LTC1746 LINER [Linear Technology], LTC1746 Datasheet - Page 17

• Manufacturer Part Number: LTC1746
• Description: Low Power,14-Bit, 25Msps ADC
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Output Loading
As with all high speed/high resolution converters the
digital output loading can affect the performance. The
digital outputs of the LTC1746 should drive a minimal
capacitive load to avoid possible interaction between the
digital outputs and sensitive input circuitry. The output
should be buffered with a device such as an 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 43 on chip.
Lower OV
from the digital outputs.
Format
The LTC1746 parallel digital output can be selected for
offset binary or 2’s complement format. The format is
selected with the MSBINV pin; high selects offset binary.
Overflow Bit
An overflow output bit indicates when the converter is
overranged or underranged. When OF outputs a logic high
the converter is either overranged or underranged.
Output Clock
The ADC has a delayed version of the ENC input available
as a digital output, CLKOUT. The CLKOUT pin can be used
to synchronize the converter data to the digital system.
This is necessary when using a sinusoidal encode. Data
will be updated just after CLKOUT falls and can be latched
on the rising edge of CLKOUT.
DD
voltages will also help reduce interference
U
U
W
U
Output Driver Power
Separate output power and ground pins allow the output
drivers to be isolated from the analog circuitry. The power
supply for the digital output buffers, OV
to the same power supply as for the logic being driven. For
example if the converter is driving a DSP powered by a 3V
supply then OV
OV
outputs will swing between OGND and OV
Output Enable
The outputs may be disabled with the output enable pin,
OE. OE high disables all data outputs including OF and
CLKOUT. The data access and bus relinquish times are too
slow to allow the outputs to be enabled and disabled
during full speed operation. The output Hi-Z state is
intended for use during long periods of inactivity.
GROUNDING AND BYPASSING
The LTC1746 requires a printed circuit board with a clean
unbroken ground plane. A multilayer board with an inter-
nal ground plane is recommended. The pinout of the
LTC1746 has been optimized for a flowthrough layout so
that the interaction between inputs and digital outputs is
minimized. Layout for the printed circuit board should
ensure that digital and analog signal lines are separated as
much as possible. In particular, care should be taken not
to run any digital track alongside an analog signal track or
underneath the ADC.
DD
can be powered with any voltage up to 5V. The logic
DD
should be tied to that same 3V supply.
DD
LTC1746
, should be tied
DD
.
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1746f