Datasheet

AD7891
–13–
REV. D
Table I. Ideal Code Transition Table for the AD7891-1, ⴞ10 V and ⴞ5 V Ranges and the AD7891-2, ⴞ2.5 V Range
Digital Output Code Transition
1
Analog Input Input Voltage Twos Complement Straight Binary
+FSR
2
/2 – 3/2 LSB
3
(9.99268 V, 4.99634 V or 2.49817 V)
4
011...110 to 011...111 111...110 to 111...111
+FSR/2 – 5/2 LSB (9.98779 V, 4.99390 V or 2.49695 V) 011...101 to 011...110 111...101 to 111...110
+FSR/2 – 7/2 LSB (9.99145 V, 4.99146 V or 2.49573 V) 011...100 to 011...101 111...100 to 111...101
AGND + 3/2 LSB (7.3242 mV, 3.6621 mV or 1.8310 mV) 000...001 to 000...010 100...001 to 100...010
AGND + 1/2 LSB (2.4414 mV, 1.2207 mV or 0.6103 mV) 000...000 to 000...001 100...000 to 100...001
AGND – 1/2 LSB (–2.4414 mV, –1.2207 mV or –0.6103 mV) 111...111 to 000...000 011...111 to 100...000
AGND – 3/2 LSB (–7.3242 mV, –3.6621 mV or –1.8310 mV) 111...110 to 111...111 011...110 to 011...111
–FSR/2 + 5/2 LSB (–9.98779 V, –4.99390 V or –2.49695 V) 100...010 to 100...011 000...010 to 000...011
–FSR/2 + 3/2 LSB (–9.99268 V, –4.99634 V or –2.49817 V) 100...001 to 100...010 000...001 to 000...010
–FSR/2 + 1/2 LSB (–9.99756 V, –4.99878 V or –2.49939 V) 100...000 to 100...001 000...000 to 000...001
NOTES
1
Output code format is determined by the FORMAT bit in the control register.
2
FSR 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.
3
1 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
Digital Output Code Transition
1
Analog Input Input Voltage Twos Complement Straight Binary
+FSR
2
– 3/2 LSB
3
(4.99817 V or 2.49908 V)
4
011...110 to 011...111 111...110 to 111...111
+FSR – 5/2 LSB (4.99695 V or 2.49847 V) 011...101 to 011...110 111...101 to 111...110
+FSR – 7/2 LSB (4.99573 V or 2.49786 V) 011...100 to 011...101 111...100 to 111...101
AGND + 5/2 LSB (3.0518 mV or 1.52588 mV) 100...010 to 000...011 000...010 to 000...011
AGND + 3/2 LSB (1.83105 mV or 0.9155 mV) 100...001 to 000...010 000...001 to 000...010
AGND + 1/2 LSB (0.6103 mV or 0.3052 mV) 100...000 to 000...001 000...000 to 000...001
NOTES
1
Output code format is determined by the FORMAT bit in the control register.
2
FSR 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.
3
1 LSB = F
S
/4096 = 1.22 mV (0 to 5 V range) or 610 mV (0 to 2.5 V range), with REF IN = 2.5 V.
4
0 V to 5 V range or 0 V to 2.5 V range.
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 Straight Binary 2 –1
± 2.5 V Twos Complement 2 0
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 N REF IN=¥ ¥
()
+¥
()
/4096
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.