1. Overview The CS5460 is CRYSTAL's latest single-phase bidirectional power/energy metering integrated circuit chip with a serial interface. Compared to the AD7750 and AD7755, which are widely used in electronic electricity meters (see the article in "Foreign Electronic Components" Issue 3, 1999), the CS5460 adds the following functions: ● On-chip watchdog timer and internal power monitor; ● Instantaneous current, instantaneous voltage, instantaneous power, RMS current, RMS voltage, RMS power measurement, and energy metering functions; ● External reset pin; ● Bidirectional serial interface and internal register array for easy connection to microprocessors; ● External clock frequency up to 20MHz; ● Power direction output indication. These added functions facilitate interfacing with microprocessors (MPUs) and enable convenient implementation of voltage, current, power measurement, and energy consumption accumulation functions. [img=325,187]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gwdzyqj/2000-7/2-1.jpg[/img] 2. Basic Structure and Technical Specifications 2.1 Internal Structure The CS5460 integrates two Δ-Σ A/D converters, high-pass and low-pass digital filters, an energy calculation unit, a serial interface, a digital-to-frequency converter, a register array, and a watchdog timer, among other analog and digital signal processing units. Its internal block diagram is shown in Figure 1. 2.2 Pin Arrangement and Functions The pin arrangement of the CS5460 is shown in Figure 2. The functions of each pin are as follows: Pin 1 XOUT: Crystal oscillator output; Pin 2 CPUCLK: CPU clock output; Pin 3 VD+: Digital circuit power supply positive terminal; Pin 4 DGND: Digital ground; Pin 5 SCLK: Serial clock input; Pin 6 SDO: Serial data output; Pin 7 CS: Chip select; Pin 8 NC: No connection; Pin 9 VIN+: Differential voltage positive input terminal; Pin 10 VIN-: Differential voltage negative input terminal; Pin 11 VREFOUT: Reference voltage output; Pin 12 VREFIN: Reference voltage input; Pin 13 VA-: Analog ground; Pin 14 VA+: Analog power supply positive terminal; Pin 15 IIN-: Differential current negative input terminal; Pin 16 IIN+: Differential current positive input terminal; Pin 17 PFMON: Power-down monitoring output; Pin 18 NC: No connection; Pin 19 RESET: Reset input; Pin 20 INT: Interrupt output; Pin 21 EOUT: Power pulse output; Pin 22 EDIR: Power direction indicator output; Pin 23 SDI: Serial data input; Pin 24 XIN: Crystal oscillator input. [img=135,174]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gwdzyqj/2000-7/2-2.jpg[/img] 2.3 Main Technical Specifications ● Differential voltage input range: 150mV; ● Temperature coefficient: <60ppm/℃ ● Power consumption: <10mW; ● Energy metering accuracy: 0.1% per second above the 300: dynamic range; ● Voltage measurement accuracy: 0.1% of the reading; ● Current measurement accuracy: 0.1% of the reading; ● Instantaneous power measurement accuracy: 0.1% of the reading. [img=357,253]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gwdzyqj/2000-7/2-3.jpg[/img] [b]3. Serial Interface and Its Operation[/b] 3.1 Serial Interface The CS5460's serial port includes four control lines: CS, SDI, SDO, and SCLK. If the chip select CS is directly connected to logic 0, only three lines are needed to complete the serial port operation. Experiments also showed that if the serial data input SDI and the serial data output SDO are connected together, serial reading can also be performed, and only two interface lines are needed. This is extremely advantageous for systems using AT89C1051 and AT89C2051. Data transmission always begins with sending an 8-bit command to the SDI pin of the serial interface. When the command includes a write oscillation, the serial port will continuously read serial data from the SDI pin for the next 24 SCLK cycles. When a read command is issued, the serial port will serially output the register contents from the SDO pin for the next 8, 16, and 24 SCLK cycles, respectively, according to the issued command. Figure 3 shows the timing diagram for reading the register. 3.2 Internal Register Allocation The CS5460 integrates 16 registers, including a bias register, gain register, pulse rate register, and parameter register. It also integrates a serial port transmit register, a serial port receive register, and a command interpretation state machine. These registers are used to configure the CS5460, store acquired data, and control serial input/output. The internal register allocation diagram of the CS5460 is shown in Figure 4. After system initialization or reset, the CS5460 internal registers are initialized to the following states: Configuration Register: 0X000001 Bias Register: 0X000000 Gain Register: 0X400000 Pulse Rate Register: 0X0FA000 Cycle Count Register: 0X000FA0 Time Base Register: 0X800000 Status Register: 0X000001 Mask Register: 0X000000 Signed Register: 0X000000 Unsigned Register: 0X000000 [img=217,155]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gwdzyqj/2000-7/2-4.jpg[/img] 3.3 Command Explanation and Operation Operations of the CS5460 are achieved by transmitting command words to it. The CS5460 provides seven operation commands, including register read/write and calibration control, all of which are 1 byte (8 bits) long. The command state machine interprets the 8-bit command word on the rising edge of SCLK, interpreting it as a recognized standard and preparing for data transfer. This article only briefly explains the register read/write command as an example; for detailed information, please refer to the CS5460 user manual. Register Read/Write Command: This command notifies the state machine that a register access is needed. Over eight SCLK clock cycles, the address register is read and loaded into the output buffer; on the 24th SCLK, the write data is transferred to the input buffer. Where: W/R: Write/Read Control 0 = Read Register 1 = Write Register RA0～RA4: Register Address Bits [img=228,191]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gwdzyqj/2000-7/2-5.jpg[/img] 4. Application of CS5460 4.1 Electricity Meter The CS5460 can be used to measure instantaneous current, instantaneous voltage, instantaneous power, electrical energy, and the effective values ​​of voltage and current. The measurement results will be stored in the internal register in 24-bit signed or unsigned form. In addition, the CS5460 also provides an energy metering pulse output port EOUT and a power direction port EDIR, so it can be easily connected with a stepper motor counter to form a simple electricity meter. When the crystal oscillator frequency is 4.096MHz, the frequency division ratio is 1, and the DC input of both converters is at its maximum value, the frequency of the output pulse is the same as the frequency of the pulse speed register. Figure 5 shows a typical electricity meter circuit. Its basic current RMS value is Ib = 20A, phase line voltage RMS value is V = 220V (50Hz), and metering constant is K = 500imp/kWh. Assuming the maximum current RMS value is Imax = 100A and the maximum voltage RMS value is Vmax = 300V, based on the CS5460's technical specifications of a differential voltage input and differential current input maximum of 150mV, the transformation ratios Ki and Kv of the current and voltage channels are 1/10000 and 1/20000, respectively. When the maximum current on the secondary side of the current transformer is selected as 10mA, the value of the secondary side sampling resistor R1 should be 15Ω. 4.2 Distributed Electricity Metering Control System Based on CS5460 Currently, university student dormitories in my country generally use power rationing measures to control school electricity usage. After the socialization of dormitory management, the restriction on student electricity consumption will be changed to encouraging safe electricity use, thus adopting a system of limiting safe power, limiting basic electricity fees, and charging for excess usage. To meet market demands, we designed a distributed power control system using the CS5460, achieving both decentralized and centralized management of electricity consumption in the apartment complex. Figure 6 shows the distributed power metering control system based on the CS5460. The system's features are: [img=145,129]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/gwdzyqj/2000-7/2-6.jpg[/img] ● Single-line (or power line carrier) transmission reduces engineering construction and line costs. ● The front-end uses the AT89C2051 series microcontroller and CS5460 chip, realizing functions such as power, current, voltage measurement, and power metering, offering a high performance-price ratio and stable, reliable operation. ● It adopts the RS485 (or CAN bus) communication standard, enabling long transmission distances and easy networking. ● It allows for centralized critical measurement and control of power consumption, current, and energy usage.