EL4089 查看數據表（PDF） - Intersil
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EL4089 Datasheet PDF : 9 Pages
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EL4089
component. Likewise for RX2. The 75Ω back terminating
resistor RXT is recommended when driving 75Ω cables.
The board layout should have a ground plane underneath
the EL4089, with the ground plane cut away from the vicinity
of the VIN- pin, (pin 1). This helps to minimize the stray
capacitance on pin 1.
Power supply bypassing is important, and a 0.1µF ceramic
capacitor, from each power pin to ground, placed very close
to the power pins, together with a 4.7µF tantalum bead
capacitor, is recommended.
When both digital and analog grounds are on the same
board, the EL4089 should be on the analog ground. The
digital ground can be connected to the Analog ground
through a 100Ω-300Ω resistor, near the EL4089. This allows
the digital signal a return path, while preventing the digital
noise from corrupting the analog ground.
The S/H amplifier is current output and causes a small load
on the input source during sampling. When sampling is done
on the back porch with color burst there will be a small load
on the color burst. Therefore for best performance, the input
should be driven from an amplifier output or a 75Ω cable with
75Ω termination.
TABLE OF CHARGE STORAGE CAPACITOR VS DROOP
CHARGING RATES (NOTE)
CAP VALUE
nF
DROOP IN
60µs
mV
CHARGE IN
1.2µs
mV
CHARGE IN
4µs
mV
10
6
36
120
33
1.8
11
36
100
0.6
3.6
12
NOTE: Basic formulae are: V (droop) = Ib+ * (Line time - Sample
time) / Capacitor and V (charge) = IOUT * Sample time / Capacitor
For best results the source impedance should be kept low,
using a buffer for example.
FIGURE 1.
7
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