LMH730245 National Semiconductor, LMH730245 Datasheet

LMH730245

Manufacturer Part Number

LMH730245

Description

BOARD EVALUATION

Manufacturer

National Semiconductor

Datasheet

1.LMH730245.pdf (5 pages)

Specifications of LMH730245

Channels Per Ic

1 - Single

Amplifier Type

Buffer

Board Type

Bare (Unpopulated)

Utilized Ic / Part

8-SOIC Package

Lead Free Status / RoHS Status

Contains lead / RoHS non-compliant

Operating Temperature

Output Type

Current - Output / Channel

Voltage - Supply, Single/dual (±)

-3db Bandwidth

Slew Rate

Current - Supply (main Ic)

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General Description

The CLC730245 and the CLC730136 evaluation boards are

designed to aid in the characterization of National Semicon-

ductor’s High Speed SOIC and SOT23 buffers. Use these

evaluation boards as a guide for high frequency layout and

as a tool to aid in device testing and characterization. The

evaluation boards schematic are shown in Figure 1 and

Figure 2. Refer to the product data sheets for recommenda-

tions for component values.

Basic Operation

These boards are a very straight forward design and are

intended to evaluate the parts behavior by offering 50Ω

inputs and outputs traces for connection to coaxial cables

with the same impedance. For other impedances the termi-

nating resistors can be modified to help match different

impedances. Both board and part are designed to handle

very high frequencies. By changing the resistor connected to

the input pin and ground the input impedance can be

matched but keep in mind that the input trace is designed for

50Ω. By using e.g. 75Ω impedance, the results will be no-

ticeable different especially for the highest frequencies. Also

at the output it is possible to match different impedances but

the output trace is designed for 50Ω. With the series resistor

at the output the output cable can be matched, however this

is not necessary. It is absolutely necessary to have the

impedance at the end of the connected cable matched to the

cable impedance but not the resistor at the beginning. Hav-

ing the output series resistor matched to the cable imped-

ance gives only an additional attenuation of −6dB. The SMA

connectors are optimized for 50Ω operation. Even with opti-

mal layout, board parasitics play a large part in high fre-

quency performance and different termination resistors will

change the frequency of the dominant parasitic poles/zeros.

Layout Considerations

Printed circuit board layout and supply bypassing play major

roles in determining high frequency performance. When de-

signing your own board use these evaluation boards as a

guide and follow these steps to optimize high frequency

performance:

• Use a ground plane

• Include large (10µF) capacitors on both supplies.

• Near the device use 10nF ceramic capacitors from both

supplies to ground.

Single High-Speed Buffer Evaluation Boards

CLC730245, CLC730136 (SOIC and SOT23)

MS200707

• Near the device use a 0.1µF ceramic capacitor between

• Minimize all trace lengths

• Terminated always all transmission lines used.

The Capacitor between both supplies is recommended for

best 2nd Harmonic Distortion performance. The zenerdiode

between both supplies protect the device from reverse po-

larity supply connections under the condition these supplies

have the current limitation on. Most high-speed buffers per-

form best with capacitive loads if a small resistor is used in

series between the amplifier and the capacitor. In that case

change the output series resistor to a value of about 10Ω

and evaluate what the output signal will do. Determine the

right value by trial and error. While using rather high capaci-

tive loads the matching at the output become less important

because the frequency response will be dramatically lower,

so a flat response will be more important. See the part’s

datasheets for recommended values.

Sample artwork for the CLC730245 and the CLC730136

Evaluation board is included on Figure 3.

Measurement Hints

Do not use normal oscilloscope probes to test these circuits.

The capacitive loading will change circuit performance dras-

tically. Instead use high frequency low ohmic passive

probes. These probes have a load resistance in the range of

several hundred ohms until some kΩ. For best performance

use ground leads as short as possible otherwise ringing on

pulse shaped signals will occur. The use of active probes

gives also good results if basic rules are obtained, such as

the short ground leads. Another good idea to isolate the load

from the device is to change the output series resistor to a

value of 450Ω. While measuring with a coaxial cable in a

50Ω system an attenuation of 10x (20dB) will occur and this

acts as a resistive probe of 10:1. Even the best probes will

interfere with circuit operation to some degree. Also, tools,

power cables, fingers etc. near the device will change mea-

surement results. If the circuit has a good layout and there-

fore exhibits a stable behavior the measurement results will

only slightly changed by e.g. a fingertip on the circuit. If

measurement results will change dramatically it is likely the

circuit exhibits oscillations or other unwanted behavior.

the supplies.

www.national.com

April 2003

Related parts for LMH730245

LMH730245 Summary of contents

Page 1

... Include large (10µF) capacitors on both supplies. • Near the device use 10nF ceramic capacitors from both supplies to ground. © 2003 National Semiconductor Corporation • Near the device use a 0.1µF ceramic capacitor between the supplies. • Minimize all trace lengths • ...

Page 2

Board Schematics FIGURE 1. Test Board Schematic SOIC (CLC730245) www.national.com 2 20070707 ...

Page 3

Board Schematics (Continued) FIGURE 2. Test Board Schematic SOT23 (CLC730136) 3 20070708 www.national.com ...

Page 4

Board Layout SOIC Package (CLC730245) Top Silk Top Copper Bottom Copper www.national.com SOT23 Package (CLC730136) 20070701 20070703 20070705 FIGURE 3. Test Board Lay-Outs 4 20070702 Top Silk 20070704 Top Copper 20070706 Bottom Copper ...

Page 5

... NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant ...

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