71M6521DE Datasheet, PDF (63/107 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6521DE/DH/FE Data Sheet
1400
1000
600
200
-200
-600
-1000
-1400
-40
Error Band (PPM) over Temperature (°C)
±20 PPM/°C
±20 PPM/°C
-20
0
20
40
60
80
Figure 31: Error Band for VREF over Temperature (High-Accuracy Parts)
Temperature Compensation: The CE provides the bandgap temperature to the MPU, which then may digitally com-
pensate the power outputs for the temperature dependence of VREF, using the CE register GAIN_ADJ. Since the
band gap amplifier is chopper-stabilized via the CHOP_EN bits, the most significant long-term drift mechanism in the
voltage reference is removed.
The MPU, not the CE, is entirely in charge of providing temperature compensation. The MPU applies the following
formula to determine GAIN_ADJ (address 0x12). In this formula TEMP_X is the deviation from nominal or calibration
temperature expressed in multiples of 0.1°C:
GAIN
_
ADJ
= 16385 +
TEMP
_ X ⋅ PPMC
2¹⁴
+
TEMP
_
X²â‹…
2²³
PPMC 2
In a production electricity meter, the 71M6521DE/DH/FE is not the only component contributing to temperature de-
pendency. A whole range of components (e.g. current transformers, resistor dividers, power sources, filter capacitors)
will contribute temperature effects.
Since the output of the on-chip temperature sensor is accessible to the MPU, temperature-compensation
mechanisms with great flexibility are possible. MPU access to GAIN_ADJ permits a system-wide temperature
correction over the entire meter rather than local to the chip.
Rev 2
Page: 63 of 107