AD7682 データシートの表示（PDF） - Analog Devices
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AD7682 Datasheet PDF : 28 Pages
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AD7682/AD7689
CH0+
CH1+
CH2+
CH3+
CH4+
CH5+
CH6+
CH7+
IN0
IN1
IN2
IN3
IN4
IN5
IN6
IN7
COM
GND
A—8 CHANNELS,
SINGLE ENDED
CH0+
CH1+
CH2+
CH3+
CH4+
CH5+
CH6+
CH7+
COM–
IN0
IN1
IN2
IN3
IN4
IN5
IN6
IN7
COM
GND
B—8 CHANNELS,
COMMON REFERNCE
channel pairs are always paired IN (even) = INx+ and IN (odd)
= INx− regardless of CFG[7].
To enable the sequencer, CFG[2:1] are written to for initializing
the sequencer. After CFG[13:0] are updated, DIN must be held
low while reading data out (at least for Bit 13), or the CFG will
begin updating again.
While operating in a sequence, the CFG can be changed by
writing 012 to CFG[2:1]. However, if changing CFG11 (paired
or single channel) or CFG[9:7] (last channel in sequence), the
sequence reinitializes and converts IN0 (or IN1) after CFG is
updated.
Examples
CH0+ (–)
CH0– (+)
CH1+ (–)
CH1– (+)
CH2+ (–)
CH2– (+)
CH3+ (–)
CH3– (+)
IN0
IN1
IN2
IN3
IN4
IN5
IN6
IN7
COM
GND
CH0+ (–)
CH0– (+)
CH1+ (–)
CH1– (+)
CH2+
CH3+
CH4+
CH5+
COM–
IN0
IN1
IN2
IN3
IN4
IN5
IN6
IN7
COM
GND
C—4 CHANNELS,
DIFFERENTIAL
D—COMBINATION
Figure 30. Multiplexed Analog Input Configuraitons
The analog inputs can be configured as
• Figure 30A, single ended referenced to system ground;
CFG[12:10] = 1112.
• Figure 30B, bipolar differential with a common reference
point; COM = VREF/2; CFG[12:10] = 0102.
Unipolar differential with COM connected to a ground
sense; CFG[12:10] = 1102.
• Figure 30C, bipolar differential pairs with INx− referenced
to VREF/2; CFG[12:10] = 00X2.
Unipolar differential pairs with INx− referenced to a
ground sense; CFG[12:10] = 10X2.
In this configuration, the INx+ is identified by the channel
in CFG[9:7]. Example: for IN0 = IN1+ and IN1 = IN1−,
CFG[9:7] = 0002; for IN1 = IN1+ and IN0 = IN1−,
CFG[9:7] = 0012.
• Figure 30D, inputs configured in any of the above
combinations (showing that the AD7682/AD7689 can be
configured dynamically).
Sequencer
The AD7682/AD7689 include a channel sequencer useful for
scanning channels in a IN0 to INx fashion. Channels are
scanned as singles or pairs, with or without the temperature
sensor, after the last channel is sequenced.
Only the bits for input and sequencer are highlighted.
As a first example, scan all IN[7:0] referenced to COM = GND
with temperature sensor.
13 12 11 10 9 8 7 6 5 4 3 2 1 0
CFG
INCC
INx
BW
REF
SEQ RB
-
1 1 0 111- - - - 10-
As a second example, scan three paired channels without
temperature sensor and referenced to VREF/2.
13 12 11 10 9 8 7 6 5 4 3 2 1 0
CFG
INCC
INx
BW
REF
SEQ RB
-
0 0 X 10X- - - - 11-
Source Resistance
When the source impedance of the driving circuit is low, the
AD7682/AD7689 can be driven directly. Large source
impedances significantly affect the ac performance, especially
total harmonic distortion (THD). The dc performances are less
sensitive to the input impedance. The maximum source imped-
ance depends on the amount of THD that can be tolerated. The
THD degrades as a function of the source impedance and the
maximum input frequency.
DRIVER AMPLIFIER CHOICE
Although the AD7682/AD7689 are easy to drive, the driver
amplifier must meet the following requirements:
• The noise generated by the driver amplifier must be kept as
low as possible to preserve the SNR and transition noise
performance of the AD7682/AD7689. Note that the AD7682/
AD7689 have a noise much lower than most of the other
16-bit ADCs and, therefore, can be driven by a noisier
amplifier to meet a given system noise specification. The
noise from the amplifier is filtered by the AD7682/AD7689
analog input circuit low-pass filter made by RIN and CIN or
by an external filter, if one is used. Because the typical noise
of the AD7682/AD7689 is 35 μV rms (with VREF = 5 V), the
SNR degradation due to the amplifier is
The sequencer starts with IN0 and finishes with INx set in
CFG[9:7]. For paired channels, the channels are paired
depending on the last channel set in CFG[9:7]. Note that the
Rev. 0 | Page 19 of 28
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