ISL59532_07 INTERSIL [Intersil Corporation], ISL59532_07 Datasheet - Page 22

• Manufacturer Part Number: ISL59532_07
• Description: 32x32 Video Crosspoint
• Manufacturer: INTERSIL [Intersil Corporation]

0.2% of the video signal. Because 1.3mV is only 0.2% of a
0.7V video signal, this droop is imperceptible to the human
eye.
This is how the video is “DC-restored” after being AC
coupled into the ISL59532. The sync tip voltage will be equal
to V
the video on the left side of C
offset in the actual clamp function, the actual sync tip level is
typically about 75mV higher than V
It is important to choose the correct value for C
a value will generate too much droop, and the image will be
visibly darker on the right than on the left. A C
too large may cause the clamp to fail to converge. The droop
rate (dV/dt) is i
voltage should be limited to <1 IRE over a period of one line
of video; so for 1 IRE = 7mV, I
NTSC waveform we will set C
SS12
VIDEO
D
REF
3
IN
FIGURE 50. DC RESTORE VIDEO WAVEFORMS
~0.4V
on the right side of C
FIGURE 49. DC RESTORE BLOCK DIAGRAM
C
0.1µF
1
2
75
R
/C
1
(110µA)
C
IN
1
volts/second. In general, the droop
0.1µF
V
INx
REF
22
1
1
IN
B
, regardless of the DC level of
. Due to various sources of
i
1
= 10µA maximum, and an
> 10µA*60µs/7mV =
Q
1
REF
D
1
(for V
Q
ENABLE
2
CLAMP
D
REF
IN
2
IN
value that is
. Too small
= 0.4V).
BUFFER
INPUT
TO
ISL59532
0.086µF. Figure 50 shows the result of C
delivering acceptable droop and C
excessive droop
When the clamp function is disabled in the CONTROL
register (Clamp = 0) to allow DC-coupled operation, the
I
passes through the DC Restore block unaffected. In this
application V
Overlay Operation
The ISL59532 features an overlay feature, that allows an
external video signal or DC level to be inserted in place of
that output channel’s video. When the OVER
taken high, the output signal on the OUT
with the signal on the VOVER
There are several ways the overlay feature can be used.
Toggling the OVER
replace the video frame(s) on the OUT
supplied on the VOVER
Another option (for OSD displays, for example), is to put a
DC level on the VOVER
at the pixel rate to create a monocolor image “overlaid” on
channel N’s output signal.
Finally, by enabling the OVER
each line over a certain amount of lines, a picture-in-picture
function can be constructed.
It’s important to note that the overlay inputs do not have the
DC Restore function previously described - the overlay
signal is DC coupled into the output. It is the system
designer’s responsibility to ensure that the video levels are
in the ISL59532’s linear region and matching the output
channel’s offset and amplitude. One easy way to do this is to
run the video to be overlaid through one of the ISL59532’s
unused channels and then into the VOVER
The OVER
unused, they can either be left unconnected or tied to GND.
Power Dissipation and Thermal Resistance
With a large number of switches, it is possible to exceed the
+150°C absolute maximum junction temperature under
certain load current conditions. Therefore, it is important to
calculate the maximum junction temperature for an
application to determine if load conditions or package types
need to be modified to assure operation of the crosspoint
switch in a safe operating area.
The maximum power dissipation allowed in a package is
determined according to:
PD
CLAMP
MAX
current sinks/sources are disabled and the input
=
T
-------------------------------------------- -
N
JMAX
REF
pins all have weak pulldowns, so if they are
Θ
–
may be tied to GND.
JA
T
N
AMAX
signal at the frame rate or slower will
N
N
pin.
line and toggle the OVER
N
N
pin.
signal for some portion of
IN
= 0.001µF producing
N
N
IN
pin with the video
pin is replaced
N
= 0.1µF
N
input.
signal is
February 7, 2007
N
FN7432.5
signal
(EQ. 1)