3. Understanding CatSink
You can find the project schematic at Hw/CatSink/CatSink.kicad_sch.
To understand the CatSink circuit more easily, we can divide it into 4 parts:
- Charger input by USB type C
- Charging controller
- Voltage output
- Status indicators
The charger is connected with the PD protocol and capacitors are added to remove the noise from the power line. This improves the output signal quality of the circuit.
The charge controller is responsible for controlling the amount of current supplied to the connected circuit. In this case, the charge controller is an integrated circuit called CYFD3177 or EZ-PD™ BCR.
The charge controller has different parts for its operation, some of the most important to understand its operation (taking the previous image as a reference) are:
- Energy Negotiator (Circuit enclosed in black)
- PD profile selector (Pins are circled in green)
The Energy Negotiator is responsible for ensuring that the output given by the chip is the desired one, for this it constantly compares the voltage provided by the charger with the one that the chip delivers to the output, and in this way an output of correct voltage.
By means of VBUS_MAX (Pin 2) and ISNK_COARSE (pin5) the desired output profile is chosen, and for this purpose voltage dividers are used, which by changing each switch position generate a different configuration for each PD profile available.
The chip that makes all this work and manages the energy is the EZ-PD™ BCR (CYPD3177). And you can find the datasheet at EZ-PD™ BCR (CYPD3177) Datasheet.
The voltage output consists of a capacitor to help filter the signal and help the output to be stable and a terminal block. In addition of the circuit that helps to negotiate the output and ensure that it is correct.
CatSink has two LED indicators:
- Power LED: which indicates if the board is being powered correctly.
- Fault LED: indicates that the selected configuration is not correct.
In the previous picture, you can observe two 4-position switches: The first switch selects the amount of current you want to provide (1 to 5 amperes). The second switch selects the output voltage (5, 9, 12, and 20 volts).
These values depend on the charger you use when connecting to the USB port.
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