LM5642 High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization
September 2003
LM5642
High Voltage, Dual Synchronous Buck Converter with
Oscillator Synchronization
General Description
The LM5642 consists of two current mode synchronous
buck regulator controllers operating 180˚ out of phase with
each other at a normal switching frequency of 200kHz.
Out of phase operation reduces the input ripple RMS cur-
rent, thereby significantly reducing the required input capaci-
tance. The switching frequency can be synchronized to an
external clock between 150kHz and 250kHz. The two switch-
ing regulator outputs can also be paralleled to operate as a
dual-phase single output regulator.
The output of each channel can be independently adjusted
from 1.3 to 90% of Vin. An internal 5V rail is also available
externally for driving bootstrap circuitry.
Current-mode feedback control assures excellent line and
load regulation and a wide loop bandwidth for excellent
response to fast load transients. Current is sensed across
either the Vds of the top FET or across an external current-
sense resistor connected in series with the drain of the top
FET.
The LM5642 features analog soft-start circuitry that is inde-
pendent of the output load and output capacitance making
the soft-start behavior more predictable and controllable
than traditional soft-start circuits.
Over-voltage protection is available for both outputs. A UV-
Delay pin is also available to allow delayed shut off time for
the IC during an output under-voltage event.
Features
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Two synchronous buck regulators
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180˚ out of phase operation
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Synchronizable switching frequency from 150kHz to
250kHz
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4.5V to 36V input range
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50µA Shutdown current
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Adjustable output from 1.3V to 90% of Vin
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0.04% (typical) line and load regulation error
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Current mode control with or without a sense resistor
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Independent enable/soft-start pins allow simple
sequential startup configuration.
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Configurable for single output parallel operation. (See
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Adjustable cycle-by-cycle current limit
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Input under-voltage lockout
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Output over-voltage latch protection
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Output under-voltage protection with delay
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Thermal shutdown
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Self discharge of output capacitors when the regulator is
OFF
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TSSOP package
Applications
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Embedded Computer Systems
Telecom Systems
Set-Top Boxes
WebPAD
Point Of Load Power Architectures
Typical Application Circuit
20060101
© 2003 National Semiconductor Corporation
DS200601
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
