參數(shù)資料
型號： AD7865ASZ-2
廠商： Analog Devices Inc
文件頁數(shù)： 2/19頁
文件大?。?/td> 0K
描述： IC ADC 14BIT 4CHAN 5V 44MQFP
標準包裝： 1
位數(shù)： 14
采樣率（每秒）： 350k
數(shù)據(jù)接口： 并聯(lián)
轉(zhuǎn)換器數(shù)目： 1
功率耗散（最大）： 160mW
電壓電源： 模擬和數(shù)字
工作溫度： -40°C ~ 85°C
安裝類型： 表面貼裝
封裝/外殼： 44-QFP
供應(yīng)商設(shè)備封裝： 44-MQFP（10x10）
包裝： 托盤
輸入數(shù)目和類型： 4 個差分，單極
REV. B
AD7865
–10–
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
INxA 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.
AD7865-1
VINxA
TRACK/
HOLD
TO ADC
REFERENCE
CIRCUITRY
TO INTERNAL
COMPARATOR
R4
R1
R2
6k
2.5V
REFERENCE
R3
GND
VINxB
VREF
Figure 2. AD7865-1 Analog Input Structure
For the AD7865-1, R1 = 4 k
, R2 = 16 k, R3 = 16 k and R4
= 8 k
. 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 V. 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 Input
1
Digital Output Code Transition
+FSR/2 – 3/2 LSB
2
011 . . . 110 to 011 . . . 111
+FSR/2 – 5/2 LSB
011 . . . 101 to 011 . . . 110
+FSR/2 – 7/2 LSB
011 . . . 100 to 011 . . . 101
AGND + 3/2 LSB
000 . . . 001 to 000 . . . 010
AGND + 1/2 LSB
000 . . . 000 to 000 . . . 001
AGND – 1/2 LSB
111 . . . 111 to 000 . . . 000
AGND – 3/2 LSB
111 . . . 110 to 111 . . . 111
–FSR/2 + 5/2 LSB
100 . . . 010 to 100 . . . 011
–FSR/2 + 3/2 LSB
100 . . . 001 to 100 . . . 010
–FSR/2 + 1/2 LSB
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 k
and R2 = 4 k. 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.
AD7865-2
VINxA
TRACK/
HOLD
TO ADC
REFERENCE
CIRCUITRY
TO INTERNAL
COMPARATOR
R1
6k
2.5V
REFERENCE
R2
VINxB
VREF
Figure 3. AD7865-2 Analog Input Structure
Table II. Ideal Input/Output Code Table for the AD7865-2
Analog Input
1
Digital Output Code Transition
+FSR/2 – 3/2 LSB
2
111 . . . 110 to 111 . . . 111
+FSR/2 – 5/2 LSB
111 . . . 101 to 111 . . . 110
+FSR/2 – 7/2 LSB
111 . . . 100 to 111 . . . 101
AGND + 5/2 LSB
000 . . . 010 to 000 . . . 011
AGND + 3/2 LSB
000 . . . 001 to 000 . . . 010
AGND – 1/2 LSB
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.
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