Hardware Design differences between the adk board and the Arduino rj2560 Board

The adk Board (a board) released by Google was designed with reference to the Arduino Board (M board). Let's see what's different.

	Adk	Arduino mege2560
Power Supply	Lt3480edd # PBF LP2985-33DBVR	MC33269D-5.0 LP2985-33DBVR
MCU	ATMEGA2560-16AU	ATMEGA2560-16AU
USB to serial port	FT232RL-REEL	Atmega8u2
USB Host	Max3421eetj +	None

1. Power Supply Design:

The power supply of the two Boards is designed to convert the external power input to the 5 V and 3 V operating voltages required by the Boards.

Figure 1-1 m board Power Supply Design (5 V)

The M-Board uses a voltage conversion chip (MC33269D-5.0) to convert the input voltage to + 5 V operating voltage, the maximum input voltage of the chip is 20 V. Figure 1-1 shows two mc33269 chips, and the actual board uses only one chip. Why is this design required? In fact, this is only compatible with different chip packages. On the PCB diagram, we can see that the cables of these two chips are stacked together.

Figure 1-2 a board Power Supply Design (5 V)

A Board uses a switching voltage regulator chip (lt3480edd # Pbf) to convert the input voltage into a + 5 V operating voltage. The input voltage range of the switching voltage regulator chip is 3.6 V-36 v, output voltage range: 0.79 V-20 V; switch frequency range: 200 kHz-2.4 MHz.

Figure 1-3 m board Power Supply Design (3.3 V)

Figure 1-4 A board Power Supply Design (3.3 V)

Both board m and board a use a LP2985-33DBVR chip to convert 5 V voltage to the required 3.3v voltage, both circuits use a p-channel power MOS tube fdn340p as the switching switch between DC power input and USB power input. As shown in figure 1-3 and 1-4, when Vin does not have an external DC power supply, the 5 V voltage of the board is provided by usbvcc, and the current in the mos tube flows from the drain pole to the source level. When Vin has an electrical input, when the voltage reaches the threshold (calculated, about Vin> 6.6 V of the M-board; Vin> 7 V of the-board), the voltage on the gate of the mos tube is + 5 V, the source-to-drain current of the mos tube is truncated, preventing the current in the Board from flowing to the USB interface.

2. USB to serial port design:

Figure 1-5 m-board USB-to-serial port design

A Board uses a chip (FT232RL-REEL) that occupies USB to RS232 to realize the function of communication between the circuit board and PC. The chip is produced by ftdichip, at the same time, the company also provides drivers for users to download on the website. After the driver is installed step by step according to the installation guide provided on the website, a new serial port will appear in the Device Manager of windows. This serial port is not a real serial port, the virtual serial port is a virtual serial port of the driver. However, when we develop a PC program, the virtual serial port can be controlled in the same way as the real serial port.

Figure 1-6 USB-to-serial port design of board