參數(shù)資料
型號(hào)： ADS1217
英文描述： 8-Channel, 24-Bit ANALOG-TO-DIGITAL CONVERTER
中文描述： 8通道，24位模擬數(shù)字轉(zhuǎn)換器
文件頁(yè)數(shù)： 12/28頁(yè)
文件大?。?/td> 458K
代理商： ADS1217
ADS1217
SBAS260B
12
www.ti.com
OVERVIEW
INPUT MULTIPLEXER
The input multiplexer (mux) provides for any combination of
differential inputs to be selected on any of the input channels,
as shown in Figure 1. If channel 1 is selected as the positive
differential input channel, any other channel can be selected
as the negative differential input channel. With this method,
it is possible to have up to eight fully differential input
channels.
In addition, current sources are supplied that will source or
sink current to detect open or short circuits on the pins.
BURNOUT CURRENT SOURCES
When the Burnout bit is set in the ACR configuration register,
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 ap-
proximately 2
μ
A. This allows for the detection of an open circuit
(full-scale reading) or short circuit (0V differential reading) on
the selected input differential pair.
INPUT BUFFER
The input impedance of the ADS1217 without the buffer
is 10M
/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 Applica-
tion Report Input Currents for High-Resolution ADCs
(SBAA090) for more information.
IDAC1 AND IDAC2
The ADS1217 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 = (V
REF
/8R
DAC
) (2
RANGE
–
1
) (DAC CODE). With
V
REFOUT
= 2.5V and R
DAC
= 150k
, the full-scale output can
be selected to be 0.5, 1, or 2mA. The compliance voltage
range is AGND to within 1V of AV
DD
. When the internal
voltage reference of the ADS1217 is used, it is the refer-
ence for the IDAC. An external reference may be used for
the IDACs by disabling the internal reference and tying the
external reference input to the V
REFOUT
pin.
PGA
The PGA can be set to gains of 1, 2, 4, 8, 16, 32, 64, or 128.
Using the PGA can improve the effective resolution of the A/D
converter. For instance, with a PGA of 1 on a 10V full-scale
range, the A/D converter can resolve to 2
μ
V. With a PGA of
128 on a 80mV full-scale range, the A/D converter can resolve
to 150nV.
PGA OFFSET DAC
The input to the PGA can be shifted by half the full-scale input
range of the PGA by using the ODAC register. The ODAC
(Offset DAC) register is an 8-bit value; the MSB is the sign and
the seven LSBs provide the magnitude of the offset. Using the
ODAC does not reduce the performance of the A/D converter.
See Application Report The Offset DAC(SBAA077) for more
information.
MODULATOR
The modulator is a single-loop, 2nd-order system. The modu-
lator runs at a clock speed (f
MOD
) that is derived from the
external clock (f
OSC
). The frequency division is determined by
the SPEED bit in the setup register.
A
IN
3
A
IN
4
A
IN+
A
IN
–
A
IN
5
A
IN
6
A
IN
0
A
IN
1
A
IN
2
A
IN
7
A
INCOM
Burnout Current Source On
Burnout Current Source On
IDAC1
AGND
AV
DD
FIGURE 1. Input Multiplexer Configuration.
TEMPERATURE SENSOR
An on-chip diode provides temperature sensing capability.
When the configuration register for the input MUX is set to all
1s, the diode is connected to 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 of the diode is connected to 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 diode is also
connected to ground to complete the circuit.
In this mode, the output of IDAC1 is also connected to the
output pin, so some current may flow into an external load
from IDAC1, rather than the diode. See Application Report
Measuring Temperature with the ADS1216, ADS1217, or
ADS1218 (SBAA073) for more information.
SPEED BIT
f
MOD
f
OSC
/128
f
OSC
/256
0
1
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