71m6545h-igtr/f Maxim Integrated Products, Inc., 71m6545h-igtr/f Datasheet - Page 76

• Manufacturer Part Number: 71m6545h-igtr/f
• Description: Metrology Processors
• Manufacturer: Maxim Integrated Products, Inc.

directly connected to the 71M6545/H. Thus, the precision of the voltage sensors is primarily affected by
Data Sheet 71M6545/H
Referring to
VREF in the 71M6545/H. The temperature coefficient of the resistors used to implement the voltage dividers
for the voltage sensors (see
temperature. It is recommended to use resistors with low temperature coefficients, while forming the entire
voltage divider using resistors belonging to the same technology family, in order to minimize the temperature
dependency of the voltage division ratio. The resistors must also have suitable voltage ratings.
The 71M6545/H also may have one local current shunt sensor that is connected directly to it via the IADC0-
IADC1 input pins, and therefore this local current sensor is also affected by the VREF in the 71M6545/H.
The shunt current sensor resistance has a temperature dependency, which also may require
compensation, depending on the required accuracy class.
The IADC2-IADC3, IADC4-IADC5 and IADC6-IADC7 current sensors are isolated by the 71M6xx3 and
depend on the VREF of the 71M6xx3, plus the variation of the corresponding remote shunt current sensor
with temperature.
The MPU has the responsibility of computing the necessary sample gain compensation values required for
each sensor channel based on the sensed temperature. Teridian provides demonstration code that
implements the GAIN_ADJx compensation equation shown below. The resulting GAIN_ADJx values are
stored by the MPU in five CE RAM locations GAIN_ADJ0-GAIN_ADJ5 (CE RAM 0x40-0x44). The
demonstration code thus provides a suitable implementation of temperature compensation, but other
methods are possible in MPU firmware by utilizing the on-chip temperature sensors while storing the
sample gain adjustment results in the CE RAM GAIN_ADJx storage locations for use by the CE. The
demonstration code maintains five separate sets of PPMC and PPMC2 coefficients and computes five
separate GAIN_ADJx values based on the sensed temperature using the equation below:
The GAIN_ADJx values stored by the MPU in CE RAM are used by the CE to gain adjust (i.e., multiply)
the sample in each corresponding sensor channel. A GAIN_ADJx value of 16,384 (i.e., 2
unity gain, while values less than 16,384 attenuate the samples and values greater than 16,384 amplify
the samples.
In the above equation, TEMP_X is the deviation from nominal or calibration temperature expressed in
multiples of 0.1 °C. The 10x and 100x factors seen in the above equation are due to 0.1
TEMP_X. For example, if the calibration (reference) temperature is 22
is 27
In the demonstration code, TEMP_X is calculated in the MPU from the STEMP[10:0] temperature sensor
reading using the equation provided below and is scaled in 0.1°C units. See
Temperature Sensor
STEMP[10:0] value.
Table 57
channels for which they compensate for the 1 Local / 3 Remote configuration shown in
76
Gain Adjustment Output
o
C, then 10*TEMP_X = (27-22) x 10 = 50 (decimal), which represents a +5
shows the five GAIN_ADJx equation output storage locations and the voltage or current sensor
GAIN_ADJ0
GAIN_ADJ1
GAIN_ADJ2
GAIN_ADJ3
GAIN_ADJ4
Table 57: GAIN_ADJn Compensation Channels
Figure
GAIN
27, the VADC8 (VA), VADC9 (VB) and VADC10 (VC) voltage sensors are always
_
on page
ADJx
Figure
© 2008–2011 Teridian Semiconductor Corporation
=
53
16385
CE RAM Address
for the equation to calculate temperature in degrees °C from the
23) determine the behavior of the voltage division ratio with respect to
+
0x41
0x42
0x43
0x44
0x40
10
⋅
TEMP
2
_
14
Sensor Channel(s)
X
VADC10 (VC)
IADC0-IADC1
IADC2-IADC3
IADC4-IADC5
IADC6-IADC7
(pin names)
VADC8 (VA)
VADC9 (VB)
⋅
PPMC
+
(Figure
100
⋅
TEMP
VREF in 71M6545/H and Voltage Divider
o
2,
C and the measured temperature
Figure 27, Table
VREF in 71M6545/H and Shunt
VREF in 71M6xx3 and Shunt
VREF in 71M6xx3 and Shunt
VREF in 71M6xx3 and Shunt
2.5.5 71M6545/H
_
2
23
Compensation For:
X
(Neutral Current)
o
2
C deviation from 22
⋅
(Phase A)
(Phase B)
Resistors
PPMC
Figure
14
o
C scaling of
)corresponds to
PDS_6545_009
2
1)
27.
o
v1.0
C.