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Weak Internal Pull-up Resistor

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davyzhu

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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
 

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.
 

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.
 

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

Regards,

Davy
 

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

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 .
 

Is weak pull-up result in small current?

And the 'weak' mean 'weak current'?

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

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

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

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.
 

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

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