG EFFICIENCY (%) SENSE+ + 70 C R2 VCC 4.7µF 40.2k SENSE– PGOOD PGND 600.01 0.1 1 10 VFB R1 LOAD CURRENT (A) 12.7k 3778 F01b 3778 F01a
Figure 1. High Efficiency Step-Down Converter
3778f 1