STPM11 datasheet(15/46 Pages) STMICROELECTRONICS

15 / 46 page

STPM11, STPM12, STPM13, STPM14

Theory of operation

Doc ID 13167 Rev 8

15/46

Theory of operation

7.1

General operation

The STPM1X is able to perform active energy measurement (wide band or fundamental) in

single-phase energy meter systems.

Due to the proprietary energy computation algorithm, STPM1X active energy is not affected

by any ripple at twice the line frequency. The calibration is very easy and fast allowing

calibration in only one point over the whole current range which allows saving time during

the calibration phase of the meter. The calibration parameters are permanently stored in the

OTP (one time programmable) cells, preventing calibration tampering.

Several functions are programmable using internal configuration bits accessible through the

configuration interface. The most important configuration bits are two configuration bits

called PST that allow the selection of the sensor and the gain of the input amplifiers.

The STPM1X is able to directly drive a stepper motor with the MOP and MON pins, and

provides information on tamper, no-load and negative power.

Two kinds of active energy can be selected to be brought to the LED pin: the total active

energy that includes all harmonic content in bandwidth or the active energy limited to the 1st

harmonic only. This last energy value is obtained by filtering the wide band active energy.

7.2

Analog inputs

Input amplifiers

The STPM1X has one fully differential voltage input channel and one (STPM11/12) or two

(STPM13/14) fully differential current input channels.

The voltage channel consists of a differential amplifier with a gain of 4. The maximum

differential input voltage for the voltage channel is ± 0.3 V.

In STPM13/14, the two current channels are multiplexed (see tamper section for details) to

provide a single input to a preamplifier with a gain of 4. The output of this preamplifier is

connected to the input of a programmable gain amplifier (PGA) with possible gain selections

of 2, 4, 6, 8. The total gain of the current channels will be then 8, 16, 24, 32. The gain

selections are made by writing to the gain configuration bits PST and it can be different for

the two current channels. The maximum differential input voltage is dependent on the

selected gain according to the Table 7:

Table 7.

Voltage channel

Voltage channels

Current channels

Gain

Max input voltage (V)

Gain

Max input voltage (V)

±0.30

±0.15

16X

±0.075

24X

±0.05

32X

±0.035

Obsolete

Product(s)

- Obsolete

Product(s)

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