MSK164 Datasheet, PDF (3/5 Pages) List of Unclassifed Manufacturers – ULTRA HIGH VOLTAGE OPERATIONAL AMPLIFIER

APPLICATION NOTES
CURRENT LIMIT
Current limit resistor value can be calculated as follows:
RCL=3/ILIM
It is recommended that the user set up the value of current limit
as close as possible to the maximum expected output current
to protect the amplifier. The minumum value of current limit
resistance is 33 ohms. The maximum practical value is 500
ohms. Current limit will vary with case temperature. Refer to
the typical performance graphs as a guide. Since load current
passes through the current limit resistor, a loss in output volt-
age swing will occur. The following formula approximates out-
put voltage swing reduction:
VR=IO _* RCL
When the device is in current limit, there will be spurious oscil-
lations present on the negative half cycle. The frequency of
the oscillation is application dependent and can not be pre-
dicted. Oscillation will cease when the device comes out of
current limit.
SAFE OPERATING AREA (SOA)
The MOSFET output stage of this power operational ampli-
fier has two distinct limitations:
1. The current handling capability of the die metallization.
2. The junction temperature of the output MOSFET's.
NOTE: The output stage is protected against transient flyback.
However, for protection against sustained, high energy flyback,
external fast-recovery reverse biased diodes should be connected
from the output to ground.
INPUT PROTECTION
Input protection circuitry within the MSK 164 will clip differ-
ential input voltages greater than 16 volts. The inputs are also
protected against common mode voltages up to the supply rails
as well as static discharge. There are 300 ohm current limiting
resistors in series with each input. These resistors may be-
come damaged in the event the input overload is capable of
driving currents above 1mA. If severe overload conditions are
expected, external input current limiting resistors are recom-
mended.
OUTPUT SNUBBER NETWORK
A 100 ohm resistor and a 330pF capacitor connected in se-
ries from the output of the amplifier to ground is recommended
for applications where load capacitance is less than 330pF.
For larger values of load capacitance, the output snubber net-
work may be omitted. If loop stability becomes a problem due
to excessively high load capacitance, a 100 ohm resistor may
be added between the output of the amplifier (the junction of
RCL and pin 8) and the load. A small tradeoff with bandwidth
must be made in this configuration. The graph below illus-
trates the effect of capacitive load on open loop gain. Note
that the snubber capacitor must have a voltage rating greater
than or equal to the total rail to rail power supply voltage.
STABILITY
The MSK 164 has sufficient phase margin when compen-
sated for unity gain to be stable with capacitive loads of at
least 10nF. However, it is recommended that the parallel sum
of the input and feedback resistor be 1000 ohms or less for
closed loop gains of ten or less to minimize phase shift caused
by the R-C network formed by the input resistor, feedback re-
sistor and input capacitance. The user can tailor the perfor-
mance of the MSK 164 to their application using the external
compensation pins. The graphs of small signal gain and phase
as well as the graphs of slew rate and power response demon-
strate the effect of various forms of compensation. The com-
pensation capacitor must be rated at 350 volts working voltage
if maximum power supply voltages are used. The compensa-
tion resistor and capacitor lead lengths must be kept as short
as possible to minimize spurious oscillations. A high quality
NPO capacitor is recommended for the compensation capaci-
tor.
EXTERNAL COMPENSATION
External compensation is only necessary at gains of 30V/V
or less. For larger gains, the compensation resistor and capaci-
tor may be omitted. An effective method of checking amplifier
stability is to apply the worst case capacitive load to the output
of the amplifier and drive a small signal square wave across it.
If overshoot is less than 25%, the system will generally be
stable.
3
Rev. A 8/00