LM5041A

Cascaded PWM Controller

General Description

The LM5041A PWM controller contains all of the features

necessary to implement either current-fed or voltage-fed

push-pull or bridge power converters. These “Cascaded”

topologies are well suited for multiple output and higher

power applications. The LM5041A’s four control outputs in-

clude: the buck stage controls (HD and LD) and the push-

pull control outputs (PUSH and PULL). Push-pull outputs are

driven at 50% nominal duty cycle at one half of the switching

frequency of the buck stage and can be configured for either

a guaranteed overlap time (for current-fed applications) or a

guaranteed both-off time (for voltage-fed applications).

Push-pull stage MOSFETs can be driven directly from the

internal gate drivers while the buck stage requires an exter-

nal driver such as the LM5102. The LM5041A includes a

high-voltage start-up regulator that operates over a wide

input range of 15V to 100V. The PWM controller is designed

for high-speed capability including an oscillator frequency

range up to 1 MHz and total propagation delays of less than

100ns. Additional features include: line Under-Voltage Lock-

out (UVLO), soft-start, an error amplifier, precision voltage

reference, and thermal shutdown.

The two differences between the LM5041 and the LM5041A

are: No second level current limit in the ’A’ version No

softstart (SS) shutdown comparator in the ’A’ version .

Features

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Internal Start-up Bias Regulator

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Programmable Line Under-Voltage Lockout (UVLO) with

Adjustable Hysteresis

n

Current Mode Control

n

Internal Error Amplifier with Reference

n

Cycle-by-cycle Over-Current Protection

n

Leading Edge Blanking

n

Programmable Push-Pull Overlap or Dead Time

n

Internal 1.5A Push-Pull Gate Drivers

n

Programmable Soft-start

n

Programmable Oscillator with Sync Capability

n

Precision Reference

n

Thermal Shutdown

Applications

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Telecommunication Power Converters

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Industrial Power Converters

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Multi-Output Power Converters

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+42V Automotive Systems

Packages

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TSSOP-16

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LLP-16 (5x5 mm) Thermally Enhanced

Typical Application Circuit

20137801

Simplified Cascaded Push-Pull Power Converter

May 2005

© 2005 National Semiconductor Corporation

DS201378

www.national.com