Datasheet

SAR
ADC
AVDD
AIN0P
AVDD
AIN0N
AVDD
AIN1N
AVDD
AIN1P
GND
GND
GND
GND
ADS7945
SAR
ADC
AVDD
AIN0
AVDD
AIN0GND
AVDD
AIN1GND
AVDD
AIN1
GND
GND
GND
GND
ADS7946
ADS7945
ADS7946
SBAS539B –JUNE 2011– REVISED SEPTEMBER 2011 www.ti.com
OVERVIEW
The ADS7945 and ADS7946 are 14-bit, miniature, dual-channel, low-power SAR ADCs. The ADS7945 is a
differential input device and the ADS7946 is a single-ended device with ground sensing input. These devices
feature very low power consumption at rated speed. The PDEN pin enables an auto power-down mode that
further reduces power consumption at lower speeds.
MULTIPLEXER AND ADC INPUT
The ADS7945/46 devices feature differential/single-ended inputs respectively with a double-pole, double-throw
multiplexer. The analog input circuit shown in Figure 75 is similar for for ADS7945 and ADS7946.
The ADS7945 features a differential input. Each of the positive (AINxP) and negative (AINxN) inputs can swing
from –V
REF
/2 to +V
REF
/2 around the common-mode voltage (AINxP + AINxN)/2 so that AINxP and AINxN swing
in opposite directions equally from common-mode voltage (differential input swing V
AINxP
– V
AINxN
ranges
from –V
REF
to +V
REF
). The ADC converts the difference in voltage: V
AINxP
– V
AINxN
. This feature allows the
devices to reject the common-mode noise in the input signal.
For the ADS7946, the ground sense inputs (AINxGND) can accept swings of ±0.2 V whereas the inputs (AINx)
allow signals in the range of 0 V to V
REF
over the ground sense input. The ADC converts the difference in
voltage: V
AINx
– V
AINxGND
. This feature can be used in multiple ways. For example, two signals can be connected
from different sensors with unequal ground potentials (within ±0.2 V) to a single ADC. The ADC rejects the
common-mode offset and noise. This feature also allows the use of a single-supply op amp. The signal and the
AINxGND input can be offset by +0.2 V, which provides the ground clearance required for a single-supply op
amp.
Figure 75 shows the electrostatic discharge (ESD) diodes to supply and ground at every analog input. Make sure
that these diodes do not turn on by keeping the supply voltage within the specified input range.
Figure 75. Analog Inputs
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Product Folder Link(s): ADS7945 ADS7946