Datasheet

STPMC1 Theory of operation
Doc ID 15728 Rev 7 19/77
9 Theory of operation
9.1 General operation
The STPMC1 (also called a calculator) is an ASSP designed for effective measurement in
power line systems utilizing the Rogowski coil, current transformer, Shunt or Hall current
sensors. This device, used with the STMicroelectronics STPMSx companion chip (an
analog front-end device), can be implemented as standalone or as a peripheral in a
microprocessor based 1-, 2- or 3-phase energy meter.
The calculator consists of three sections: analog, digital and OTP (see
Figure 1 ):
● The analog section is composed of a band-gap voltage reference and a low-drop
voltage regulator.
● The digital section consists of a system control, clock generator, three PDSP and a
NDSP, a SPI interface.
● The 112-bit OTP block and the 16 system signals, used for testing, configuration and
calibration purposes, are controlled through SPI by means of a dedicated command
set.
The calculator has five input data pins, of which four are fed by signals generated by the
STPMSx, see
Ta bl e 9 .
Three of them (DAR/DAS/DAT) are used to receive multiplexed signals of voltage and
current, implementing energy measurement in 1-, 2- and 3-phase (3 and 4 wires) systems.
After being de-multiplexed, each phase input is sent to the correspondent DSP unit that
processes voltage and current information and performs energy calculation, according to
the settings of the configuration bits (see
Tabl e 3 3 ).
The DAN input, which also receives a multiplexed signal output from STPMSx device, is
typically used to monitor neutral current for anti tampering functions in 1-, 2- and 3-phase (4
wires) systems. Normally the STPMSx monitors current and voltage but in case of neutral
monitoring the voltage channel can be connected to a different type of sensor, for example a
temperature sensor.
The fifth input data pin (DAH) accepts non-multiplexed ΔΣ signals. It can be used for EMI
sensing through Hall sensors or for temperature sensing.
The companion chip (STPMSx) embeds 2 ΔΣ ADC converters and the necessary logic
capable of providing the multiplexed ΔΣ streams.
See the STPMSx documentation for more details.
Table 9. Input channels from the STPMSx
Channel name Property Signal 1 Signal 2
DAR Multiplexed Voltage Current
DAS Multiplexed Voltage Current
DAT Multiplexed Voltage Current
DAN Multiplexed Temperature Current
DAH Not multiplexed EMI or temperature