ADR02WARZ-REEL7 查看數據表（PDF） - Analog Devices
零件编号
产品描述 (功能)
生产厂家
ADR02WARZ-REEL7 Datasheet PDF : 21 Pages
| |||
Data Sheet
PROGRAMMABLE 4 mA TO 20 mA CURRENT
TRANSMITTER
Because of their precision, adequate current handling, and small
footprint, the devices are suitable as the reference sources for
many high performance converter circuits. One of these
applications is the multichannel 16-bit, 4 mA to 20 mA current
transmitter in the industrial control market (see Figure 40).
This circuit employs a Howland current pump at the output to
yield better efficiency, a lower component count, and a higher
voltage compliance than the conventional design with op amps
and MOSFETs. In this circuit, if the resistors are matched such
that R1 = R1′, R2 = R2′, R3 = R3′, the load current is
IL
=
(R2 + R3)
R3′
R1
×
VREF ×
2N
D
(2)
where D is similarly the decimal equivalent of the DAC input
code and N is the number of bits of the DAC.
According to Equation 2, R3′ can be used to set the sensitivity.
R3′ can be made as small as necessary to achieve the current
needed within U4 output current driving capability. Alter-
natively, other resistors can be kept high to conserve power.
In this circuit, the AD8512 is capable of delivering 20 mA of
current, and the voltage compliance approaches 15.0 V.
0V TO –10V
5V
U2
U1
15V
VIN VOUT
TEMP TRIM
VDD
RF
IO
10V VREF AD5544
GND
IO
GND
DIGITAL INPUT
CODE 20%–100% FULL SCALE
U1 = ADR01/ADR02/ADR03/ADR06, REF01
U2 = AD5543/AD5544/AD5554
U3, U4 = AD8512
+15V
R1
R2
150kΩ 15kΩ
U3
VX
VP
–15V
C1
AD8512
10pF
U4
R3
50Ω
VO
R1'
150kΩ
R2'
15kΩ
VN
R3'
50Ω
VL
LOAD
500Ω
4mA TO 20mA
Figure 40. Programmable 4 mA to 20 mA Transmitter
The Howland current pump yields a potentially infinite output
impedance, that is highly desirable, but resistance matching is
critical in this application. The output impedance can be deter-
mined using Equation 3. As shown by this equation, if the
resistors are perfectly matched, ZO is infinite. Alternatively, if
they are not matched, ZO is either positive or negative. If the
latter is true, oscillation can occur. For this reason, connect
Capacitor C1 in the range of 1 pF to 10 pF between VP and the
output terminal of U4 to filter any oscillation.
ADR01/ADR02/ADR03/ADR06
ZO
= Vt
It
= R1′
R1′R2 −1
(3)
R1R2′
In this circuit, an ADR01 provides the stable 10.000 V reference
for the AD5544 quad 16-bit DAC. The resolution of the adjust-
able current is 0.3 µA/step; the total worst-case INL error is
merely 4 LSBs. Such error is equivalent to 1.2 µA or a 0.006%
system error, which is well below most systems’ requirements.
The result is shown in Figure 41 with measurement taken at 25°C
and 70°C; total system error of 4 LSBs at both 25°C and 70°C.
5
RL = 500Ω
IL = 0mA TO 20mA
4
3
2
70°C
1
25°C
0
–1
0 8192 16384 24576 32768 40960 49152 57344 65536
CODE (Decimal)
Figure 41. Result of Programmable 4 mA to 20 mA Current Transmitter
PRECISION BOOSTED OUTPUT REGULATOR
A precision voltage output with boosted current capability can
be realized with the circuit shown in Figure 42. In this circuit,
U2 forces VO to be equal to VREF by regulating the turn-on of
N1, thereby making the load current furnished by VIN. In this
configuration, a 50 mA load is achievable at VIN of 15.0 V.
Moderate heat is generated on the MOSFET, and higher current
can be achieved with a replacement of a larger device. In
addition, for a heavy capacitive load with a fast edging input
signal, a buffer should be added at the output to enhance the
transient response.
N1
VIN
U1
ADR01/
2N7002
RL
200Ω
CL VO
1µF
ADR02/
ADR03/
ADR06
VIN
VOUT
15V
R1
R2
100Ω
100Ω
V+
OP1177
TEMP TRIM
V–
GND
U2
C1
1000pF
Figure 42. Precision Boosted Output Regulator
Rev. R | Page 17 of 20
Share Link: 