adc12dl066civs National Semiconductor Corporation, adc12dl066civs Datasheet - Page 20

• Manufacturer Part Number: adc12dl066civs
• Description: Dual 12-bit, 66 Msps, 450 Mhz Input Bandwidth A/d Converter W/internal Reference
• Manufacturer: National Semiconductor Corporation

www.national.com
Applications Information
to the ground plane will reduce this problem. Additionally,
bus capacitance beyond the specified 15 pF/pin will cause
t
output data. The result could be an apparent reduction in
dynamic performance.
To minimize noise due to output switching, minimize the load
currents at the digital outputs. This can be done by connect-
ing buffers (74AC541, for example) between the ADC out-
puts and any other circuitry. Only one driven input should be
connected to each output pin. Additionally, inserting series
resistors of about 100Ω at the digital outputs, close to the
ADC pins, will isolate the outputs from trace and other circuit
capacitances and limit the output currents, which could oth-
erwise result in performance degradation. See Figure 4.
Note that, although the ADC12DL066 has Tri-State outputs,
these outputs should not be used to drive a bus and the
charging and discharging of large capacitances can degrade
SNR performance. Each output pin should drive only one pin
of a receiving device and the interconnecting lines should be
as short as practical.
4.0 POWER SUPPLY CONSIDERATIONS
The power supply pins should be bypassed with a 10 µF
capacitor and with a 0.1 µF ceramic chip capacitor within a
centimeter of each power pin. Leadless chip capacitors are
preferred because they have low series inductance.
OD
to increase, making it difficult to properly latch the ADC
FIGURE 6. Example of a Suitable Layout
(Continued)
20
As is the case with all high-speed converters, the
ADC12DL066 is sensitive to power supply noise. Accord-
ingly, the noise on the analog supply pin should be kept
below 100 mV
No pin should ever have a voltage on it that is in excess of
the supply voltages, not even on a transient basis. Be espe-
cially careful of this during power turn on and turn off.
The V
be operated from a supply in the range of 2.4V to V
(nominal 5V). This can simplify interfacing to lower voltage
devices and systems. Note, however, that t
reduced V
higher than V
5.0 LAYOUT AND GROUNDING
Proper grounding and proper routing of all signals are es-
sential to ensure accurate conversion. Maintaining separate
analog and digital areas of the board, with the ADC12DL066
between these areas, is required to achieve specified per-
formance.
The ground return for the data outputs (DR GND) carries the
ground current for the output drivers. The output current can
exhibit high transients that could add noise to the conversion
process. To prevent this from happening, the DR GND pins
should NOT be connected to system ground in close prox-
imity to any of the ADC12DL066’s other ground pins.
DR
pin provides power for the output drivers and may
DR
. DO NOT operate the V
P-P
D
.
.
DR
20055216
OD
pin at a voltage
increases with
D