Value of internal pullup resistors in PIC16F1704

[treez]

Hello,
The PIC16F1704 datasheet doesnt say what is the value of the internal pullup resistors.
Do you know?

PIC16F1704 datasheet
https://ww1.microchip.com/downloads/en/DeviceDoc/40001715D.pdf

 

[KlausST]

Hi,

The pull-up current is specified with 25uA ... 200uA at 3.3V.
This should be enough information.

Klaus

 

[Aussie Susan]

The data sheet does refer to 'weak pull-up' (or 'pull-down') but this is not ever followed by the word 'resistor' (except referring to an external resistor that you need to add for various situations - e.g.I2C).
I'm not sure about that device but often the 'pull-up' and 'pull-down' is implemented with a FET and not a resistor.
Susan

 

[FvM]

The data sheet does refer to 'weak pull-up' (or 'pull-down') but this is not ever followed by the word 'resistor' (except referring to an external resistor that you need to add for various situations - e.g.I2C).

The opposite is true. The datasheet is very clear about the weak pull-up implementation as PMOS transistor, see e.g. PIC18 family reference manual. Respectively it's better specified by a saturation current than a resistance value.

 

[andre_luis]

The data sheet does refer to 'weak pull-up'

In fact, they should be used more for asserting a default logic level at the input of some digital-like operating circuit (eg saturating or cutting) than any other circuit that drains current of certain value as inherent part of its operation.

 

[treez]

Thanks,

The pull-up current is specified with 25uA ... 200uA at 3.3V.

I cant see where you found that...you have brilliant search skills.
I looked thru entire dc and ac characteristics section adn elec spec section but couldnt see it.

I did CTRL F's on "Pullup resistor", pullup current" etc but couldnt find
Thankyou

 

[KlausST]

Hi,

I cant see where you found that

* Datasheet: PIC16(L)F1704/8
* Chapter: 32.0 ELECTRICAL SPECIFICATIONS -->
* Chapter: 32.3 DC Characteristics
* TABLE 32-4: I/O PORTS
* Param No: D070, I_PUR

Klaus

 

[andre_luis]

I did CTRL F's on "Pullup resistor"

Sometimes is better to start with partial search in datasheet not with entire word, "Pullup" would not find "pull-up", space (' ') and minus ('-') symbols are not wildcard characters.

The pull-up current is specified with 25uA ... 200uA at 3.3V.

 

[treez]

Our software guy has used the PIC18F26K20’s weak internal pullup in RB3 in a Dual Opto Zero Crossing detector as in the attached. (schematic and also LTspice simulation attached)

Page 378 says the pullup is 50uA to 400uA at Vdd = 3V3.
That means an effective resistance of 8250R to 66k

With a 66k pullup the zero cross detector does not work due to the time constant fo the pullup resistor with the stray capacitance of the opto transistor.

PIC18F26K20 datasheet:
**broken link removed**

Do you know why the internal pullups have such poor tolerance? Would the Pullup be a greater effective resistance at a lower Vdd?