Temperature calibration

AN2299

22/26

Rev2

6

Temperature calibration

A calibration of Band Gap should be performed during EWS by means of production tester

which could permanently write one or two OTP lower bits of TC. Namely, on the die, there is

an additional test pad which enables the tester to measure the output of Band Gap

generator. The upper two bits of TC are intended for compensation of temperature variation

of the whole meter. We saw on some of our applications that we can rotate the temperature

curve of the whole meter by changing the value of configurator TC. But, in practice, it is very

difficult and time consuming to calibrate the temperature dependency of the meter.

Therefore, it is advisable to control temperature dependency during the meter design phase.

This would enable us to perform such compensation at the base.

6.1

APPENDIX A - Traditional calibration approach

It is possible to calibrate a STPM01 based energy meter also in a traditional way, setting the

calibrators Cv and Ci in order to fix LED frequency rather than voltage and current values.

The procedure requires an accurate frequency meter that allows reading frequency out of

the LED pin.

LED pin outputs a pulse train with frequency that can be chosen proportional to wide band

APL=0 (CFG03=APL0=0, CFG04=APL1=0) and then by setting another 2-bit configurator

KMOT respectively to:

●

0 - Type 0 active energy - (CFG14=KMOT0=0, CFG15=KMOT1=0)

●

1 - Type 1 active energy - (CFG14=KMOT0=1, CFG15=KMOT1=0)

●

2 - Reactive energy - (CFG14=KMOT0=0, CFG15=KMOT1=1)

●

3 - Apparent energy - (CFG14=KMOT0=1, CFG15=KMOT1=1)

To perform the calibration, the following steps need to be performed.

6.1.1

Working point setting

Voltage and current nominal values must be defined before running the calibration

procedure, for example:

●

Line RMS voltage:

–

Vn=230V

●

Line RMS current:

–

In=5A

●

Active Power:

–

Pn=Vn*In=1150W

Target active power is calculated assuming no phase shift between line voltage and current.

Parameters reported in Table 3. are always valid for calculation.

In STPM01 active power is calculated from voltage and current registers. Eq. 9 and Eq. 10

show a proportional relationship between measured voltage and current and calibration