Powering the LinkIt 7697
In this article, we'll explain the power rails on LinkIt 7697 for developers to have a clear view about how to supply power to LinkIt 7697 and what voltage output you can get from the board in different use cases.
Power related pins
There are five types of pins:
Ground pins. 4 GND pins are broken out on LinkIt 7697 pin header.
General signal pins (P0 ~ P17). They work with 3.3V power for all functions except ADC (see the item #5 below).
Two 3V3 pins (marked as yellow in the figure below). When LinkIt 7697 is powered with a 5V power source, 3V3 pins would output 3.3V. If there is no 5V input, developers can feed 3.3V into any one of 3V3 pins for powering up LinkIt 7697.
5V pins (marked as red). There are two ways to feed 5V into LinkIt 7697:
from the USB connector, and
from the 5V pin.
Both pins are connected together so when one of them is fed with 5V, the other pin will output 5V. If neither of the pins are fed with 5V and 3V3 pins are fed with 3.3V, those 5V pins will output 3.3V.
ADC pins. When P14 ~ P17 pins are set to ADC function, the input voltage range would be from 0 ~ 2.5V. Make sure when doing ADC operations, the input voltage for P14 ~ P17 would not exceed 2.5V.
When P14 ~ P17 work under functions other than ADC (e.g. GPIO or PWM), the working voltage is still 0 ~ 3.3V.
3.3V and 5V power flow
Here we show different scenarios mentioned above for 3.3V and 5V I/O relation.
USB 5V input
This is a typical application scenario. LinkIt 7697 is powered through a USB cable. So there is a 5V input from the USB connector. In this case, developers can get 5V output from the 5V pin and 3.3V output from both 3V3 pins.
When LinkIt 7697 is not connected with a USB cable, it can still be powered on by feeding 3.3V power source through pin headers. In this way, one of the 3V3 pins is the power input pin and the other 3V3 pin is a 3.3V output pin. Moreover, the 5V pin would also output 3.3V in this case (not output 5V).
or
In this case, developers can still connect the D+ / D- wires from a USB cable to the D+ / D- headers on LinkIt 7697 to access the system serial port.
5V input through pin header
This is an extended use case where 5V power source only comes from the pin header, not from the USB connector. In this way, the 5V pin is used as the power input and both 3V3 pins output 3.3V. Since the 5V pin are connected with the 5V wire in the USB connector(*), the LinkIt 7697 can server as a 5V USB power provider as in the video shown below.
Not only the 5V pin and the USB 5V wire are connected together, D+ / D- header pins are also connected to the D+ / D- wires in the USB connector. Using the USB interface through pin headers provides more flexibilities to developers for designing their own breakout boards without connecting a USB cable to the LinkIt 7697.
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