90E21 Datasheet, PDF (15/57 Pages) Integrated Device Technology – Single-Phase High-Performance Wide-Span Energy Metering IC

90E21/22/23/24
SINGLE-PHASE HIGH-PERFORMANCE WIDE-SPAN ENERGY METERING IC
3.6 CALIBRATION
Metering Calibration
Only single-point calibration is needed over the entire dynamic
range.
Metering calibration is realized by first calibrating gain at unity power
factor and then calibrating phase angle compensation at 0.5 inductive
power factor.
However, due to very small signal in L line current sampling circuits,
any external interference, e.g., a tens of nano volts influence voltage on
shunt resistor conducted by transformer in the energy meter’s power
supply may cause perceptible metering error, especially in low current
state. For this nearly constant external interference, the 90E21/22/23/24
also provides power offset compensation.
L line and N line need to be calibrated sequentially. Reactive does
not need to be calibrated.
Measurement Calibration
Measurement calibration is realized by calibrating the gains for volt-
age rms and current rms. Considering the possible nonlinearity around
zero caused by external components, the chip also provides offset com-
pensation for voltage rms, current rms, mean active power and mean
reactive power.
Frequency, phase angle and power factor do not need calibration.
For more calibration details, please refer to Application Note AN-641.
3.7 RESET
The 90E21/22/23/24 has an on-chip power supply monitor circuit with
built-in hysteresis. The 90E21/22/23/24 only works within the voltage
range.
The 90E21/22/23/24 has three means of reset: power-on reset, hard-
ware reset and software reset. All registers resume to their default value
after reset.
Power-on Reset: Power-on reset is initiated during power-up. Refer
to section 6.3.
Hardware Reset: Hardware Reset is initiated when the reset pin is
pulled low. The width of the reset signal should be over 200µs.
Software Reset: Software Reset is initiated when ‘789AH’ is written
to the software reset register (SoftReset, 00H).
Functional Description
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January 10, 2012