Power Supply Communication Interface

Most of the power supply right now are controlled by a power supply internal microcontroller unit which plays a
great part on all the functions and features of the power supply.
I2C is one of the most common communication interface used in a power supply with embedded features.
I2C bus physically consists of 2 active wires and a ground connection. The active wires, called SDA and SCL, are both bi-directional. SDA is the Serial DAta line, and SCL is the Serial CLock line. The SCL & SDA lines are connected to all devices on the I2C bus. There needs to be a third wire which is just the ground or 0 volts. You need to provide pull-up resistors to the 5v supply for both SCL and SDA lines. There should be a resistor from the SCL line to the 5v line and another from the SDA line to the 5v line. You only need one set of pull-up resistors for the whole I2C bus, not for each device, see figures below:

On the illustration above, Devices can be the power supply which serves as the unit under test.
Since this site discuss all about power supply testing, using I2C bus interface, you can connect multiple slave devices or mulitple power supplies connected to common i2c bus to the Test system or Host PC.
Each slave devices or power supply should have a unique address in order for a Host PC to communicate each devices.

Communicating the UUT thru I2C communication
The Host PC or the Master will send or issue a start sequence to begin the communication to the slave devices. A start sequence is one of two special sequences defined for the I2C bus, the other being the stop sequence. The start sequence and stop sequence are special in that these are the only places where the SDA (data line) is allowed to change while the SCL (clock line) is high. The start and stop sequences mark the beginning and end of a transaction with the slave device.

Once the host will send the START SEQUENCE, this will act as and attention signal for all the slave devices on the bus. Next the master will send out the ADDRESS of the device it wants to access.  Along with the indication either it is READ or WRITE operation. The slave that matches this address will continue with the transaction and produce an ACKNOWLEDGE SIGNAL, any others will ignore the rest of this transaction and wait for the next. Having addressed the slave device the master can now start transmitting or recieving DTA. The master can continue to send data bytes to the slave. When the master has finished writing all data to the slave, it sends a STOP SEQUENCE which completes the transaction.




Here's the i2c addressing on power supplies works:
On most common practices, or standard, each power supply has an address lines that can be configurable thru the 3 address lines , A2, A1 and A0. Some power supplies have only 2 hardware address lines, some have only one address lines.
In the illustration below, it shows the three hardware address lines, which can be confiurable either 0 or 1 (0V or 5V).




In the example, the MSB which equivalent to x8 (hex) will vary based on customer requirements. But the LSB will vary on what were confirgured on the hardware address lines. EEPROM Address of the power supply will follow also on the setting of the hardware lines but on different MSB.