AD7859 Analog Devices, AD7859 Datasheet - Page 16

• Manufacturer Part Number: AD7859
• Description: 3 V to 5 V Single Supply, 200 kSPS 8-Channel, 12-Bit, Parallel Sampling ADCs
• Manufacturer: Analog Devices

Specifications of AD7859

• Resolution (bits): 12bit
• # Chan: 8
• Sample Rate: 200kSPS
• Interface: Byte,Par
• Analog Input Type: SE-Bip,SE-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: LCC,QFP

AD7859/AD7859L
Input Ranges
The analog input range for the AD7859/AD7859L is 0 V to
V
The difference between the unipolar range and the bipolar range
is that in the bipolar range the AIN(–) should be biased up to at
least +V
Table VI and Figures 14 and 15).
Analog Input
Range
0 V to V
NOTES
1
2
Note that the AIN(–) channel on the AD7859/AD7859L can be
biased up above AGND in the unipolar mode, or above V
in bipolar mode if required. The advantage of biasing the lower
end of the analog input range away from AGND is that the ana-
log input does not have to swing all the way down to AGND.
Thus, in single supply applications the input amplifier does not
have to swing all the way down to AGND. The upper end of the
analog input range is shifted up by the same amount. Care must
be taken so that the bias applied does not shift the upper end of
the analog input above the AV
reference is the supply, AV
AGND in unipolar mode or to AV
Output code format is straight binary.
Range is V
V
Figure 13. V
V
REF
IN
(–V
V
REF
IN
= 0 TO V
REF
= 0 TO V
Figure 12. 0 to V
in both the unipolar and bipolar ranges.
/2
/2 TO +V
V
+3V TO +5V
2
REF
REF
REF
REF
REF
REF
/2
/2 and the output coding is 2s complement (See
1
V
REF
/2 biased about V
REF
Table VI. Analog Input Connections
Figure 11. Analog Input Buffering
V
/2)
IN
/2
REF
/2 about V
10k
10k
10k
AIN(+)
AIN(–)
AIN(+)
AIN(–)
Input Connections
AIN(+)
V
V
REF
IN
IN
REF
DD
Unipolar Input Configuration
AD7859/AD7859L
IC1
AD7859/AD7859L
REF
/2. Output code format is 2s complement.
, the AIN(–) should be tied to
V+
V–
DD
10k
TRACK AND HOLD
/2 Bipolar Input Configuration
AD820
AD820-3V
TRACK AND HOLD
10µF
supply. In the case where the
DD
AMPLIFIER
AMPLIFIER
AIN(–)
AGND
V
/2 in bipolar mode.
REF
50
/2
0.1µF
10nF
(NPO)
DB15
DB0
DB15
DB0
TO AIN(+) OF
AD7854/AD7854L
Connection
Diagram
Figure 12
Figure 13
2'S
COMPLEMENT
FORMAT
STRAIGHT
BINARY
FORMAT
REF
/2
–16–
Transfer Functions
For the unipolar range the designed code transitions occur mid-
way between successive integer LSB values (i.e., 1/2 LSB,
3/2 LSBs, 5/2 LSBs . . . FS –3/2 LSBs). The output coding is
straight binary for the unipolar range with 1 LSB = FS/4096 =
3.3 V/4096 = 0.8 mV when V
unipolar analog input configuration. The ideal input/output
transfer characteristic for the unipolar range is shown in
Figure 14.
Figure 13 shows the AD7859/AD7859L’s V
log input configuration. AIN(+) cannot go below 0 ,V so for
the full bipolar range, AIN(–) should be biased to at least
+V
way between successive integer LSB values. The output coding
is 2s complement with 1 LSB = 4096 = 3.3 V/4096 = 0.8 mV.
The ideal input/output transfer characteristic is shown in Fig-
ure 15.
Figure 15. AD7859/AD7859L Bipolar Transfer Characteristic
REF
Figure 14. AD7859/AD7859L Unipolar Transfer
Characteristic
/2. Once again the designed code transitions occur mid-
OUTPUT
111...111
111...110
111...101
111...100
000...011
000...010
000...001
000...000
OUTPUT
011...111
011...110
000...001
000...000
111...111
000...010
000...001
000...000
CODE
CODE
0V 1LSB
0V
V
IN
V
IN
=
(
=
AIN(+) – AIN(–)
(
AIN(+) –AIN(–)
(V
REF
REF
/2) –1LSB
= 3.3 V. Figure 12 shows the
(V
V
REF
REF
)
, INPUT VOLTAGE
)
, INPUT VOLTAGE
1LSB =
/2
/2) +1LSB
1LSB =
FS = V
4096
+FS –1LSB
FS
REF
4096
FS
REF
V
+FS –1LSB
/2 bipolar ana-
REV. A