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 (V RMS and I RMS), instantaneous, and harmonic voltage and current. This application note describes the STPM01 external circuits which are comprised of: Note: April 2006 ● a crystal oscillator, ● a power supply circuit, ● a voltage sensing circuit, and ● two current sensing circuits. This document should be used in conjunction with the STPM01 datasheet. Rev 1 1/27 www.st.com Contents AN2317 - Application Contents 1 External Circuit Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 2/27 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 1.6 2 Current Sensing Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.5.1 Varistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.5.2 Capacitive Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.5.3 EMC Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Clock Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 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 3/27 External Circuit Design 1 AN2317 - Application 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: 4/27 ● 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). AN2317 - Application External Circuit Design STPM01 External Circuit Schematics 10N C19 2 PI G08 10-2V D1 20 LED 1 2 1 VDD 4 5 8 9 10 CLKIN VDDA VIN VOIP VIP IIP1 IIN2 IIN1 IIP2 6 VDDA 7 8 D9 SRD 200mcd 9 10 2 1 2 2.4K R17 1 2 SBG SDA SCL SCS SYN 19 18 3 15 17 16 14 13 12 1 R15 2 11 2 10N 2 1 1 4194.304kHz 1 2 R13 2 1 1.0k 2M 2 15P R1 1M Y1 C13 21 SYN 2 4 5 C12 1 VDD 1 2 3 1 C8 30.1R TR1 SCS 1 1 2 1.0k 1 R5 E4622/X503 4 SCL MOP VCC 7 R2 MON VSS CLKOUT 6 VDDA SDA D8 SRD 200mcd D7 SRD 200mcd U1 STPM01E 2 2 1 1 R18 1 1 2 2.4K 2 2 2.4K 1 2 1 1MY C4 1.0N C5 C7 2 1 R19 1 1MY 1MY 2 1 1N4148 1 VDD 2 2 2 R20 2 D5 2 1 1N4148 R23 2 1.0N C6 C2 1.0N C3 1 10N 2 47K 1 1 15P Q4 BC8578 31 D4 2 1 1N4148 2.4K 3 1 W5 VODNIK 1 D6 SRD 200mcd 2 W6 VODNIK 1 D3 2 1 1N4148 C17 C16 1MY 1K R22 R21 33.0R 2 Q3 BC8578 2 2 1 2 1 1 1N4148 C18 D2 2 1 1 1 10N Figure 1. 2 ANTI-ALIASING FILTER 30.1R 1 2 1 21 R4 2 R14 2 1 10N TR2 R3 1.0k C9 1 R6 E4622/X503 1 4 CRYSTAL OR RTC OSCILLATOR 2M 2 1.0k CURRENT SENSING 1 C11 1 2 4.7my 2 1 L3 82R 1 C14 510V V4 N 1 R24 2 2 220MYH 1 W4 VODNIK 1 L6 1.0N 1 F 2 2 1 R10 2 2 1 C20 220N C1 1 261K R7 2 VOLTAGE SENSING 10N 2 475R 1 R11 2 1 R12 2 150K 2.21k 2 2 2 1 470N 2 D11 W1 VODNIK VDD 1 1 1 DIF60 2 CAPACITIVE POWER SUPPLY 1 5.6V 1 W3 VODNIK 1 R9 261K 1000M D12 1 C15 + 2 DIF60 R8 261K D10 1 C10 2 W2 VODNIK 1 220MYH AI12296 5/27 External Circuit Design 1.1 AN2317 - Application Current Sensing Circuit The STPM01 has two external current sensing circuits (see Figure 1 on page 5): 1.1.1 1. Primary channel, and 2. Secondary channel. 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. Primary Current Sensing Circuit I1 I2 Burden Resistor LPF 1 2 2 2 VIN1 1 C9 6.8R 1 R25 1R R23 1 R2 1.0k 1 R1 2 + 10N Figure 2. 2 U0 – VIP1 1.0k AI12297 6/27 AN2317 - Application External Circuit Design Primary current sensing is calculated as follows: Equation 1 N1 I 2 = ------- ⋅ I 1 N2 Equation 2 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 1PEAK N 2 2000 ------------------ = ------- = ------------I 2PEAK N 1 1 Equation 4 I 1PEAK I 2PEAK = -----------------= 3mA 2000 Equation 5 R 23 ⋅ R 25 U 0PEAK = U APEAK = I 2PEAK ⋅ -------------------------- = 2.6mV R 23 + R 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 APEAK = U 0PEAK = 0.15V Equation 7 R 23 + R 25 I 2PEAK = U APEAK ⋅ -------------------------- = 172mA R 23 ⋅ R 25 Equation 8 I 1PEAK = 2000I 2 PEAK = 344A Equation 9 I 1PEAK I 1RMS = ------------------ = 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 F Hot Load N TR2 TR1 W6 W5 * Comp side P1 AI12298 8/27 AN2317 - Application 1.1.2 External Circuit Design Secondary 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: 2 ( 20A ) × 420μΩ = 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 = 220V RMS, – Ib = 2A, and – Shunt resistance = 420µΩ. The remaining design elements calculated from these values are as follows: – Voltage across shunt: 2A × 420μΩ = 0.00084V – Mains power dissipation: 220V × 2A = 0.44kW – Error: 1.68 × 10 –3 ⁄ 0.44 × 10 –3 × 100percent = 0.0004percent 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. 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 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 Hot Load N Shunt * Comp side P1 W6 W5 LED NLC TPR DIR AI12299 10/27 AN2317 - Application 1.2 External Circuit Design 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 C UO 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 jωc 1 A u = -------- = -------------------- = ------------------------1 1 + jωRC UI R + --------jωc Note: The cutoff frequency is expressed as: 1 1 f p = --------- = ---------------2πτ 2πRC 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 = ---------------------f 2 1 + ⎛ ----⎞ ⎝ f p⎠ The phase is expressed as: Equation 13 f ϕ = – arc tan ---fp In the module: R = 2 • 103KΩ and C = 10nF, so then 1 f p = ---------------- = 7961.8Hz 2πRC 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 ϕ = – 0.35° and Equation 15 Au ≈ 1 ● When f = 60Hz: Equation 16 ϕ = – 0.43° and Equation 17 Au ≈ 1 Assume that the current lags the voltage by a phase angle, δ. After an anti-aliasing filter, a phase error (ϕ) is introduced into the STPM01. The power factor (PF) error is calculated as: Equation 18 cos δ – cos ( δ + ϕ ) error PF = ----------------------------------------------- ⋅ 100percent cos δ When, δ = –60° (PF = –0.5), and f = 50Hz, according to Equation 14, a phase error, ϕ = –0.35° has occurred: Equation 19 cos ( – 60° ) – cos ( – 60° – 0.35° ) error PF = ---------------------------------------------------------------------------------- ⋅ 100percent = 1percent 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. AN2317 - Application Anti-aliasing Filter Magnitude Response Decibels (dB) 0 –20 –40 –60 Figure 8. 10 100 1000 10000 Frequency (Hz) 100000 1000000 AI12902 Anti-aliasing Filter Phase Response 0 Degrees (°) –20 –40 –60 –80 –100 10 100 1000 10000 Frequency (Hz) 100000 1000000 AI12903 14/27 AN2317 - Application 1.3 External Circuit Design Voltage Sensing Circuit The STPM01 normally uses a resistor divider as voltage input channel (see Figure 9). The 783kΩ resistor is separated into three 261kΩ, 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‘ = 783KΩ, and ● R5=475Ω. 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 Z1 R19 42.2k Z2 L2 1m C11 22n R6 475 R' R15 100 V2 783k AI12904 15/27 External Circuit Design AN2317 - Application Equation 20 Z 1 = ( R 19 + R 15 ) = 42.3KΩ Equation 21 ( R 5 + R6 ) ⋅ Z 1 Z 2 = -----------------------------------= 930Ω R 5 + R6 + Z 1 Equation 22 Z ⎧ -----2= 110 2V , U 1 = 0.046V ⎪ V 2 U 1 = – U 2 = ---------------------- ⋅ V mains = ⎨ m ains 2R′ + Z 2 ⎪ V m ains = 220 2V , U 1 = 0.092V ⎩ Equation 23 Z2 ⎧ -----= 110 2V , U 0 = 0.092V ⎪ V 2 U 0 = U 1 – U 2 = ------------------- ⋅ V mains = ⎨ mains Z ⎪ V mains = 220 2V , U 0 = 0.185V R′ + ------2⎩ 2 Z1 has little influence on the U0, thus: Equation 24 R5 U 0 ≈ ------------------R′ + R 5 Note: 16/27 For a specific U 0, choose an appropriate combination of resistors (R5 and R’) to get that particular U 0 value. AN2317 - Application 1.4 External Circuit Design 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 R15 R15 V R15 = ----------------------------- ⋅ V VCI ≅ ----------- ⋅ V VCI R19 + R15 R19 Equation 26 –6 R1 R15 R1 R1 V CCI = ------------------------- ⋅ V R15 ≅ ----------- ⋅ V R15 = ----------- ⋅ ----------- ⋅ V VCI ≅ 1.18e V VCI R21 R19 R21 + R1 R21 Note: 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 1.5 AN2317 - Application 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 Filter 1 L1 220m LINE Current Limiter R1 Voltage Divider C2 82R 470n Filter 2 D1 VDD DIF60 2 RV1 510V C1 1n D2 DIF60 C3 1000m D3 5.1V 1 NEUTRAL L2 220m 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 1.5.2 External Circuit Design 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 C2 82R 470n IIN D1 VDD LINE DIF60 2 UIN D2 DIF60 C3 1000m D3 5.1V 1 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 V IN ( RMS ) I IN = -----------------------X C2 + 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 V PEAK – V Z V IN ( RM 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: Equation 29 1 X C2 = ---------------2πfC 2 By substituting the values expressed in Equation 27 with those in Equation 28 and Equation 29, the results are as follows: Equation 30 2V m ains – V Z V PEAK – V Z I IN = ---------------------------------------= ---------------------------------------2 2 ( X C2 + R 1 ) 2 2 ( X C2 + R 1 ) Assuming that the voltage drop across each diode is 0.7V, then the total voltage drop is expressed as: Equation 31 V Z = V D1 + V D3 = 5 + 0.7 ⋅ 2 = 6.4V 20/27 AN2317 - Application External Circuit Design 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 IN = 15.7mA 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 2 V DD = I IN ⋅ R 1 = 0.02W and Equation 34 P D3 = V D3 ⋅ I IN = 5.1 ⋅ 0.0157 = 0.08W Thus, a ZMM SOD 80*5.1V G Zener Diode is used. 21/27 External Circuit Design 1.5.3 AN2317 - Application 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 ≈ ----------------------------------------------- = 7.59Hz 2π ( L 1 + L2 ) ⋅ C 1 Note: 22/27 Generally, a specific f C value is chosen, then the inductors are tuned to that value. 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 ΔV = ---C then the capacitor C value can be calculated by using a fixed voltage ripple value: Equation 39 IL T ΔV = ------C then, fixing our ripple to ΔV=200mV we can calculate C value accordingly. For the purposes of this application, C is calculated as follows: Equation 40 10mA C = -------------------------------------- = 1000μF 200mV ⋅ 50Hz 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. Note: Usually it is not necessary to use resistor R1 in the circuit. 23/27 External Circuit Design 1.6 AN2317 - Application 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. Note: For 4MHz operation, the suggested settling resistor is 12k. ● Quartz (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 External 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 b) 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. Figure 15. External Clock Source Recommended Connections VSS CLKIN CLKOUT – AI12917 25/27 Revision History 2 AN2317 - Application Revision History Table 1. 26/27 Document revision history Date Revision 14-Apr-2006 1 Changes Initial release. AN2317 - Application Please Read Carefully: Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any time, without notice. All ST products are sold pursuant to ST’s terms and conditions of sale. Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no liability whatsoever relating to the choice, selection or use of the ST products and services described herein. No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such third party products or services or any intellectual property contained therein. UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT. UNLESS EXPRESSLY APPROVED IN WRITING BY AN AUTHORIZE REPRESENTATIVE OF ST, ST PRODUCTS ARE NOT DESIGNED, AUTHORIZED OR WARRANTED FOR USE IN MILITARY, AIR CRAFT, SPACE, LIFE SAVING, OR LIFE SUSTAINING APPLICATIONS, NOR IN PRODUCTS OR SYSTEMS, WHERE FAILURE OR MALFUNCTION MAY RESULT IN PERSONAL INJURY, DEATH, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE. Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any liability of ST. ST and the ST logo are trademarks or registered trademarks of ST in various countries. Information in this document supersedes and replaces all information previously supplied. The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners. © 2006 STMicroelectronics - All rights reserved STMicroelectronics group of companies Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America www.st.com 27/27

- Similar pages