LMH6642_16 Datasheet, PDF (25/39 Pages) Texas Instruments – LMH664x Low Power, 130 MHz, 75 mA Rail-to-Rail Output Amplifiers

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11 Layout
LMH6642, LMH6643, LMH6644
SNOS966Q – MAY 2001 – REVISED SEPTEMBER 2014
11.1 Layout Guidelines
Generally, a good high frequency layout will keep power supply and ground traces away from the inverting input
and output pins. Parasitic capacitances on these nodes to ground will cause frequency response peaking and
possible circuit oscillations (see Application Note OA-15, "Frequent Faux Pas in Applying Wideband Current
Feedback Amplifiers", SNOA367, for more information). Texas Instruments suggests the following evaluation
boards as a guide for high frequency layout and as an aid in device testing and characterization:
Table 1. Printed Circuit Board Layout And Component Values
DEVICE
LMH6642MF
LMH6642MA
LMH6643MA
LMH6643MM
LMH6644MA
LMH6644MT
PACKAGE
5-Pin SOT-23
8-Pin SOIC
8-Pin SOIC
8-Pin VSSOP
14-Pin SOIC
14-Pin TSSOP
EVALUATION BOARD PN
LMH730216
LMH730227
LMH730036
LMH730123
LMH730231
LMH730131
Another important parameter in working with high speed/high performance amplifiers, is the component values
selection. Choosing external resistors that are large in value will effect the closed loop behavior of the stage
because of the interaction of these resistors with parasitic capacitances. These capacitors could be inherent to
the device or a by-product of the board layout and component placement. Either way, keeping the resistor values
lower, will diminish this interaction to a large extent. On the other hand, choosing very low value resistors could
load down nodes and will contribute to higher overall power dissipation.
11.2 Layout Example
Figure 59. LMH6642/LMH6643/LMH6644 Layer 1
Figure 60. LMH6642/LMH6643/LMH6644 Layer 2
Copyright © 2001–2014, Texas Instruments Incorporated
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