MAX9511 Maxim Integrated Products, MAX9511 Datasheet - Page 9

• Manufacturer Part Number: MAX9511
• Description: Complete VGA Interface
• Manufacturer: Maxim Integrated Products

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resistor to the input. This results in an equivalent imped-
ance of 75Ω at the DAC output, which indicates to the
video controller’s internal load-detection circuit that the
load is disconnected and the video controller shuts down
the video output. Figure 2 and Table 1 demonstrate how
the MAX9511 load-detection circuit operates in conjunc-
tion with the video controller load detection.
The video signal at the MAX9511 output is shifted
upwards by approximately 240mV from the input to
keep the output stage of the video driver in a linear
region of operation. At the connector, the video signal
is attenuated by 6dB, canceling the 6dB gain of the
video driver. The 240mV level shift is also attenuated by
Figure 1. Conventional Load-Detection Scheme
Figure 2. Load-Detection Scheme with MAX9511
CURRENT DAC
Output Video Signal Level Shift
VIDEO CONTROLLER
I
OUT
_______________________________________________________________________________________
REF
CURRENT DAC
VIDEO CONTROLLER
I
OUT
REF
R
37.5Ω
T
Complete VGA Interface with
-75Ω
R
G = 2
ISENSE
R
75Ω
T
6dB, and hence the actual video signal seen by the
load is only 120mV higher than the video signal at the
input of the MAX9511. Monitors and other display
devices AC-couple the input signal so the 120mV level
shift should not affect the displayed video image.
Table 1. Function of Load-Detection
Scheme
Connected to External Load
Not Connected to External Load
FOR EMI SUPPRESSION
V
V
LOWPASS FILTER
AMPLIFIER OUTPUT
IS
Y
MAX9511
EMI Suppression
V
X
OUT
MONITOR
R
75Ω
75Ω
R
L
T
INTERNAL
MAX9511
SWITCH
Closed
Open
MONITOR
R
75Ω
L
RESISTANCE
OUTPUT
AT DAC
37.5Ω
75Ω
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