AD7869JN Analog Devices Inc, AD7869JN Datasheet - Page 7

• Manufacturer Part Number: AD7869JN
• Description: IC I/O PORT 14BIT ANLG 24-DIP
• Manufacturer: Analog Devices Inc

Specifications of AD7869JN

• Rohs Status: RoHS non-compliant
• Applications: Analog I/O
• Interface: TTL/CMOS
• Voltage - Supply: 4.75 V ~ 5.25 V
• Package / Case: 24-DIP (0.300", 7.62mm)
• Mounting Type: Through Hole
• Converter Type: ADC/DAC
• Resolution: 14b
• Number Of Dac's: Single
• Data Rate: 0.083MSPS
• Digital Interface Type: Serial
• Pin Count: 24
• Package Type: PDIP
• Lead Free Status / Rohs Status: Not Compliant

INPUT/OUTPUT TRANSFER FUNCTIONS
A bipolar circuit for the AD7869 is shown in Figure 4.
The analog input/output voltage range of the AD7869 is 3 V.
The designed code transitions for the ADC occur midway be-
tween successive integer LSB values (i.e., 1/2 LSB, 3/2 LSB,
5/2 LSB . . . FS –3/2 LSBs). The input/output code is 2s
Complement Binary with 1 LSB = FS/16384 = 366 V. The
ideal transfer function is shown in Figure 5.
OFFSET AND FULL SCALE ADJUSTMENT
In most digital signal processing (DSP) applications, offset and
full-scale errors have little or no effect on system performance.
Offset error can always be eliminated in the analog domain by
ac coupling. Full-scale errors do not cause problems as long as
the input signal is within the full dynamic range of the ADC.
For applications requiring that the input signal range match the
full analog input dynamic range of the ADC, offset and full-
scale errors have to be adjusted to zero.
REV. A
Figure 3. Noise Spectral Density vs. Frequency
ANALOG INPUT
RANGE = ±3V
Figure 5. Input/Output Transfer Function
500
200
100
50
20
10
OUTPUT
CODE
50
011...111
011...110
000...010
000...001
000...000
111...111
111...110
100...000
Figure 4. Basic Bipolar Operation
100...001
10µF
C1
*ADDITIONAL PINS OMITTED FOR CLARITY
100
200
-FS
2
C2
0.1µF
200
R1
1k
FREQUENCY – Hz
REF OUT DECOUPLED
AS SHOWN IN
FIGURE 2
OUTPUT WITH
ALL 0s LOADED
REF OUT
INPUT VOLTAGE
2k
V
RI DAC
RO ADC
AGND
IN
AD7869*
0V
10k
V
OUT
1LSB =
20k
ANALOG OUTPUT
RANGE = ±3V
T
V
V
FS = 6V
+
A
DD
SS
FS
2
= +25 C
= –5V
= +5V
-1LSB
16384
FS
100k
–7–
ADC ADJUSTMENT
Figure 6 has signal conditioning at the input and output of the
AD7869 for trimming the endpoints of the transfer functions of
both the ADC and the DAC. Offset error must be adjusted be-
fore full-scale error. For the ADC, this is achieved by trimming
the offset of A1 while the input voltage, V1, is 1/2 LSB below
ground. The trim procedure is as follows: apply a voltage of
–183 V (–1/2 LSB) at V1 in Figure 6 and adjust the offset volt-
age of A1 until the ADC output code flickers between 11 1111
1111 1111 (3FFF HEX) and 00 0000 0000 0000 (0000 HEX).
ADC gain error can be adjusted at either the first code transi-
tion (ADC negative full scale) or the last code transition (ADC
positive full scale). The trim procedures for both cases are as
follows (see Figure 6).
ADC Positive Full-Scale Adjustment
Apply a voltage of 2.99945 V (FS/2 – 3/2 LSBs) at V1. Adjust
R2 until the ADC output code flickers between 01 1111 1111
1110 (1FFE HEX) and 01 1111 1111 1111 (1FFF HEX).
ADC Negative Full-Scale Adjustment
Apply a voltage of –2.99982 V (–FS/2 + 1/2 LSB) at V1 and ad-
just R2 until the ADC output code flickers between 10 0000
0000 0000 (2000 HEX) and 10 0000 0000 0001 (2001 HEX).
DAC ADJUSTMENT
Op amp A2 is included in Figure 6 for the DAC transfer func-
tion adjustment. Again, offset must be adjusted before full scale.
To adjust offset, load the DAC with 00 0000 0000 0000 (0000
HEX) and trim the offset of A2 to 0 V. As with the ADC adjust-
ment, gain error can be adjusted at either the first code transi-
tion (DAC negative full scale) or the last code transition (DAC
positive full scale). The trim procedures for both cases are as
follows:
DAC Positive Full-Scale Adjustment
Load the DAC with 01 1111 1111 1111 (1FFF HEX) and ad-
just R7 until the op amp output voltage is equal to 2.99963 V
(FS/2 – 1 LSB).
DAC Negative Full-Scale Adjustment
Load the DAC with 10 0000 0000 0000 (2000 HEX) and adjust
R7 until the op amp output voltage is equal to –3 V (–FS/2).
INPUT VOLTAGE
RANGE = 3V
Figure 6. AD7869 with Input/Output Adjustment
10k
500
V1
10k
R1
R2
R3
*ADDITIONAL PINS
OMITTED FOR
CLARITY
10k
R5
A1
10k
R4
AGND
V
AD7869*
IN
V
OUT
10k
500
10k
R6
R7
R8
R10
10k
A2
10k
R9
AD7869
OUTPUT VOLTAGE
RANGE =
V0
3V