ST AN2317 APPLICATION NOTE

AN2317

Application Note

STPM01 Programmable, Single-Phase

Energy Metering IC External Circuits

Introduction

The STPM01 is implemented in an advanced 0.35µm BCD6 technology. It is designed for active, reactive, and apparent energy measurement, including Root Mean Square (VRMS and I RMS), instantaneous, and harmonic voltage and current.

This application note describes the STPM01 external circuits which are comprised of:

●a crystal oscillator,

●a power supply circuit,

●a voltage sensing circuit, and

●two current sensing circuits.

Note:

This document should be used in conjunction with the STPM01 datasheet.

April 2006

Rev 1

1/27

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Contents	AN2317 - Application

Contents

1	External Circuit Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .			. 4
	1.1	Current Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
		1.1.1	Primary Current Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 6
		1.1.2	Secondary current sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. 9
	1.2	Anti-aliasing Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		11
	1.3	Voltage Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		15
	1.4	Crosstalk Cancellation Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		17
	1.5	Capacitive Power Supply Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		18

1.5.1 Varistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

1.5.2 Capacitive Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1.5.3 EMC Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

	1.6	Clock Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	24
2	Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		26

2/27

AN2317 - Application	List of Figures

List of Figures

Figure 1. STPM01 External Circuit Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 2. Primary Current Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Figure 3. Current Sense Transformer-to-Power Line Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Figure 4. Shunt Module-to-Power Line Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Figure 5. Anti-aliasing Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 6. Anti-aliasing Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Figure 7. Anti-aliasing Filter Magnitude Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Figure 8. Anti-aliasing Filter Phase Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Figure 9. Voltage Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Figure 10. Crosstalk Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Figure 11. Capacitive power supply (with EMC Filter) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Figure 12. Capacitive Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Figure 13. Internal RC Recommended Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 14. Quartz Recommended Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Figure 15. External Clock Source Recommended Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3/27

External Circuit Design	AN2317 - Application

1 External Circuit Design

Figure 1 on page 5 shows an implementation example of the STPM01 in a simple Stepper Counter Connector design. The main external circuits include:

●a Current Sensing Circuit,

●an Anti-aliasing Filter on page 11,

●a Voltage Sensing Circuit on page 15,

●a Capacitive Power Supply Circuit on page 18, and

●a Clock Generation on page 24 (RC oscillator, quartz, or external clock).

4/27

AN2317 - Application	External Circuit Design

Figure 1. STPM01 External Circuit Schematics

															2	D2	1		2	D3		1	2		D4	1	2		D5		1
			1				1			1					1N4148				1	1N4148			1	1N4148			1	1N4148
	R21		33.0R		R22		1K		C16	1MY		W6					C17		10N			C18	10N			C19	10N
											VODNIK
												1
			2				2			2									2				2				2						PI
			1				1					W5																					G08 10-2V		2
				2	2						VODNIK																						1
							Q4																										3
Q3	BC8578											1																							4
							BC8578
																																	5		6
			3				31	R23																						VDD
									2																								VDDA 7		8
								47K												SRD 200mcd	1					SRD 200mcd		2	SRD 200mcd		2		9		10
																																	2
			1		1			2		2		1			2				D6		2							1			1SRD200mcd		1
C2			1.0N	C3	1.0N	C6		1MY	C7	1MY	C4	1.0N	C5		1MY						1					D7		1	D8		1D9		1
																				R20	2.4K						R19	2.4K		R18	2.4K	R17	2.4K
			2		2			1		1		2			1								U1
																					2							2			2		2				SBG
								2															STPM01E
						1N4148															20					19											SDA
								D1														LED			SDA
																					1					18											SCL
																						MON			SCL
																					2					3											SCS
																						MOP			SCS
								1 VDD													4					15											SYN
																						VDD			SYN
																					5					17
																						VSS		CLKOUT
																					6					16
																						VCC		CLKIN
																			VDDA		8					14
																						VDDA			VIN
																					7					13
																						VOIP			VIP
																					9					12
																						IIP1			IIN2
																					10					11								1	R15	2
															R2							IIN1			IIP2
														1		2
																																			1M
								E4622/X503	4				1		1.0k		1																	2	Y1	1
												R5	30.1R			C8		10N
									TR1																									14194.304kHz			1
									1				2 1		R1	2	2				1	R13		2									C12	15P		C13	15P
															1.0k							2M
																																		2			2
											ANTI-ALIASING FILTER
														1	R3	2
								E4622/X503	4				1		1.0k		1
									TR2			R6	30.1R			C9		10N			1	R14		2									CRYSTAL OR RTC
																						2M												OSCILLATOR
									1				2	1	R4		2
																2
		CURRENT SENSING													1.0k												C11					C10
																										1			2		1		2
																											4.7my					10N	VOLTAGE SENSING
															1	R8	2		1	R9	2	1	R10		2	1	R7		2
															261K				261K				261K				475R
																										1	R11		2		1	R12	2
																											150K					2.21k
																		1	C20 2
						W3													220N								VDD			W1
					VODNIK						L6								C1 2				D11							VODNIK
										1		2			1 R24 2			1				2			1
							1	F																						1			CAPACITIVE POWER SUPPLY
									1	220MYH				1	82R				470N			1	DIF60			1		1
						W4		V4		510V		C14			1.0N					D10		DIF60			C15 +	1000M	D12		5.6V	W2
					VODNIK																									VODNIK
								N	2	1	L3	2		2								2				2		2
							1																							1
										220MYH
																																				AI12296
																																					5/27

External Circuit Design	AN2317 - Application

1.1Current Sensing Circuit

The STPM01 has two external current sensing circuits (see Figure 1 on page 5):

1.Primary channel, and

2.Secondary channel.

1.1.1Primary Current Sensing

The primary channel uses a current transformer to couple the mains current (see Figure 2).

The Burden resistor is used to produce a voltage between VIN1 and VIP1. The Low-pass filter (LPF) is used to filter out the high frequency interference and has little influence on the voltage drop between VIN1 and VIP1.

Figure 2. Primary Current Sensing Circuit

I1	I2	Burden Resistor						LPF
						1	R2	2
			1		1		1.0k		1
		R23	1R	R25	6.8R			C9	10N
			2		2	1	R1	2	2
							1.0k

VIN1

+

U0

–

VIP1

AI12297

6/27

AN2317 - Application	External Circuit Design

Primary current sensing is calculated as follows:

Equation 1

I2

=

N1

I1

------

N2

Equation 2

R23 R25

R23 R25

U0 ≈ UA

= I2

=

N1

I1

R

+ R

N

R

+ R

-------------------------------

--------

-------------------------------

23

25

2

23

25

Assuming I1PEAK, the calculation will proceed as:

Equation 3

I1PEAK

=

N2

=

2000

I------------------2PEAK

N------1

------------

1

Equation 4

I2PEAK =

I1PEAK

= 3mA

------------------2000

Equation 5

R23 R25

U0PEAK = UAPEAK = I2PEAK

= 2.6mV

R-------------------

23

+ R------

25

The maximum differential input voltage between VIN1 and VIP1 is dependent on the Programmable Gain Amplifier (PGA) selection. For the purposes of this application, use 8x as the gain value, then U0PEAK = 0.15V.

Equation 6

UAPEAK = U0PEAK = 0.15V

Equation 7

I2PEAK	= UAPEAK	R23	+ R25
		------------------------- = 172mA
		R23	R25

Equation 8

I1PEAK = 2000I2 PEAK = 344A

Equation 9

I1PEAK

I1RMS = ------------------ = 243A

2

7/27

External Circuit Design	AN2317 - Application

The primary current sensing circuit can be connected to mains as follows (see Figure 3):

1.The hot line voltage wire must be connected to pin F of the module.

Normally, this wire is also connected to the hot line current wire. However, during production or to verify phases, this wire may be connected to some other line voltage source.

2.The neutral line voltage wire must be connected to pin N of the module. This wire is also connected to the neutral line current wire.

3.The hot line current wire must be placed through the current transformer TR1 hole (becoming the hot load wire).

Use insulated 4mm2 copper wire.

4.The neutral line current wire must be placed through the current transformer TR2 hole. Use insulated 4mm2 copper wire.

Figure 3. Current Sense Transformer-to-Power Line Connections

Neutral Line			Neutral Load
Hot Line			Hot Load
F	N	TR2	TR1
			W6
			W5
		*	P1
	Comp side
			AI12298

8/27

AN2317 - Application	External Circuit Design

1.1.2Secondary current sensing

The secondary channel uses shunt resistor structure (see Figure 4). The 420µW shunt resistor is used to maximize the use of the dynamic range of the current sensing circuit. However, there are some important considerations when selecting a shunt structure for energy metering applications.

●The power dissipation in the shunt must be minimized.

The maximum rated current for this design element is 20A, so the maximum power dissipated in the shunt is calculated as follows:

(20A)2 × 420μ Ω = 168mW

●The higher power dissipation may make it difficult to manage the thermal issues.

Although the shunt is manufactured from manganin material, which is an alloy with a low thermal resistance, an apparent error may occur when it reaches a high temperature.

●The shunt should be able to resist the shortage of the phase circuit. This reduces the shunt resistance is much as possible.

The design values used are:

–Mains voltage = 220VRMS,

–Ib = 2A, and

–Shunt resistance = 420µΩ.

The remaining design elements calculated from these values are as follows:

–Voltage across shunt:

2A × 420μΩ = 0.00084V

–Mains power dissipation:

220V × 2A = 0.44kW

–Error:

1.68 × 10–3 ⁄ 0.44 × 10–3 × 100percent = 0.0004percent

9/27