LM34914EVAL National Semiconductor, LM34914EVAL Datasheet

LM34914EVAL

Manufacturer Part Number

LM34914EVAL

Description

BOARD EVALUATION LM34914

Manufacturer

National Semiconductor

Datasheets

1.LM34914SDNOPB.pdf (14 pages)

2.LM34914EVAL.pdf (8 pages)

Specifications of LM34914EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

1, Non-Isolated

Voltage - Output

Current - Output

Voltage - Input

8 ~ 40V

Regulator Topology

Buck

Frequency - Switching

275kHz

Board Type

Fully Populated

Utilized Ic / Part

LM34914

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Power - Output

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LM34914 Evaluation Board

Introduction

The LM34914EVAL 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 40V.

The circuit delivers load currents to 1A, with current limit set

R3, C2, C11 and C12. These components provide options for

managing the output ripple as described later in this docu-

ment.

Example Circuit

Theory of Operation

Refer to the evaluation board schematic in Figure 5, which

contains a simplified block diagram of the LM34914. When

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

a time determined by R4 and VIN according to the equation:

The on-time of this evaluation board ranges from

at VIN = 8V, to

inversely with VIN to maintain a nearly constant switching fre-

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

ensures the buck switch is off for at least 265 ns. In normal

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

load current is supplied by the output capacitor (C7). 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, which varies with Vin, is

≊

1.2A. The board is populated with all components except

≊

500 ns at VIN = 40V. The on-time varies

300003

FIGURE 1. Evaluation Board - Top Side

≊

2700 ns

National Semiconductor

Application Note 1549

Dennis Morgan

January 2007

The board’s specification are:

•

≊

LM34914 data sheet for a more detailed block diagram, and

a complete description of the various functional blocks.

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 air flow may be necessary.

2) The LM34914, and diode D1 may be hot to the touch when

operating at high input voltage and high load current.

3) Use CAUTION when probing the circuit at high input volt-

ages to prevent injury, as well as possible damage to the

circuit.

4) At maximum load current (1A), the wire size and length

used to connect the load becomes important. Ensure there is

not a significant drop in the wires between this evaluation

board and the load.

1.2A at Vin = 8V, and

Input Voltage: 8V to 40V

Output Voltage: 5V

Maximum load current: 1.0A

Minimum load current: 0A

Current Limit:

Measured Efficiency: 94.5% (V

Nominal Switching Frequency: 275 kHz

Size: 2.0 in. x 1.0 in. x 0.53 in

≊

1.2A (Vin = 8V)

≊

1.05A at Vin = 40V. Refer to the

= 8V, I

30000301

OUT

www.national.com

= 200 mA)

Related parts for LM34914EVAL

LM34914EVAL Summary of contents

Page 1

... LM34914 Evaluation Board Introduction The LM34914EVAL 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 40V. The circuit delivers load currents to 1A, with current limit set ≊ ...

Page 2

Board Connection/Start-up The input connections are made to the J1 connector. The load is connected to the J2 (OUT) and J3 (GND) terminals. Ensure the wires are adequately sized for the intended load current. Before start-up a voltmeter should be ...

Page 3

FIGURE 3. Intermediate Ripple Configuration Using C12 and chosen to generate 25-30 mVp the minimum ripple current is 85 mAp-p at minimum V couples that ripple to the FB pin without the attenuation of the ...

Page 4

... TDK C2012X7R2A104M TDK C2012X7R2A332M TDK C2012X7R2A103M Unpopulated Unpopulated Zetex ZLLS2000 TDK SLF12575T-101M1R9, or Cooper Bussmann DR125-101 CRCW08054991F CRCW08054991F Unpopulated CRCW08051503F CRCW08059092F National Semiconductor LM34914SD 4 30000309 Package Value 1210 4.7 µF, 50V 1206 0805 0.1 µF, 16V 0805 0.022 µF, 16V 0805 0.1 µF, 100V 0805 0.022 µ ...

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LM34914EVAL National Semiconductor, LM34914EVAL Datasheet

LM34914EVAL

Specifications of LM34914EVAL

Related parts for LM34914EVAL

LM34914EVAL Summary of contents

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