LM34919EVAL National Semiconductor, LM34919EVAL Datasheet

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LM34919EVAL

Manufacturer Part Number
LM34919EVAL
Description
BOARD EVAL FOR LM34919 SW REG
Manufacturer
National Semiconductor
Series
PowerWise®r
Datasheets
1.LM34919TLNOPB.pdf (18 pages)
2.LM34919EVAL.pdf (10 pages)

Specifications of LM34919EVAL

Main Purpose
DC/DC, Step Down
Outputs And Type
1, Non-Isolated
Voltage - Output
5V
Current - Output
600mA
Voltage - Input
8 ~ 40V
Regulator Topology
Buck
Frequency - Switching
800kHz
Board Type
Fully Populated
Utilized Ic / Part
LM34919
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Power - Output
-
Lead Free Status / Rohs Status
Supplier Unconfirmed
© 2007 National Semiconductor Corporation
LM34919 Evaluation Board
Introduction
The LM34919EVAL 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 600 mA, with current limit
set at a nominal 700 mA. The board is populated with all
components except R5, C9 and C10. These components pro-
vide options for managing the output ripple as described later
in this document.
Theory of Operation
Refer to the evaluation board schematic in Figure 5, which
contains a simplified block diagram of the LM34919. When
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-
≊
231 ns at VIN = 40V. The on-time varies in-
300242
FIGURE 1. Evaluation Board - Top Side
≊
875 ns at
National Semiconductor
Application Note 1650
Dennis Morgan
June 2007
The board’s specification are:
•
•
•
•
•
•
•
•
quency. At the end of each on-time the Minimum Off-Timer
ensures the buck switch is off for at least 155 ns. In normal
operation, the off-time is much longer. During the off-time, the
load current is supplied by the output capacitor (C7, C8).
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 min-
imum of 25 mV of ripple is required at FB to switch the
regulation comparator. The current limit threshold, is
mA at Vin = 8V, and
due to the change in ripple current amplitude as Vin varies.
Refer to the LM34919 data sheet for a more detailed block
diagram, and a complete description of the various functional
blocks.
Input Voltage: 8V to 40V
Output Voltage: 5V
Maximum load current: 600 mA
Minimum load current: 0A
Current Limit: 640 mA to 730 mA
Measured Efficiency: 92.7% (V
Nominal Switching Frequency: 800 kHz
Size: 2.6 in. x 1.6 in. x 0.5 in
≊
730 mA at Vin = 40V. The variation is
IN
= 8V, I
OUT
www.national.com
= 300 mA)
30024201
≊
640

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LM34919EVAL Summary of contents

Page 1

... LM34919 Evaluation Board Introduction The LM34919EVAL 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 600 mA, with current limit set at a nominal 700 mA ...

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

Since the output ripple is passed by Cff to the FB pin with little or no attenuation, R4 can be reduced so the minimum ripple ≊ mVp-p. The minimum value for Cff is calculated OUT from: ...

Page 4

Monitor The Inductor Current The inductor’s current can be monitored or viewed on a scope with a current probe. Remove R6, and install an appropriate current loop across the two large pads where R6 was located. In this way the ...

Page 5

... TDK C3216X7R1C106K Unpopulated Unpopulated Zetex ZLLS2000 SOT23-6 Bussman DR73-150 7 7.6 mm Vishay CRCW06034322F Vishay CRCW06032491F Panasonic ERJ3RQFR39 Unpopulated Vishay CRCW08050000Z National Semiconductor 10 Bump µSMD LM34919TL 5 Value 1210 1.0 µF, 50V 0603 0.1 µF, 50V 0603 0.1 µF, 50V 0603 0.022 µF, 50V 1206 10 µ ...

Page 6

Circuit Performance www.national.com 30024210 FIGURE 6. Efficiency vs Load Current 30024211 FIGURE 7. Efficiency vs Input Voltage 6 ...

Page 7

FIGURE 8. Output Voltage Ripple FIGURE 9. Switching Frequency vs. Input Voltage FIGURE 10. Load Current Limit vs Input Voltage 7 30024212 30024213 30024214 www.national.com ...

Page 8

Typical Waveforms Trace OUT Trace 3 = inductor Current Trace Pin Vin = 24V, Iout = 400 mA Trace OUT Trace 3 = inductor Current Trace Pin Vin ...

Page 9

PC Board Layout Board Silkscreen Board Top Layer 9 30024217 30024218 www.national.com ...

Page 10

... National Semiconductor and the National Semiconductor logo are registered trademarks of National Semiconductor Corporation. All other brand or product names may be trademarks or registered trademarks of their respective holders. ...

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