The AD-ACEVSECRDSET-SL design incorporates the ADE9113 3-Channel, Isolated, Sigma Delta (Σ-Δ) ADC and the MAX32655 low-power, Arm Cortex-M4 processor with FPU-Based microcontroller and Bluetooth 5.2 allowing the implementation of type 2 EVSE charging cables. The ADE9113 has two voltage measurement channels and a current measurement one used to implement the safety functions in the firmware. The integrated isolation makes the connection with the MAX32655 straightforward. The communication between the two components is implemented over SPI.
The system is powered from the single phase 230V AC input. An isolated AC-DC SMPS is used to deliver 12V to the board and the MAX20457 high-efficiency dual synchronous buck converters for automotive applications are used to step down the voltage to 5V and 3.3V providing power to the isolated side of the board. The LT8330 used in the inverting configuration generates the 12V negative voltage needed for the low side of the CP signal.
The MAX32655 exposes all the necessary debug and programming features enabling a complete software development experience. The Bluetooth 5.2 LE radio with the available fully open-source Bluetooth 5.2 stack makes it easy to develop an interaction method between the user and the board. Four user buttons and 4 LEDs are also provided to complete the user interface. Serial communication (RS-232) is used for sending debug messages during testing or development.
The ADT75 12-Bit digital temperature sensor monitors the temperature of the device and sends it to the MCU unit for implementing overtemperature protection.
The main components used in the design are highlighted in the following figures.
In order to power up the board the “grid connector” must be connected to a single phase 230V AC line. A 3-wire cable rated at 16A is the minimum acceptable. The output can be connected to an EVSE test adapter, a type 2 cable (and EV) or it can be left disconnected for the first-time power up or for programming. The prog/debug connector which is a 10-pin ARM Cortex debug connector must be connected to a programmer e.g. MAX32625PICO MAXDAP DAPLink programmer based on the MAX32625 through a cable in case a firmware update is available. The MAXDAP can be also used to read the debug messages during the development stage. The messages are sent via RS-232. The UART device ID is 0 with the following settings (57600 8N1). In the following figure the messages received on a computer connected to the board through the MAXDAP with the debug print option being active are presented. After the self-test finishes a charging session can be initiated by the EV or the device connected to the “EV connector”. The following image presents the debug messages received during a charging session.
The buttons and LEDs are connected to the MCU as indicated in the above image. The LEDs are used to display the current state of the EVSE or the type of error in case that one has been detected.
For evaluation and debugging purpose, test points are provided at every important point on the PCB. The names of the test points are printed on the silkscreen.
The CP signal is presented for each state (A, B, C, D and diode error) in the following images, measured at two different points on the board. The first image for each case represents the value measured at the CP test point highlighted in the following image and the second one at the CP_READ test point corresponding to the MCU ADC input.
The values of the CP signal must be in the limits indicated in the next table for each state.
|State||CP signal type||CP high value [V]||CP low Value [V]||Equivalent resistance [Ω]||EV status|
|State A||PWM/DC||12 [11;13]||-||-||Not connected|
|State B||PWM/DC||9 [8;10]||-12||2740||Connected|
|State C||PWM/DC||6 [5;7]||-12||882||Charging, does not require charging ventilation|
|State D||PWM/DC||3 [2;4]||-12||246||Charging, ventilation required|
|State E||DC||0 [-1;1]||0||-||Fault in control circuit|
|State F||DC||-||-12||-||Unknown fault|
Two measurements are presented following a complete run of the state machine from power-up to charging and EV disconnected. The tests are done using the following test bench setup.
Setup of the EVSE with the type 2 cable connected on the EV side.
If you want to go back to the SOFTWARE SETUP, click here: AD-ACEVSECRDSET-SL Software User Guide