LTC3851-1

1

38511f

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Synchronous

Step-Down Switching

Regulator Controller

The LTC

step-down switching regulator controller that drives

an all N-channel synchronous power MOSFET stage. A

constant frequency current mode architecture allows a

phase-lockable frequency of up to 750kHz.

OPTI-LOOP compensation allows the transient response

to be optimized over a wide range of output capacitance

and ESR values. The LTC3851-1 features a precision 0.8V

reference and a power good indicator. A wide 4V to 38V (40V

absolute maximum) input supply range encompasses most

battery configurations and intermediate bus voltages.

The TK/SS pin ramps the output voltage during start-up

and shutdown with coincident or ratiometric tracking.

Current foldback limits MOSFET heat dissipation during

short-circuit conditions. The MODE/PLLIN pin selects

among Burst Mode operation, pulse skipping mode or

continuous inductor current mode at light loads and allows

the IC to be synchronized to an external clock.

The LTC3851-1 is identical to the LTC3851 except that the

High Efficiency Synchronous Step-Down Converter

Burst Mode

or 3mm

× 3mm QFN Package

Efficiency and Power Loss

vs Load Current

L, LT, LTC, LTM, Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology

Corporation. All other trademarks are the property of their respective owners.

Protected by U.S. Patents including 5408150, 5481178, 5705919, 5929620, 6304066,

6498466, 6580258, 6611131.

PGO0D

RUN

TK/SS

FREQ/PLLFLTR

TG

SW

PLLIN/MODE

BG

GND

0.047μF

0.1μF

4.7μF

3.01k

LTC3851-1

22μF

4.5V TO 38V

3.3V

15A

38511 TA01a

0.68μH

330pF

2200pF

0.1μF

0.1μF

330μF

2

BOOST

15k

154k

48.7k

30.1k

82.5k

100k

LOAD CURRENT (mA)

10

70

75

80

85

90

100

1000

10000

100000

38511TA01b

65

60

55

50

95

100

1000

100

10

10000

EFFICIENCY

POWER LOSS