AD7864 Analog Devices, AD7864 Datasheet - Page 14

• Manufacturer Part Number: AD7864
• Description: High Speed, Low Power, 4-channel Simultaneous Sampling, 12-Bit ADC
• Manufacturer: Analog Devices

Specifications of AD7864

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 520kSPS
• Interface: Par
• Analog Input Type: SE-Bip,SE-Uni
• Ain Range: Bip 10V,Bip 2.5V,Bip 5.0V,Uni 2.5V,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: QFP

AD7864
Table 6. Ideal Input/Output Code Table for the AD7864-2
Analog Input
+FSR − 3/2 LSB
+FSR − 5/2 LSB
+FSR − 7/2 LSB
AGND + 5/2 LSB
AGND + 3/2 LSB
AGND + 1/2 LSB
1
2
AD7864-3
Figure 6 shows the analog input section of the AD7864-3. The
analog input range is ±2.5 V on the V
can be left unconnected, but if it is connected to a potential,
that potential must be AGND.
For the AD7864-3, R1 = 6 kΩ and R2 = 6 kΩ. As a result, drive
the V
stage is followed by the high input impedance stage of the track-
and-hold amplifier.
FSR is the full-scale range and is 0 V to 2.5 V and 0 V to 5 V for the AD7864-2
with V
1 LSB = FSR/4096 and is 0.61 mV (0 V to 2.5 V) and 1.22 mV (0 V to 5 V) for the
AD7864-2 with V
V
V
V
IN1A
IN1B
REF
IN1A
REF
= 2.5 V.
input from a low impedance source. The resistor input
1
Figure 6. AD7864-3 Analog Input Structure
2
REF
R2
= 2.5 V.
6kΩ
Digital Output Code Transition
111...110 to 111...111
111...101 to 111...110
111...100 to 111...101
000...010 to 000...011
000...001 to 000...010
000...000 to 000...001
R1
REFERENCE
TO ADC
REFERENCE
CIRCUITRY
IN1A
T/H
2.5V
input. The V
TO INTERNAL
COMPARATOR
AD7864-3
IN1B
input
Rev. D | Page 14 of 28
The designed code transitions take place midway between
successive integer least significant bit values (that is, 1/2 LSB,
3/2 LSB, 5/2 LSB, and so on). Least significant bit size is given by
the formula 1 LSB = FSR/4096. Output coding is twos comple-
ment binary with 1 LSB = FSR/4096 = 5 V/4096 = 1.22 mV. The
ideal input/ output transfer function for the AD7864-3 is shown
in Table 7.
Table 7. Ideal Input/Output Code Table for the AD7864-3
Analog Input
+FSR/2 − 3/2 LSB
+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
1
2
FSR is the full-scale range and is 5 V, with V
1 LSB = FSR/4096 = 1.22 mV (±2.5 V − AD7864-3) with V
1
2
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
REF
= 2.5 V.
REF
= 2.5 V.