ad420-32-reel Analog Devices, Inc., ad420-32-reel Datasheet - Page 7

• Manufacturer Part Number: ad420-32-reel
• Description: Serial Input 16-bit 4 Ma-20 Ma, 0 Ma-20 Ma Dac
• Manufacturer: Analog Devices, Inc.

REV. F
APPLICATIONS
CURRENT OUTPUT
The AD420 can provide 4 mA–20 mA, 0 mA–20 mA, or 0 mA–
24 mA output without any active external components. Filter
capacitors C1 and C2 can be any type of low cost ceramic ca-
pacitors. To meet the specified full-scale settling time of 3 ms,
low dielectric absorption capacitors (NPO) are required. Suit-
able values are C1 = 0.01 F and C2 = 0.01 F.
DRIVING INDUCTIVE LOADS
When driving inductive or poorly defined loads connect a
0.01 F capacitor between I
This will ensure stability of the AD420 with loads beyond
50 mH. There is no maximum capacitance limit. The capacitive
component of the load may cause slower settling, though this
may be masked by the settling time of the AD420. A pro-
grammed change in the current may cause a back EMF voltage
on the output that may exceed the compliance of the AD420.
To prevent this voltage from exceeding the supply rails connect
protective diodes between I
VOLTAGE-MODE OUTPUT
Since the AD420 is a single supply device, it is necessary to add
an external buffer amplifier to the V
tion of bipolar output voltage ranges as shown in Figure 6.
DATA IN
CLOCK
CLEAR
LATCH
SELECT 1
SELECT 2
DATA IN
RANGE
RANGE
CLOCK
CLEAR
LATCH
0.1 F
SELECT 1
SELECT 2
RANGE
RANGE
0.1 F
Figure 5. Standard Configuration
5
4
6
7
8
9
V
OUT
LL
REF
5
4
6
7
8
9
2
OUT
REF
V
14
20
2
LL
C1
14
AD420
C1
15
OUT
Figure 6.
20
OUT
21
AD420
REF
IN
15
C2
V
and each of V
C2
(Pin 18) and GND (Pin 11).
CC
REF
IN
11
21
23
OUT
GND
V
0.1 F
11
CC
23
pin to obtain a selec-
17
GND
V
R1
OUT
18
0.1 F
I
OUT
CC
R
(4mA–20mA)
LOAD
and GND.
R2
R3
V
OUT
–7–
OPTIONAL SPAN AND ZERO TRIM
For those users who would like lower than specified values of
offset and gain error, Figure 7 shows a simple way to trim these
parameters. Care should be taken to select low drift resistors
because they will affect the temperature drift performance of the
DAC.
The adjustment algorithm is iterative. The procedure for trim-
ming the AD420 in the 4 mA–20 mA mode can be accom-
plished as follows:
STEP I . . . OFFSET ADJUST
Load all zeros. Adjust RZERO for 4.00000 mA of output
current.
STEP II . . . GAIN ADJUST
Load all ones. Adjust RSPAN for 19.99976 mA (FS – 1 LSB) of
output current.
Return to STEP I and iterate until convergence is obtained.
Variation of RZERO between REF OUT (5 V) and GND leads
to an offset adjust range from –1.5 mA to 6 mA, (1.5 mA/V
centered at 1 V).
The 5 k RSPAN2 resistor is connected in parallel with the
internal 40
+0.8%.
As RSPAN is changed to 500 , the voltage on REF IN is
attenuated by the combination of RSPAN and the 30 k
REF IN input resistance. When added together with RSPAN2
this results in an adjustment range of –0.8% to +0.8%.
DATA IN
CLOCK
CLEAR
LATCH
0.1 F
SELECT1
SELECT2
RANGE
RANGE
R1
Open
Open
R
R
Suitable R = 5 k .
Table IV. Buffer Amplifier Configuration
sense resistor, which leads to a gain increase of
Figure 7. Offset and Gain Adjust
5
4
6
8
9
7
V
V
REF
2
LL
R2
Open
R
Open
2R
14
RSPAN
C1
500
20
AD420
15
C2
R3
0
R
R
2R
RZERO
21
10k
16
23
11
GND
0 V–10 V
V
0 V–5 V
5 V
10 V
OUT
V
CC
19
18
I
OUT
R
AD420
5k
RSPAN2
BOOST
(4mA–20mA)
LOAD
0.1 F