78M6612 Hardware Design Guidelines
AN_6612_007
10
Rev 2
4 Calibration Considerations
All power measurement ICs must employ in-system calibration to achieve higher accuracy. In-system
calibration compensates for the PCB trace lengths, LINE input voltage divider resistor network, current
sensor tolerances, and 78M6612 IC tolerances. Using tighter tolerance components can help reduce or
even eliminate in-system calibration depending on the required measurement accuracy.
As an example, the following table shows different levels of accuracies that can be achieved with different
levels of calibration. The Current Only Calibration compensates for only the current sensing resistor
tolerance and utilizes 0.1% tolerance resistors for the voltage sensor. The Full Calibration compensates
for both the voltage divider plus the current sensor tolerances.
If the system does not require a high level of accuracy relative to the initial tolerance of the voltage divider
and current sensor components, predetermined coefficients can also be hard coded into the firmware to
eliminate production line calibration and maximize cost savings. Invoke the requisite CLI temperature
calibration command for all systems. See the applicable 78M6612 Firmware Description Document for
more information on the firmware interface.
Calibration Type
Time
Accuracy
Full Calibration
< 15s
< 0.5%
Current Only Calibration
1
< 7.5s
< 1%
No Calibration (fixed coeff.)
1 2
0
< 2.5
Notes:
1. Use 0.1% tolerance resistors voltage divider.
2. Use 1% tolerance shunt resistor or burden resistor when using a current transformer.
Refer to the
78M661x Calibration Procedure
for additional information.
