AN1235 Rev 0.00
Page 3 of 7
Feb 2, 2006
ISL59481EVAL1
The following tests should be performed in the order shown.
Power Supply Tests
1. Connect an ammeter in series with the +5V and -5V
supply.
2. Connect power supplies to the resp5V, -5V and
ground banana jacks.
3. Set supplies to +5V; ±50mV and -5V; ±50mV. Supply
power to the board.
4. M5V supply current = +110mA ±20mA
5. Measure -5V supply current = -100mA ±20mA
Channel Select Logic and Video Performance Test
1. Calibrate the video test source with the video monitor by
connecting the source(s) to the video monitor and
selecting a display suitable for verifying correct
luminance, display resolution and H/V sync lock. The test
display in the following evaluation board tests should be
identical to the test display.
2. Re-connect the video monitor to the VIDEO_OUT VGA
connector on the evaluation board.
3. Connect the video test source to IN0. Additional video
sources can speed up the verification process. If more
than 1 test source is available connect each in sequential
fashion to IN1, IN2 etc.
4. Set switches S0, S1 and S2 to the GND position and
apply power.
5. After ~3s the test display supplied to IN0 should appear
on the test monitor exactly as it appeared in step 1.
NOTE: The ~3s delay is a built in delay common in many display
devices to lock onto the H/V sync signals and adjust the picture prior
to enabling the display screen.
6. Perform the display test on the remaining video inputs by
moving the video input source to the appropriate input
according to the truth table in Table 1.
Auto-Scan Test
1. Connect scope probe to the J1 AUTO pin and observe a
logic level (0 to +5V) square wave with ~3s period.
2. Connect jumpers J-S0, J-S1, and J-S2 to the AUTO
position (center to left post).
3. Connect jumper J1 to the AUTO position and observe
that the display scans all the test sources connected to
the input channels (center to right post).
4. Connect jumper J1 to the single-step position and use the
momentary contact switch S4 to manually all the test
sources.
Test completed.
RGB Video Signal Path
The video inputs are terminated with 75
resulting in an
overall RGB video path gain of 1 when using 75
video
source impedance and load terminations (Figure 2). The
RGB outputs contain series-connected 75
back-
termination resistors for cable driving. The ISL59481
operates in unity gain, and the EL5364 triple op amp gain is
set to 2.3 to compensate for the interstage and output
impedance matching loss. Two methods of gain adjustment
are provided. Increasing gain to compensate for cable
attenuation can be accomplished using the EL5364 R
f
and
R
g
gain resistors. Gain reduction is best achieved using the
divider network R
s
and Rt. Capacitor pads (C
np
) are
provided to adjust the frequency response of the amplifier.
Channel Select Logic
The ISL59481 RGB MUX and the H/V sync MUX share the
same 1 of 8 input channel select logic inputs (S0, S1, S2).
The channel select logic is shown in Table 1. Three methods
of channel select logic control are provided using jumpers.
Auto Sequencing Using the On-Board
Oscillator
An on-board 0.3Hz R-C oscillator (Figure 3) drives the
master clock of the 4-bit binary counter, which generates the
channel select logic inputs S0, S1 and S2. The default 6s
channel scan rate provides the time needed by the display to
sync-lock and adjust the picture prior to enabling the display.
The 2.2M
(R1) resistor value can be reduced to speed up
the channel scan time. Jumper J1 is provided to select either
the 6s auto-step timer, or the momentary contact switch for
manual stepping.
FIGURE 2. VIDEO SIGNAL PATH
TABLE 1. CHANNEL SELECT TRUTH TABLE
S2
S1
S0
VIDEO OUT
0
0
0
IN0
0
0
1
IN1
0
1
0
IN2
0
1
1
IN3
1
0
0
IN4
1
0
1
IN5
1
1
0
IN6
1
1
1
IN7
ISL59481
V
IN
75
C
np
*
R
S
, 75
+
-
1/3 EL5364
75
+1
V
OUT
R
f
R
g
Rt,
* Cnp is not populated and is provided for
frequency response adjustment
562
432
499
