Data Sheet AD8479
Rev. A | Page 15 of 16
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.
REF(–)
OUTPUT
CURRENT
60Hz
POWER LINE
1Ω
SHUNT
REF(+)
–V
S
+V
S
V
OUT
NC
–IN
+IN
0.1µF
0.1µF
NC = NO CONNECT
AD8479
1
2
3
4
8
7
6
5
10A
600V
CM
DC
TO GROUND
11118-042
Figure 41. Error Budget Analysis Example: V
IN
= 10 V Full Scale, V
CM
= 600 V DC,
R
SHUNT
= 1 Ω, 1 V p-p, 60 Hz Power Line Interference
Table 6. Error Budget Analysis Example (V
CM
= 600 V DC)
Error Source Calculation of Error Error (ppm of FS)
ACCURACY, T
A
= 25°C
Initial Gain Error (0.0001 × 10)/10 V × 10
6
100
Offset Voltage (0.001 V/10 V) × 10
6
100
DC CMR (Over Temperature)
−6
6
Total Accuracy Error 2120
TEMPERATURE DRIFT (85°C)
Gain Drift 5 ppm/°C × 60°C 300
Offset Voltage Drift (10 μV/°C × 60°C) × 10
6
/10 V 60
Total Temperature Drift Error 360
RESOLUTION
Noise, Typical, 0.01 Hz to 10 Hz, µV p-p 35 μV/10 V × 10
6
4
CMR, 60 Hz (32 × 10
−6
× 1 V)/10 V × 10
6
3
Nonlinearity (5 × 10
−6
× 10 V)/10 V × 10
6
5
Total Resolution Error 12
