AD8479 Datasheet, PDF (15/16 Pages) Analog Devices – Very High Common-Mode Voltage Precision Difference Amplifier

Data Sheet
AD8479
ERROR BUDGET ANALYSIS EXAMPLE
In the dc application described in this section, the 10 A output
current from a device with a high common-mode voltage (such
as a power supply or current-mode amplifier) is sensed across a
1 Ω shunt resistor (see Figure 41). The common-mode voltage is
600 V, and the resistor terminals are connected through a long
pair of lead wires located in a high noise environment, for example,
50 Hz/60 Hz, 440 V ac power lines.
The calculations in Table 6 assume an induced noise level of
1 V p-p at 60 Hz on the lead wires, in addition to a full-scale dc
differential voltage of 10 V. The error budget table quantifies the
contribution of each error source. Note that the dominant error
source in this example is due to the dc common-mode voltage.
OUTPUT
CURRENT
10A
600V_CMDC
TO GROUND
1Ω
SHUNT
REF(–)
1
–IN
2
+IN
3
AD8479
8 NC
+V_S
7
0.1µF
6
V_OUT
60Hz
–V_S
POWER LINE
REF(+)
4
5
0.1µF
NC = NO CONNECT
Figure 41. Error Budget Analysis Example: VIN = 10 V Full Scale, VCM = 600 V DC,
RSHUNT = 1 Ω, 1 V p-p, 60 Hz Power Line Interference
Table 6. Error Budget Analysis Example (VCM = 600 V DC)
Error Source
Calculation of Error
ACCURACY, TA = 25°C
Initial Gain Error
(0.0001 × 10)/10 V × 10⁶
Offset Voltage
(0.001 V/10 V) × 10⁶
DC CMR (Over Temperature)
(32 × 10^−6 × 600 V)/10 V × 10⁶
Total Accuracy Error
TEMPERATURE DRIFT (85°C)
Gain Drift
5 ppm/°C × 60°C
Offset Voltage Drift
(10 μV/°C × 60°C) × 10⁶/10 V
Total Temperature Drift Error
RESOLUTION
Noise, Typical, 0.01 Hz to 10 Hz, μV p-p 35 μV/10 V × 10⁶
CMR, 60 Hz
(32 × 10^−6 × 1 V)/10 V × 10⁶
Nonlinearity
(5 × 10^−6 × 10 V)/10 V × 10⁶
Total Resolution Error
Total Error
Error (ppm of FS)
100
100
1920
2120
300
60
360
4
3
5
12
2492
Rev. 0 | Page 15 of 16