71M6513/71M6513H Demo Board User’s Manual
Page: 53 of 112
©
2005-2006 TERIDIAN Semiconductor Corporation
Revision 5.6
2.2.5 COMPENSATING
FOR NON-LINEARITIES
Nonlinearity is most noticeable at low currents, as shown in Figure 2-6, and can result from input noise and
truncation. Nonlinearities can be eliminated using the
QUANT
variable.
0
2
4
6
8
10
12
0.1
1
10
100
I [A]
er
ro
r [%
]
error
Figure 2-6: Non-Linearity Caused by Quantification Noise
The error can be seen as the presence of a virtual constant noise current. While 10mA hardly contribute any
error at currents of 10A and above, the noise becomes dominant at small currents.
The value to be used for QUANT can be determined by the following formula:
LSB
IMAX
VMAX
I
V
error
QUANT
⋅
⋅
⋅
−
=
100
Where error = observed error at a given voltage (V) and current (I),
VMAX = voltage scaling factor, as described in section 1.8.3,
IMAX = current scaling factor, as described in section 1.8.3,
LSB = QUANT LSB value = 7.4162*10
-10
W
Example: Assuming an observed error as in Figure 2-6, we determine the error at 1A to be +1%. If VMAX is
600V and IMAX = 208A, and if the measurement was taken at 240V, we determine QUANT as follows:
11339
10
4162
.
7
208
600
1
240
100
1
10
−
=
⋅
⋅
⋅
⋅
−
=
−
QUANT
QUANT
is to be written to the CE location 0x2F. It does not matter which current value is chosen as long as the
corresponding error value is significant (5% error at 0.2A used in the above equation will produce the same
result for
QUANT
).
Input noise and truncation can cause similar errors in the VAR calculation that can be eliminated using the
QUANT_VAR
variable.
QUANT_VAR
is determined using the same formula as
QUANT
.
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