LMH6505MASLASHNOPB datasheet(21/30 Pages) TI1

21 / 30 page

LMH6505

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SNOSAT4E – DECEMBER 2005 – REVISED APRIL 2013

CIRCUIT LAYOUT CONSIDERATIONS & EVALUATION BOARDS

A good high frequency PCB layout including ground plane construction and power supply bypassing close to the

package is critical to achieving full performance. The amplifier is sensitive to stray capacitance to ground at the I-

input (pin 7) so it is best to keep the 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 removing the

ground plane from under the body of RG. Parasitic or load capacitance directly on the output (pin 6) degrades

phase margin leading to frequency response peaking.

The LMH6505 is fully stable when driving a 100

Ω 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 LMH6505 is

connected to a light load as such, it is recommended to add a snubber network to the output (e.g. 100

Ω and 39

pF in series tied between the LMH6505 output and ground). CL can also be isolated from 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.

Texas Instruments suggests the following evaluation board as a guide for high frequency layout and as an aid in

device testing and characterization:

Device

Package

Evaluation Board

Part Number

LMH6505

SOIC

LMH730066

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LMH6505MA/NOPB Datasheet(PDF) 21 Page - Texas Instruments