Datasheet

STPM10 Theory of operation
Doc ID 17728 Rev 4 21/53
It means that if FRS is set and BFR is also set, all the energy computation is carried on as
BFR was cleared. In this case then p=u*i, where u could be zero or not (if BFR was set
because voltage RMS register value is below 64).
When the line frequency re-enters the nominal band, the BFR flag is automatically reset.
This BFR error flag is also assembled as part of the 8-bit status register (see Ta bl e 10 ).
7.6 Power supply
The main STPM10 supply pin is the VCC pin. From the VCC pin two linear regulators
provide the necessary voltage for the analog part VDDA (3 V) and for the digital part VDDD
(1.8 V).
The VSS pin represents the reference point for all the internal signals. A 100 nF low ESR
capacitor should be connected between VCC and VSS, VDDA and VSS, VDDD and VSS.
All these capacitors must be located very close to the device.
The STPM10 contains a power on reset (POR) detection circuit. If the VCC supply is less
than 2.5 V, then the STPM10 goes into an inactive state, all the functions are blocked and a
reset condition is asserted. This is useful to ensure correct device operation at power-up
and during power-down. The power supply monitor has built-in hysteresis and filtering,
which give a high degree of immunity from false triggering due to noisy supplies.
A band-gap voltage reference (VBG) of 1.23 V ±1% is used as the reference voltage level
source for the two linear regulators and for the A/D converters. Also, this module produces
several bias currents and voltages for all other analog modules. The band-gap voltage can
be compensated regardless of the temperature variations with the BGTC bits.
7.7 Load monitoring
The STPM10 includes a no-load condition detection circuit with adjustable threshold. This
circuit monitors the voltage and the current channels and, when the measured voltage is
below the set threshold, the internal signal BIL becomes high. Information about this signal
is also available in the status bit BIL.
Figure 17. Band-gap temperature variation
1,20
1,21
1,22
1,23
1,24
1,25
1,26
1,27
1,28
1,29
-40 0 40 80
Temperature °C
VBG
BGTC=0
BGTC=1
BGTC=2
BGTC=3
100
1,20
1,21
1,22
1,23
1,24
1,25
1,26
1,27
1,28
1,29
-40 0 40 80
Temperature °C
VBG
BGTC=0
BGTC=1
BGTC=2
BGTC=3
100