APPLICATION NOTES
STABILITY AND LAYOUT CONSIDERATIONS
As with all wideband devices, proper decoupling of the power
lines is extremely important. The power supplies should be
bypassed, as near to the power supply pins as possible, with a
parallel grouping of a 0.1µF ceramic disc and a 4.7µF tantalum
capacitor. Ferrite beads can also be very helpful in some demanding
applications. A small resistor should be used in series with the
supply pins (4.7Ω TYP.). Wideband devices are also sensitive to
printed circuit board layout. Be sure to keep all runs as short as
possible, especially those associated with the summing junction
and power lines. Circuit traces should be surrounded by ground
planes whenever possible to reduce unwanted resistance and induc-
tance. The curve below shows the relationship between resonant
frequency and capacitor value for 3 trace lengths.
OPTIONAL OFFSET NULL
Typically, the MSK 450 has an input offset voltage of only
50µV. When the feedback resistor value is
≥
1KΩ, it may be
desirable to null the offset externally, because of the bias current at
the inverting input. Figure 1 below illustrates optional offset null for
one side of the MSK 450 Q.
Figure 1
LARGE CAPACITIVE LOADS
When it is required to drive capacitive loads greater than 100pF,
an external network can be connected as shown in Figure 2. For
CL=1000pF, R3 should be 750Ω and C1 should be 22pF. This
network should be connected between the output and feed forward
pins of the hybrid. This circuit will yield a maximum slew rate of
approximately 100V/µS. For bandwidth and stability, the optimum
value of R3 should be emperically determined.
EXTERNAL COMPONENT SELECTION
The table below illustrates nominal values for the feedback and
input resistors for various closed loop gain settings. These values
were chosen to yield high bandwidth with minimal peaking.
External Component Selection Guide
Gain (V/V)
-1
-5
-10
+10
R1
1KΩ
200Ω
50Ω
50Ω
R2
1KΩ
1KΩ
500Ω
450Ω
Figure 2
NON-INVERTING APPLICATIONS
The MSK 450 is suited for use at gains of 10 or greater when
being used in the non-inverting mode. The reason for this is that the
non-inverting input cannot tolerate transients greater than ±1V.
However, the MSK 450 can be used at lower non-inverting gains if
the input voltage remains small. Please consult factory for further
information.
3
Rev. A 6/02
MSK [ M.S. KENNEDY CORPORATION ]
