ST STPM01 User Manual

Programmable single phase energy metering IC

Features

■ Active, reactive, apparent energies and RMS

values

■ Ripple free active energy pulsed output

■ Live and neutral monitoring for tamper

detection

■ Easy and fast digital calibration in only one

point over the whole current range

■ OTP for calibration and configuration

■ Integrated linear VREGs for digital and analog

supply

■ Selectable RC or crystal oscillator

■ Support 50 ÷ 60 Hz – IEC62052-11, IEC62053-

2x specification

■ Less than 0.1 % error

■ Precision voltage reference: 1.23 V and 30

ppm/°C max

Description

The STPM01 is designed for effective measurement of active, reactive and apparent energy in a power line system using Rogowski coil, current transformer and shunt sensors. This device can be implemented as a single chip monophase energy meter or as a peripheral measurement in a microcontroller based monophase or 3-phase energy meter. The STPM01 consists, essentially, of two parts: the analog part and the digital part. The former, is composed by preamplifier and 1 converter blocks, band gap voltage reference, low drop voltage regulator, the latter, is composed by system control, oscillator, hard wired DSP and SPI interface. There is also an OTP block, which is controlled through the SPI by means of a

order Δ ∑ A/D

STPM01

with tamper detection

TSSOP20

dedicated command set. The configured bits are used for testing, configuration and calibration purpose. From a pair of Δ from analog section, a DSP unit computes the amount of consummated active, reactive and apparent energy, RMS and instantaneous values of voltage and current. The results of computation are available as pulse frequency and states on the digital outputs of the device or as data bits in a data stream, which can be read from the device by means of SPI interface. This system bus interface is used also during production testing of the device and/or for temporary or permanent programming of bits of internal OTP. In the STPM01 an output signal with pulse frequency proportional to energy is generated, this signal is used in the calibration phase of the energy meter application allowing a very easy approach. When the device is fully configured and calibrated, a dedicated bit of OTP block can be written permanently in order to prevent accidental entering into some test mode or changing any configuration bit.

∑ output signals coming

Table 1. Device summary

Order code Temperature range Package Packaging

STPM01FTR - 40 to 85 °C TSSOP20 (tape and reel) 2500 parts per reel

June 2011 Doc ID 10853 Rev 8 1/60

www.st.com

Contents STPM01

Contents

1 Schematic diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1 Measurement error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.2 ADC offset error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.3 Gain error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.4 Power supply DC and AC rejection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.5 Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

7 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

8 Theory of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8.1 General operation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8.2 Analog inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

8.3 ∑Δ A/D converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8.4 Zero crossing detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

8.5 Period and line voltage measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

8.6 Single wire meter mode (only Rogowsky coil sensor) . . . . . . . . . . . . . . . 21

8.7 Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

8.8 Load monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8.9 Error detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8.10 Tamper detection module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8.10.1 Detailed operational description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

8.11 Phase compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

8.12 Clock generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

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STPM01 Contents

8.12.1 RC Startup procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

8.13 Resetting the STPM01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

8.14 Energy to frequency conversion (standalone) . . . . . . . . . . . . . . . . . . . . . 28

8.15 Driving a stepper motor (standalone) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8.16 Using STPM01 in microcontroller based meter (peripheral) . . . . . . . . . . 30

8.17 Status bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

8.18 Programming the STPM01 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

8.19 Configuration bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

8.20 Mode signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

8.21 SPI interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

8.21.1 Remote reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

8.22 Reading data records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

8.23 Writing procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

8.24 Energy calculation algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

8.24.1 Active power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

8.24.2 Reactive power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

8.24.3 Apparent power and RMS values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

9 STPM01 calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

10 Application design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

11 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Doc ID 10853 Rev 8 3/60

List of tables STPM01

List of tables

Table 1. Device summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Table 2. Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 3. Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 4. Thermal data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Table 5. Programmable pin functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Table 6. Internal signal description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Table 7. Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Table 8. Gain of voltage and current channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 9. Configuration of current sensors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 10. Nominal voltage values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 11. No load detection thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Table 12. Different settings for LED signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Table 13. Configuration of MOP and MON pins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Table 14. LED pin configuration in peripheral mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Table 15. Status bit description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 16. Configuration bits map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Table 17. Mode signals description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Table 18. Working point settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Table 19. Device constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Table 20. Resistor divider ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Table 21. Current channel typical components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Table 22. Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4/60 Doc ID 10853 Rev 8

STPM01 List of figures

List of figures

Figure 1. Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 2. Pin connections (top view) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 3. Supply current vs. supply voltage, T Figure 4. RC oscillator frequency vs. V

Figure 5. RC oscillator: frequency jitter vs. temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 6. Analog voltage regulator: line - load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 7. Digital voltage regulator: line - load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 8. Voltage channel linearity at different V Figure 9. Power supply AC rejection vs. V Figure 10. Power supply DC rejection vs. V

Figure 11. Error over dynamic range gain dependence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 12. Primary current channel linearity at different V

Figure 13. Gain response of ΔΣ AD converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 14. First order ∑ Δ A/D converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 15. ZCR signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 16. LIN and BFR signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 17. Bandgap temperature variation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 18. Timings of tamper module - Primary channel selected. . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 19. Timings of tamper module - Secondary channel selected . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 20. Different oscillator circuits (a): with quartz; (b): internal oscillator; (c): with external source27

Figure 21. Positive energy stepper driving signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 22. Negative energy stepper driving signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 23. STPM01 data records map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Figure 24. Timing for providing remote reset request . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Figure 25. Data records reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 26. Timing for data records reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 27. Timing for writing configuration and mode bits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 28. Active energy computation diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Figure 29. STPM01 reference schematic with one current transformer and one shunt. . . . . . . . . . . . 54

Figure 30. STPM01 with 3X charge pump DC-DC converter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

= 25 °C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

, R = 12 kΩ, TA = 25 °C . . . . . . . . . . . . . . . . . . . . . . . . . . 15

voltages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Doc ID 10853 Rev 8 5/60

Schematic diagram STPM01

1 Schematic diagram

Figure 1. Block diagram

6/60 Doc ID 10853 Rev 8

STPM01 Pin configuration

2 Pin configuration

Figure 2. Pin connections (top view)

Table 2. Pin description

Pin n° Symbol Type

1 MON P O Programmable output pin, see Ta bl e 5

2 MOP P O Programmable output pin, see Ta b l e 5

3 SCS D IN Digital input/output pin, see Ta b le 5

10 I

11 I

12 I

13 V

14 V

DDD

OTP

DDA

IP1

IN1

IP2

IN2

15 SYN D I/O Programmable input/output pin, see Ta bl e 5

16 CLKIN A IN Crystal oscillator input or resistor connection if RC oscillator is selected

17 CLKOUT A OUT Oscillator Output (RC or crystal)

18 SCL/NLC D I/O Programmable input/output pin, seeTa bl e 5

19 SDA/TD D I/O Programmable input/output pin, see Ta bl e 5

20 LED D O Programmable output pin, see Ta bl e 5

1. A: Analog, D: Digital, P: Power

(1)

Name and function

A OUT 1.5 V Output of internal low drop regulator which supplies the digital core

GND Ground

P IN Supply voltage

P INr Supply voltage for OTP cells

A OUT 3 V Output of internal low drop regulator which supplies the analog part

A IN Positive input of primary current channel

A IN Negative input of primary current channel

A IN Positive input of secondary current channel

A IN Negative input of secondary current channel

A IN Positive input of voltage channel

A IN Negative input of voltage channel

Doc ID 10853 Rev 8 7/60

Maximum ratings STPM01

3 Maximum ratings

Table 3. Absolute maximum ratings

Symbol Parameter Value Unit

OTP

DC Input voltage -0.3 to 6 V

Current on any pin (sink/source) ± 150 mA

Input voltage at digital pins (SCS, MOP, MON, SYN, SDATD, SCLNLC, LED)

Input voltage at analog pins (I

IP1

, I

IN1

, VIP, VIN) -0.7 to 0.7 V

IP2

IN2

-0.3 to V

+ 0.3 V

Input voltage at OTP pin -0.3 to 25 V

ESD Human body model (all pins) ± 3.5 kV

Operating ambient temperature - 40 to 85 °C

Junction temperature - 40 to 150 °C

Storage temperature range - 55 to 150 °C

STG

Note: Absolute maximum ratings are those values beyond which damage to the device may occur.

Functional operation under these condition is not implied.

Table 4. Thermal data

Symbol Parameter Value Unit

thJA

1. This value is referred to single-layer PCB, JEDEC standard test board.

Thermal resistance junction-ambient 114.5

(1)

°C/W

8/60 Doc ID 10853 Rev 8

STPM01 Functions

4 Functions

Table 5. Programmable pin functions

Programmable

MON Output for Stepper’s node (MB)

MOP Output for Stepper’s node (MA)

If APL=2 then LED provides high frequency pulses proportional to Active Energy with 50% duty cycle.

LED

SCLNLC

SDATD

SYN

SCS

If APL=3 then LED provides pulses proportional to Active Energy (internal signal AW). The number of pulses per kWh can be selected according to the value of KMOT configuration bit.

No-load indicator: when low, a no-load condition is detected

Tamper indicator: when low tamper condition is detected

Negative active power indicator: when low a negative active power condition is detected

Must be high to activate SCLNLC, SDATAD and SYN indications

Stand-alone mode

(APL register=2 or 3)

Peripheral mode

(APL register=0 or 1)

If APL=0 then Watchdog signal. If APL=1 then ΔΣ signal of current channel

If APL=0 then ZCR If APL=1 then ΔΣ signal of voltage channel

If APL=0 then LED can provide Active, Reactive or Apparent Energy according to value of KMOT configuration bit. If APL=1 then LED is connected to the MUX signal generated from the tamper detection circuit. When LED=low then the primary current channel is selected, if LED=high the secondary current channel is selected.

Used for SPI interface (see SPI interface section for details)

Doc ID 10853 Rev 8 9/60

Functions STPM01

Table 6. Internal signal description

Symbol Name Description

ZCR Zero crossing signal Provides positive pulse every time the line voltage crosses zero

AW Active energy Pulse frequency signal proportional to active energy

RW Reactive energy Pulse frequency signal proportional to reactive energy

SW Apparent energy Pulse frequency signal proportional to apparent energy

LIN Line frequency signal

BFR Base frequency range

Stepper motor signals Signal available in MOP and MON to drive a stepper motor

BIT Tamper flag

BIL No load condition

This signal is high when the voltage channel value is rising and it is low when the voltage channel is falling. Basically this signal is the sign of dv/dt.

This signal is high when either the voltage line frequency is outside the nominal band or the voltage register is below 64.

It is cleared when the voltage line frequency is inside the nominal band and the voltage register goes above 128.

This signal provides the information on the tamper status. If low no tamper is detected, when high a tamper condition has been detected. This signal is part of the status register but is also available on the SDATD pin when in standalone mode.

Provides information on the load condition. This signal is part of the status register but is also available on the SCLNLC pin when in standalone mode. BIL=1 no load condition, BIL=0 normal operation.

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STPM01 Electrical characteristics

5 Electrical characteristics

VCC = 5 V, TA = 25 °C, 100 nF to 1 uF between V and V

Table 7. Electrical characteristics

, 100 nF to 1 uF between VCC and VSS unless otherwise specified.

and VSS, 100 nF to 1 uF between V

DDA

Symbol Parameter Test conditions Min. Typ. Max. Unit

Energy measurement accuracy

Effective bandwidth Limited by digital filtering 5 400 Hz

Accuracy of active power

Accuracy of reactive power

Accuracy of apparent power Over 1 to 500 of dynamic range 0.1 %

Over 1 to 1000 of dynamic range

0.1 %

SNR Signal to noise ratio Over the entire bandwidth 52 db

rms

/50Hz

0.2 %

PSRR

Power supply DC rejection

Voltage signal: 200 mV Current signal: 10 mV

= 4.194 MHz

CLK

VCC=3.3V±10%, 5V±10%

PSRR

Power supply AC rejection

Voltage signal: 200 mV Current signal: 10 mV f

= 4.194 MHz

CLK

VCC=3.3V+0.2V

=5.0V+0.2V

rms

/50Hz

rms

/50Hz

rms

1@100Hz 1@100Hz

0.1 %

General section

DDD

Operating supply voltage 3.165 5.5 V

Supply current configuration

registers cleared or device

locked (TSTD=1)

Increase of supply current per configuration bit, during programming

ΔI

Increase of supply current per configuration bit with device locked

POR Power on reset on V

LINE

Analog supply voltage 2.85 3.0 3.15 V

DDA

Digital supply voltage 1.425 1.50 1.575 V

DDD

Oscillator clock frequency

CLK

Nominal line frequency 45 65 Hz

OTP programming voltage 14 20 V

OTP

4 MHz, V

= 5V 3 4

8 MHz, V

4 MHz, V

= 5V 5 6

= 5V 120

µA/bit

4 MHz, V

= 5V 2

2.5 V

MDIV bit = 0 4.000 4.194 MHz

MDIV bit = 1 8.000 8.192 MHz

Doc ID 10853 Rev 8 11/60

Electrical characteristics STPM01

Table 7. Electrical characteristics (continued)

Symbol Parameter Test conditions Min. Typ. Max. Unit

LATCH

OTP programming current per

OTP

bit

OTP programming time per bit 100 300 µs

OTP

Current injection latch-up immunity

Analog Inputs (I

ADC

LEAK

Maximum input signal levels

MAX

A/D Converter bandwidth 10 kHz

A/D Sampling frequency F

SPL

Amplifier offset ±20 mV

OFF

VIP, VIN Impedance

, V

ERR

IP1

Impedance

Current channels gain error ±10 %

Voltage channel leakage current -1 1 µA

Current channel leakage current

IP1

IN1

, I

, V

IN1

IP2

2.5 mA

300 mA

, I

, VIP, VIN)

IP2

IN2

Voltage channel -0.3 0.3 V

Gain 8X -0.15 0.15

Current channels

Gain 16X -0.075 0.075

Gain 24X -0.05 0.05

Gain 32X -0.035 0.035

/4 Hz

CLK

, V

IN2

Over the total operating voltage range

100 400 kΩ

100 kΩ

Channel disabled (PST=0 to 3; CH2 disabled if C disabled if C

SEL

=0; CH1

SEL

=1) or device off

-1 1 µA

Input enabled -10 10

Digital I/O Characteristics (SDA, CLKIN, CLKOUT, SCS, SYN, LED)

SDA, SCS, SYN, LED 0.75V

Input high voltage

CLKIN 1.5

SDA, SCS, SYN, LED 0.25V

Input low voltage

Output high voltage IO = -2mA VCC-0.4 V

Output low voltage IO = +2mA 0.4 V

Pull up current 15 µA

Transition time C

CLKIN 0.8

= 50pF 10 ns

LOAD

Power I/O Characteristics (MOP, MON)

Output high voltage IO = -14mA VCC-0.5 V

Output low voltage IO = +14mA 0.5 V

Transition time C

= 50pF 5 10 ns

LOAD

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STPM01 Electrical characteristics

Table 7. Electrical characteristics (continued)

Symbol Parameter Test conditions Min. Typ. Max. Unit

Crystal oscillator (see circuit Figure 20)

Input current on CLKIN 1 µA

External resistor 1 4 MΩ

External capacitors 22 pF

Nominal output frequency

CLK

RC oscillator (see circuit Figure 20)

44.194 MHz

88.192

CLKIN

Settling current

Settling resistor 12 kΩ

SET

Frequency jitter 1 ns

JIT

On chip reference voltage

Reference voltage 1.23 V

REF

Reference accuracy ±1 %

Temperature coefficient After calibration 30 50

SPI interface timing

SCLKr

SCLKw

Data read speed 32 MHz

Data write speed 100 kHz

Data setup time 20 ns

Data hold time 0 ns

Data driver on time 20 ns

Data driver off time 20 ns

OFF

SYN active width 2/f

SYN

CLK

= 4 MHz

40 60 µA

ppm/

°C

CLK

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Terminology STPM01

6 Terminology

6.1 Measurement error

The error associated with the energy measurement made by the STPM01 is defined as:

Percentage error = [STPM01 (reading) - true energy] / true energy

6.2 ADC offset error

This is the error due to the DC component associated with the analog inputs of the A/D converters. Due to the internal automatic DC offset cancellation the STPM01 measurement is not affected by DC components in voltage and current channel. The DC offset cancellation is implemented in the DSP.

6.3 Gain error

The gain error is gain due to the signal channel gain amplifiers. This is the difference between the measured ADC code and the ideal output code. The difference is expressed as percentage of the ideal code.

6.4 Power supply DC and AC rejection

This parameter quantifies the STPM01 measurement error as a percentage of reading when the power supplies are varied. For the PSRRAC measurement, a reading at two nominal supplies voltages (3.3 and 5 V) is taken. A second reading is obtained with the same input signal levels when an ac (200 mV error introduced by this ac signal is expressed as a percentage of reading.

For the PSRRDC measurement, a reading at two nominal supplies voltages (3.3 and 5V) is taken. A second reading is obtained with the same input signal levels when the supplies are varied ± 10 %. Any error introduced is again expressed as a percentage of the reading.

/100 Hz) signal is introduced onto the supplies. Any

RMS

6.5 Conventions

The lowest analog and digital power supply voltage is named VSS which represent the system ground (GND). All voltage specifications for digital input/output pins are referred to GND.

Positive currents flow into a pin. Sinking current means that the current is flowing into the pin and then it is positive. Sourcing current means that the current is flowing out of the pin and then it is negative.

Timing specifications of signal treated by a digital control part are relative to CLKOUT. This signal is provided from the crystal oscillator of 4.194 MHz nominal frequency or from the internal RC oscillator, eventually an external source of 4.194 MHz or 8.192 MHz can be used.

Timing specifications of signals of the SPI interface are relative to the SCLNLC, there is no direct relationship between the clock (SCLNLC) of the SPI interface and the clock of the DSP block. A positive logic convention is used in all equations.

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STPM01 Typical performance characteristics

7 Typical performance characteristics

Figure 3. Supply current vs. supply voltage,

= 25 °C

Figure 5. RC oscillator: frequency jitter vs.

temperature

Figure 4. RC oscillator frequency vs. V

R = 12 kΩ, T

= 25 °C

Figure 6. Analog voltage regulator: line - load

regulation

Figure 7. Digital voltage regulator: line - load

regulation

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Figure 8. Voltage channel linearity at

different V

voltages

Typical performance characteristics STPM01

Figure 9. Power supply AC rejection vs. V

Figure 11. Error over dynamic range gain

dependence

Figure 10. Power supply DC rejection vs. V

Figure 12. Primary current channel linearity at

different V

Figure 13. Gain response of ΔΣ AD converters

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STPM01 Theory of operation

8 Theory of operation

8.1 General operation description

The STPM01 is able to perform active, reactive and apparent energy measurements, RMS and instantaneous values for voltage and current, line frequency information.

Most of the functions are fully programmable using internal configuration bits accessible through SPI interface. The most important configuration bits are the two application bits (APL - see Ta bl e 1 6 for configuration register). Using these bits the STPM01 can be programmed as peripheral (APL = 0 or APL = 1) in microcontroller based meter systems or as standalone meter device (APL = 2 or APL = 3).

In standalone mode, the STPM01 is able to drive a stepper motor with the MOP and MON pins, while some of the SPI pins (see Ta b le 5 ) are used to provide information on tamper, no load and negative power.

In peripheral mode, due to the fact that the stepper motor is not used, the MOP and MON pins are used to provide different information (see Ta bl e 5 ), while the SPI pins are used to communicate with the microcontroller.

The STPM01 includes internal registers that hold the useful information for the meter system. Two kinds of active energy are available: the total active energy that includes all harmonic content called type 0 and the active energy limited to the 1st harmonic called type

1. This last energy value is obtained filtering the type 0 active energy. The resolution of both the two active energies is 20-bit. Reactive and Apparent energies are also available with a 20-bit resolution.

STPM01 provides also the RMS values of voltage and current. Due to the modest dynamic variation of the voltage, the RMS value is stored with a resolution of 11 bit. While the RMS current value has a resolution of 16 bit. The momentary sampled value of voltage and current are available also with a resolution of 11 and 16 bit respectively. The line frequency value is stored with a resolution of 14 bits.

Due to the proprietary energy computation algorithm, STPM01 calibration is very easy and fast allowing calibration in only one point over the whole current range. The calibration parameters are stored permanently in the OTP (one time programmable) cells, preventing calibration tampering.

8.2 Analog inputs

Input amplifiers

The STPM01 has one fully differential voltage input channel and two 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.

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 are then 8, 16, 24, 32. The gain selections are made by writing to the gain register and it can be different for the two current channels. In case the tamper function is not used, the secondary current can be disabled.

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Theory of operation STPM01

The maximum differential input voltage is dependent on the selected gain according to the following table.

Table 8. Gain of voltage and current channels

Voltage channels Current channels

Gain Max Input voltage (V) Gain Max input voltage (V)

8X ±0.15

4 ±0.30

16X ±0.075

24X ±0.05

32X ±0.035

The gain register is included in the device configuration register with the address names PST and ADDG. The table below shows the gain configuration according to the register values:

Table 9. Configuration of current sensors

Primary Secondary Configuration Bits

Gain Sensor Gain Sensor PST (3 bits) ADDG (1 bit)

16 01

24 10

32 11

8CT 2 X

32 Shunt 3 X

16 16 4 1

24 24 5 0

32 32 5 1

8 32 Shunt 7 X

Rogowsky Coil

Disabled (No Tamper)

Rogowsky Coil

8CT6 X

Note: If the device is used in configuration PST = 7 (primary channel with CT, secondary channel

with Shunt), the shunt Ks must always be equal to one fourth of the current transformer Ks.

Both the voltage and current channels implement an active offset correction architecture which gives the benefit to avoid 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 make possible avoiding any manual offset calibration on the analog inputs.

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