Supply voltages and ground levels

The board operates with three supply voltages (V3P3, V6P0 and V3P3A) and two grounds (PGND and GND).

The VP3P3 (3.5V) and VP6P0 (6.3V) are the supply voltage for the ATmega644 and other miscellaneous parts of the design, such as the electronic load, that are used to support the development of an application.

The V3P3A (3.3V) is an adjustable mixed analog and digital supply voltage for the ATtiny devices - this is used for the core part of the battery-charger. The mega644 can adjust this voltage, if desired. The PWM from OC2B set the adjustment and the output Q3 on the port expanded U202 enables the adjustment.

PGND is used as ground reference for all power electronics (buck converter, electronic load and so on), while GND is used as ground reference for other noise sensitive analog circuits and low-current part of the circuits such as the microcontrollers. The PGND and GND are connected at two points, the R142 and the R143, which are both 0 ohm resistors