MAX71020 Single-Chip Electricity Meter AFE General Description Features The MAX71020 is a single-chip analog front-end (AFE) for use in high-performance revenue meters. It contains the compute engine (CE) found in Maxim Integrated’s fourth-generation meter system-on-chip (SoC) and an improved analog-to-digital converter (ADC), and interfaces to the host controller of choice over a SPI interface. S S S S S The MAX71020 comes in a 28-pin TSSOP package.
MAX71020 Single-Chip Electricity Meter AFE ABSOLUTE MAXIMUM RATINGS (All voltages with respect to GNDA.) Voltage and Current Supplies and Ground Pins V3P3SYS, V3P3A...................................................-0.5V to +4.6V GNDD....................................................................-0.1V to +0.1V Analog Input Pins IAP, IAN, IBP, IBN, VA, VB.............................(-10mA to +10mA), (-0.5V to +0.5V) XIN, XOUT.......................... (-10mA to +10mA), (-0.5V to +3.
MAX71020 Single-Chip Electricity Meter AFE ELECTRICAL CHARACTERISTICS (continued) PARAMETER CONDITIONS MIN TYP MAX UNITS TEMPERATURE MONITOR TNOM (Nominal Value at 22°C) VV3P3A = 3.3V Temperature Measurement Equation Temperature Error (Note 4) Duration of Temperature Measurement After Setting TEMP_START 956 LSB Temp = 0.33 x STEMP + 21.77 TA = -40°C to +85°C -6 +6 TA = -20°C to +60°C -4.8 +4.8 TEMP_PER = 0 °C °C 15 60 ms 3 4.
MAX71020 Single-Chip Electricity Meter AFE ELECTRICAL CHARACTERISTICS (continued) PARAMETER CONDITIONS MIN TYP MAX UNITS -250 +250 mVpk IAP, IAN: preamplifier enabled -27.78 +27.
MAX71020 Single-Chip Electricity Meter AFE ELECTRICAL CHARACTERISTICS (continued) PARAMETER CONDITIONS MIN TYP MAX UNITS Preamplifier and ADC Total Harmonic (VIN = 28mV Differential) TA = +25°C; VV3P3A = 3.3V, PRE_E = 1 -80 dB Preamplifier and ADC Total Harmonic Distortion (VIN = 15mV Differential) TA = +25°C; VV3P3A = 3.
MAX71020 Single-Chip Electricity Meter AFE RECOMMENDED EXTERNAL COMPONENTS NAME FROM TO FUNCTION VALUE UNITS C1 V3P3A GNDA Bypass capacitor for 3.3V supply R 0.1 ±20% CSYS V3P3SYS GNDD R 1.0 ±30% µF C1P8 VDD GNDD Bypass capacitor for V3P3SYS Bypass capacitor for V1P8 regulator 0.1 ±20% µF XTAL XIN XOUT At cut crystal specified for 18pF load 9.
MAX71020 Single-Chip Electricity Meter AFE Pin Description (Pin types: P = Power, O = Output, I = Input, I/O = Input/Output. The circuit number denotes the equivalent circuit, as specified under Figure 1). PIN NAME TYPE CIRCUIT DESCRIPTION P — Analog Ground. GNDA should be connected directly to the ground plane. POWER AND GROUND PINS 2 GNDA 3 V3P3A P — Analog Power Supply. A 3.3V power supply should be connected to V3P3A. V3P3A must be the same voltage as V3P3SYS.
MAX71020 Single-Chip Electricity Meter AFE V3P3SYS V3P3SYS DIGITAL INPUT PIN CMOS INPUT ANALOG INPUT PIN GNDA GNDD DIGITAL INPUT EQUIVALENT CIRCUIT TYPE 3 V3P3SYS TO MUX ANALOG INPUT EQUIVALENT CIRCUIT TYPE 6: ADC INPUT V3P3SYS V3P3SYS DIGITAL OUPUT PIN CMOS OUTPUT GNDD GNDA GNDD DIGITAL OUTPUT EQUIVALENT CIRCUIT TYPE 4 TO OSCILLATOR OSCILLATOR PIN GNDA OSCILLATOR EQUIVALENT CIRCUIT TYPE 8: OSCILLATOR I/O Figure 1.
MAX71020 Single-Chip Electricity Meter AFE Functional Diagram GNDA V3P3A IAP MAX71020 IAN IBP IBN DC MODULATOR INPUT MULTIPLEXER PREAMPLIFIER FIR DECIMATOR VB VA VREF VREF MULTIPLEXER CONTROL XIN XOUT V3P3SYS CRYSTAL OSCILLATOR 9.83MHz MASTER CLOCK PLL VOLTAGE REGULATOR MCK VDD CKADC (2.5MHz) CLOCK GENERATOR GNDD 1.
MAX71020 Single-Chip Electricity Meter AFE Hardware Description Hardware Overview The MAX71020 energy meter analog front-end (AFE) integrates all primary functional blocks required to implement a solid-state residential electricity meter.
MAX71020 Single-Chip Electricity Meter AFE For a standard single-phase application with tamper sensor in the neutral path, two current inputs are configured for differential mode, using the pin pairs IAP-IAN and IBPIBN. The MAX71020 uses two locally connected current sensors via IAP-IAN and IBP-IBN for this configuration. The VA pin is typically connected to the phase voltage via resistor-dividers.
MAX71020 Single-Chip Electricity Meter AFE Analog-to-Digital Converter (ADC) A single second-order delta-sigma ADC digitizes the voltage and current inputs to the device. The resolution of the ADC is dependent on several factors. Initiation of each ADC conversion is automatically controlled by logic internal to the MAX71020. At the end of each ADC conversion, the FIR filter output data is stored into the register determined by the multiplexer selection.
MAX71020 Single-Chip Electricity Meter AFE Table 3. Pulse Output Function Assignments OUTPUT FUNCTION XPULSE Pulse output on each zero crossing on voltage input YPULSE Pulse output when voltage sag detected VPULSE Pulse output when programmed VARh consumption has occurred WPULSE Pulse output when programmed Wh consumption has occurred XPULSE and YPULSE Pulses generated by the CE may be exported to the XPULSE and YPULSE pulse output pins. Pins D2 and D3 are used for these pulses, respectively.
MAX71020 Single-Chip Electricity Meter AFE Table 4. Temperature Measurement Registers NAME RST WK DIR DESCRIPTION Sets the period between temperature measurements. TEMP_PER TEMP_PER[1:0] 0 — R/W TIME 0 Manual updates (see TEMP_START description) 1 Every accumulation cycle 2 Continuous 3 No updates TEMP_PER[1:0] must be zero in order for TEMP_START to function. If TEMP_ PER[1:0] = 0, then setting TEMP_START starts a temperature measurement.
MAX71020 Single-Chip Electricity Meter AFE Table 5.
MAX71020 Single-Chip Electricity Meter AFE During a power failure, as V3P3A falls, two thresholds are detected. The first threshold, at 3.0V, warns the host controller that the analog modules are no longer accurate. The second threshold, at 2.8V, warns the host controller that a serious reduction in supply voltage has occurred and that the reliability of OTP reads may be affected.
MAX71020 Single-Chip Electricity Meter AFE RIN VA VIN ROUT GNDA Figure 5. Resistive Voltage-Divider (Voltage Sensing) IOUT IIN IAP RBURDEN CT VOUT GNDA 1:N Figure 6. CT With Single-Ended Input Connection (Current Sensing) IOUT IIN IAP GNDA CT RBURDEN VOUT IAN BIAS NETWORK AND NOISE FILTER 1:N Figure 7. CT With Differential Input Connection (Current Sensing) IAP GNDA RSHUNT VOUT IAN BIAS NETWORK AND NOISE FILTER Figure 8.
MAX71020 Single-Chip Electricity Meter AFE Connecting the MAX71020 The analog input pins of the MAX71020 are designed for sensors with low source impedance. RC filters with resistance or capacitance values higher than those implemented in the demo boards must not be used. Refer to the demo board schematics for complete sensor input circuits and corresponding component values. Maxim Integrated does not recommend the use of ferrites directly at the analog signal input.
MAX71020 Single-Chip Electricity Meter AFE Host connections include the INTZ pin, the RESETZ pin, and an optional YPULSE pin. In the host controller, the DIO pin connected to INTZ should generate an interrupt. This interrupt signals to the host that an accumulation cycle has been completed.
MAX71020 Single-Chip Electricity Meter AFE Crystal Oscillator The oscillator drives an AT cut microprocessor crystal at a frequency of 9.8304MHz. Board layouts with minimum capacitance from XIN to XOUT require less current. Good layouts have XIN and XOUT shielded from each other and from digital signals. Since the oscillator is self-biasing, an external resistor must not be connected across the crystal.
MAX71020 Single-Chip Electricity Meter AFE Table 7. Register Map (continued) NAME BYTE ADDRESS R/W DEFAULT VALUE PPMC 0x01B R/W 0x0000 0000 Linear coefficient for temperature compensation. A default coefficient can be established by copying PPMCATE into PPMC. Host PPMC2 0x01C R/W 0x0000 0000 Quadratic coefficient for temperature compensation. A default coefficient can be obtained by copying PPMC2ATE into PPMC2.
MAX71020 Single-Chip Electricity Meter AFE Table 7.
MAX71020 Single-Chip Electricity Meter AFE Table 7.
MAX71020 Single-Chip Electricity Meter AFE Table 8. Hardware Control Register Map (continued) NAME BYTE R/W ADDRESS DEFAULT VALUE* DESCRIPTION Contains the characteristics of the four digital I/O pins.
MAX71020 Single-Chip Electricity Meter AFE Table 8. Hardware Control Register Map (continued) NAME BYTE R/W ADDRESS DEFAULT VALUE* DESCRIPTION Interrupt configuration register: configure the behavior of the INTZ pin.
MAX71020 Single-Chip Electricity Meter AFE Table 8. Hardware Control Register Map (continued) NAME BYTE R/W ADDRESS DEFAULT VALUE* DESCRIPTION Reflects the status of several asynchronous events in the AFE. Bits are automatically cleared after the host controller reads M_STAT.
MAX71020 Single-Chip Electricity Meter AFE Table 8. Hardware Control Register Map (continued) NAME BYTE R/W ADDRESS DEFAULT VALUE* DESCRIPTION VSTAT 0x312 R — AFE Supply Voltage Status. Bits 1:0 reflect system power status: 00: System power-OK: VV3P3A > 3.0V 01: System power-low: 2.8V < VV3P3A < 3.0V 11: System power-fail: VV3P3A < 2.8V RESET 0x322 WO — Write 0x8100 0000 to this register to reset the AFE. Configures aspects of the temperature measurement subsystem. Loaded by the LE.
MAX71020 Single-Chip Electricity Meter AFE Table 9. CE EQU Equations and Element Input Mapping WATT AND VAR FORMULA (WSUM/VARSUM) EQU 0 VA IA – 1 element, 2W 1f 1* VA x (IA-IB)/2 – 1 element, 3W 1f 2* VA x IA + VB x IB– 2 element, 3W 1f INPUTS USED FOR ENERGY/CURRENT CALCULATION W0SUM/ VAR0SUM W1SUM/ VAR1SUM I0SQ SUM I1SQ SUM VA x IA VA x IB IA — VA x (IA-IB)/2 — IA-IB IB VA x IA VB x IB IA IB *Not supported by standard CE codes. Table 10.
MAX71020 Single-Chip Electricity Meter AFE Table 11. CESTATUS Register CE ADDRESS NAME 0x80 CESTATUS DESCRIPTION See the description of CESTATUS bits in Table 7 Table 12. Sag Threshold and Gain Adjust Control CE ADDRESS 0x24 NAME DEFAULT SAG_THR 2.39 x 107 DESCRIPTION The voltage threshold for sag warnings. The default value is equivalent to 113Vpk or 80VRMS if VMAX = 600VRMS. üüü = VRMS × 2 VMAX × 7.
MAX71020 Single-Chip Electricity Meter AFE one second. Additionally, the hardware does not permit output values to fold back upon overflow. WSUM_X (register 0x084) and VARSUM_X (register 0x088) are the signed sum of Phase-A and Phase-B Wh or VARh values according to the metering equation implemented by the CE code. WxSUM_X (x = 0 or 1, registers 0x085 and 0x086) is the watt-hour value accumulated for phase x in the last accumulation interval and can be computed based on the specified LSB value.
MAX71020 Single-Chip Electricity Meter AFE The meter constant Kh is derived from WRATE and represents the amount of energy measured for each pulse. If Kh = 1Wh/pulse and 120V and 30A is applied in-phase to the meter, the meter will produce one pulse per second (120V and 30A results in a load of 3600W, or put another way, energy consumption of one watt-hour per second). If the load is 240V at 150A, 10 pulses per second are generated. To compute the WRATE value, see Table 16. The maximum pulse rate is 7.
MAX71020 Single-Chip Electricity Meter AFE Table 17. CE Parameters for Noise Suppression and Code Version CE ADDRESS NAME DEFAULT 0x25 QUANT_VA 0 0x26 QUANT_IA 0 0x27 QUANT_A 0 0x28 QUANT_VARA 0 0x29 QUANT_VB 0 0x2A QUANT_IB 0 0x2B QUANT_B 0 0x2C QUANT_VARB 0 DESCRIPTION Compensation factors for truncation and noise in voltage, current, real energy, and reactive energy for phase A.
MAX71020 Single-Chip Electricity Meter AFE MULTIPLEXER I0 V0 I1 VREF DC MOD DEMULTIPLEXER I0_RAW V0_RAW I1_RAW DECIMATOR fS = 2520Hz (ON EACH CHANNEL) fCLK = 2.458MHz Figure 10. CE Data Flow (Multiplexer and ADC) I0_RAW I0 OFFSET NULL F0 CAL_I0 PHASE COMP LPF W0 PHADJ_0 LPF VAR0 V0_RAW V0 OFFSET NULL 90° F0 CAL_V0 I1_RAW OFFSET NULL F0 PHASE COMP CAL_I1 GAIN_ADJ LPF VAR1 LPF W1 PHADJ_1 I1 F0 GENERATOR F0 Figure 11.
MAX71020 Single-Chip Electricity Meter AFE SUM W0 C W1 C VAR0 C VAR1 C W0SUM_X W1SUM_X VAS0SUM_X VAR1SUM_X SUM_SAMPS = 2520 I2 V0 V2 I1 I2 HOST SUM SQUARE I0 REGISTERS IOSQ VOSQ IISQ C C C IOSQSUM_X VOSQSUM_X IISQSUM_X F0 Figure 12. CE Data Flow (Squaring and Summation Stages) Ordering Information PART ACCURACY (%) PIN-PACKAGE MAX71020AEUI+ 0.5 28 TSSOP MAX71020AEUI+R 0.5 28 TSSOP Note: All devices are specified over the -40°C to +105°C operating temperature range.
MAX71020 Single-Chip Electricity Meter AFE Revision History REVISION NUMBER REVISION DATE 0 7/12 Initial release — 1/13 Updated the Electrical Characteristics table, Functional Diagram, and Table 7; replaced the Reset Sequence section; added a Mechanism description to the Metrology Temperature Compensation section; added new Table 8; removed original Tables 11, 12, and 13; updated Figures 3, 5−12 All 1 DESCRIPTION PAGES CHANGED Maxim Integrated cannot assume responsibility for use of any circuit
