Datasheet AD707 (Analog Devices) - 8

AD707 PRECISION CURRENT TRANSMITTER
The performance and accuracy of this circuit will depend almost The AD707’s excellent dc performance, especially the low offset entirely on the tolerance and selection of the resistors. The scale voltage, low offset voltage drift and high CMRR, makes it resistor (RSCALE) and the four feedback resistors directly affect possible to make a high precision voltage-controlled current the accuracy of the load current and should be chosen carefully transmitter using a variation of the Howland Current Source or trimmed. circuit (Figure 26). This circuit provides a bidirectional load As an example of the accuracy achievable, assume I current which is derived from a differential input voltage. L must be 10 mA, and the available VIN is only 10 mV.
R3 R4
RSCALE = 10 mV/10 mA = 1 Ω
100k
Ω
100k
Ω IERROR due to the AD707C:
+V 0.1µF S
Maximum IERROR = 2(VOS)/RSCALE + 2(VOS Drift)/RSCALE + C1164a–2–12/95
2 7
IOS (100 k/RSCALE)
V AD707 6
= 2 (15 µV)/l Ω +2 (0.1 µV/°C)/l Ω
IN
+ 1 nA (100 k)/l Ω (1.5 nA @ 125°C)
3 4 0.1µF RSCALE
= 30 µA + 0.2 µA/°C + 100 µA
–VS
(150 µA @ 125°C)
OBSOLETE R1 R2 100k
Ω
100k
Ω = 130 µA/10 mA = 1.3% @ 25°C
V R
= 180 µA/10 mA = 1.8% @ 125°C
IN R2 L tL = ––––––– –––
( )
RSCALE R1 IL
Low drift, high accuracy resistors are required to achieve high precision. Figure 26. Precision Current Source/Sink
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Pin Metal Can 8-Pin Plastic DIP (H-08A) (N-8) REFERENCE PLANE 0.430 (10.92) 0.750 (19.05) 0.348 (8.84) 0.185 (4.70) 0.500 (12.70) 0.165 (4.19) 8 5 0.250 (6.35) 0.280 (7.11) 0.050 MIN 0.100 0.240 (6.10) (1.27) 1 4 (2.54) MAX BSC 0.160 (4.06) 0.325 (8.25) 0.110 (2.79) 0.300 (7.62) 5 PIN 1 0.060 (1.52) 4 6 0.015 (0.38) 0.335 (8.51) 0.195 (4.95) 0.045 (1.14) 0.210 (5.33) 0.305 (7.75) 0.200 0.115 (2.93) 0.027 (0.69) MAX 0.130 (5.08) 3 7 0.370 (9.40) BSC 0.160 (4.06) (3.30) 0.335 (8.51) MIN 2 8 0.115 (2.93) 0.015 (0.381) SEATING 0.022 (0.558) 0.070 (1.77) 0.008 (0.204) 0.100 1 0.100 PLANE 0.014 (0.356) 0.045 (1.15) (2.54) (2.54) 0.040 (1.02) MAX 0.019 (0.48) BSC BSC 0.016 (0.41) 0.034 (0.86) 0.045 (1.14) 0.027 (0.69) 0.021 (0.53) 0.010 (0.25) 0.016 (0.41) 45
°
BSC 8-Lead SOIC BASE & SEATING PLANE (SO-8) 8-Pin Cerdip 0.1968 (5.00) (Q-8) 0.1890 (4.80) 0.005 (0.13) MIN 0.055 (1.4) MAX 8 5 0.1574 (4.00) 0.2440 (6.20) 1 4 8 5 0.1497 (3.80) 0.2284 (5.80) 0.310 (7.87)
PRINTED IN U.S.A.
PIN 1 0.220 (5.59) PIN 1 0.0688 (1.75) 0.0196 (0.50) 1 4 x 45
°
0.0098 (0.25) 0.0532 (1.35) 0.0099 (0.25) 0.320 (8.13) 0.0040 (0.10) 0.405 (10.29) MAX 0.290 (7.37) 0.060 (1.52) 0.200 8
°
0.015 (0.38) (5.08) 0.0500 0.0192 (0.49) 0
°
SEATING 0.0098 (0.25) 0.0500 (1.27) MAX (1.27) PLANE 0.0138 (0.35) BSC 0.0075 (0.19) 0.0160 (0.41) 0.150 0.015 (0.38) 0.200 (5.08) (3.81) 0.008 (0.20) MIN 0.125 (3.18) 15
°
0
°
0.023 (0.58) 0.100 0.070 (1.78) SEATING 0.014 (0.36) (2.54) 0.030 (0.76) PLANE BSC
–8– REV. B