AN2317 Application Note
STPM01 Programmable, Single-Phase Energy Metering IC External Circuits
Introduction
The STPM01 is implemented in an advanced 0.35m BCD6 technology. It is designed for active, reactive, and apparent energy measurement, including Root Mean Square (V RMS 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.
Not e:
This document should be used in conjunction with the STPM01 datasheet.
April 2006
Rev 1
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Contents
AN2317 - Application
Contents
1 External Circuit Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Current Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1. 1. 1 1. 1. 2 Pr imar y Current Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Secondar y current sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2 1.3 1.4 1.5
Anti-aliasing Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Voltage Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Crosstalk Cancellation Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Capacitive Power Supply Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1. 5. 1 1. 5. 2 1. 5. 3 Var istor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Capacitive Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 EMC Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.6
Clock Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2/27
AN2317 - Application
List of Figures
List of Figures
Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. STPM01 External Circuit Schematics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Primary Current Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Current Sense Transformer-to-Power Line Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Shunt Module-to-Power Line Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Anti-aliasing Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Anti-aliasing Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Anti-aliasing Filter Magnitude Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Anti-aliasing Filter Phase Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Voltage Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Crosstalk Network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Capacitive power supply (with EMC Filter) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Capacitive Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Internal RC Recommended Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Quartz Recommended Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 External Clock Source Recommended Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
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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 Figure 1.
1 33.0R R21 R22
External Circuit Design STPM01 External Circuit Schematics
2 1 C16 1K 1 1MY W6 VODNIK 1 W5 VODNIK 1 VDD D6 SRD 200mcd D7 SRD 200mcd D8 SRD 200mcd 1 2 2 D9 SRD 200mcd 2 D2 1N4148 C17 1 2 D3 1 2 D4 1 2 D5 1 1 1N4148 C18 10N 1 1N4148 C19 10N 1 1N4148 10N 2
1 3 5
2 1 2 Q3 BC8578 3 2
2 1 Q4 BC8578 31 R23 2 47K
2
2
2
PI G08 10-2V
2 4 6 8 10
VDDA 7
9
1 1.0N C3 C2
1 1.0N C6
2 1MY C7
2 1MY C4
1 1.0N C5
2 1MY
2 1 2.4K
1 1 R19
1 1 R18
1 1 2.4K 2 R17
2.4K
2
2 1N4148
1 2
1
2
1
2
20
U1 STPM01E
1 2 4 5 6 LED MON MOP VDD VCC VDDA VOIP IIP1 IIN1 SDA SCL SCS SYN CLKIN VIN VIP IIN2 IIP2 19 18 3 15 17 16 14 13 12 11
2
2
2.4K
R20
1 VDD
SBG SDA SCL SCS SYN
D1
VSS CLKOUT
VDDA
8 7 9 10
1 R15 2 1M Y1
1 E4622/X503 4 TR1 1 R5 1 30.1R
R2 1.0k
2 1 10N C8 2
1
1 4194.304kHz 1 C12 15P 1 2M 15P 2 R13 2 C13
21
R1 1.0k
2
2
2
ANTI-ALIASING FILTER
1 E4622/X503 4 TR2 1 R6 1 30.1R R3 1.0k C9 2 1 10N 1 R14 2 2M
CRYSTAL OR RTC OSCILLATOR
21
R4 1.0k
2
2 C11 4.7my C10 10N 2 1 R12 2 2.21k
CURRENT SENSING
1
2
1
2
VOLTAGE SENSING
1
R8 261K
2
1
R9 261K
2
1 R10 2 261K
1
R7 475R
1 R11 2 150K C20 220N C1 470N D10
1 W3 VODNIK 1
2 VDD 1 1 1000M D12 C15 + 1 5.6V W2 VODNIK 1 1 W1 VODNIK
F 1 510V
1
L6
2 1
1 R24 2 82R 1.0N
1
2
2 1 DIF60
D11 DIF60
CAPACITIVE POWER SUPPLY
220MYH C14 L3
W4 VODNIK 1
V4 2
N
1
2
2
2
2
2
220MYH
AI12296
5/27
External Circuit Design
AN2317 - Application
1.1
Current Sensing Circuit
The STPM01 has two external current sensing circuits (see Figure 1 on page 5): 1. 2. Primar y channel, and Secondary channel.
1.1.1
Primary 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 1 1 R23 R25 1R 1 6.8R R2 1.0k C9 2 1 10N + U0 VIP1 LPF VIN1
2
2
1
R1 1.0k
2
2
AI12297
6/27
AN2317 - Application Pr imar y current sensing is calculated as follows: Equation 1 N1 I 2 = ------ I 1 N2 Equation 2
External Circuit Design
N1 R 23 R 25 R 23 R 25 U 0 U A = I 2 ------------------------------- = -------- I 1 ------------------------------N2 R 23 + R 25 R 23 + R 25 Assuming I1PEAK, the calculation will proceed as: Equation 3 I 1 P E A K N 2 200 0 ------------------ = ------ = -----------I2 P E AK N 1 1 Equation 4 I 1 P EA K I 2 P E A K = ------------------ = 3 m A 2000 Equation 5 R 23 R 25 U 0 P E A K = U A P E A K = I 2 P E A K ------------------------- = 2.6 m V R +R
23 25
The maximum differential input voltage between VIN1 and V IP1 is dependent on the 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 A P E A K = U 0 P E A K = 0.15 V Equation 7 R 23 + R 25 I 2 P E A K = U A P E A K ------------------------- = 172 m A R R
23 25
Equation 8 I 1 P E A K = 20 00 I 2 P E A K = 344 A Equation 9 I1 P E A K I 1 R M S = ------------------ = 243 A 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. Nor mally, 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. 3. 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. 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 Hot Line F N TR2 TR1 W6 W5 Neutral Load Hot Load
* Comp side
P1
AI12298
8/27
AN2317 - Application
External Circuit Design
1.1.2
Secondary current sensing
The secondary channel uses shunt resistor structure (see Figure 4). The 420W 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: ( 20 A ) × 420 = 168 m W
2
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 = 220V RMS, Ib = 2A, and Shunt resistance = 420. Voltage across shunt: 2 A × 420 = 0. 0008 4 V Mains power dissipation: 220 V × 2 A = 0.44 k W Error : 1.68 × 10
3
The remaining design elements calculated from these values are as follows:
/ 0. 44 × 10
3
× 100 p e r c e n t = 0.0004 p e r c e n t
9/27
External Circuit Design
AN2317 - Application
The secondary current sensing circuit can be connected to the mains as shown in Figure 4: 1. The hot line voltage wire must be connected to pin N of the module. Nor mally, 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 F of the module. This wire is also connected to the neutral line current wire, which passes by the module. 3. The hot line current wire must be connected to the Shunt pole which is close to pin N of the module. Use insulated 4mm2 copper wire. 4. The hot load current wire must be connected to the Shunt pole which is close to the edge of the module. Use insulated 4mm2 copper wire. Figure 4. Shunt Module-to-Power Line Connections
Neutral Hot Line F N Shunt W6 W5 LED NLC TPR DIR
AI12299
Hot Load
* Comp side
P1
10/27
AN2317 - Application
External Circuit Design
1.2
Anti-aliasing Filter
The anti-aliasing filter (Figure 5) is a low-pass filter. It reduces high frequency levels which may cause distortion due to the sampling (aliasing) that occurs before the analog inputs of an analog-to-digital converter (ADC) are introduced into the application (see Figure 6). Filtering is easily implemented with a resistor-capacitor (RC) single-pole circuit which obtains an attenuation of 20dB/dec. Figure 5. Anti-aliasing Filter
R UO
C UI R
C
AI12900
Figure 6.
Anti-aliasing Effect
Image Frequencies
0
2
450 Frequency - kHz
900
AI12901
11/27
External Circuit Design
AN2317 - Application
The anti-aliasing filter magnitude and phase response can be calculated as follows: Equation 10 1 -------UO j c 1 A u = ------- = ------------------- = -----------------------1 1 + jRC UI R + -------jc
Not e:
The cutoff frequency is expressed as: 1 1 f p = --------- = --------------2 2 R C
So Equation 10 can be changed to: Equation 11 1 1 A u = ------------------- = ------------------f f 1 + j --1 + j --fp fp Equation 12 1 A u = ---------------------f2 1 + --- f p The phase is expressed as: Equation 13 f = a r c tan --fp In the module: R = 2 · 103K and C = 10nF, so then 1 f p = --------------- = 7961.8 H z 2R C
12/27
AN2317 - Application
External Circuit Design
According to Equation 12 and Equation 13 on page 12, the filter's magnitude and phase response can be seen in Figure 7 and Figure 8 on page 14.
When f = 50Hz:
Equation 14 = 0.35 and Equation 15 Au 1
When f = 60Hz:
Equation 16 = 0.43 and Equation 17 Au 1 Assume that the current lags the voltage by a phase angle, . After an anti-aliasing filter, a phase error () is introduced into the STPM01. The power factor (PF) error is calculated as: Equation 18 cos cos ( + ) e r r o r P F = ---------------------------------------------- 100 p e r c e n t c os When, = 60 (PF = 0.5), and f = 50Hz, according to Equation 14, a phase error, = 0.35 has occurred: Equation 19 cos ( 60 ) cos ( 60 0.35 ) e r r o r P F = ---------------------------------------------------------------------------------- 100 p e r c e n t = 1 p e r c e n t cos ( 60 )
This indicates that even a small phase error will translate into a significant measurement error at a low power factor. Thus correct phase matching is required in this situation.
13/27
External Circuit Design Figure 7. Anti-aliasing Filter Magnitude Response
0
AN2317 - Application
Decibels (dB)
20
40
60
10
100
1000 10000 Frequency (Hz)
10 0 0
10 0 00
AI12902
Figure 8.
Anti-aliasing Filter Phase Response
0 20 Degrees () 40 60 80 100 10 100 1000 10000 Frequency (Hz) 10 0 0 10 0 00
AI12903
14/27
AN2317 - Application
External Circuit Design
1.3
Voltage Sensing Circuit
The STPM01 normally uses a resistor divider as voltage input channel (see Figure 9). The 783k resistor is separated into three 261k, in-series resistors (see Figure 1 on page 5), which ensure that a high voltage transient will not bypass the resistor. These three resistors also reduce the potential across the resistors, thereby decreasing the possibility of arcing. The following resistors are used as the resistor divider when the mains voltage is present:
R` = 783K, and R5=475.
C11 and (R 19+ R15) create a filter which prevents Electromagnetic Interference (EMI) created by the circuit from migrating onto the Line or Neutral busses (see Equation 20 through Equation 24 on page 16). Figure 9. Voltage Sensing Circuit
R' V1 783k R5 475 Z2 R19 42.2k C11 22n R6 475 R' 783k
AI12904
Z1
L2 1m
R15 100 V2
15/27
External Circuit Design Equation 20 Z 1 = ( R 19 + R 15 ) = 42.3 K Equation 21 ( R 5 + R6 ) Z 1 Z 2 = ------------------------------------ = 930 R 5 + R6 + Z 1
AN2317 - Application
Equation 22 Z ----2 = 110 2 V , U 1 = 0.046 V V 2 U 1 = U 2 = --------------------- V m a i n s = m a i n s 2R + Z2 V m a i n s = 220 2 V , U 1 = 0.092 V
Equation 23 Z2 ----= 110 2 V , U 0 = 0. 092 V V 2 U 0 = U 1 U 2 = ------------------ V m a i n s = m a i n s Z2 V m a i n s = 220 2 V , U 0 = 0. 185 V R + ----- 2 Z1 has little influence on the U0, thus: Equation 24 R5 U 0 ------------------R + R5
Not e:
For a specific U 0, choose an appropriate combination of resistors (R5 and R') to get that particular U 0 value.
16/27
AN2317 - Application
External Circuit Design
1.4
Crosstalk Cancellation Network
The voltage front end handles voltages of considerable amplitude, which makes it a potential source of noise. Disturbances are readily emitted into current measurement circuitry where it will interfere with the actual signal to be measured. Typically, this shows as a non-linear error at small signal amplitudes and non-unity power factors. At unity power factor, voltage and current signals are in phase and crosstalk between voltage and current channels merely appears as a gain error, which can be calibrated. When voltage and current are not in phase, crosstalk will have a non-linear effect on the measurements, which cannot be calibrated. Crosstalk is minimized by means of good PCB planning and the proper use of filter components in the crosstalk network. Recommended filter components are shown in Figure 10. The network subtracts a signal proportional to the voltage input from the current input. This prevents crosstalking within the STPM01. The signal subtraction is calculated in Equation 25 and Equation 26. Equation 25 R 15 R 15 V R 15 = ---------------------------- V V C I ---------- V V C I R 1 9 + R 15 R 19 Equation 26 6 R 1 R 15 R1 R1 V C C I = ------------------------- V R 15 ---------- V R 15 = ---------- ---------- V V C I 1.18 e V V C I R 2 1 R 19 R 21 + R 1 R 21
Not e:
This network must be applied to every STPM01 design, from the voltage channel to each current channel.
Figure 10. Crosstalk Network
+ R19 42.2k VVCI Voltage Channel Input R21 2M R15 100 R1 1k VCCI Current Channel Input +
AI12908
17/27
External Circuit Design
AN2317 - Application
1.5
Capacitive Power Supply Circuit
The capacitive power supply circuit is shown in Figure 10 and includes:
a varistor, the capacitive power supply, and the Electromagnetic Compatibility (EMC) filter.
Figure 11. Capacitive power supply (with EMC Filter)
Transient Protection LINE Filter 1 L1 220m Current Limiter R1 82R Voltage Divider C2 470n Filter 2 D1 VDD DIF60 2 RV1 510V C1 1n D2 DIF60 C3 1000m D3 5.1V 1 L2 220m
NEUTRAL
GND
AI12909
1.5.1
Varistor
The varistor is a surge protection device that is connected directly across the AC input. When a power surge or voltage spike exceeding a specified voltage (varistor voltage) is sensed, the varistor's resistance rapidly decreases, creating an instant shunt path for the overvoltage, thereby saving the sensitive control panel components. The varistor and the line fuse are subject to damage or weakened because the shunt path creates a short circuit. An essential point of varistor selection is that the varistor can handle the peak pulse current, which is 110% of the maximum current at which the varistor voltage does not change. If the peak pulse current rating is insufficient, then the varistor may be damaged. The main voltage is 220V RMS, and sometimes the maximum will reach 265VRMS.Thus, an MOKS K10*300V varistor is chosen for this application.
18/27
AN2317 - Application
External Circuit Design
1.5.2
Capacitive Power Supply
There are several ways to convert AC voltage into the DC voltage required by STPM01. Traditionally, this is done with a transformer and rectifier circuit. There is also switching power supply solution. However, these two solutions are expensive and take up a considerable amount of PCB space. To provide a low-cost, alternative solution, a transformerless power supply can be used (see Figure 12). Figure 12. Capacitive Power Supply
R1 LINE 82R 470n DIF60 2 UIN D2 DIF60 C3 1000m D3 5.1V 1 C2 IIN D1 VDD
NEUTRAL
GND
AI12914
19/27
External Circuit Design
AN2317 - Application
The input current (IIN) is limited by R 1 and the capacitive reactance of C2 (see Equation 28 and Equation 29), and is expressed as: Equation 27 VI N ( R M S) I I N = -----------------------XC 2 + R 1 where, XC2 = C2 reactance.
Note:
R1 is used to limit inrush current, but it dissipates power.
By adding a low-cost half-wave rectifier, current is allowed to be supplied by the source during the positive half, where,
VINRMS = RMS voltage of the half-wave AC waveform, and is expressed as follows:
Equation 28 1 VPE A K VZ V I N ( R M S ) = -- -----------------------------2 2 where, VPEAK = mains peak voltage (i.e. United States = 115V/60Hz and Europe = 220V/50Hz), and VZ = the voltage drop across D1 and D 3.
XC2 = Capacitor reactance, and is expressed as: 1 X C 2 = --------------2 f C2
Equation 29
By substituting the values expressed in Equation 27 with those in Equation 28 and Equation 29, the results are as follows: Equation 30 2V ai VZ VP EA K V Z I I N = ---------------------------------------- = -------------m------n-s--------------- ---2 2 (XC2 + R1) 2 2 ( X C 2 + R1 ) Assuming that the voltage drop across each diode is 0.7V, then the total voltage drop is expressed as: Equation 31 V Z = V D 1 + V D 3 = 5 + 0. 7 2 = 6. 4 V
20/27
AN2317 - Application When these application parameters are considered: Vmains = 220VAC, f = 50Hz, and VZ = 6.4V (see Equation 31), the calculated IIN would be: Equation 32 I I N = 15. 7 m A
External Circuit Design
Selecting components in the circuit is a critical consideration. As a general rule, components should be sized at twice the maximum power calculated for each device. For example, by using the IIN value in Equation 32 and VDD = 5V to choose an appropriate Zener diode, the results required to make the selection are expressed as follows: Equation 33 V D D = I I N R 1 = 0.02 W and Equation 34 P D 3 = V D 3 I I N = 5.1 0.0157 = 0.08 W Thus, a ZMM SOD 80*5.1V G Zener Diode is used.
2
21/27
External Circuit Design
AN2317 - Application
1.5.3
EMC Filter
EMC has become an important power supply parameter. In order to deal with common and differential mode noise, a two-part AC filter is added (see Figure 11 on page 18).
Differential filter (Filter 1) Inductors L1/L2, and C 1 represent a differential filter for DM (differential mode) noise trying to enter the power supply. DM noise is produced by current flowing along either the Line or Neutral conductor, and returning by the respective other. This produces a noise voltage between the Line and Neutral conductors. The filter will be designed for at least 10 times the line frequency, thereby resulting in a frequency of 600Hz. The indication is then, that the cutoff frequency (fC) must not be below 600Hz. Capacitor C1 is X Class capacitor, used to reduce differential noise. To ensure that C 1 does not fail because of the surge or short circuit current, it must be able to withstand twice the mains voltage value. Keeping this requirement in mind, fC is calculated as follows:
Equation 35 1 f C ---------------------------------------------- = 7.59 H z 2 ( L 1 + L2 ) C 1
Not e:
Generally, a specific f C value is chosen, then the inductors are tuned to that value.
22/27
AN2317 - Application
External Circuit Design
Capacitor filter (C3, Filter 2) Capacitor C3 is used as a filter. Considering load RL, the size of C3 must satisfy the requirements expressed in Equation 36:
Equation 36 R L C = ( 15 25 ) T In fact, considering that the charge stored in the capacitor is: Equation 37 IL T = Q where, IL = the load current, and T = the AC sine wave period, and the output ripple voltage is expressed as: Equation 38 Q V = --C then the capacitor C value can be calculated by using a fixed voltage ripple value: Equation 39 IT V = --L---- C then, fixing our ripple to V=200mV we can calculate C value accordingly. For the purposes of this application, C is calculated as follows: Equation 40 10 m A C = ------------------------------------- = 1000 F 200 m V 50 H z The STPM01 power supply (VCC) configuration range is from 3.3V to 6V. While it seems to be enough to change the D3 diode (see Equation 34) from the previously selected ZMM SOD 80*5.1V G Zener Diode, if the output current is too high, then the C2 value must be reduced.
Not e:
Usually it is not necessary to use resistor R1 in the circuit.
23/27
External Circuit Design
AN2317 - Application
1.6
Clock Generation
All of the STPM01 internal timing is based on the CLKOUT oscillation signal. This signal can be generated in three different ways:
RC (see Figure 13) This oscillator mode can be selected using the RC configuration bit. If RC = 1, then the STPM01 will run using the RC oscillator. A resistor connected between CLKIN and Ground will set the RC current.
Not e:
For 4MHz operation, the suggested settling resistor is 12k. Quar tz (see Figure 14)
The oscillator will work with an external crystal. Figure 13. Internal RC Recommended Connections
VSS
CLKIN
CLKOUT
12k
AI12915
Figure 14. Quartz Recommended Connections
VSS
CLKIN
CLKOUT
1M 4194MHz 15pF 15pF
AI12916
24/27
AN2317 - Application
External Circuit Design
Exter nal Clock (see Figure 15) The clock generator is powered from analog supply, and is responsible for two tasks: a) to retard the turning on of some of the function blocks after Power-on Reset (POR) in order to help smooth start the external power supply circuitry and keep all major loads off of the circuit, and to provide all necessary clocks for the analog and digital parts. Two nominal frequency ranges are expected,(1) from 4.000MHz to 4.194MHz, or (2) from 8.000MHz to 8.192MHz.
b)
Figure 15. External Clock Source Recommended Connections
VSS
CLKIN
CLKOUT
AI12917
25/27
Revision History
AN2317 - Application
2
Revision History
Table 1.
Dat e 14-Apr-2006
Document revision history
Revision 1 Initial release. Changes
26/27
AN2317 - Application
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