AD7865AS-3 Analog Devices Inc, AD7865AS-3 Datasheet - Page 10

• Manufacturer Part Number: AD7865AS-3
• Description: IC ADC 14BIT 4CH 5V 44-MQFP
• Manufacturer: Analog Devices Inc

Specifications of AD7865AS-3

• Rohs Status: RoHS non-compliant
• Number Of Bits: 14
• Sampling Rate (per Second): 350k
• Data Interface: Parallel
• Number Of Converters: 1
• Power Dissipation (max): 160mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 44-MQFP, 44-PQFP

AD7865
CIRCUIT DESCRIPTION
Analog Input Section
The AD7865 is offered as three part types, the AD7865-1 where
each input can be configured for ± 10 V or a ± 5 V input voltage
range, the AD7865-3 which handles input voltage range ± 2.5 V
and the AD7865-2 which has an input voltage range of 0 V to
2.5 V or 0 V to 5 V. The amount of current flowing into the
analog input will depend on the analog input range and the analog
input voltage. The maximum current flows when negative full
scale is applied.
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
tied together and the input voltage is applied to both. For ± 10 V
operation, the V
age is applied to the V
symmetrical and fully interchangeable. Thus for ease of PCB
layout on the ± 10 V range, the input voltage may be applied to
the V
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.
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
Table I. Ideal Input/Output Code Table for the AD7865-1
INxB
V
V
V
INxB
INxA
REF
input while the V
6k
1
INxB
2
R2
R3
input is tied to AGND and the input volt-
INxA
REFERENCE
input. The V
INxA
R1
R4
2.5V
GND
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
input is tied to AGND.
TO ADC
REFERENCE
CIRCUITRY
TRACK/
HOLD
INxA
INxA
and V
AD7865-1
and V
TO INTERNAL
COMPARATOR
INxB
INxB
inputs are
inputs are
NOTES
1
2
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
to AGND and the input voltage is applied to V
0 V to 2.5 V operation, the V
and the input voltage is applied to both. The V
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
For the AD7865-2, R1 = 4 kΩ and R2 = 4 kΩ. Once again,
the designed code transitions occur on successive integer LSB
values. 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 respectively.
Table II shows the ideal input and output transfer function
for the AD7865-2.
Analog Input
+FSR/2 – 3/2 LSB
+FSR/2 – 5/2 LSB
+FSR/2 – 7/2 LSB
AGND + 5/2 LSB
AGND + 3/2 LSB
AGND – 1/2 LSB
NOTES
1
2
FSR is full-scale range and is 20 V for the ± 10 V range and 10 V for the ± 5 V
range, with V
1 LSB = FSR/16384 = 1.22 mV (± 10 V—AD7865-1) and 610.4 mV (± 5 V—
AD7865-1) with V
FSR is full-scale range and is 0 V to 2.5 V and 0 V to 5 V for AD7865-2 with
V
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
Table II. Ideal Input/Output Code Table for the AD7865-2
= 2.5 V.
V
V
V
INxA
INxB
REF
REF
6k
1
= 2.5 V.
INxB
REF
REF
2
= 2.5 V.
R1
R2
input while the V
= 2.5 V.
REFERENCE
INxA
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
Digital Output Code Transition
111 . . . 110 to 111 . . . 111
2.5V
and V
TO ADC
REFERENCE
CIRCUITRY
INxA
TRACK/
HOLD
INxB
input is tied to AGND.
inputs are tied together
AD7865-2
TO INTERNAL
COMPARATOR
INxB
INxA
INxA
input is tied
and V
input. For
INxB