Freescale Semiconductor, Inc. Document Number: DRM146 Design Reference Manual Rev. 0, 03/2014 Three-Phase Power Meter Hardware Design Reference Manual by: Albert Chen and Shawn Shi 1 Overview Freescale three-phase power meter reference design is structured in accordance with the standard by China state grid corporation Q/GDW 354 2012 (functional specification for smart electricity meters), Q/GDW 356 2012 (the type specification for smart poly-phase electricity meters). The reference design aims at shortening time to market for power meter customers and partners, and it can be tailored to customer s unique need in powering system. Contents 1 Overview...1 2 Introduction...2 3 Demo board content...4 4 Demo board hardware features...6 5 Three-phase power meter demo board...6 5.1 System power...6 5.2 Clock...7 5.3 Debug interface...8 5.4 Voltage sampling...9 5.5 Current sampling...10 5.6 Frequency measuring...11 5.7 External memory...11 5.8 Tamper protection...12 5.9 Pulse output...13 5.10 RS485 interface...14 5.11 LCM display...15 5.12 Backlight control...15 5.13 Jumper table...16 6 Conclusions...16 7 References...16 8 Revision history...16 2014 Freescale Semiconductor, Inc.
2 Introduction The three-phase power meter reference design is uses the Freescale ARM Cortex -M0+ core 44PIN KM14 as the metering IC and ARM Cortex-M0+ KL36 core 100PIN KL36 as the IC controller. The reference design primarily consists of a power board, main control board, and LCM board. Figure 1, Figure 2, and Figure 3 represent the block diagram of power board, control board, and LCM board respectively. Figure 1. Power board block diagram 2 Freescale Semiconductor, Inc.
Figure 2. Control board block diagram Freescale Semiconductor, Inc. 3
Figure 3. LCM board block diagram 3 Demo board content Figure 4. Power board top side content 4 Freescale Semiconductor, Inc.
Figure 5. Control board top side content Figure 6. LCM board top side content Freescale Semiconductor, Inc. 5
4 Demo board hardware features The Freescale three-phase power meter includes the following hardware features: ARM Cortex-M0+ core MKM14Z64CHH5, 44 LGA (5 mm x 5 mm), 50 MHz, 64 KB Program flash memory, and 16 KB SRAM. ARM Cortex-M0+ core MKL36Z256VLL4, 100 LQFP (14 mm x 14 mm), 48 MHz, 256 KB Program flash memory, and 32 KB SRAM. 3 220/380 V voltage input to generate two isolated 5 V DC output, one is used for the system while the other is used for 485 communication. Current sampling: using 0.05% accuracy CT, 25ppm shunt, and 24-bit SD ADC. Voltage sampling: using 25ppm resistor divider, 16-bit SAR ADC. KM14 internal ACMP module used for zero cross point detection. 5PPM RTC achieved using external 0.5C resolution temporary sensor, external 32.768 Hz crystal, and internal RTC module. Two isolated RS485 output in half duplex mode, ISL3152EIBZ used. Infrared circuit use AT205B as transmitter and TSOP4838 as receiver. External 512 KB I2C EEPROM 24LC512, 64 MB SPI Flash MX25L6406EM2I-12G used as memory extension. 3 isolated electrical pulse output, 3 light pulse output used for meter calibration/indication/test. Tamper protection: Temper input pin detection for box opening, I 2 C based magnetic sensor for activity detection. Display: I 2 C port based LCD drive chip HT16C23 and JIYA 8*32 LCD display module used with backlight control. 5 Three-phase power meter demo board 5.1 System power The demo board is powered by 220 V AC, the power board will transfer the grid AC voltage into two isolated linear 5 V DC outputs. One 5 V DC output is used to power the MCU system while the other is used for isolated RS485 communication. In power line off mode, the system will use 6 V lithium battery as backup power. Also, there is one 3.6 V battery which powers the RTC alone and should work for the duration of the meter s life. Because the MCU system requires 3.3 V DC input, it must use LDO to transfer the 5 V input to 3.3 V output in system. This LDO needs to be low in quiescent current and low in noise. 6 Freescale Semiconductor, Inc.
Figure 7. DC power supply Figure 8. External VREF supply option 5.2 Clock The KM14 system is uses an external 32.768 KHz crystal, while the KL36 system uses an 8 MHz external crystal. For the Km14 system, a Citizen +/-20ppm 32.768 KHz crystal is used. This crystal can be used for RTC clock generation, which requires high consistency in production. For the Kl36 system, an Abracon +/-20ppm 8 MHz crystal is used. The customer can use an internal RC clock as an alternate. Freescale Semiconductor, Inc. 7
Figure 9. Oscillator circuit 5.3 Debug interface Both the KM14 and KL36 system use a SWD debug port. The customer can use Jlink and Multilink tools to develop and debug the code. The software uses an IAR tool chain and only needs to configure the IDE to run the selected hardware debugger. Figure 10. KL debug port Figure 11. KM debug port 8 Freescale Semiconductor, Inc.
5.4 Voltage sampling Power line voltage sampling is uses a 16-bit SAR ADC, 220 V AC transfer to around 0.17V AC using a resistor divider, then the circuit adds 0.6 V DC offset to this AC signal before putting into SAR ADC for sampling. The 0.6 V DC offset is generated using the KM14 internal 1.2 V VREF output and external amplifier divider circuit by default. There is an option for using external 1.2 V VREF for the system which also requires software switch configuration. Figure 12. Voltage sampling circuit Freescale Semiconductor, Inc. 9
5.5 Current sampling Current sampling is uses AFE 24-bit ΣΔ ADC module, load current is through the original side of CT(5/60A current, 0.05% accuracy, 2000 ratio). The second side current will pass through the 4.7R shunt resistor to generate differential voltage to ΣΔ ADC. Figure 13. Current sampling circuit 10 Freescale Semiconductor, Inc.
5.6 Frequency measuring Grid AC frequency is monitored using a Photon internal ACMP module. The ACMP module has two inputs. One of the ACMP inputs is the AC voltage after resistor divider and adding offset while the other ACMP input is 0.6 V offset. Figure 14. Frequency measuring circuit option 5.7 External memory The system uses 512 KB EEPROM which is based on the I 2 C port and 64 MB SPI flash for memory extension. The choice of memory type and size is quite application-dependent, so those memories are reserved for customer application usage; only low level read/write logic is implemented in the software. Figure 15. External SPI based flash Figure 16. External I 2 C based EEPROM Freescale Semiconductor, Inc. 11
5.8 Tamper protection There are various types of tamper protection available in the system, few of them are as follows: Tamper detection pin: It monitors the box open action. Magnetic sensor: It detects the activity in the system. Voltage missing mode: The system can enter into low-power mode and periodically sample the current to prevent tampering. Figure 17. Tamper input circuit Figure 18. Magnetic sensor 12 Freescale Semiconductor, Inc.
5.9 Pulse output The power meter has an isolated electrical output and light pulse output, which is used for accuracy test/calibration, RTC test/calibration, and status indication. Figure 19. Isolated pulse output circuit Figure 20. Light pulse output circuit Freescale Semiconductor, Inc. 13
5.10 RS485 interface The power meter system has two isolated RS485 port. Those ports are in half-duplex mode and could be used for multiple purposes by end users. Figure 21. Isolated RS485I circuit Figure 22. Isolated RS485II circuit 14 Freescale Semiconductor, Inc.
5.11 LCM display The power meter system has the LCM display which uses the HT16C23 LCD drive IC and 8*32 segment LCD display. In application, the KL36 will send data periodically to HT16C23 to update the content displayed on segment LCD. Figure 23. LCM display 5.12 Backlight control The LCM module uses 2*15 ma diodes as backlight. The system could switch it on/off according to the application. Figure 24. LCD backlight control circuit Freescale Semiconductor, Inc. 15
5.13 Jumper table Table 1. System jumper table option Jumper Option Setting Description J2 RTC power supply 1-2 RTC power supply on J3 System 3.3V power supply 1-2 System power supply on J38 External VREF power supply off Internal VREF is used by default J30 ACMP pin function multiplexed with debugging port on Switch SWD_IO_KM/CMP0_P2 pin as ACMP function during demo J31 ADC pin function multiplexed with debugging port on Switch SWD_CLK_KM/AD6 pin as ADC function during demo 6 Conclusions This design reference manual describes hardware design points with the three-phase power meter demo boards. For technical details about the board design and solution implemented, see the documentation section on freescale.com. 7 References Following references are available on freescale.com: Kinetis M Series MCUs Kinetis L Series MCUs 8 Revision history Table 2. Revision history Revision number Date Substantial changes 0 03/2014 Initial release 16 Freescale Semiconductor, Inc.
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