-40

-20

0

20

40

60

80

100

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

TEMPERATURE (°C)

225 LFPM FORCED AIR

STILL AIR

LMH6739

www.ti.com

SNOSAD2G – MAY 2004 – REVISED MARCH 2013

DRIVING CAPACITIVE LOADS

loads of 5 to 120 pF are the most critical, causing ringing, frequency response peaking and possible oscillation.

mitigating capacitive loads. The values suggested in the charts are selected for .5 dB or less of peaking in the

frequency response. This gives a good compromise between settling time and bandwidth. For applications where

slightly from the recommended values.

LAYOUT CONSIDERATIONS

Whenever questions about layout arise, use the evaluation board as a guide. The LMH730275 is the evaluation

board for the LMH6739.

To reduce parasitic capacitances ground and power planes should be removed near the input and output pins.

Components in the feedback loop should be placed as close to the device as possible. For long signal paths

controlled impedance lines should be used, along with impedance matching elements at both ends.

Bypass capacitors should be placed as close to the device as possible. Bypass capacitors from each rail to

ground are applied in pairs. The larger electrolytic bypass capacitors can be located farther from the device, the

smaller ceramic capacitors should be placed as close to the device as possible. The LMH6739 has multiple

power and ground pins for enhanced supply bypassing. Every pin should ideally have a separate bypass

capacitor. Sharing bypass capacitors may slightly degrade second order harmonic performance, especially if the

for each supply bypass.

VIDEO PERFORMANCE

The LMH6739 has been designed to provide excellent performance with production quality video signals in a

wide variety of formats such as HDTV and High Resolution VGA. NTSC and PAL performance is nearly flawless.

Best performance will be obtained with back terminated loads. The back termination reduces reflections from the

transmission line and effectively masks transmission line and other parasitic capacitances from the amplifier

output stage. Figure 24 shows a typical configuration for driving a 75

Ω Cable. The amplifier is configured for a

Figure 29. Maximum Power Dissipation

Copyright © 2004–2013, Texas Instruments Incorporated

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