LTC6605-14
16
660514f
Board Layout and Bypass Capacitors
For single-supply applications it is recommended that a
high quality X5R or X7R, 0.1μF bypass capacitor be placed
directly between V
+
and the adjacent V
–
pin. The V
–
pins,
including the Exposed Pad, should be tied directly to a
low impedance ground plane with minimal routing.
For split power supplies, it is recommended that addi-
tional high quality X5R or X7R, 0.1μF capacitors be used
to bypass pin V
+
to ground and V
–
to ground, again with
minimal routing.
For driving heavy differential loads (< 200Ω), additional
bypass capacitance may be needed between V
+
and V
–
for
optimal performance. Keep in mind that small geometry
(e.g., 0603) surface mount ceramic capacitors have a much
higher self-resonant frequency than do leaded capacitors,
and perform best in high speed applications.
The V
OCM
pins should be bypassed to ground with a high
quality ceramic capacitor (at least 0.01μF). In split-sup-
ply applications, the V
OCM
pin can be either bypassed to
ground or directly hard wired to ground.
Stray parasitic capacitances to any unused input pins
should be kept to a minimum to prevent deviations from the
ideal frequency response. The best approach is to remove
the solder pads for the unused component pins and strip
APPLICATIONS INFORMATION
away any ground plane underneath. Floating unused pins
does not reduce the reliability of the part.
At the output, always keep in mind the differential nature
of the LTC6605-14, because it is important that the load
impedances seen by both outputs (stray or intended) be
as balanced and symmetric as possible. This will help pre-
serve the balanced operation that minimizes the generation
of even-order harmonics and maximizes the rejection of
common mode signals and noise.
Driving ADCs
The LTC6605-14’s rail-to-rail differential output and ad-
justable output common mode voltage make it ideal for
interfacing to differential input ADCs. These ADCs are
typically supplied from a single-supply voltage which can
be as low as 3V (2.7V minimum), and have an optimal com-
mon mode input range near mid-supply. The LTC6605-14
makes interfacing to these ADCs easy, by providing
antialiasing, single-ended to differential conversion and
common mode level shifting.
The sampling process of ADCs creates a transient that is
caused by the switching in of the ADC sampling capaci-
tor. This momentarily “shorts” the output of the amplifi er
as charge is transferred between amplifi er and sampling
capacitor. The amplifi er must recover and settle from this
