AD7865BS-2(1999) 查看數據表（PDF） - Analog Devices
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AD7865BS-2 Datasheet PDF : 19 Pages
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AD7865
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 VINxA and VINxB inputs are
tied together and the input voltage is applied to both. For ± 10 V
operation, the VINxB input is tied to AGND and the input volt-
age is applied to the VINxA input. The VINxA and VINxB 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 VINxB input while the VINxA input is tied to AGND.
6k⍀
VREF
R2
VINxA
R3
VINxB
+2.5V
REFERENCE
AD7865-1
TO ADC
REFERENCE
CIRCUITRY
R1
TRACK/
HOLD
TO INTERNAL
COMPARATOR
R4
GND
Figure 2. AD7865-1 Analog Input Structure
For the AD7865-1, R1 = 4 kΩ, R2 = 16 kΩ, R3 = 16 kΩ and
R4 = 8 kΩ. 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 µV. 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 Input1
Digital Output Code Transition
+FSR/2 – 3/2 LSB2
+FSR/2 – 5/2 LSB
+FSR/2 – 7/2 LSB
011 . . . 110 to 011 . . . 111
011 . . . 101 to 011 . . . 110
011 . . . 100 to 011 . . . 101
AGND + 3/2 LSB
AGND + 1/2 LSB
AGND – 1/2 LSB
AGND – 3/2 LSB
000 . . . 001 to 000 . . . 010
000 . . . 000 to 000 . . . 001
111 . . . 111 to 000 . . . 000
111 . . . 110 to 111 . . . 111
–FSR/2 + 5/2 LSB
–FSR/2 + 3/2 LSB
–FSR/2 + 1/2 LSB
100 . . . 010 to 100 . . . 011
100 . . . 001 to 100 . . . 010
100 . . . 000 to 100 . . . 001
NOTES
1FSR is full-scale range and is 20 V for the ± 10 V range and 10 V for the ±5 V
range, with VREF = +2.5 V.
21 LSB = FSR/16384 = 1.22 mV (±10 V—AD7865-1) and 610.4 mV (± 5 V—
AD7865-1) with VREF = +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 VINxB input is tied
to AGND and the input voltage is applied to VINxA input. For
0 V to +2.5 V operation, the VINxA and VINxB inputs are tied
together and the input voltage is applied to both. The VINxA and
VINxB 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 VINxB input while the VINxA input is tied to
AGND.
For the AD7865-2, R1 = 4 kΩ and R2 = 4 kΩ. 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.
6k⍀
VREF
R1
VINxA
R2
VINxB
+2.5V
REFERENCE
AD7865-2
TO ADC
REFERENCE
CIRCUITRY
TRACK/
HOLD
TO INTERNAL
COMPARATOR
Figure 3. AD7865-2 Analog Input Structure
Table II. Ideal Input/Output Code Table for the AD7865-2
Analog Input1
+FSR/2 – 3/2 LSB2
+FSR/2 – 5/2 LSB
+FSR/2 – 7/2 LSB
Digital Output Code Transition
111 . . . 110 to 111 . . . 111
111 . . . 101 to 111 . . . 110
111 . . . 100 to 111 . . . 101
AGND + 5/2 LSB
AGND + 3/2 LSB
AGND – 1/2 LSB
000 . . . 010 to 000 . . . 011
000 . . . 001 to 000 . . . 010
000 . . . 000 to 000 . . . 001
NOTES
1FSR is full-scale range and is 0 V to +2.5 V and 0 V to +5 V for AD7865-2
with VREF = +2.5 V.
21 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 VREF = +2.5 V.
–10–
REV. A
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