Weak Internal Pull-up Resistor

[davyzhu]

Hello all,
I have read datasheet of some IC and found "Internal Pull-up Resistor", "Open drain", and "Weak Internal Pull-up", why use these?

Regards,

Davy Zhu

 

[papyaki]

Hi,

Internal pull-up are generaly used to have a known state on inputs, even if the input pin is left unconnected.

Open drain is related to output, but need to be connected to a pull-up for correct operation.

Open drain outputs can be connected together or can be connected internaly to an input. This generaly the case on I/O port pins. The port, or pin direction (input or output) is selected through an internal register.

 

[kinysh]

Internal pull is to make sure there is no floating input. Other wise there will be big power, even damage the pad.

Open Drain is a IO that will be used in several bus spec.
such as I2c.

 

[Rayengine]

Open-drain apps likes I2C bus and IOM bus.

 

[davyzhu]

But what the difference "Weak Internal Pull-up" and "Internal Pull-up".

Regards,

Davy

 

[zcq]

Another question,usually,what's the internal pull-up resistor value can be called weak pull-up?

 

[Nobody]

The pull-up can result in large leakage current .
Therefore it need some kind of weak pull-up instead .
It is usually implemented by pmos and change a lot from process variation .

 

[davyzhu]

Is weak pull-up result in small current?

And the 'weak' mean 'weak current'?

If it means 'weak current', is it <1mA?

 

[sean]

Usually, the weak pull-up resistance is lower than 50kohm. If you supply 3.3 voltage to power pad, the current is under 1mA.

 

[dumbfrog]

weak pullup/pulldown usually implemented using P/NMOS
and it is much less than 1mA (~30uA range)

 

[giggs11]

The I/O pads can be characterized according to their Pull-up or Pull-down resistor values which may range between 25kOhm and 100kOhm. Therefore the distinction between a weak pull-up/down and a large one is dependent on the designers perspective.

 

[alphi]

weak pull-up general for input signal pull-up
Pull-up is use for open drain output