AD5280BRU200 查看數據表（PDF） - Analog Devices
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AD5280BRU200 Datasheet PDF : 20 Pages
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AD5280/AD5282
Table III shows the result of adjusting D, with A2 configured as
a unity gain, a gain of 2, and a gain of 10. The result is a bipolar
amplifier with linearly programmable gain and 256-step resolution.
Table III. Result of Bipolar Gain Amplifier
D
R1 = ؕ, R2 = 0
R1 = R2
R2 = 9R1
0
–1
–2
–10
64
–0.5
–1
–5
128
0
0
0
192
0.5
1
5
255
0.968
1.937
9.680
Programmable Voltage Source with Boosted Output
For applications that require high current adjustments such as a
laser diode driver or tunable laser, a boosted voltage source can
be considered (see Figure 18).
Vi
5V
A
W
U1
B
V+
A1
V–
VO
N1
RBIAS
CC
IL
SIGNAL
LD
U1 = AD5280
A1 = AD8601, AD8605, AD8541
N1 = FDV301N, 2N7002
Figure 18. Programmable Booster Voltage Source
In this circuit, the inverting input of the op amp forces the VBIAS
to be equal to the wiper voltage set by the digital potentiometer.
The load current is then delivered by the supply via the N-Ch
FET N1. N1’s power handling must be adequate to dissipate
(Vi–VO) × IL power. This circuit can source a maximum of
100 mA with a 5 V supply. A1 needs to be a rail-to-rail input
type. Fore precision applications, a voltage reference such as
ADR423, ADR292, or AD1584 can be applied at the input of
the digital potentiometer.
Programmable 4 to 20 mA Current Source
A programmable 4 to 20 mA current source can be implemented
with the circuit shown in Figure 19. REF191 is a unique, low
supply headroom and high current handling precision reference
that can deliver 20 mA at 2.048 V. The load current is simply
the voltage across terminals B to W of the digital potentiometer
divided by RS:
IL
= VREF × D
RS × 2N
(8)
+5V
2
U1
VIN
3 SLEEP
0 TO (2.048 + VL)
6
VOUT
B
REF191
C1
GND
1F
W
4
A
AD5280
+5V
V+
RS
102⍀
–2.048V TO VL
OP8510
U2
V–
–5V
RL
100⍀
VL
IL
Figure 19. Programmable 4 to 20 mA Current Source
The circuit is simple, but beware of two things. First, dual sup-
ply op amps are ideal because the ground potential of REF191
can swing from –2.048 V at zero scale to VL at full scale of the
potentiometer setting. Although the circuit works under single
supply, the programmable resolution of the system will be reduced.
For applications that demand higher current capabilities, a few
changes to the circuit in Figure 19 will produce an adjustable
current in the range of hundreds of mA. First, the voltage reference
needs to be replaced with a high current, low dropout regulator,
such as the ADP3333, and the op amp needs to be swapped
with a high current dual-supply model, such as the AD8532.
Depending on the desired range of current, an appropriate value
for RS must be calculated. Because of the high current flowing
to the load, the user must pay attention to the load impedance
so as not to drive the op amp beyond the positive rail.
Programmable Bidirectional Current Source
For applications that require bidirectional current control or
higher voltage compliance, a Howland current pump can be a
solution (see Figure 20). If the resistors are matched, the load
current is:
(R2A + R2B )
IL =
R1
R2B
×VW
(9)
R1
150k⍀
R2
15k⍀
+15V
C1
10pF
+5V
A
AD5280
W
–5V
+15V
+ V+
OP2177
– V–
A1
–15V
R1
150k⍀
– V+
OP2177
+ V– A2
–15V
R2A
14.95k⍀
R2B
50⍀
VL
RL
500⍀
IL
Figure 20. Programmable Bidirectional Current Source
–16–
REV. 0
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