lmh6504mmx National Semiconductor Corporation, lmh6504mmx Datasheet - Page 17

• Manufacturer Part Number: lmh6504mmx
• Description: Wideband, Low Power, Variable Gain Amplifier
• Manufacturer: National Semiconductor Corporation

Application Information
CIRCUIT LAYOUT CONSIDERATIONS & EVALUATION
BOARD
A good high frequency PCB layout including ground plane
construction and power supply bypassing close to the pack-
age are critical to achieving full performance. The amplifier is
sensitive to stray capacitance to ground at the I
keep node trace area small. Shunt capacitance across the
feedback resistor should not be used to compensate for this
effect. Capacitance to ground should be minimized by re-
moving the ground plane from under the body of R
sitic or load capacitance directly on the output (pin 6) de-
grades phase margin leading to frequency response
peaking.
The LMH6504 is fully stable when driving a 100Ω load. With
reduced load (e.g. 1k.) there is a possibility of instability at
very high frequencies beyond 400 MHz especially with a
capacitive load. When the LMH6504 is connected to a light
load as such, it is recommended to add a snubber network to
FIGURE 9. Automatic Gain Control Circuit #2
(Continued)
-
input (pin 7);
G
. Para-
17
the output (e.g. 100Ω and 39 pF in series tied between the
LMH6504 output and ground). C
the output by placing a small resistor in series with the output
(pin 6).
Component parasitics also influence high frequency results.
Therefore it is recommended to use metal film resistors such
as RN55D or leadless components such as surface mount
devices. High profile sockets are not recommended.
National Semiconductor suggests the following evaluation
board as a guide for high frequency layout and as an aid in
device testing and characterization:
The evaluation board is shipped when a device sample
request is placed with National Semiconductor.
Device
LMH6504
Package
SOIC
L
can also be isolated from
Evaluation Board
Part Number
CLC730066
20084360
www.national.com