ltc3851-1 Linear Technology Corporation, ltc3851-1 Datasheet

ltc3851-1

Manufacturer Part Number

ltc3851-1

Description

Synchronous Step-down Switching Regulator Controller

Manufacturer

Linear Technology Corporation

Datasheet

1.LTC3851-1.pdf (28 pages)

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FEATURES

APPLICATIONS

TYPICAL APPLICATION

Wide V

±1% Output Voltage Accuracy

Power Good Output Voltage Monitor

Phase-Lockable Fixed Frequency: 250kHz to 750kHz

Dual N-Channel MOSFET Synchronous Drive

Very Low Dropout Operation: 99% Duty Cycle

Adjustable Output Voltage Soft-Start or Tracking

Output Current Foldback Limiting

Output Overvoltage Protection

OPTI-LOOP

Selectable Continuous, Pulse-Skipping or

Burst Mode

Low Shutdown I

Thermally Enhanced 16-Lead MSOP

or 3mm × 3mm QFN Package

Automotive Systems

Telecom Systems

Industrial Equipment

Distributed DC Power Systems

OUT

SENSE

82.5k

15k

2200pF

INTV

Range: 0.8V to 5.5V

or DCR Current Sensing

Range: 4V to 38V Operation

0.1μF

High Efﬁ ciency Synchronous Step-Down Converter

100k

0.1μF

330pF

Compensation Minimizes C

Operation at Light Loads

PGO0D

FREQ/PLLFLTR

RUN

TK/SS

PLLIN/MODE

: 20μA

LTC3851-1

SENSE

INTV

BOOST

GND

–

0.1μF

0.047μF

4.7μF

30.1k

OUT

3.01k

0.68μH

22μF

154k

48.7k

38511 TA01a

330μF

4.5V TO 38V

3.3V

15A

DESCRIPTION

OUT

The LTC

step-down switching regulator controller that drives

an all N-channel synchronous power MOSFET stage. A

con stant 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 conﬁ gurations 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

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.

LIM

pin is replaced by PGOOD.

3851-1 is a high performance synchronous

Step-Down Switching

Regulator Controller

100

OUT

Efﬁ ciency and Power Loss

= 12V

= 3.3V

100

vs Load Current

LOAD CURRENT (mA)

EFFICIENCY

Synchronous

1000

POWER LOSS

LTC3851-1

10000

38511TA01b

100000

10000

1000

100

38511f

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