Datasheet

1 V/DIV
1 µs/DIV
V
OUT
SELECT
LMH6645, LMH6646, LMH6647
www.ti.com SNOS970C –JUNE 2001–REVISED APRIL 2013
Figure 52. 2:1 MUX Output
As can be seen in Figure 52, the output is well behaved and there are no spikes or glitches due to the switching.
Switching times are approximately around 500ns based on the time when the output is considered “valid”.
PRINTED CIRCUIT BOARD LAYOUT, COMPONENT VALUES SELECTION, AND EVALUATION
BOARDS
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 for more information).
Another important parameter in working with high speed/high performance amplifiers, is the component values
selection. Choosing large valued external resistors, 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. On the other hand, choosing very low value resistors could load down nodes and will
contribute to higher overall power dissipation.
National Semiconductor suggests the following evaluation boards as a guide for high frequency layout and as an
aid in device testing and characterization:
Device Package Evaluation Board PN
LMH6645MF SOT-23-5 CLC730068
LMH6645MA 8-Pin SOIC CLC730027
LMH6646MA 8-Pin SOIC CLC730036
LMH6646MM 8-Pin VSSOP CLC730123
LMH6647MA 8-Pin SOIC CLC730027
LMH6647MF SOT-23-6 CLC730116
These free evaluation boards are shipped when a device sample request is placed with National Semiconductor.
LMH6647 Evaluation
For normal operation, tie the SD pin to V
−
.
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Product Folder Links: LMH6645 LMH6646 LMH6647