Use the 50-Ohm Antenna as voltage input.

[WFKwok]

Hello, we are developing a BLE application using nRf52833.
Because of the waterproof & stainless steel casing requirement with rechargeable battery charging capability,
we would like to ask if we can use the 50-ohm antenna as a 5V power input and for battery charging.

Here is the idea: (refer to the attached picture for details)
- First of all, there are only 2 pins exposed on the casing, GND and VCC/ANT(50-ohm antenna),
where VCC/ANT pin is used as 50-ohm antenna or for +5V input.
(i) In normal case, the 50-ohm antenna pin is BLE antenna.
(ii) If 5V is detected from the antenna pin, stop the BLE and set LDO enable for battery charging.
(iii) If 5V is no longer detected from the antenna pin, set LDO disable and turn on the BLE.

Questions:
1: Is the idea mentioned above feasible?
2: There will be some voltage on the ANT pin while 5V input from antenna pin.
What is the maximum voltage to the ANT pin without affecting the function or causing damage?
3. Or is it possible to isolate the ANT pins if we use the antenna pin as 5V input by GPIO configuration in the firmware?
so that we can isolate the ANT pins or set it to other usage for protection.
4. How about if we change the charging voltage from 5V to 2.7V, i.e. we use +2.7V input instead, is it much better and feasible?

Thanks a lot.

[WFKwok]

Some more info, we do plan to add an RF switch to isolate the charging path while not in BLE usage.
And we will apply 2.7V instead of 5V for battery charging.
Just not sure whether the RF switch can stand for the load 2.7V with 20mA.
So is it still feasible to achieve the idea with an RF switch?  

[Kazi Afroza Sultana]

Hello,

1: Is the idea mentioned above feasible?

2: There will be some voltage on the ANT pin while 5V input from antenna pin.
What is the maximum voltage to the ANT pin without affecting the function or causing damage?

4. How about if we change the charging voltage from 5V to 2.7V, i.e. we use +2.7V input instead, is it much better and feasible?

The idea is not feasible as ANT pin is designed for RF signals and should be connected to a 50-ohm antenna through properly matching RF network. The ANT pin is not designed to work on DC power input or battery charging current. 

General PCB design guidelines for nRF52 series  

3. Or is it possible to isolate the ANT pins if we use the antenna pin as 5V input by GPIO configuration in the firmware?
so that we can isolate the ANT pins or set it to other usage for protection.

As I mentioned in my previous reply, ANT pin is only dedicated for RF performance. So, it can not be reconfigured or isolated via firmware. It is not possible to multiplexed with GPIO unlike NFCT pin. You can use NFC pin as GPIO pin with some modification in hardware and software.