Datasheet

START
DRDY
CLK
t
START
t
SETTLE
(1)
t
SETTLE
(1)
t
START_CLKR
Ongoingconversionflushed;
newconversionstarted
START
DRDY
CLK
t
START
t
SETTLE
(1)
t
START_CLKR
ADS1675
www.ti.com SBAS416D –DECEMBER 2008–REVISED AUGUST 2010
VOLTAGE REFERENCE INPUTS CONVERSION START
(VREFN, VREFP)
The START pin provides an easy and precise
The voltage reference for the ADS1675 is the conversion control. To perform a single conversion,
differential voltage between VREFP and VREFN: pulse the START pin as shown in Figure 36. The
START signal is latched internally on the rising edge
V
REF
= (VREFP – VREFN) (2)
of CLK. Multiple conversions are performed by
A high-quality reference voltage with the appropriate
continuing to hold START high after the first
drive strength is essential for achieving the best
conversion completes; see the digital filter
performance from the ADS1675. Noise and drift on
descriptions for more details on multiple conversions,
the reference degrade overall system performance.
because the timing depends on the filter path
See the Application Information section for reference
selected.
circuit examples.
A conversion can be interrupted by issuing another
It is recommended that a minimum 10mF and 0.1mF
START pulse before the ongoing conversion
ceramic bypass capacitors be used directly across
completes. When an interruption occurs, the data for
the reference inputs, VREFP and VREFN. These
the ongoing conversion are flushed and a new
capacitors should be placed as close as possible to
conversion begins. DRDY indicates that data are
the device under test for optimal performance.
ready for retrieval after the filter has settled, as shown
in Figure 37.
COMMON-MODE VOLTAGE (VCM)
The VCM pin outputs a voltage of AVDD/2. This pin
must be bypassed with a 1µF capacitor placed close
to the package pin. The VCM pin connects an
external capacitor to compensate the internal
amplifier; it is not intended to drive an external load.
Figure 36. START Pin Used for Single Conversions
(1) See the Low-Latency Filter and Wide-Bandwidth Filter sections for specific values of settling time t
SETTLE
.
Figure 37. Example of Restarting a Conversion with START
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