USER’S MANUAL
ISL59481EVAL1
Evaluation Board User’s Guide
Introduction
The ISL59481EVAL1 evaluation board contains the ISL59481
Dual 4:1 RGB MUX amp and associated components needed
to implement an 8:1 RGB+H/V sync video multiplexer. The 8
video input ports, and single output port are accessed using
standard 15 pin VGA female connectors. The I/O connectors
are compatible with most VGA, SVGA and XGA video
sources and video monitors with VGA cable interfaces. A
typical application would use the ISL59481EVAL1 board to
multiplex anywhere from 2 to 8 PC’s or laptops to a single
video monitor or projector.
Evaluation Board Description and Key Features
The multiplexing of the RGB video is performed by the
ISL59481. Multiplexing the H and V sync signals is
accomplished using two ISL84051 8:1 analog switches. The
ISL59481 Video MUX and the analog H and V sync
multiplexers have the same input channel select logic
coding, and are parallel-connected to form a single 3 input
binary coded interface (S0, S1, S2). The evaluation board
contains three different channel select options via jumpers
on the board. Switches on the board enable direct logic
control in binary format. The on-board oscillator and 4-bit
counter can be connected to provide a continuous channel-
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by-channel scan of as few as 2 input channels up to all 8. An
added option allows the user to disconnect the auto-scan
oscillator and use the on-board momentary-contact switch to
manually scan through the selected channels.
Reference Documents
• ISL59481 Data Sheet, FN7456
Getting Started
The evaluation board should have the same appearance as
the silk screen shown in Figure 1. Prior to applying power,
connect the source input VGA cables and the evaluation
board output VGA cable to the respective video
components. The evaluation board, as supplied, is designed
for 75 source impedances and requires a 75 termination
impedance in the output display device.
Applying Power to the Evaluation Board
The following safeguards will ensure correct power-up.
1. Limit the current on ±5V supplies to 250mA.
2. Turn on the power supplies after the power cables are
attached to the evaluation board.
Power supply protection Schottky diodes are included on the
±5V supplies to prevent damage due to reverse polarity.
Evaluation Board Jumper, Cable Header, and Switch Descriptions
COMPONENT DESCRIPTION
JUMPERS
J1 Selects channel select via single-step momentary contact switch S4, or auto mode using on-board oscillator
J-S0 Selects S0 logic input to manual control via switch S0 or through external control ribbon cable header
J-S1 Selects S1 logic input to manual control via switch S1 or through external control ribbon cable header
J-S2 Selects S2 logic input to manual control via switch S2 or through external control ribbon cable header
HEADERS
EN External MUX enable: Internal pull-down (logic 0) enables RGB+H/V output, logic high disables RGB and H/V sync output
S0 External S0 channel select logic input
S1 External S1 channel select logic input
S2 External S2 channel select logic input
SWITCHES
S0 Manual channel select logic input S0
S1 Manual channel select logic input S1
S2 Manual channel select logic input S2
S3 Momentary contact channel select step control
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ISL59481EVAL1
FIGURE 1. ISL59481EVAL1 TOP VIEW
Testing the Evaluation Board
Testing the video and sync signal paths is accomplished
using 1 or more RGB+H/V test video sources and a video
monitor as the measurement device. Before powering the
board, connect the jumpers as follows:
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1. Connect jumpers J-S0, J-S1 and J-S2 to the MANUAL
position (center to right post).
2. Connect jumper J1 to the single-step position (center to
left post).
ISL59481EVAL1
ISL59481
V
IN
75
Cnp*
RS, 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
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 respective +5V, -5V and
ground banana jacks.
3. Set supplies to +5V; ±50mV and -5V; ±50mV. Supply
power to the board.
4. Measure +5V 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 backtermination resistors for cable driving. The ISL59481
operates in unity gain, and the EL5364 triple op amp gain is
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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
R
gain resistors. Gain reduction is best achieved using the
g
divider network R
and Rt. Capacitor pads (Cnp) are
s
and
f
provided to adjust the frequency response of the amplifier.
FIGURE 2. VIDEO SIGNAL PATH
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.
TABLE 1. CHANNEL SELECT TRUTH TABLE
S2 S1 S0 VIDEO OUT
000 IN0
001 IN1
010 IN2
011 IN3
100 IN4
101 IN5
110 IN6
111 IN7
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.
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