STPM11ATR datasheet(16/45 Pages) STMICROELECTRONICS

16 / 45 page

Theory of operation

STPM11/12/13/14

16/45

The Table 7 and Table 8: below show the gain values according to the configuration bits:

Both the voltage and current channels implement an active offset correction architecture

which has the benefit of avoiding any offset compensation.

The analog voltage and current signals are processed by the

∑Δ Analog to digital converters

that feed the hardwired DSP. The DSP implements an automatic digital offset cancellation

that makes possible avoiding any manual offset calibration on the analog inputs.

7.3

∑Δ A/D Converters

The analog to digital conversion in the STPM1X is carried out using two first order

∑Δ

converters. The device performs A/D conversions of analog signals on two independent

channels in parallel. In STPM13/14, the current channel is multiplexed as primary or

secondary current channel in order to be able to perform a tamper function. The converted

∑Δ signals are supplied to the internal hardwired DSP unit, which filters and integrates

those signals in order to boost the resolution and to yield all the necessary signals for

computations.

∑Δ modulator converts the input signal into a continuous serial stream of 1s and 0s at a

rate determined by the sampling clock. In the STPM1X, the sampling clock is equal to

Table 7.

Configuration of current sensors

STPM11/12

Current channel

Configuration Bits

Gain

Sensor

PST (2bits)

ADDG (1 bit)

Rogowsky Coil

8CT

Shunt

Table 8.

Configuration of current sensors

STPM13/14

Primary

Secondary

Configuration Bits

Gain

Sensor

Gain

Sensor

PST (2bits)

ADDG (1 bit)

Rogowsky Coil

8CT

Shunt

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