What to do with the unconnected PIns...........

[rakesh_aadhimoolam]

what to do with unconnected op amps

Hi.....

i have an elementary Q abt ckts that we design.......

A chip has 12 pins(let us say).......only 7 pins are being used..............

what should i do with the remaining Pins........as they can introduce Noise......


waiting for your replies.......

thanks

 

[IanP]

what to do with unconnected pins

If in the data sheet there is an indication on how to "treat" unconnected pins, follow this instruction ..
Otherwise, leave them not connected ..

However, if they are internally "connected" and serve as unused inputs or outputs, see:
**broken link removed**
http://www.piclist.com/techref/logic/xtrapins.htm

Regards,
IanP

 

[The Joy of Electronics]

unconnected pins op amp

Some chips requre their so-called unused pins to be pulled up or pulled down but follow the instructions provided in the data sheets.

G.L.

 

[codeking911]

electronics unconnected pin

In my electronics kit that I learned electronics from it says to ground all unused pins.

 

[sivasujith]

what to do with pins that are left open

hi...

Follow datasheet for gud results and i prefer either pull-up or pull-down as per the sheet is an optimal way......

Regards,

Sujith

 

[ted]

why do we place pullups on unconnected pins

To summarize the above, and to clarify some of my experiences:

-- The data sheet recommendation should be used, if available.
-- Unused input ports of most devices should not be left floating, but connected to an "inactive" state. If active-high, you should ground, if active-low, you should pull them up.
-- If in doubt (and if you can afford due to space, etc) - use a resistor to pull up or down. It may be safer, and give you an option to change the circuit without any dramatic things such as PWB re-design, if you regret/find otherwise during a test. For most modern CMOS devices there is a negligible DC current present, so the resistor may be quite large, for example in tens of kilo-ohms range.
-- Unused output pins should generally be left floating.
-- The initial state of programmable pins is essential: If an I/O pin is initially input, you should not let it float, if initially an output, do not hard ground or connect to the supply. A resistor may be here the most fail-safe way to pull "weakly" during floating times, while allowing the output to work normally...
-- In case of pull-up, be aware of the input voltage range, and use a correct voltage to pull it up.

br ted

 

[rosarioantony]

unconnected pin should be grounded

You can connect to positive supply or ground or left the pin open.
take the advice from the datasheet.Unless the manufacturer says "should not left open ... connect a capacitor or res to ground if not used" , you dont need to worry about the unconnected pin. If you think the unconnected pin will cause some noise then you connect the pin to ground if wont affect the circuit.

 

[mannnish]

cmos unconnected pins

i think the unconnected pins should be grounded

 

[khaila]

for safe mode:
1. connecet the the input pins to prallel PULL-UP and PULL-DOWN. This way will give you more flexability. Generally input PINs should be grounded but who knows??? so take into consideration the option of PULL-UP.

2. Output PIns should be left...but if where are dealing with FPGA you should drive internally the UNUSED outputs with GROUND.

Finally, as the other friends opinion, you should consider the DATASHEET of the IC.
99.99999999% of every IC datasheet consider unconnected pins.

 

[ankit12345]

I think,In FPGA ,keeper circuit will take care of this problem

 

[lizardk]

I would ground all unused pins.

 

[Kral]

rakesh_aadhimoolam,
For analog circuits, such as op amps, you should connect the input pins in such a way that the output is in a defined state. For example, if you have an unused op-amp in a quad op amp package.
.
For digital devices, the same advice is generally applicable. However, if you want to be able to use an unused input for troubleshooting purposes, it's a good idea to pull the input up or down through a resistor. For example, a device might have an active low reset pin that is not used in your application. If you pull it up through a resistor, then you have the option of resetting the device by pulling it down by shorting it to ground, for troubleshooting purposes. If you tied the input directly to Vcc, then you don't have this option.
Regards,
Kral

 

[xgladiox]

the other uses for bandwidth extension cases

 

[jsps]

It is better to connect to circuit common, as they may introduce noise.
But one should refer manufacturer's datasheet