Datasheet

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OVERVIEW
INPUT MULTIPLEXER
BURNOUT CURRENT SOURCES
INPUT BUFFER
IDAC1 AND IDAC2
A 3
IN
A 4
IN
A 5
IN
A 6
IN
A 0
IN
A 1
IN
A 2
IN
A 7
IN
A
INCOM
BurnoutCurrent
SourceOn
BurnoutCurrent
SourceOn
IDAC1
AGND
AV
DD
TEMPERATURE SENSOR
ADS1216
SBAS171D – NOVEMBER 2000 – REVISED SEPTEMBER 2006
of the diode is connected to the negative input of the
A/D converter. The output of IDAC1 is connected to
the anode to bias the diode and the cathode of the
The input multiplexer provides for any combination of
diode is also connected to ground to complete the
differential inputs to be selected on any of the input
circuit.
channels, as shown in Figure 25 . If channel 1 is
In this mode, the output of IDAC1 is also connected
selected as the positive differential input channel,
to the output pin, so some current may flow into an
any other channel can be selected as the negative
external load from IDAC1, rather than the diode. See
differential input channel. With this method, it is
Application Report Measuring Temperature with the
possible to have up to eight fully-differential input
ADS1216, ADS1217, or ADS1216 (SBAA073 ),
channels.
available for download at www.ti.com , for more
In addition, current sources are supplied that will
information.
source or sink current to detect open or short circuits
on the pins.
When the Burnout bit is set in the ACR Configuration
Register (see the Register Map section), two current
sources are enabled. The current source on the
positive input channel sources approximately 2 µ A of
current. The current source on the negative input
channel sinks approximately 2 µ A. This sinking allows
for the detection of an open circuit (full-scale
reading) or short circuit (0V differential reading) on
the selected input differential pair.
The input impedance of the ADS1216 without the
buffer is 5M Ω /PGA. With the buffer enabled, the
input voltage range is reduced and the analog
power-supply current is higher. The buffer is
controlled by ANDing the state of the buffer pin with
the state of the BUFFER bit in the ACR Register
(see the Register Map section). See Application
Report Input Currents for High-Resolution ADCs
(SBAA080 ), available for download at www.ti.com ,
for more information.
The ADS1216 has two 8-bit current output DACs that
can be controlled independently. The output current
is set with R
DAC
, the range select bits in the ACR
register, and the 8-bit digital value in the IDAC
register. The output current equals V
REF
/(8 ×
R
DAC
)(2
RANGE – 1
)(DAC CODE). With V
REFOUT
= 2.5V
and R
DAC
= 150k Ω , the full-scale output can be
Figure 25. Input Multiplexer Configuration
selected to be 0.5, 1, or 2mA. The compliance
voltage range is 0 to within 1V of AV
DD
. When the
internal voltage reference of the ADS1216 is used, it
is the reference for the IDAC. An external reference
An on-chip diode provides temperature sensing
may be used for the IDACs by disabling the internal
capability. When the configuration register for the
reference and tying the external reference input to
input MUX is set to all 1s, the diode is connected to
the V
REFOUT
pin.
the input of the A/D converter. All other channels are
open. The anode of the diode is connected to the
positive input of the A/D converter, and the cathode
15
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