APPLICATION NOTES CON'T
BLANK INPUT
VOFF CONTROL INPUT
The video input can be electrically disconnected from the
amplifier by applying a TTL high input to the blank pin. When
this occurs, the output will be set to approximately +VHV. The
VGAIN and VOFF control pins have little or no effect on the out-
put when it is in blank mode.
The brightness (output offset) can be linearly adjusted by
applying a 0 to VREF DC voltage to the VOFF input pin. The
output quiescent voltage range is from approximately (5µA)
(Rp) to (100mA) (Rp) from +VHV. This control voltage is nor-
mally generated by connecting the VOFF control pin to a 5K
potentiometer between VREF and ground. The VOFF input pin
should be bypassed with a 0.1µF capacitor to ground placed as
close as possible to the hybrid. This DC voltage can be any
stable system source.
When the TTL compatible blank input is not used, the pin
must be connected to ground to enable the amplifier. The blank
input will float high when left unconnected which will disable
the video output.
Keep hybrid power dissipation in mind when adjusting the
output quiescent voltage. Practically all of the voltage is seen
across Rp. This power must be taken into account when high
Rp currents are used. If the quiescent level is set too close to
+VHV, the power dissipation will be minimal but the rise time
will suffer slightly. If the quiescent level is set too far from
VHV, the power dissipation will increase dramatically and the
output fall time will be limited. The output black level is obvi-
ously dependent on system requirements but a little experi-
mentation will strike the optimum balance between power dis-
sipation and bandwidth. Total current through Rp should be
limited to less than 290mA when operating from power sup-
plies greater than 90V. The gain adjust alone can set the AC
current to 250mA (ie: 250mApp=100Vpp/400Ω). Typically,
most applications use about 10V from +VHV for a black level.
VREF OUTPUT
The MSK 1902 has an on board buffered DC zener reference
output. The VREF output is nominally 5.5V DC and has full tem-
perature test limits of 5.2V to 5.8V DC. This output is provided
for gain and offset adjustment and can source up to 4mA of
current.
THERMAL MANAGEMENT
The MSK 1902 package has mounting holes that allow the
user to connect the amplifier to a heat sink or chassis. Since
the package is electrically isolated from the internal circuitry,
mounting insulators are not required or desired for best thermal
performance. Use 4 to 6 inch/pounds for mounting the device
to the heat sink.
The power dissipation of the amplifier depends mainly on the
load requirements, bandwidth, pixel size, black level and the
value of Rp. The following table illustrates a few examples:
PERCENT OF SIGNAL
WHITE
LEVEL
TOTAL
AVE. Pd
BLACK
LEVEL
OUTPUT
VOLTAGE
OUTPUT
AVE. Pd
DEVICE
TYPE
+VHV
BLACK
0%
WHITE
0%
BLANK
100%
20%
0V
90V
0V
0W
13.3W
0W
1902-6
1902-6
1902-4
1902-4
120V
120V
70V
110V
110V
65V
20V
20V
15V
15V
2.5W
15.7W
2.5W
40%
0%
40%
0%
100%
20%
40%
40%
50V
8.4W
70V
65V
10.6W
This table does not include power dissipation due to output switching since this is dependent on individual load requirements. The input stage power
dissipation is typically 2.5 watts and is essentially independent of output levels.
RESOLUTION TABLE FOR A TYPICAL CRT
Maximun
Pixel
Minimum Pixel
Clock
Required System
Bandwidth
(F-3dB)
Required Rise Time
at CRT
Display
Resolution
Time
Frequency
320 x 200
640 x 350
182nS
52nS
5MHz
19MHz
26MHz
38MHz
80MHz
90MHz
112MHz
170MHz
360MHz
1.2GHz
60nS
17nS
6MHz
20MHz
28MHz
41MHz
84MHz
95MHz
120MHz
180MHz
380MHz
1.23GHz
640 x 480
38nS
12.5nS
8.6nS
4.2nS
3.7nS
2.9nS
1.9nS
1nS
800 x 560
26nS
1024 x 900
1024 x 1024
1280 x 1024
1664 x 1200
2048 x 2048
4096 x 3300
12.6nS
11nS
8.9nS
5.8nS
2.8nS
860pS
280pS
All data assumes retrace time equal to 30% of frame time and a 60Hz refresh rate.
Rev. B 2/03
4
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