LM5115

Secondary Side Post Regulator Controller

General Description

The LM5115 controller contains all of the features necessary

to implement multiple output power converters utilizing the

Secondary Side Post Regulation (SSPR) technique. The

SSPR technique develops a highly efficient and well regu-

lated auxiliary output from the secondary side switching

waveform of an isolated power converter. Regulation of the

auxiliary output voltage is achieved by leading edge pulse

width modulation (PWM) of the main channel duty cycle.

Leading edge modulation is compatible with either current

mode or voltage mode control of the main output. The

LM5115 drives external high side and low side NMOS power

switches configured as a synchronous buck regulator. A

current sense amplifier provides overload protection and

operates over a wide common mode input range. Additional

features include a low dropout (LDO) bias regulator, error

amplifier, precision reference, adaptive dead time control of

the gate signals and thermal shutdown.

Features

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Self-synchronization to main channel output

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Free-run mode for buck regulation of DC input

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Leading edge pulse width modulation

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Voltage-mode control with current injection and input line

feed-forward

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Operates from AC or DC input up to 75V

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Wide 4.5V to 30V bias supply range

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Wide 0.75V to 12V output range.

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Top and bottom gate drivers sink 2.5A peak

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Adaptive gate driver dead-time control

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Wide bandwidth error amplifier (4MHz)

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Programmable soft-start

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Thermal shutdown protection

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TSSOP-16 or thermally enhanced LLP-16 packages

Typical Application Circuit

20134901

FIGURE 1. Simplified Multiple Output Power Converter Utilizing SSPR Technique

PRELIMINARY

March 2005

© 2005 National Semiconductor Corporation

DS201349

www.national.com