LM5008AEVAL/NOPB National Semiconductor, LM5008AEVAL/NOPB Datasheet

LM5008AEVAL/NOPB

Manufacturer Part Number

LM5008AEVAL/NOPB

Description

BOARD EVAL LM5008

Manufacturer

National Semiconductor

Datasheets

1.LM5008ASDNOPB.pdf (16 pages)

2.LM5008AEVALNOPB.pdf (14 pages)

Specifications of LM5008AEVAL/NOPB

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

Current - Output

300mA

Voltage - Input

8 ~ 75 V

Regulator Topology

Buck

Frequency - Switching

130kHz

Board Type

Fully Populated

Utilized Ic / Part

LM5008A

Lead Free Status / RoHS Status

Lead free / RoHS Compliant

Power - Output

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LM5008A Evaluation Board

Introduction

The LM5008AEVAL evaluation board provides the design en-

gineer with a fully functional buck regulator, employing the

constant on-time (COT) operating principle. This evaluation

board provides a 5V output over an input range of 8V to 75V.

The circuit delivers load currents to 300 mA, with current limit

set at a nominal 440 mA.

The board’s specification are:

Theory of Operation

Refer to the evaluation board schematic in

the circuit is in regulation, the buck switch is on each cycle for

a time determined by R1 and VIN according to the equation:

The on-time of this evaluation board ranges from

VIN = 8V, to

versely with VIN to maintain a nearly constant switching fre-

≊

517 ns at VIN = 75V. The on-time varies in-

300863

FIGURE 1. Evaluation Board - Top Side

Figure

≊

4.85 µs at

5. When

National Semiconductor

Application Note 1925

Dennis Morgan

March 25, 2010

•

quency. At the end of each on-time the Minimum Off-Timer

ensures the buck switch is off for at least 300 ns. In normal

operation, the off-time is much longer. During the off-time, the

load current is supplied by the output capacitor (C2). When

the output voltage falls sufficiently that the voltage at FB is

below 2.5V, the regulation comparator initiates a new on-time

period. For stable, fixed frequency operation, a minimum of

25 mV of ripple is required at FB to switch the regulation com-

parator. The current limit threshold is

and

for a more detailed block diagram, and a complete description

of the various functional blocks.

Input Voltage: 8V to 75V

Output Voltage: 5V

Maximum load current: 300 mA

Minimum load current: 0A

Current Limit: 440 mA (nominal)

Measured Efficiency: 92.4% (V

Nominal Switching Frequency: 130 kHz

Size: 2.6 in. x 1.6 in.

≊

415 mA at Vin = 75V. Refer to the LM5008A data sheet

= 8V, I

≊

470 mA at Vin = 8V,

OUT

www.national.com

= 100 mA)

30086301

Related parts for LM5008AEVAL/NOPB

LM5008AEVAL/NOPB Summary of contents

Page 1

... R1 and VIN according to the equation: The on-time of this evaluation board ranges from ≊ VIN = 8V, to 517 ns at VIN = 75V. The on-time varies in- versely with VIN to maintain a nearly constant switching fre- © 2010 National Semiconductor Corporation National Semiconductor Application Note 1925 Dennis Morgan March 25, 2010 • ...

Page 2

Board Layout and Probing The pictorial in Figure 1 shows the placement of the circuit components. The following should be kept in mind when the board is powered: 1) When operating at high input voltage and high load current, forced ...

Page 3

Option B) Intermediate Ripple Configuration: This config- uration generates less ripple at V than option A above by OUT Since the output ripple is passed by Cff to the FB pin with little or no attenuation, R5 can be reduced ...

Page 4

Current Limit Off-Time When current limit is detected the on-time period is immedi- ately terminated, and the off-time forced by the LM5008A must be greater than the maximum normal off-time, which occurs at maximum input voltage. The longer-than-normal off-time is ...

Page 5

... R5 Resistor R6 Resistor U1 Switching Regulator Mfg., Part Number TDK C1608X7R1H103M Vishay CRCW06032803F Vishay CRCW06037153F Vishay CRCW06033011F Panasonic ERJ-3RQFR82V Vishay CRCW08050000Z National Semiconductor LM5008AMM 5 Package Value 1206 1 µF, 100V 1210 22 µF, 16V 0603 0.47 µF, 16V 0603 0.01 µF, 50V 0805 0.1 µF, 100V ...

Page 6

Circuit Performance www.national.com FIGURE 6. Efficiency vs Load Current FIGURE 7. Efficiency vs Input Voltage 6 30086310 30086311 ...

Page 7

FIGURE 8. Output Voltage Ripple FIGURE 9. Switching Frequency vs. Input Voltage 7 30086312 30086313 www.national.com ...

Page 8

FIGURE 10. Current Limit vs Input Voltage FIGURE 11. Line Regulation 8 30086314 30086320 ...

Page 9

FIGURE 12. Load Regulation 9 www.national.com ...

Page 10

Typical Waveforms Trace Pin Trace OUT Trace 4 = Inductor Current Vin = 12V, Iout = 200 mA Trace Pin Trace OUT Trace 4 = Inductor Current Vin ...

Page 11

Trace Pin Trace OUT Trace 4 = Inductor Current Vin = 12V, Iout = 0 mA FIGURE 15. Discontinuous Conduction Mode 11 30086322 www.national.com ...

Page 12

PC Board Layout www.national.com Board Silkscreen Board Top Layer 12 30086317 30086318 ...

Page 13

Board Bottom Layer (Viewed from Top) 13 30086319 www.national.com ...

Page 14

... For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Amplifiers www.national.com/amplifiers Audio www.national.com/audio Clock and Timing www.national.com/timing Data Converters www.national.com/adc Interface www.national.com/interface LVDS www.national.com/lvds Power Management www.national.com/power Switching Regulators www.national.com/switchers LDOs www.national.com/ldo LED Lighting www ...

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