AD420AN-32(1999) データシートの表示（PDF） - Analog Devices
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AD420AN-32 Datasheet PDF : 11 Pages
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AD420
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 µF and C2 = 0.01 µF.
0.1F
RANGE
SELECT 1
RANGE
SELECT 2
CLEAR
LATCH
CLOCK
DATA IN
VLL
C1
VCC
0.1F
C2
2
20
21
23
5
4
IOUT (4mA–20mA)
6
AD420
18
7
RLOAD
8
9
14
REF
OUT
15
REF
IN
11
GND
Figure 5. Standard Configuration
DRIVING INDUCTIVE LOADS
When driving inductive or poorly defined loads connect a
0.01 µF capacitor between IOUT (Pin 18) and GND (Pin 11).
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 IOUT and each of VCC and GND.
VOLTAGE-MODE OUTPUT
Since the AD420 is a single supply device, it is necessary to add
an external buffer amplifier to the VOUT pin to obtain a selec-
tion of bipolar output voltage ranges as shown in Figure 6.
0.1F
RANGE
SELECT 1
RANGE
SELECT 2
CLEAR
LATCH
CLOCK
DATA IN
VLL
2
5
4
VCC
C1 C2
0.1F
20
21
23
VOUT
17
6
AD420
R3
7
8
R1
R2
9
14
REF
OUT
15
11
REF
GND
IN
VOUT
Figure 6.
Table IV. Buffer Amplifier Configuration
R1
R2
R3
Open
Open
R
R
Open 0
R
R
Open R
2R
2R
Suitable R = 5 kΩ.
VOUT
0 V–5 V
0 V–10 V
±5 V
± 10 V
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.
0.1F
RANGE
SELECT1
RANGE
SELECT2
CLEAR
LATCH
CLOCK
DATA IN
VLL
C1
2
20
5
4
C2
21
VCC
0.1F
23
5k⍀
RSPAN2
19 BOOST
6
AD420
IOUT (4mA–20mA)
18
7
RLOAD
8
9
14
VREF
15 16
11
500⍀
RSPAN
10k⍀ GND
RZERO
Figure 7. Offset and Gain Adjust
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 kΩ RSPAN2 resistor is connected in parallel with the
internal 40 Ω sense resistor, which leads to a gain increase of
+0.8%.
As RSPAN is changed to 500 Ω, the voltage on REF IN is
attenuated by the combination of RSPAN and the 30 kΩ
REF IN input resistance. When added together with RSPAN2
this results in an adjustment range of –0.8% to +0.8%.
REV. F
–7–
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