LM5008EVAL National Semiconductor, LM5008EVAL Datasheet

LM5008EVAL

Manufacturer Part Number

LM5008EVAL

Description

EVALUATION BOARD FOR LM5008

Manufacturer

National Semiconductor

Datasheets

1.LM5008MMNOPB.pdf (16 pages)

2.LM5008EVAL.pdf (6 pages)

Specifications of LM5008EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

10V

Current - Output

300mA

Voltage - Input

12 ~ 95V

Regulator Topology

Buck

Board Type

Fully Populated

Utilized Ic / Part

LM5008

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Power - Output

Frequency - Switching

Other names

*LM5008EVAL

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LM5008 Evaluation Board

Introduction

The LM5008 evaluation board is designed to provide the

design engineer with a fully functional step down switching

regulator to evaluate LM5008 regulator IC,in a typical envi-

ronment.

The performance of evaluation board is as follows:

• Input range: 12V to 95V, transients upto 100V (absolute

• Output voltage: 10V

• Output current: 300mA

• Measured efficiency: 89% at 200mA and V

• Board size: 31.9mm x 44.4mm

Theory of Operation

The LM5008 Step down switching regulator features all of

the functions needed to implement low cost, efficient, Buck

bias regulators. This high voltage regulator contains an

100V, 0.5A N-channel Buck switch. The regulator is based

on hysteretic control scheme using an on-time inversely

proportional to input voltage (V

operating frequency to remain relatively constant with load

and input voltage voltage variations. The hysteretic control

requires no control loop compensation, while providing fast

load transient response. Additional protection features in-

clude : Thermal Shutdown, V

maximum duty–cycle limiter. LM5008 can be used in numer-

ous applications to efficiently regulate step down higher

voltage inputs. This regulator is well suited for 48V telecom

and the new 42V automotive power bus ranges.

The LM5008 operates in discontinuous conduction mode at

light load currents or continuous conduction mode at heavier

load currents. In discontinuous conduction mode, current

through the output inductor starts at zero and ramps up to

the peak value during the buck switch on time, and then back

to zero during buck switch off time. In discontinuous conduc-

tion mode, the operating frequency can be relatively low and

maximum)

). This feature allows the

undervoltage lockout and

AN201055

= 30V

National Semiconductor

Application Note 1330

Ravi Murugeshappa

May 2004

will vary with load. Therefore at light loads the conversion

efficiency is maintained , since switching losses decrease

with reduction in switching frequency.

The evaluation board just needs one high voltage power-

supply (upto 100V and current rating of 0.5A). The maximum

output power is 3 watts. Either an electronic load or resistor

bank can be used for testing evaluation board.

Start-up Feature

There is no soft-start feature in LM5008, and it normally

comes up with full load current to supply the power de-

manded by the load within a short time.The LM5008 con-

tains an intelligent current limit OFF timer intended to reduce

the foldback characteristic inherent with fixed off-time over-

current protection. If the current in the Buck FET exceeds

550mA the present cycle is immediately terminated (cycle by

cycle current limit). Following the termination of the cycle a

non-resetable current limit off timer is initiated. The duration

of off time is a function of the external setting resistor (Rcl)

and the FB pin voltage. When FB pin voltage = 0V the

current limit off time is internally preset to 35µs. This condi-

tion occurs in short circuit operation when a maximum

amount of off time is required.

In cases of overload (not complete short circuit) the current

limit off time can be reduced as a function of the output

voltage (measured at the FB pin). Reducing the off time

during smaller overloads reduces the amount of foldback

and also reduces the initial start-up time.

Low Ripple Configuration

For applications where lower output voltage ripple is re-

quired the output load can be connected directly to the low

ESR output capacitor, as shown below. The evaluation board

is laid out in such a way that, user can use either (high ripple

or low ripple) options by simply shifting the output connector.

The series resistor (R) will degrade the load regulation

however.

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Related parts for LM5008EVAL

LM5008EVAL Summary of contents

Page 1

... In discontinuous conduc- tion mode, the operating frequency can be relatively low and © 2004 National Semiconductor Corporation National Semiconductor Application Note 1330 Ravi Murugeshappa May 2004 will vary with load ...

Page 2

Low Ripple Configuration www.national.com (Continued) Low Ripple Configuration Output Evaluation Board Schematic Diagram 2 20105501 20105502 ...

Page 3

Bill of Materials ITEM PART NUMBER C 1 C4532X7R2A105M C 2 C3225X7R1C226M C 3 C1206C104K5RAC C 4 C1206C103K5RAC C 5 C3216X7R2A104KT D 1 MURA110T3 L 1 SLF10145T-221MR65 CRCW12063573F R 2 CRCW12062803F R 3 CRCW12063011F R 4 CRCW12061001F R ...

Page 4

Efficiency Measurements LM5008 Efficiency Start-up Behavior V = 50V 10V, Load Resistance = 30Ω IN OUT CH1: Switch Node Voltage CH2: Output Voltage CH3: Inductor Current Normal Operation V = 50V 10V, Load Resistance = 30Ω ...

Page 5

PCB Layouts 20105513 Top Layer 20105514 Silk Screen 20105515 Bottom Layer 5 www.national.com ...

Page 6

... BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. ...

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