LTC2205 Linear Technology, LTC2205 Datasheet - Page 26

• Manufacturer Part Number: LTC2205
• Description: (LTC2204 / LTC2205) 65Msps/40Msps
• Manufacturer: Linear Technology

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APPLICATIONS INFORMATION
LTC2205/LTC2204
DIGITAL OUTPUTS
Digital Output Buffers
Figure 11 shows an equivalent circuit for a single output
buffer. Each buffer is powered by OV
from the ADC power and ground. The additional N-channel
transistor in the output driver allows operation down to
low voltages. The internal resistor in series with the output
eliminates the need for external damping resistors.
As with all high speed/high resolution converters, the digi-
tal output loading can affect the performance. The digital
outputs of the LTC2205/LTC2204 should drive a minimum
capacitive load to avoid possible interaction between the
digital outputs and sensitive input circuitry. The output
should be buffered with a device such as a ALVCH16373
CMOS latch. For full speed operation the capacitive load
should be kept under 10pF . A resistor in series with the
output may be used but is not required since the ADC has
a series resistor of 33Ω on chip.
Lower OV
from the digital outputs.
26
DD
voltages will also help reduce interference
LATCH
FROM
DATA
Figure 11. Equivalent Circuit for a Digital Output Buffer
DD
and OGND, isolated
PREDRIVER
LOGIC
V
DD
V
DD
Data Format
The LTC2205/LTC2204 parallel digital output can be
selected for offset binary or 2’s complement format. The
format is selected with the MODE pin. This pin has a four
level logic input, centered at 0, 1/3V
An external resistor divider can be user to set the 1/3V
and 2/3V
for the MODE pin.
Table 1. MODE Pin Function
Overfl ow Bit
An overfl ow output bit (OF) indicates when the converter
is over-ranged or under-ranged. A logic high on the OF
pin indicates an overfl ow or underfl ow.
LTC2205/LTC2204
0(GND)
1/3V
2/3V
MODE
V
OV
DD
DD
DD
DD
DD
logic levels. Table 1 shows the logic states
33
22054 F11
W
OV
OGND
DD
TYPICAL
DATA
OUTPUT
2’s Complement
2’s Complement
Output Format
0.5V
TO 3.6V
0.1 F
Offset Binary
Offset Binary
DD
, 2/3V
Cycle Stabilizer
Clock Duty
DD
Off
On
On
Off
and V
22054fb
DD
DD
.