ST AN2317 APPLICATION NOTE
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 (V
and I
This application note describes the STPM01 external circuits which are comprised of:
● a cry sta l os c illator,
● 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.
), instantaneous, and harmonic voltage and current.
RMS
AN2317
RMS
April 2006 Rev 1 1/27
www.st.com
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
● a
● a
● a
Anti-aliasing Filter on page 11
Voltage Sensing Circuit on page 15
Capacitive Power Supply Circuit on page 18
Clock Generation on page 24
,
,
,
, and
(RC oscillator, quartz, or external clock).
4/27
AN2317 - Application External Circuit Design
Figure 1. ST PM01 External Circuit Sc hema t ic s
D2
12121212
1
33.0R
R22
R21
2
22
Q3
3
BC8578
112
C3
C2
1.0N
1.0N
221
CURRENT SENSING
W3
VODNIK
W4
VODNIK
1
1K
2
11
Q4
BC8578
3
12
1
C16
2
R23
47K
21
C6
1MYC71MY
12
2
D1
1N4148
1
VDD
4121
TR1
12
E4622/X503
4121
TR2
12
E4622/X503
1
1
F
1
V4
510V
2
12
N
1
W6
1MY
VODNIK
1
W5
VODNIK
1
2
C5
C4
1.0N
1
R2
12
1.0k
R5
30.1R
R1
12 12
1.0k
ANTI-ALIASING FILTER
R3
12
1.0k
R6
30.1R
R4
12
1.0k
12
L6
220MYH
L3
220MYH
R24
21 21 2
82R
1
C14
1.0N
2
1
1N4148D31N4148D41N4148D51N4148
C17
2
D6
1MY
VDDA
C8
10N
10N
1
SRD 200mcd
2
1
R20
2.4K
2
20
1
2
4
5
6
8
7
9
10
1
C18
2
U1
STPM01E
LED
MON
MOP
VDD
VSS
VCC
VDDA
VOIP
IIP1
IIN1
10N
SDA
SCL
SCS
SYN
CLKOUT
CLKIN
VIN
IIN2
IIP2
1
C19
2
D7 SRD 200mcd
19
18
3
15
17
16
14
13
VIP
12
11
10N
2
1
12121
R19
2.4K
R13
2M
10N
12
2M
C11
1
2
C9
R14
4.7my
R8
261K
12
12
261K
R10
261K
R7
12
475R
R11
12
R9
150K
C20
12
220N
C1
470N
D11
21
1
DIF60
D10
DIF60
2
C15
+
VDD
121
D12
1000M
2
VDD
2
1
D8 SRD 200mcd
D9 SRD 200mcd
R18
R17
2.4K
C10
1
10N
R12
12
2.21k
W1
VODNIK
1
W2
5.6V
VODNIK
1
PI
G08 10-2V
1
3
5
VDDA
7
2
9
1
2.4K
2
12
2
1
4194.304kHz
C12
2
CRYSTAL OR RTC
OSCILLATOR
2
VOLTAGE SENSING
CAPACITIVE POWER SUPPLY
15P
2
4
6
8
10
R15
1M
Y1
1
1
C13
2
AI12296
SBG
SDA
SCL
SCS
SYN
15P
5/27
External Circuit Design AN2317 - Application
1.1 Current Sensing Circuit
The STPM01 has two external current sensing circuits (see
1. Primar y channe l, and
2. Secondary channel.
1.1.1 Primary Current Sensing
The primary channel uses a current transformer to couple the mains current (see
The Burden resistor is used to produce a voltage between V
filter (LPF) is used to filter out the high frequency interference and has little influence on the
voltage drop between V
Figure 2. Pr imary Curr ent S ens i ng Ci rcui t
I1
IN1
I2
and V
.
IP1
Burden Resistor LPF
R2
12
1.0k
6.8R
R1
12
1.0k
R23
1R
1
R25
2
1
2
Figure 1 on page 5
IN1
and V
1
C9
2
. The Low-pass
IP1
VIN1
+
U0
10N
–
VIP1
AI12297
):
Figure 2
).
6/27
AN2317 - Application External Circuit Design
Primary current sensing is calculated as follows:
Equation 1
N
1
------ -
I
2
⋅=
I
1
N
2
Equation 2
U
0UAI2
R23R25⋅
------- ----------- ----------- ---
⋅
+
R
23R25
N
------ --
N
1
2
I
⋅⋅==≈
1
R23R25⋅
------ ----------- ----------- ----
+
R
23R25
Assuming I
, the calculation will proceed as:
1PEAK
Equation 3
I
1PEAK
-----------------I
2PEAK
N
2000
2
=
=
------ -
------------ -
N
1
1
Equation 4
I
I
2PEAK
1PEAK
------------------ 3 m A==
2000
Equation 5
R23R25⋅
U
0PEAKUAPEAKI2PEAK
The maximum differential input voltage between V
------------------------- -
⋅ 2.6mV===
+
R
23R25
and V
IN1
is dependent on the
IP1
Programmable Gain Amplifier (PGA) selection. For the purposes of this application, use 8x
as the gain value, then U
0PEAK
= 0.15V.
Equation 6
U
APEAK
U
0PEAK
0.15V==
Equation 7
Equation 8
Equation 9
I
2PEAK
I
1PEAK
I
1RMS
R
+
23R25
2000I
I
1PEAK
------------------
------------------------- -
⋅ 172mA==
⋅
R
23R25
2PEAK
344A==
243A==
U
APEAK
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).
2
Use insulated 4mm
copper wire.
4. The neutral line current wire must be placed through the current transformer TR2 hole.
2
Use insulated 4mm
copper wire.
Figure 3. Current Sense Transformer-to-Power Line Connections
Neutral Line
Hot Line
FN
TR2 TR1
Neutral Load
Hot Load
W6
W5
Comp side
*
P1
AI12298
8/27
AN2317 - Application External Circuit Design
1.1.2 Secondary current sens ing
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 conside rations 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:
2
20A()
● The higher power dissipation may make it difficult to manage the thermal issues.
420μΩ 168mW=×
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 = 220V
RMS
,
– Ib = 2A, and
– Shunt resistance = 420µΩ.
The remaining design elements calculated from these values are as follows:
– Voltage across shunt:
2A 420μΩ 0. 00084 V=×
– Mains power dissipation:
– Error:
1.68 10
3–
× 0.44 103–× 100percent 0.0004percent=×⁄
220V 2A 0.44kW=×
9/27
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