LINEAR TECHNOLOGY LTC1876 User's Manual

LTC1876

High Efficiency, 2-Phase,

Dual Synchronous Step-Down Switching Controller and Step-Up Regulator

FEATURES DESCRIPTIO Step-Down Controller The LTC®1876 is a high performance triple output switching

Out-of-Phase Controllers Reduce Required Input regulator. It incorporates a dual step-down switching con- Capacitance and Power Supply Induced Noise troller that drives all N-channel synchronous power MOSFET Power Good Output Voltage Indicator stages. A step-up regulator with an internal 1A, 36V switch OPTI-LOOPTM Compensation Minimizes COUT provides the third output.

DC Programmed Fixed Frequency 150k Hz to 300k Hz

The step-down controllers minimize power loss and noise

Wide VIN Range: 3.5V to 36V Operation

by operating the output stage of each controller out of

Very Low Dropout Operation: 99% Duty Cycle phase. OPTI-LOOP compensation allows the transient Adjustable Soft-Start Current Ramping response to be optimized over a wide range of output Latched Short-Circuit Shutdown with Defeat Option capacitance and ESR values. A RUN/SS pin for each Remote Output Voltage Sense and OV Protection controller provides both soft-start and an optional timed, 5V and 3.3V Standby Regulators short-circuit shutdown that can be configured to latch off Selectable Const. Freq. or Burst Mode TM Operation one or both controllers. Current foldback provides

Step-Up Regulator additional short-circuit protection. In an overvoltage High Operating Switching Frequency of 1.2MHz condition, the bottom MOSFET is latched on until VOUT Low Internal VCESAT Switch: 400m V @ 1A, VIN = 3V returns to normal. The FCB pin can be used to inhibit Burst Wide VIN Range: 2.6V to 16V Operation Mode operation or to enable regulation of a secondary High Output Voltage: Up to 34V output voltage. The step-up regulator operates at 1.2MHz, allowing the

APPLICATIO S

use of tiny low cost capacitors and inductors. In addition, 3.3V Input Step-Down Converter its internal 1A switch allows high current outputs to be Notebook and Palmtop Computers, PDAs generated. Its current mode control scheme provides Battery-Operated Digital Devices excellent line and load regulation. , LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.

TYPICAL APPLICATIO

VIN 5.2V

TO 28V

35V 1µF VOUT3

CER CER 12V

ALUM 10V

AUXVIN VININTVCC

M3 TG2 TG1 M1 10µF

BOOST2 BOOST1

SW2 SW1

LTC1876 6.8µH

M4 BG2 BG1 M2

AUXSW

PGND AUXVFB

PGOOD AUXSD

SENSE2+ SENSE1+

VOUT2 SENSE2– SENSE1– VOUT1 3.3V 5V

VOSENSE2 VOSENSE1 4A

1% ITH2 ITH1

4V 220p F RUN/SS2 SGND RUN/SS1 220p F 6.3V

SP SP

M1, M2, M3, M4: FDS6680A

1876 TA01

Figure 1. High Efficiency Triple 5V/3.3V/12V Power Supply

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