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參數(shù)資料
| 型號： | AD7865YS-2 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | Four-Channel, Simultaneous Sampling, Fast, 14-Bit ADC |
| 中文描述： | 4-CH 14-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, PQFP44 |
| 封裝： | PLASTIC, QFP-44 |
| 文件頁數(shù)： | 10/19頁 |
| 文件大小： | 195K |
| 代理商： | AD7865YS-2 |
AD7865
–10–
REV. A
AD7865-1
Figure 2 shows the analog input section of the AD7865-1. Each
input can be configured for
±
5 V or
±
10 V operation on the
AD7865-1. For
±
5 V operation, the V
INxA
and V
INxB
inputs are
tied together and the input voltage is applied to both. For
±
10 V
operation, the V
INxB
input is tied to AGND and the input volt-
age is applied to the V
INxA
input. The V
INxA
and V
INxB
inputs are
symmetrical and fully interchangeable. Thus for ease of PCB
layout on the
±
10 V range, the input voltage may be applied to
the V
INxB
input while the V
INxA
input is tied to AGND.
AD7865-1
V
INxA
TRACK/
HOLD
TO ADC
REFERENCE
CIRCUITRY
TO INTERNAL
COMPARATOR
R4
R1
R2
6k
V
+2.5V
REFERENCE
R3
GND
V
INxB
V
REF
Figure 2. AD7865-1 Analog Input Structure
For the AD7865-1, R1 = 4 k
, R2 = 16 k
,
R3 = 16 k
and
R4 = 8 k
. The resistor input stage is followed by the high
input impedance stage of the track/hold amplifier.
The designed code transitions take place midway between suc-
cessive integer LSB values (i.e., 1/2 LSB, 3/2 LSBs, 5/2 LSBs
etc.) LSB size is given by the formula, 1 LSB = FSR/16384. For
the
±
5 V range, 1 LSB = 10 V/16384 = 610.4
μ
V. For the
±
10 V
range, 1 LSB = 20 V/16384 = 1.22 mV. Output coding is twos
complement binary with 1 LSB = FSR/16384. The ideal input/
output transfer function for the AD7865-1 is shown in Table I.
Table I. Ideal Input/Output Code Table for the AD7865-1
Analog Input
1
+FSR/2 – 3/2 LSB
2
+FSR/2 – 5/2 LSB
+FSR/2 – 7/2 LSB
AGND + 3/2 LSB
AGND + 1/2 LSB
AGND – 1/2 LSB
AGND – 3/2 LSB
–FSR/2 + 5/2 LSB
–FSR/2 + 3/2 LSB
–FSR/2 + 1/2 LSB
Digital Output Code Transition
011 . . . 110 to 011 . . . 111
011 . . . 101 to 011 . . . 110
011 . . . 100 to 011 . . . 101
000 . . . 001 to 000 . . . 010
000 . . . 000 to 000 . . . 001
111 . . . 111 to 000 . . . 000
111 . . . 110 to 111 . . . 111
100 . . . 010 to 100 . . . 011
100 . . . 001 to 100 . . . 010
100 . . . 000 to 100 . . . 001
NOTES
1
FSR is full-scale range and is 20 V for the
±
10 V range and 10 V for the
±
5 V
range, with V
= +2.5 V.
2
1 LSB = FSR/16384 = 1.22 mV (
±
10 V—AD7865-1) and 610.4 mV (
±
5 V—
AD7865-1) with V
REF
= +2.5 V.
AD7865-2
Figure 3 shows the analog input section of the AD7865-2. Each
input can be configured for 0 V to +5 V operation or 0 V to +2.5 V
operation. For the 0 V to +5 V operation, the V
INxB
input is tied
to AGND and the input voltage is applied to V
INxA
input. For
0 V to +2.5 V operation, the V
INxA
and V
INxB
inputs are tied
together and the input voltage is applied to both. The V
INxA
and
V
INxB
inputs are symmetrical and fully interchangeable. Thus for
ease of PCB layout on the 0 V to +5 V range the input voltage
may be applied to the V
INxB
input while the V
INxA
input is tied to
AGND.
For the AD7865-2, R1 = 4 k
and R2 = 4 k
. Once again, the
designed code transitions occur on successive integer LSB val-
ues. Output coding is straight (natural) binary with 1 LSB =
FSR/16384 = +2.5 V/16384 = 0.153 mV, and +5 V/16384 =
0.305 mV, for 0 V to +2.5 V and 0 V to +5 V options respec-
tively. Table II shows the ideal input and output transfer
function for the AD7865-2.
AD7865-2
V
INxA
TRACK/
HOLD
TO ADC
REFERENCE
CIRCUITRY
TO INTERNAL
COMPARATOR
R1
6k
V
+2.5V
REFERENCE
R2
V
INxB
V
REF
Figure 3. AD7865-2 Analog Input Structure
Table II. Ideal Input/Output Code Table for the AD7865-2
Analog Input
1
Digital Output Code Transition
+FSR/2 – 3/2 LSB
2
111 . . . 110 to 111 . . . 111
+FSR/2 – 5/2 LSB
111 . . . 101 to 111 . . . 110
+FSR/2 – 7/2 LSB
111 . . . 100 to 111 . . . 101
AGND + 5/2 LSB
000 . . . 010 to 000 . . . 011
AGND + 3/2 LSB
000 . . . 001 to 000 . . . 010
AGND – 1/2 LSB
000 . . . 000 to 000 . . . 001
NOTES
1
FSR is full-scale range and is 0 V to +2.5 V and 0 V to +5 V for AD7865-2
with V
REF
= +2.5 V.
2
1 LSB = FSR/16384 and is 0.153 mV (0 V to +2.5 V) and 0.305 mV (0 V to +5 V)
for AD7865-2) with V
REF
= +2.5 V.
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