AD7891 View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD7891 Datasheet PDF : 20 Pages
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AD7891
Table I. Ideal Code Transition Table for the AD7891-1, ؎10 V and ؎5 V Ranges and the AD7891-2, ؎2.5 V Range
Analog Input
Input Voltage
Digital Output Code Transition1
Twos Complement Straight Binary
+FSR2/2 – 3/2 LSB3
+FSR/2 – 5/2 LSB
+FSR/2 – 7/2 LSB
(9.99268 V, 4.99634 V or 2.49817 V)4
(9.98779 V, 4.99390 V or 2.49695 V)
(9.99145 V, 4.99146 V or 2.49573 V)
011...110 to 011...111
011...101 to 011...110
011...100 to 011...101
111...110 to 111...111
111...101 to 111...110
111...100 to 111...101
AGND + 3/2 LSB
AGND + 1/2 LSB
AGND – 1/2 LSB
AGND – 3/2 LSB
(7.3242 mV, 3.6621 mV or 1.8310 mV)
(2.4414 mV, 1.2207 mV or 0.6103 mV)
(–2.4414 mV, –1.2207 mV or –0.6103 mV)
(–7.3242 mV, –3.6621 mV or –1.8310 mV)
000...001 to 000...010
000...000 to 000...001
111...111 to 000...000
111...110 to 111...111
100...001 to 100...010
100...000 to 100...001
011...111 to 100...000
011...110 to 011...111
–FSR/2 + 5/2 LSB
–FSR/2 + 3/2 LSB
–FSR/2 + 1/2 LSB
(–9.98779 V, –4.99390 V or –2.49695 V)
(–9.99268 V, –4.99634 V or –2.49817 V)
(–9.99756 V, –4.99878 V or –2.49939 V)
100...010 to 100...011
100...001 to 100...010
100...000 to 100...001
000...010 to 000...011
000...001 to 000...010
000...000 to 000...001
NOTES
1Output code format is determined by the FORMAT bit in the control register.
2FSR is full-scale range and is +20 V for the ± 10 V range, +10 V for the ± 5 V range, and +5 V for the ± 2.5 V range, with REF IN = +2.5 V.
31 LSB = FSR/4096 = +4.88 mV (± 10 V range), +2.44 mV (± 5 V range), and +1.22 mV (± 2.5 V range), with REF IN = +2.5 V.
4± 10 V range, ± 5 V range, or ± 2.5 V range.
Table II. Ideal Code Transition Table for the AD7891-2, 0 V to 5 V and 0 V to 2.5 V Ranges
Analog Input
Input Voltage
Digital Output Code Transition1
Twos Complement
Straight Binary
+FSR2 – 3/2 LSB3
+FSR – 5/2 LSB
+FSR – 7/2 LSB
(4.99817 V or 2.49908 V)4
(4.99695 V or 2.49847 V)
(4.99573 V or 2.49786 V)
011...110 to 011...111
011...101 to 011...110
011...100 to 011...101
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
(3.0518 mV or 1.52588 mV)
(1.83105 mV or 0.9155 mV)
(0.6103 mV or 0.3052 mV)
100...010 to 000...011
100...001 to 000...010
100...000 to 000...001
NOTES
1Output code format is determined by the FORMAT bit in the control register.
2FSR is the full-scale range and is 5 V for the 0 to 5 V range and 2.5 V for the 0 to 2.5 V range, with REF IN = 2.5 V.
31 LSB = FS/4096 = 1.22 mV (0 to 5 V range) or 610 mV (0 to 2.5 V range), with REF IN = 2.5 V.
40 V to 5 V range or 0 V to 2.5 V range.
000...010 to 000...011
000...001 to 000...010
000...000 to 000...001
Transfer Function of the AD7891-1 and AD7891-2
The transfer function of the AD7891-1 and AD7891-2 can be
expressed as
Input Voltage = (M ¥ REF IN ¥ D/4096) + (N ¥ REF IN )
D is the output data from the AD7891 and is in the range 0 to
4095 for straight binary encoding and from –2048 to +2047 for
twos complement encoding. Values for M depend upon the
input voltage range. Values for N depend upon the input voltage
range and the output data format. These values are given in
Table III. REF IN is the reference voltage applied to the AD7891.
Table III. Transfer Function M and N Values
Range
Output Data Format M
N
AD7891-1
± 10 V
Straight Binary
8
–4
± 10 V
Twos Complement
8
0
±5 V
Straight Binary
4
–2
±5 V
Twos Complement
4
0
AD7891-2
0 V to +5 V
Straight Binary
2
0
0 V to +5 V
Twos Complement
2
1
0 V to +2.5 V Straight Binary
1
0
0 V to +2.5 V Twos Complement
1
0.5
± 2.5 V
± 2.5 V
Straight Binary
2
–1
Twos Complement
2
0
REV. D
–13–
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