Protection of GPIO using voltage divider

Nir Porat

Other Parts Discussed in Thread: CC2540

Hello,

I am using CC2540 with input GPIO which is connected to a battery (3- 4.2 V),

currenlty i am using Zener to protect the I/O--> outcome voltage of 2.4-2.76V,I just wonder if ican change it with voltage divider,

i saw that GPIO input voltage can be Vdd+0.3V and<3.9V

Assuming that i am using voltage divider that will not exceed VDD i will have votlage from 2- 2.8 V , 2 volt is below the logic 1 input voltage ,

Bacilly it is working , shuold i change the range of the divider to have 2.4V to 3.3 or 2.5 to 3.5 , but this means input voltage on I/O will be higher than VDD...

What will be the best soultion ?

8 V ,

over 8 years ago

0 Robert Chen over 8 years ago

Mastermind 8905 points

Hi,

Do NOT use zener diodes to protect because the input source is battery, not signal. There will be a lot of energy going through the diode and make it burned.

A voltage divider is acceptable but the divided output voltage may be too low when low battery.

I would like suggest you to use a transistor as a buffer. The input signal will be inverted by the transistor but It is very reliable and the cost is very cheap.

0 Nir Porat over 8 years ago in reply to Robert Chen

Intellectual 590 points

Ok,

HOwever i do not want to redesgin the circuit.

can i use voltage divider that will be higher than VDD but lower than max absulue rating?

0 Robert Chen over 8 years ago in reply to Nir Porat

Mastermind 8905 points

Sure, you can do it.

0 Nir Porat over 8 years ago in reply to Robert Chen

Intellectual 590 points

How about lower logic state of 2V?
data sheet indicate for 2.5V,

2 V is working fine ..

My concern is that if iw ill use divier that can issue 3.5 V ,(with fully battery )i will apply high voltage of 3.5V on the input while VDD is 3V(higher than VDD=) for a period of upto 30 sec.

0 Robert Chen over 8 years ago in reply to Nir Porat

Mastermind 8905 points

From CC2540 datasheet, the max low input voltage is 0.5V and the min high input voltage is 2.5V. Voltage in between is not defined. Even 2V is working now it may not work stably in mass production.

So, I still recommend you to add a transistor. It is easy to manually add it on your board.

0 Nir Porat over 8 years ago in reply to Robert Chen

Intellectual 590 points

Hey ,

this is not an option since i will need to do a new layout, i rather stay with the zener diode.

The question is simple can the GPIO voltage be higher than the VCC??

the limits for the I/O are 3.9 max...

and i am using 3V for Vcc

so i can use voltage divider of 2.5 to 3.5V , my question is if 3.5V in the GPIO may cause failure to the BLE.

In addtion is i had used 2V vcc (as recommended for this chip) i would not have any I/O info on the data sheet...

My guess is that there is a treshold below 2.5V..

0 Peter Dvorak over 8 years ago

Expert 2740 points

Nir Porat said:
I am using CC2540 with input GPIO which is connected to a battery (3- 4.2 V),

A simple 1 Megohm series current limiting resistor should work.

Peter

0 Nir Porat over 8 years ago in reply to Peter Dvorak

Intellectual 590 points

Hey,

Meaning as a buffer from the signal to the input or from the input to the Ground?

BTW dow anyone knows the results for lower working voltage such as 2.5V?

Data sheet does not refering to such case.

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Protection of GPIO using voltage divider