71m6543h-igtr/f Maxim Integrated Products, Inc., 71m6543h-igtr/f Datasheet - Page 91

• Manufacturer Part Number: 71m6543h-igtr/f
• Description: Energy Meter Ic
• Manufacturer: Maxim Integrated Products, Inc.

In the 71M6543F, the required VREF compensation coefficients PPMC and PPMC2 are calculated from
readable on-chip non-volatile fuses (see
the 71M6543F/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 Current Transformers are directly connected to the 71M6543F/H and are therefore primarily affected by
the VREF temperature dependency in the 71M6543F/H. For best performance, it is recommended to use the
differential signal conditioning circuit, as shown in
transformers may also require temperature compensation. The copper wire winding in the CT has dc
resistance with a temperature coefficient, which makes the voltage delivered to the burden resistor
temperature dependent, and the burden resistor also has a temperature coefficient. Thus, each CT sensor
channel needs to compensate for the 71M6543F/H VREF, and optionally for the temperature dependency of
the CT and its burden resistor depending on the required accuracy class.
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
In the demonstration code, the shape of the temperature compensation second-order parabolic curve is
determined by the values stored in the PPMC (1
which are typically setup by the MPU at initialization time from values that are stored in EEPROM.
To disable temperature compensation in the demonstration code, PPMC and PPMC2 are both set to zero
for each of the five GAIN_ADJx channels. To enable temperature compensation, the PPMC and PPMC2
coefficients are set with values that match the expected temperature variation of the shunt current sensor
(if required) and the corresponding VREF voltage reference (summed together).
The shunt sensor requires a second order polynomial compensation which is determined by the PPMC
and PPMC2 coefficients for the corresponding current measurement channel. The corresponding VREF
voltage reference also requires the PPMC and PPMC2 coefficients to match the second order
temperature behavior of the voltage reference. The PPMC and PPMC2 values associated with the shunt
and with the corresponding VREF are summed together to obtain the compensation coefficients for a
given current-sensing channel (i.e., the 1
order PPMC2 coefficients are summed together).
coefficients are designed to achieve ±40 ppm/°C for VREF in the 71M6543F. PPMC and PPMC2
coefficients are similarly calculated for the 71M6xx3 remote sensor (see
for the
For the 71M6543H (±0.1% energy accuracy), coefficients specific to each individual device can be
calculated from values read from additional on-chip fuses that characterize the VREF behavior of each
individual part across industrial temperatures (see
The resulting tracking of the reference VREF voltage is within ±10 ppm/°C.
For the current channels, to determine the PPMC and PPMC2 coefficients for the shunt current
sensors, the designer must either know the average temperature curve of the shunt from its
manufacturer’s data sheet or obtain these coefficients by laboratory characterization of the shunt used
in the design.
4.5.6 Temperature Compensation of VREF and Current Transformers
This section discusses metrology temperature compensation for meter designs where Current
Transformer (CT) sensors are used, as shown in
Sensors that are directly connected to the 71M6543F/H are affected by the voltage variation in the
71M6543F/H VREF due to temperature. The VREF in the 71M6543F/H can be compensated digitally
using a second-order polynomial function of temperature. The 71M6543F/H features a temperature
sensor for the purposes of temperature compensating its VREF. The compensation computations must
be implemented in MPU firmware and written to the corresponding GAIN_ADJx CE RAM location.
Referring to
connected to the 71M6543F/H. Thus, the precision of the voltage sensors is primarily affected by VREF in
implements the GAIN_ADJx compensation equation shown below. The resulting GAIN_ADJx values are
v1.0
71M6xx3).
Figure
32, the VADC8 (VA), VADC9 (VB) and VADC10 (VC) voltage sensors are directly
Figure
© 2008–2011 Teridian Semiconductor Corporation
27) determine the behavior of the voltage division ratio with respect to
st
4.5.2 Temperature Coefficients for the
order PPMC coefficients are summed together, and the 2
st
Figure
Figure 32.
order coefficient) and PPMC2 (2
4.5.3 Temperature Coefficients for the 71M6543H).
29, to connect the CTs to the 71M6543F/H. Current
4.5.4 Temperature Coefficients
71M6543F). These
71M6543F/H Data Sheet
nd
order coefficient),
nd
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