LM2642REVD EVAL National Semiconductor, LM2642REVD EVAL Datasheet

LM2642REVD EVAL

Manufacturer Part Number

LM2642REVD EVAL

Description

BOARD EVALUATION LM2642

Manufacturer

National Semiconductor

Datasheets

1.LM2642MTCNOPB.pdf (21 pages)

2.LM2642REVD_EVAL.pdf (5 pages)

Specifications of LM2642REVD EVAL

Main Purpose

DC/DC, Step Down

Outputs And Type

2, Non-Isolated

Voltage - Output

1.8V, 2.5V

Current - Output

2A, 2A

Voltage - Input

4.5 ~ 20V

Regulator Topology

Buck

Frequency - Switching

300kHz

Board Type

Fully Populated

Utilized Ic / Part

LM2642

Lead Free Status / RoHS Status

Not applicable / Not applicable

Power - Output

Lead Free Status / Rohs Status

Not Compliant

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LM2642 Evaluation Board

Introduction

The LM2642 evaluation board has been developed to aid in

the design and evaluation of dc/dc converters based on the

LM2642 controller IC. As shown in Figure 1, the evaluation

board is configured to provide two outputs of 2.5V/2A and

1.8V/2A from an input range of 4.5V to 20V. The correspond-

ing bill of materials is given in Table 1. Figure 2 and Figure 3

show the evaluation board layout.

Optional Components

The evaluation board provides several optional component

pads for flexibility in changing components.

Please refer to the LM2642 product datasheet for more

information regarding device operation and component se-

lection.

In switching power supplies, the rapid increase of drain

current in the top FET coupled with parasitic inductance will

generate unwanted L∆i/∆t noise spikes at the source node of

the FET (SWx node) and also at the VIN node.

The resistor in series with the SWx pin (R6, R11) slows down

the gate drive (HDRVx), thus slowing the rise and fall time of

the top FET, yielding a longer drain current transition time

and reducing switch node ringing. Top FET switching losses

will increase with higher resistance values. Small resistors

(1-5 ohms) can also be placed in series with the CBOOTx

pin (R7, R12). A CBOOT resistor will slow the rise time of the

FET, to reduce switch node ringing.

AN200474

National Semiconductor

Application Note 1239

Allan Fisher

March 2006

To maintain stable regulation, the FBx pins should remain

free of noise. The LM2642 evaluation board has components

C15 and C22 installed to suppress noise that may be picked

up by the FBx traces. Notice that both of these capacitors

are placed physically close to the FBx nodes. Pads C17 and

C23 are provided for additional output capacitors.

Powering Up

Before powering up the LM2642 evaluation board, all exter-

nal connections should be verified. The power supply input

must be turned off and connected with proper polarity to the

VIN post, also marked as P1. The channel 1 and channel 2

loads should be connected at the Vout posts, marked as P2

and P3. Any type of load is acceptable up to 2A. The load

can be on or off at startup. Output voltage can be monitored

with a DVM or oscilloscope by connecting probes to the Vout

posts, P2 and P3. The GND posts are provided primarily for

scope probe ground connections. The PGOOD signal can be

monitored with a scope probe or DVM at the PGOOD test

pin.

Once all connections have been verified, input power can be

applied. The input voltage must be set between 4.5V and

20V. The enable switches for each channel, ON1 and ON2,

can be used to turn on the evaluation board once the input

power is on. Each channel may be enabled or disabled

independently. The switches may also be left on for enabling

the evaluation board directly from the power supply input.

www.national.com

Related parts for LM2642REVD EVAL

LM2642REVD EVAL Summary of contents

Page 1

... Small resistors (1-5 ohms) can also be placed in series with the CBOOTx pin (R7, R12). A CBOOT resistor will slow the rise time of the FET, to reduce switch node ringing. © 2006 National Semiconductor Corporation National Semiconductor Application Note 1239 Allan Fisher ...

Page 2

FIGURE 1. Complete Evaluation Board Schematic 2 20047401 ...

Page 3

Part # Value C1 Cer Cap 1F 50V Y5V 0805 C2 Cer Cap 47nF 50V 10% 0805 C3 Cer Cap 10nF 50V 10% 0805 C4 Cer Cap 10nF 50V 10% 0805 C5 Cer Cap 220pF 25V 10% 0805 C6 Cer ...

Page 4

FIGURE 2. Top Layer FIGURE 3. Bottom Layer 4 20047446 20047447 ...

Page 5

... BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that 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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