600 Datasheet, PDF (3/6 Pages) E-SWITCH – SLIDE SWITCHES - MINIATURE

APPLICATION NOTES
FEED FORWARD TOPOLOGY
The MSK 600 employs a circuit topology known as "feed
forward". This inverting configuration allows the user to real-
ize the excellent D.C. input characteristics of a differential am-
plifier without losing system bandwidth. The incoming signal
is split at the input into its A.C. and D.C. component. The D.C.
component is allowed to run through the differential amplifier
where any common mode noise is rejected. The A.C. compo-
nent is "fed forward" to the output section through a very high
speed linear amplifier where it is mixed back together with the
D.C. component. The result is an amplifier with most of the
benefits of a differential amplifier without the loss in system
bandwidth.
INTERNAL COMPENSATION
Since the MSK 600 is a high voltage amplifier, it is com-
monly used in circuits employing large gains. Therefore, the
internal compensation was chosen for gains of -5V/V or greater.
In circuits running at gains of less than -5V/V, the user can
further compensate the device by adding compensation net-
works at the input or feedback node. Pin 1 (comp) should be
bypassed with a 0.1uF ceramic capacitor to +VHV for all appli-
cations.
HIGH VOLTAGE SUPPLIES
The positive and negative high voltage supplies on the MSK
600 can be adjusted to reduce power dissipation. The output
of the MSK 600 will typically swing to within 8V of either high
voltage power supply rail. Therefore, if the system in question
only needs the output of the amplifier to swing ±40V peak,
the power supply rails could be set to ±50V safely. For best
performance, the minimum value of ±VHV should be ±50VDC.
Unbalanced power supply rails are also allowed as long as one
or the other is not decreased to below 30V or above 90V. The
high voltage and low voltage power supplies should be decoupled
as shown in Figure 1.
TRANSITION TIMES
Transition time optimization of the MSK 600 follows the same
basic rules as most any other amplifier. Best transition times
will be realized with minumum load capacitance, minimum ex-
ternal feedback resistance and lowest circuit gain. Transition
times will degrade if the output is driven too close to either
supply rail. Feedback and input resistor values will affect tran-
sition time as well. See Figure 1 and Table 1 for recommended
component values.
VOLTAGE
GAIN
-10V/V
-20V/V
-50V/V
-RIN
RF
1KΩ
249Ω
100Ω
10KΩ
5KΩ
5KΩ
Table 1
CF
0.5-5pF
N/A
N/A
CURRENT LIMIT
Figure 2 is the recommended active short circuit protection
scheme for the MSK 600. The following formula may be used
for setting current limit:
Current Limit ≈ 0.6V / Rsc
RBASE must be selected based on the value of ±VHV as fol-
lows:
RBASE = ((+VHV - (-VHV)) - 1.2V) / 4mA
This formula guarantees that Q2 and Q4 will always have suf-
ficient base current to be in operation. This circuit can be made
tolerant of high frequency output current spikes with the addi-
tion of CSC. The corresponding time constant would be:
T = (RSC) (CSC)
A common value for CSC is approximately 1000pF. If current
limit is unnecessary, short pin 7 to pin 8 and pin 11 to pin 12 as
shown in Figure 1.
Figure 1
3
Figure 2
Rev. A 8/00