AS8228

AS8218 / AS8228 Highly Integrated Single Phase 2-Current Energy Metering Integrated Circuits with Microcontroller, RTC, Programmable Multi-Purpose I/Os and LCD Driver D ATA SHEET 1 . Key Features - - P recision single-phase, one or two current input energy measurement front-end including SigmaDelta modulators for A/D-conversion and digital signal processor (DSP). L ow current consumption of 5mA, depending on MCU activity. D igital phase correction and selectable gain on both current channels for use with two current transformers (CT) or one CT and one shunt. P ower-supply monitor (PSM) for power-on reset and reset when the supply voltage falls below a defined threshold. C ustomer programmable 8-bit 8051 compatible microcontroller (MCU). P rogrammable MCU clock with optional low power operating conditions. 2 x U niversal Asynchronous Receiver / Transmitters (UART) for external communications such as programme download and debugging. P rogrammable watchdog timer (WDT) and external system reset pin. R eal-time clock/calendar (RTC) with on-chip digital calibration and separate battery supply pin. O n-chip voltage reference (VREF) with small temperature coefficient. L ow power 3.0 – 4.0MHz crystal oscillator. S PI compatible interface for external EEPROM memory. S tandard on-chip LCD driver (LCDD) interface. P rogrammable multi-purpose I/Os (MPIO) with selectable data direction, pull-up or pull-down resistors and drive strength. M ains current lead/lag status indication for reactive energy measurement. L ow power battery operating mode for meter reading when Mains voltage is not present. T he AS8218 and AS8228 ICs offer the following options: AS8218: 20 x 4 segment LCDD 9 x multi-purpose I/O (MPIO) AS8228: 24 x 4 segment LCDD 12 x multi-purpose I/O (MPIO) - 2 . General Description T he AS8218 / AS8228 are highly integrated CMOS single-phase energy metering devices for fully electronic LCD meter systems. The AS8218 / AS8228 have been designed to ensure the meters full compliance with the international Standards IEC62052 and ANSI. The AS8218 / AS8228 ICs include all the functions required for conventional 1 current or 2-current anti-tamper meters. The functions include precision energy measurement, an 8-bit microcontroller unit (MCU), an on-chip Liquid Crystal Display driver (LCDD), programmable multi-purpose Inputs/Outputs (MPIO), a real time clock/calendar (RTC) for complex tariff functions such as time-ofuse or maximum demand billing and a Serial Peripheral Interface (SPI) for reading data from and writing data to an external non-volatile memory (EEPROM). The AS8218 / AS8228 ICs have a dedicated energy measurement front-end, which includes an analog front-end and programmable Digital Signal Processor (DSP) from which active energy, mains voltage and mains current are provided. Reactive and apparent energy can also be calculated. The on-chip 8-bit 8051 compatible microcontroller is freely programmable and provides user access to the various functional blocks. The dedicated Universal Asynchronous Receiver / Transmitter (UART1) in the System Control block provides access to various system functions and blocks. A second UART (UART2) is also provided, which may for example be used for debugging. The on-chip memory includes 24kByte program memory and 1kByte data memory. The meter system designer can select the size of the external EEPROM memory from 1kByte to 32kByte (in binary steps). - - - - - - - - - - - - R evision 3.0, 31-May-06 Page 1 of 123 D ata Sheet AS8218 / AS8228 A n on-chip programmable watchdog timer (WDT) is available to automatically initiate a system reset if a regular ‘hold-off’ signal is not detected. The system timing and real time clock (RTC) has a dedicated external battery supply pin (VDD_BAT), enabling the oscillator and RTC to continue during ‘power-down’. The RTC may be digitally calibrated for oscillator frequency accuracy. The LCD Driver (LCDD) block enables the display of information provided by the microcontroller, directly to the LCD. Two dedicated data register banks are provided to simplify programming, particularly in the case where the display data needs to be scrolled. The programmable multi-purpose I/O pins (MPIO) may be independently configured as inputs or outputs. All the I/O pins are programmable for data direction, pull-up/pull-down resistors and drive strength (4mA/8mA). Typical functions may include LED energy consumption pulse output, energy direction and fault condition indication depending on current 1 or current 2 being active for the energy calculation, push button for display scrolling, mains isolation relay control for prepayment meters, optical interface etc. An on-chip analog ground buffer (ABUF) and voltage reference (VREF) ensures that no external circuitry is required. A power-supply monitor (PSM) provides a reset, when VDD falls below a safe operating threshold. A reset pin (RES_N) is available for external system reset. The AS8218 / AS8228 ICs are available in LQFP64 plastic packages. Revision 3.0, 31-May-06 Page 2 of 123 D ata Sheet AS8218 / AS8228 3 . Typical Application Circuit 3.3V 3.3V + + LCD 3.3V XIN XOUT 32 33 Low Power Oscillator VDDA 7 Low Power Divider 13 VDDD 22 LBP0 LBP1 LBP2 LBP3 kWh Vrms Irms 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 9 LSD0 LSD1 LSD2 LSD3 LSD4 LSD5 LSD6 LSD7 LSD8 LSD9 LSD10 LSD11 LSD12 LSD13 LSD14 LSD15 LSD16 LSD17 LSD18 LSD19 LSD20 LSD21 LSD22 LSD23 IO0 IO1 IO2 IO3 IO4 IO5 IO6 IO7 IO8 IO9 IO10 IO11 LED DIRO FAULT VDD_BAT 31 RTC System Timing & RTC LOAD I1P 3 Analog Front End LCD Driver SDM I1N I2N 4 6 SDM I2P VP 5 1 DSP MCU SDM VN 2 I/Os Examples only 10 11 WDT RES_N 34 Multipurpose I/Os 12 15 16 17 18 19 26 27 28 Push-Button Reference pulses for calibration AS8228 only System Control UART1 23 20 24 25 S_N SI SO SC SPI 8 VSSA 14 VSSD 21 VSSD 29 TXD 30 RXD EEPROM S1 Q 2 3.3V W 3 VSS 4 8 VCC 3.3V HOLD 3.3V 7 6C 5D VI VO 3.3V + GND N L F igure 1: Typical application circuit of the AS8218 / AS8228 Revision 3.0, 31-May-06 AS8228 only Page 3 of 123 D ata Sheet AS8218 / AS8228 4 . Pin Out LSD19 LSD18 LSD17 LSD16 LSD15 LSD14 LSD13 LSD12 LSD11 LSD10 LSD23 LSD22 LSD21 LSD20 LSD19 LSD18 LSD17 LSD16 LSD15 LSD14 LSD13 LSD12 LSD11 LSD10 51 LSD9 LSD8 LSD9 50 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 64 63 62 61 60 59 58 57 56 55 54 53 52 VP VN I1P I1N I2P I2N VDDA VSSA IO0 IO1 IO2 IO3 VDDD VSSD IO4 IO5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 48 47 46 45 44 43 42 LSD7 LSD6 LSD5 LSD4 LSD3 LSD2 LSD1 LSD0 LBP3 LBP2 LBP1 LBP0 n.c. n.c. RES_N XOUT VP VN I1P I1N I2P I2N VDDA VSSA IO0 IO1 IO2 IO3 VDDD VSSD IO4 IO5 49 LSD8 48 47 46 45 44 43 42 n.c. n.c. n.c. n.c. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 LSD7 LSD6 LSD5 LSD4 LSD3 LSD2 LSD1 LSD0 LBP3 LBP2 LBP1 LBP0 n.c. n.c. RES_N XOUT AS8218 LQFP64 41 40 39 38 37 36 35 34 33 AS8228 LQFP64 41 40 39 38 37 36 35 34 33 VDD_BAT S_N SO VSSD TXD VDDD RXD XIN SC n.c. SI IO6 IO7 IO8 IO9 IO6 IO7 IO8 IO10 IO11 VDD_BAT S_N SO VSSD TXD 5 . Pin Description Pin No. 1 2 3 Pin Name AS8218 VP VN I1P Pin Name AS8228 VP VN I1P AI AI AI Positive input for the voltage channel. VP is a differential input with VN. The typical differential voltage is ±100mV peak. Negative input for the voltage channel. VN is a differential input with VP. Positive input for the first current channel. I1P is a differential input with I1N. The input gain is programmable depending on the desired current sensor. The typical differential voltage is ±150mV peak (Gain = 4). Negative input for the first current channel. I1N is a differential input with I1P. The input gain is programmable depending on the desired current sensor. The typical differential voltage is ±150mV peak (Gain = 4). Positive input for the second current channel. I2P is a differential input with I2N. The input gain is programmable depending on the desired current sensor. The typical differential voltage is ±150mV peak (Gain = 4). Negative input for the second current channel. I2N is a differential input with I2P. The input gain is programmable depending on the desired current sensor. The typical differential voltage is ±150mV peak (Gain = 4). Positive analog supply. VDDA provides the positive supply voltage for the analog circuitry. The required supply voltage is 3.3V ±10%. Negative analog supply. VSSA is the ground reference for the analog circuitry. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Type Description 4 I1N I1N AI 5 I2P I2P AI 6 I2N I2N AI 7 8 9 VDDA VSSA IO0 VDDA VSSA IO0 S S DIO Revision 3.0, 31-May-06 VDDD RXD XIN n.c. n.c. SC SI Page 4 of 123 D ata Sheet AS8218 / AS8228 Pin No. 10 11 12 13 Pin Name AS8218 IO1 IO2 IO3 VDDD Pin Name AS8228 IO1 IO2 IO3 VDDD Type Description DIO DIO DIO S Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Positive digital supply. VDDD provides the positive supply voltage to the digital circuitry and is internally connected to pin 22. The required supply voltage is 3.3V ±10%. Negative digital supply. VSSD is the ground reference for the digital circuitry. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. 14 15 16 17 18 19 20 21 22 VSSD IO4 IO5 IO6 IO7 IO8 SI VSSD VDDD VSSD IO4 IO5 IO6 IO7 IO8 SI VSSD VDDD S DIO DIO DIO DIO DIO DIPD Serial peripheral interface (SPI) for external EEPROM: Serial data input. SI is a digital input with an on-chip pull-down resistor. S S Negative digital supply. VSSD is the ground reference for the digital circuitry. Positive digital supply. VDDD provides the positive supply voltage to the digital circuitry and is internally connected to pin 13. The required supply voltage is 3.3V ±10%. Serial peripheral interface (SPI) for external EEPROM: Chip select (active low). Serial peripheral interface (SPI) for external EEPROM: Serial data output Serial peripheral interface (SPI) for external EEPROM: Serial clock Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Programmable multi-purpose input/output, with selectable pull-up or pull-down resistors and selectable drive strength. Universal Asynchronous Receiver/Transmitter (UART1) serial transmit data output. 23 24 25 26 27 28 29 30 31 32 S_N SO SC n.c. n.c. n.c. TXD RXD VDD_BAT XIN S_N SO SC IO9 IO10 IO11 TXD RXD VDD_BAT XIN DO DO DO DIO DIO DIO DO DIPU Universal Asynchronous Receiver/Transmitter (UART1) serial receive data input. RXD is a digital input with an on-chip pull-up resistor. S AI Battery backup supply voltage input for the system timing and real time clock (RTC). A 3.0 to 4.0MHz crystal may be connected across XIN and XOUT without the requirement for external load capacitors. Alternatively, an external clock signal may be applied to XIN. Revision 3.0, 31-May-06 Page 5 of 123 D ata Sheet AS8218 / AS8228 Pin No. 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 Pin Name AS8218 XOUT RES_N n.c. n.c. LBP0 LBP1 LBP2 LBP3 LSD0 LSD1 LSD2 LSD3 LSD4 LSD5 LSD6 LSD7 LSD8 LSD9 LSD10 LSD11 LSD12 LSD13 LSD14 LSD15 LSD16 LSD17 LSD18 LSD19 n.c. n.c. n.c. n.c. Pin Name AS8228 XOUT RES_N n.c. n.c. LBP0 LBP1 LBP2 LBP3 LSD0 LSD1 LSD2 LSD3 LSD4 LSD5 LSD6 LSD7 LSD8 LSD9 LSD10 LSD11 LSD12 LSD13 LSD14 LSD15 LSD16 LSD17 LSD18 LSD19 LSD20 LSD21 LSD22 LSD23 Type Description AO See XIN above, for the connection of a crystal. When an external clock is applied to XIN, XOUT is not connected. System reset active low. Not connected Not connected AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO AO LCD back-plane driver output signal. LCD back-plane driver output signal. LCD back-plane driver output signal. LCD back-plane driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. LCD segment driver output signal. N ote: Shaded pins above only available with AS8228 IC Revision 3.0, 31-May-06 Page 6 of 123 D ata Sheet AS8218 / AS8228 PIN Types: S AI AO DIPD DIPU DO DIO Supply pin Analog Input pin Analog Output pin Digital Input pin with pull-down resistor Digital Input pin with pull-up resistor Digital Output pin Programmable Digital Input or Output pin Revision 3.0, 31-May-06 Page 7 of 123 D ata Sheet AS8218 / AS8228 T able of Contents 1. 2. 3. 4. 5. 6. K ey Features .........................................................................................................................................1 G eneral Description ...............................................................................................................................1 T ypical Application Circuit ......................................................................................................................3 P in Out..................................................................................................................................................4 P in Description ......................................................................................................................................4 E lectrical Characteristics........................................................................................................................9 6 .1 A bsolute Maximum Ratings (Non-Operating) ......................................................................................9 6 .2 O perating Conditions ........................................................................................................................9 6 .3 D C/AC Characteristics for Digital Inputs and Outputs........................................................................ 10 6 .4 E lectrical System Specification ........................................................................................................ 11 P erformance Graphs ............................................................................................................................ 12 D etailed Functional Description ............................................................................................................ 14 8 .1 E nergy Measurement Front End (Including DSP) .............................................................................. 16 8 .2 L CD Driver (LCDD) ......................................................................................................................... 48 8 .3 P rogrammable Multi-Purpose I/Os (MPIO) ........................................................................................ 54 8 .4 S erial Peripheral Interface (SPI) ...................................................................................................... 64 8 .5 E xternal EEPROM Requirements ..................................................................................................... 70 8 .6 8 051 Microcontroller (MCU) ............................................................................................................. 77 8 .7 S ystem Control (SCT) ..................................................................................................................... 98 8 .8 S erial Interface – UART1............................................................................................................... 105 C ircuit Diagram.................................................................................................................................. 114 7. 8. 9. 1 0. P arts List........................................................................................................................................... 115 1 1. P ackaging ......................................................................................................................................... 117 1 2. P roduct Ordering Guide ..................................................................................................................... 117 1 3. C ollection of Formulae ....................................................................................................................... 118 1 4. T erminology ...................................................................................................................................... 121 1 5. R evision ............................................................................................................................................ 122 1 6. C opyright .......................................................................................................................................... 122 1 7. D isclaimer ......................................................................................................................................... 122 1 8. C ontact ............................................................................................................................................. 123 Revision 3.0, 31-May-06 Page 8 of 123 D ata Sheet AS8218 / AS8228 6 . Electrical Characteristics 6 .1 Absolute Maximum Ratings (Non-Operating) S tresses beyond the ‘Absolute Maximum Ratings’ may cause permanent damage to the AS8218 / AS8228 ICs. These are stress ratings only. Functional operation of the device at these or any other conditions beyond those indicated under ‘Operating Conditions’ is not implied. C aution: E xposure to absolute maximum rating conditions for extended periods may affect device reliability. Parameter DC supply voltage Input pin voltage Electrostatic discharge Storage temperature Lead temperature profile Humidity non-condensing Symbol VDD Vin ESD Tstrg Tlead 5 85 % -55 Min -0.3 -0.3 Max +5.0 VDD+0.3 1000 125 Unit Notes V V V °C Norm: IPC/JEDEC-020C Norm: MIL 883 E method 3015 6 .2 Operating Conditions Symbol VDDA VSSA A-D VDDD VSSD VDD_BAT Tamb Isupp fosc 3.0 Min 3.0 0 -0.1 3.0 0 2.0 -40 3.3 25 5 3.579545 4.0 3.3 Typ Max 3.6 0 0.1 3.6 0 3.6 85 Unit V V V V V V °C mA MHz Depending on MCU activity VDDA – VDDD VSSA – VSSD Referring to VSSD, typical ±10 % Notes Parameter Positive analog supply voltage Negative analog supply voltage Difference of supplies Positive digital supply voltage Negative digital supply voltage Battery supply voltage Ambient temperature Supply current System clock frequency Revision 3.0, 31-May-06 Page 9 of 123 D ata Sheet AS8218 / AS8228 6 .3 DC/AC Characteristics for Digital Inputs and Outputs C MOS Input with Schmitt Trigger and Pull-up Resistor (RXD) Parameter High level input voltage Low level input voltage Low level input current Symbol VIH VIL IIL -100 Min 0.7 x VDD 0.3 x VDD -15 Typ Max Unit V V µA Tested at VDD=3.6V and Vin=0V Notes C MOS Input (SI) Parameter High level input voltage Low level input voltage High level input current Symbol VIH VIL IIH 15 Min 0.7 x VDD 0.3 x VDD 100 Typ Max Unit V V µA Tested at VDD=3.6V and Vin=3.6V Notes C MOS Outputs (TXD, SO, SC, S_N) Parameter High level output voltage Low level output voltage High level output current Low level output current Symbol VOH VOL IOH IOL -4 Min 2.5 0.4 4 Typ Max Unit V V mA mA Notes Tested at VDD=3.0V Tested at VDD=3.0V Tested at VDD=3.0V and Vout=VOH Tested at VDD=3.0V and Vout=VOL M PIO Inputs with Schmitt Trigger and Selectable Pull-up/Pull-down Parameter High level input voltage Low level input voltage High level input current Low level input current Symbol VIH VIL IIH IIL 15 -100 Min 0.7 x VDD 0.3 x VDD 100 -15 Typ Max Unit V V µA µA Tested at VDD=3.6V and Vin=3.6V; ‘pull-down’ Tested at VDD=3.6V and Vin=0V; ‘pull-up’ Notes M PIO Outputs with Programmable Drive Strength Parameter High level output current Low level output current High level output current Low level output current Symbol VOH VOL IOH IOL -4 Min 2.5 0.4 4 Typ Max Unit V V mA mA Notes Tested at VDD=3.0V Tested at VDD=3.0V If ‘4mA’ is selected. Tested at VDD=3.0V and Vout=VOH If ‘4mA’ is selected. Tested at VDD=3.0V and Vout=VOL Revision 3.0, 31-May-06 Page 10 of 123 D ata Sheet AS8218 / AS8228 Parameter High level output current Low level output current Symbol IOH IOL Min Typ Max 8 Unit mA mA Notes If ‘8mA’ is selected. Tested at VDD=3.0V and Vout=VOH If ‘8mA’ is selected. Tested at VDD=3.0V and Vout=VOL -8 L CDD Outputs T he Liquid Crystal display driver (LCDD) outputs are specified in the LCD Driver section of this data sheet. 6 .4 Electrical System Specification Symbol |VVP| |VI1P|, |VI2P| |VI1P|, |VI2P| |VI1P|, |VI2P| fmains DR(I) DR(P) 45 600:1 2000:1 0.1 err(dr) err(temp) err(cosphi) err(VDD) J Vmains Imax BW 1.75 0.2 0.5 0.5 0.2 0.1 264 120 % % % % % % V(rms) A(rms) kHz Reading 1) Within operating temperature range, 1) From 1 to 0.5, 1) 1) 2) 240V + 10%, 3) 3) Min Typ 100 150 38 30 Max 212 212 54 42 65 Unit mVp mVp mVp mVp Hz Notes Referenced to VSSA Referenced to VSSA Referenced to VSSA Referenced to VSSA Parameter Input Signals Voltage channel input voltage Current channel input voltage (Gain=4) Current channel input voltage (Gain=16) Current channel input voltage (Gain=20) Mains frequency Dynamic range current Dynamic range power Accuracy Error variation over dyn. range Error variation over temperature Error variation over cos(phi) Error variation with VDD Output pulse jitter Mains voltage Measured current Measurement bandwidth Notes: 1) Errors determined during energy measurement using a demoboard and a reference meter with high accuracy (0.05%), which calculates the actual error. 2) Difference between largest and smallest error of 20 successive error samples; maximum meter constant: 1,600i/kWh; reference meter: 10,000 x DUT-meter-constant; measured at 5% Ib, Ib and I max . 3) What is used for system considerations/calculations. Revision 3.0, 31-May-06 Page 11 of 123 D ata Sheet AS8218 / AS8228 7 . Performance Graphs 0,5 0,4 0,3 0,2 0,5 0,4 VDD 3V6 VDD 3V3 0,3 0,2 PF=0.5 Error [% ] Error [%] 0,1 0 0,1 0 VDD 3V0 PF=0.8 -0,1 -0,2 -0,3 -0,4 -0,5 0,01 -0,1 -0,2 -0,3 -0,4 -0,5 PF=1.0 0,1 1 10 100 0,01 0,1 1 10 100 I [A] I [A] G raph 1: Error as a % of reading for gain setting 4 at 25°C G raph 4: Error as a % of reading for PF=1, PF=0.8, PF=0.5 at 25°C 0,5 0,4 0,3 0,2 0,5 0,4 0,3 VDD 3V3 0,2 Error [% ] Error [% ] 0,1 0 -0,1 -0,2 -0,3 -0,4 -0,5 0,01 0,1 0 VDD 3V6 -0,1 -0,2 -0,3 -0,4 -0,5 0,01 PF=0.5 PF=0.8 VDD 3V0 PF=1.0 0,1 1 10 100 0,1 1 10 100 I [A] I [A] G raph 2: Error as a % of reading for gain setting 16 at 25°C G raph 5: Error as a % of reading for PF=1, PF=0.8, PF=0.5 at -40°C 0,5 0,4 0,3 0,2 0,5 0,4 0,3 PF=0.5 VDD 3V0 0,2 E rro r [% ] Error [% ] 0,1 0 0,1 0 PF=0.8 VDD 3V3 -0,1 -0,2 -0,3 -0,4 -0,5 0,01 -0,1 -0,2 -0,3 -0,4 -0,5 0,01 PF=1.0 VDD 3V6 0,1 1 10 100 0,1 1 10 100 I [A] I [A] G raph 3: Error as a % of reading for gain setting 20 at 25°C G raph 6: Error as a % of reading for PF=1, PF=0.8, PF=0.5 at 85°C Revision 3.0, 31-May-06 Page 12 of 123 D ata Sheet AS8218 / AS8228 0,5 0,4 0,3 0,2 3V0 3V3 0 0,5 0,4 0,3 0,2 Error [%] E rro r [% ] 0,1 0,1 0 -0,1 -0,2 -0,3 -0,4 -0,5 -0,1 -0,2 -0,3 -0,4 -0,5 0,01 0,1 1 I [A] 10 100 3V6 45 55 65 F [Hz] G raph 7: Error as a % of reading with variation in VDD G raph 9: Error as a % of reading with mains frequency variation 0,5 0,4 0,3 2 1,5 1 Gain 20 0,2 290V 230V 170V Error [%] Error [% ] 0,1 0 0,5 0 -0,1 -0,2 -0,3 -0,4 -0,5 0,01 Gain 4 -0,5 -1 -1,5 -2 0,01 Gain16 0,1 I [A] 1 10 100 0,1 I [A] 1 10 100 G raph 8: Error as a % of reading with mains voltage variation G raph 10: Error as a % of reading using vconst for mains voltage value Revision 3.0, 31-May-06 Page 13 of 123 D ata Sheet AS8218 / AS8228 8 . Detailed Functional Description T he AS8218 / AS8228 integrated circuits have a dedicated measurement front end, which is capable of measuring active and reactive energy, RMS mains voltage, RMS mains current as well as power factor. There are two completely separate differential current channel inputs, for measurement of both the Live and Neutral currents. The two current inputs may be connected to a shunt resistor (I1) and a current transformer (I2); of which the secondary winding is terminated with a burden resistor. Both current channels have programmable gains; thus it is possible to connect the shunt resistor to any of the two differential current inputs. The option to use two current transformers is also available. The AS8218 / AS8228 ICs may be programmed to accept either of the two measured currents for the energy calculation, or may be programmed to accept the larger of the two currents for the energy calculation. The AS8218 / AS8228 ICs may also be used for conventional 1-phase single current measurement applications, where only the Live current is measured. In this case, the I2P and I2N pins are left unconnected and the second current channel modulator can be powered down. The voltage channel input for measurement of the line voltage is also differential and is connected to a tap of a resistive divider of the line voltage. The resistive divider can be set to accommodate any line voltage standard (V mains ) including 100V, 110V, 220V, 230V and 240V. A 3.0 to 4.0MHz low power oscillator generates the system clock for the AS8218 / AS8228 ICs. The absolute clock frequency may be calibrated on-chip. A low power divider is used to generate a 1Hz clock for the on-chip real time clock/calendar (RTC). The supply voltage to the low power oscillator, the low power divider and the RTC may be buffered with an external battery in case of mains power dips or failures, which results in the AS8218 / AS8228 ICs power supply being interrupted. The LCD driver (LCDD) signals LSD0 … LSD23 and LBP0 … LBP3 can be directly connected to a liquid crystal display (LCD), which is used to display the various measured parameters. A total of 80 LCD segments may be driven by the AS8218 IC and 96 LCD segments may be driven by the AS8228 IC. The measurement data and display annunciators are fully programmable. The meter system designer should define the annunciators so that the end customer’s specific meter system requirements are met. A maximum of twelve programmable multi-purpose input/output (MPIO) pins are available for various meter functions, for example light-emitting diodes (LED) to signal energy consumption, energy direction, fault condition, etc. These I/O pins may also be programmed for use as bi-directional communication channels such as an optical interface or an additional Universal Asynchronous Receiver/Transmitter (UART2) Interface, should it so be required. The AS8218 has 9 x MPIO pins, while the AS8228 has 12 x MPIO pins. A dedicated Serial Peripheral Interface (SPI) is also provided for the direct connection to an external EEPROM memory with a compatible serial peripheral interface. Depending on the meter system requirements, the external EEPROM memory capacity may be selected from 1kB up to 32kB, in binary steps. The on-chip 8051 compatible microcontroller performs all the required calculations and enables the user to customize the input and output configuration of the meter. The microcontroller has 24kB of program memory, 1kB data memory, a square root calculation facility and a second UART (UART2) for debugging purposes. A programmable watchdog timer is provided to automatically initiate a system reset when a regular hold-off signal is not detected by the watchdog timer. The watchdog timer is an optional function which is software enabled. Revision 3.0, 31-May-06 Page 14 of 123 D ata Sheet AS8218 / AS8228 A d edicated serial Universal Asynchronous Receiver/Transmitter (UART1) Interface within the System Control is provided to communicate with the AS8218 / AS8228 ICs and perform all the required programming and reading of data, especially during the meter production process. The AS8218 / AS8228 ICs supply voltages (2 x VDDD and VDDA) are typically 3.3 Volts. These supply voltages should be derived from the V mains w ith the use of a standard voltage regulated power supply circuit. A typical 3.3 Volt power supply circuit is described later. An on-chip power supply monitor (PSM) ensures that a reset is generated independently of the supply voltage rise and fall times. Monitoring of the V mains i s provided to ensure early power-down detection. A reset pin (RES_N) is also available for external system reset, which is active low. The RES_N pin can be left unconnected if not required. The individual functional elements of the AS8218 / AS8228 ICs, as well as the relationships between the various functional blocks are shown in the following block diagram. A detailed description of the AS8218 / AS8228 ICs system and the flexibility available to the kWh meter designer, through the system programmability is also described below: XIN XOUT VDD_BAT System Timing & Real Time Clock LBP3 ... 0 LCD Driver LSD23 ... 0 VP VN I1P I1N I2P I2N RXD TXD Energy Measurement Front End Analog Front End DSP 8051 MicroController Multi-purpose I/Os IO11 ... 0 UART1 System Control SPI SC S_N SO SI WDT RES_N F igure 2: AS8218 / AS8228 block diagram Revision 3.0, 31-May-06 Page 15 of 123 D ata Sheet AS8218 / AS8228 8 .1 Energy Measurement Front End (Including DSP) T he Energy Measurement Front End is made up of the analog front end and the digital signal processing block (DSP), which performs the active energy measurement calculations for the microcontroller. The analog front end comprises of the three Sigma-Delta modulators for the sampling of the mains voltage, Line current and a second current channel, for the optional measurement of the Neutral current. Also included in the analog front end is the voltage reference, which provides the temperature stability to the Sigma-Delta modulators. Setting up for the optimum input conditions for the voltage and current channels is also described in this section. The digital signal processing block (DSP) provides the filtering and processing of the output data from the sigma-delta modulators and ensures that the specified measurement accuracy is provided by the AS8218 / AS8228. The DSP offers programming flexibility and provides for fast and efficient meter production calibration procedures. A power supply monitor (PSM) is also described in this section. The PSM ensures that a reset is generated independently of the rise and fall times of the supply voltage (VDD). A nalog Front End T he analog front end comprises of three identical Sigma-Delta modulators, which convert the differentially connected analog voltage and current inputs into digital signals. The two current inputs are gain adjustable to accommodate both directly connected or galvanically isolated current sensors. The on-chip voltage reference (VREF) is the most important contributor to the accuracy of the AS8218 / AS8228 ICs due to it providing temperature stability to the circuit. Considering that the voltage and current signals are multiplied to derive the energy value, errors introduced prior to multiplication function results in errors being multiplied. Thus the introduction of errors into the voltage and the current channel inputs will result in a doubling of the percentage error after multiplication at the energy output. The temperature coefficient of the VREF is specified at 30 ppm/K typical. V oltage Reference Specifications Parameter Output voltage Temperature coefficient Symbol Vref TK Min 1.217 Typ 1.219 30 Max 1.221 Unit V ppm/K Notes C urrent Inputs for Energy Calculation T he AS8218 / AS8228 ICs have 2 identical mains current inputs, I1P/I1N and I2P/I2N, for measurement of both the Live and Neutral currents. Either of the two current inputs may be selected for calculating the energy value. These two differential current inputs are second order Sigma-Delta modulators, with each of the inputs being provided with selectable gains of 4, 16 and 20. The selectable gains are provided so that the AS8218 / AS8228 ICs may be easily adapted for use with either 2 current transformers or alternatively a shunt resistor and a current transformer for current sensing. The AS8218 / AS8228 ICs may also be used in a conventional single current configuration with either a current transformer or shunt resistor being used for current sensing. Revision 3.0, 31-May-06 Page 16 of 123 D ata Sheet AS8218 / AS8228 T he current input signal levels may be programmed by means of on-chip programmable gain settings. The required gain setting is selected as follows: C urrent Input Gain Settings G ain 20 16 4 20 16 4 I nput Voltage - 30mV ≤ V I1P ≤ 30mV -38mV ≤ V I1P ≤ 38mV - 150mV ≤ V I1P ≤ 150mV -30mV ≤ V I2P ≤ 30mV -38mV ≤ V I2P ≤ 38mV - 150mV ≤ V I2P ≤ 150mV C omments S hunt mode; default setting CT mode or shunt mode CT mode Shunt mode CT mode or shunt mode C T mode; default setting C urrent Inputs I1P, I1N C urrent Inputs I2P, I2N N otes: 1) V I1N a nd V I2N a re connected to VSSA. 2) Refer to the Settings Register (SREG) in the DSP section for programming of the Gain Settings. For optimum operating conditions, the input signal at the Maximum Current (I max ) condition should be set at ± 30mVp, when the Gain = 20, or ± 150mVp, when the Gain = 4. The default Gain, the AS8218 / AS8228 ICs current input gain settings without any programming required, is Gain = 20 for the I1 input and Gain = 4 for the I2 input. The value of an ideal shunt resistor, may be calculated as follows: Assuming an I max r ating of 60A (rms) → 8 4.85A (peak), then a shunt value of 350µ Ω w ould be suitable. Rshunt = 30mVp 84.85 A p = 354μΩ t hus a standard 300µ Ω s hunt resistor may be selected. The mains currents are sampled at 3.4956kHz, assuming that the recommended crystal oscillator frequency of 3.5795MHz, is used. The current transformer(s) must be terminated with a voltage setting resistor (R VS ) to ensure the optimum voltage input level to the current input(s) of the AS8218 / AS8228 ICs. The value of R VS i s calculated as follows: R VS = Vin (p ) IL 2 = C T RMS secondary current at rated conditions (V m ains ; I max ) w here I L V in(p) = T he peak input voltage to the IC at rated conditions (V mains ; I max ). For example, if Gain = 4, V in(p) s hould be set at 150mVpeak. Example: A current transformer is specified at 60A/24mA and the Gain = 4: Revision 3.0, 31-May-06 Page 17 of 123 D ata Sheet AS8218 / AS8228 R VS = Vin (p ) IL 2 = 150mV 24mA 2 = 4.42Ω ⇒ 4.3Ω V oltage Input for Energy Calculation T he voltage channel input consisting of inputs VP and VN is differential, with VP connected to the tap of a resistor divider circuit of the line voltage and VN connected to VSSA. For optimum operating conditions, the input signal at VP should be set at 100mVp for the rated voltage condition. The resistor values for an ideal voltage divider may be calculated as follows: Assuming a V mains o f 230V (rms) → 3 25V (peak) and R2 = 470 Ω ( according to the voltage divider shown below), the value of R1A+R1B may be calculated as follows: Vmains R1A+R1B R2 Vin R1A + R1B = R2 × ( Vmains − Vin(P) ) Vin(P) = 470Ω × 325 V − 100mV = 1.53MΩ 100mV t hus R1A = 820k Ω a nd R1B = 750k Ω r esistors may be selected. The mains voltage is also sampled at 3.4956kHz, assuming that the recommended crystal oscillator frequency of 3.5795MHz is used. D igital Signal Processing Block (DSP) T he digital signal processing (DSP) block provides the signal processing required to ensure that the specified measured accuracy is performed and that the microcontroller (MCU) is provided with the appropriate data and protocol to perform all the required meter functions. For the description below, please refer to the following block diagram (Figure 3). The DSP makes allowance for phase correction of the two current channels (i1 and i2) within the Sinc d ecimation filters in the phase correction block. The applicable phase correction setting (pcorr_i1 or pcorr_i2) is selected (sel_i), depending upon which current (i1 or i2) is being used for the power calculation. The equalization filters on the voltage and current channels which may be by-passed (sel_equ), correct for the attenuation introduced by the decimation filters at the edge of the input frequency band, while the high pass filters, which may also be by-passed (sel_hp), eliminate any DC offsets introduced into the input channels. 3 Revision 3.0, 31-May-06 Page 18 of 123 D ata Sheet AS8218 / AS8228 I ndependent calibration of the voltage (cal_v) and current signals (cal_i1 and cal_i2) is done after the voltage and current signals are provided for power calculation. This ensures that calibration of the voltage (sos_v), current channel 1 (sos_i1), current channel 2 (sos_i2) has no influence on the power (np) calibration. The iMux (current multiplexer) allows the selection of the applicable current for power calculation (sel_i), while the vMux (voltage multiplexer) allows the selection of either the mains voltage data, or a constant voltage value, vconst (sel_v). The multiplication of the appropriately selected voltage and current signals is then performed. After multiplication, the next multiplexer (sel_p) enables the selection of either instantaneous power or real power, which is filtered through a low pass filter, PLP. The direction indicator output (diro) is derived from the output of the power low pass filter (PLP). The following multiplexer (creep) allows the selection of the power signal, or blocks the power signal, depending on the required anti-creep and starting current thresholds, which may be set in the microcontroller. Only when constant voltage value (vconst) is selected by the vMux (voltage multiplexer) or when diro=1, it is necessary to derive the absolute power value, for measurement (Abs). The first pulse generator (Fast Pulse Gen) produces fast internal pulses, with the number of pulses being proportional to the measured energy. The multiplexer enables the selection of the appropriate pulse level (pulselev_i1 or pulselev_i2) depending on the current being used for energy measurement (sel_i). The output of the Fast Pulse Gen is always directly proportional to the LED pulse output, generated in the LED Pulse Gen. The LED output pulse rate is selectable (mconst). The polarity of the LED output pulses is also selectable (ledpol). To ensure that the power data transferred to the microcontroller (MCU) is identical to that of the LED pulses, the power accumulator (P_ACCU) counts the pulses generated by the Fast Pulse Gen. After a defined number of sampling periods (nsamp), an interrupt is sent to the MCU, for the MCU to collect the accumulated energy data. Revision 3.0, 31-May-06 Page 19 of 123 D ata Sheet AS8218 / AS8228 pddeton Registers PD_DET alarm v ADC P hase Correction Equ Filter HP Filter X Square Accu sos_v cal_v i1 ADC Equ Filter HP Filter X Square Accu sos_i1 cal_i1 i2 ADC Equ Filter sel_equ HP Filter sel_hp sel_i X Square Accu sos_i2 cal_i2 vconst Mux sel_i iMux vMux sel_v pcorr_i1 pcorr_i2 X PLP