1

LTC1929

2-Phase, High Efficiency,

Synchronous Step-Down

Switching Regulator

August 1999

, LTC and LT are registered trademarks of Linear Technology Corporation.

OPTI-LOOP is a trademark of Linear Technology Corporation.

The LTC

step-down current mode switching regulator controller

that drives N-channel external power MOSFET stages in a

phase-lockable fixed frequency architecture. The 2-phase

controller drives its two output stages out of phase at

frequencies up to 300kHz to minimize the RMS ripple

currents in both input and output capacitors. The 2-phase

technique effectively multiplies the fundamental frequency

by two, improving transient response while operating

each channel at an optimum frequency for efficiency.

Thermal design is also simplified.

An internal differential amplifier provides true remote

sensing of the regulated supply’s positive and negative

output terminals as required by high current applications.

The RUN/SS pin provides soft-start and a defeatable,

timed, latched short-circuit shutdown to shut down both

channels. Internal foldback current limit provides protec-

tion for the external sychronous MOSFETs in the event of

an output fault. OPTI-LOOP compensation allows the

transient response to be optimized over a wide range of

output capacitance and ESR values.

APPLICATIO S

FEATURES

DESCRIPTIO

TYPICAL APPLICATIO

Figure 1. High Current 2-Phase Step-Down Converter

s

Desktop Computers

s

Internet/Network Servers

s

Large Memory Arrays

s

DC Power Distribution Systems

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2-Phase Single Output Controller

s

Reduces Required Input Capacitance and Power

Supply Induced Noise

s

Current Mode Control Ensures Current Sharing

s

Phase-Lockable Fixed Frequency: 150kHz to 300kHz

s

True Remote Sensing Differential Amplifier

s

OPTI-LOOP

Response

s

s

s

Very Low Dropout Operation: 99% Duty Cycle

s

Adjustable Soft-Start Current Ramping

s

Internal Current Foldback

s

Short-Circuit Shutdown Timer with Defeat Option

s

Overvoltage Soft-Latch Eliminates Nuisance Trips

s

Available in 28-Lead SSOP Package

1929 TA01

TG1

BOOST1

SW1

BG1

PGND

TG2

BOOST2

SW2

BG2

RUN/SS

EAIN

–

+

LTC1929

SGND

S

0.1

µF

0.1

µF

8.06k

1000pF

S

S

S

S

S

S

S

S

S

10

Ω

10k

8.06k

10

µF ×4

35V

CERAMIC

+

1000

µF ×2

4V

1.6V/40A

L1

1

µH

0.002

Ω

5V TO 28V

L2

1

µH

D2

D1

0.47

µF

S

0.47

µF

100pF

10

µF

0.002

Ω

L1, L2: CEPH149-1ROMC

Final Electrical Specifications

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.