Decoupling capacitor value for MCLR on a PIC24

[Shipton]

For a PIC24HJ32GP202, what should the value of C, the decoupling capacitor connected to the pullup and current limiting resistors be? The manual doesn't specify a value. (section 2.4).

 

[Wp100]

Hi,

Think many folk would say 100nf straight away , but if you see the schematic in this user guide they do not use any capacitor on either chip.
https://ww1.microchip.com/downloads/en/DeviceDoc/MPLAB%20Starter%20Kit%20for%20PIC24H%20User%20Guide_ds51780a.pdf

 

[Wilksey]

Page 38 of that PDF shows a 0.1uF cap between VDD and VSS.

Wilksey

 

[AtomSoft]

0.1uF = 100nF = 100000pF

Just some info...

 

[Wilksey]

Thanks AtomSoft,

There never seems to be a standard for the cap rating unit, and I always used to get frustrated when I couldn't work out what nF, pF or uF were in other units!

I do it the lazy way now, my calculator has the units on it so I can just press a button to convert

 

[AtomSoft]

heh im lazy-er : Capacitor uF - nF - pF Conversion Chart

 

[Pommie]

There is no requirement for a decoupling capacitor on the MCLR pin.

Mike.

 

[Hayato]

Thanks AtomSoft,

There never seems to be a standard for the cap rating unit, and I always used to get frustrated when I couldn't work out what nF, pF or uF were in other units!

I do it the lazy way now, my calculator has the units on it so I can just press a button to convert

uF, nF, pF are all standard. It is like saying that the distance between two cities in meters (instead of kilometers) is not standard.

 

[Wilksey]

I know they are all standard units, it's peoples personal preference as to which one they use, it just gets confusing when beginning electronics when people mention the different units.

I'm past that now, but I was just referring back to when I started out.

Good link AtomSoft, even better than a calc! lol

Mike is correct, there is no cap on MCLR, just a pull up resistor, the decoupling capacitor is between VDD and VSS.

Wilksey

 

[AtomSoft]

Yeah No Problem ... i have seen RC (resistor/cap combos) on a MCLR before. So i assumed you all where talking about that heh.

 

[Hayato]

Yes, you can make an external Power On Reset with a RC circuit connected to the MCLR.

 

[Oznog]

Yes, you can make an external Power On Reset with a RC circuit connected to the MCLR.

But rarely do you need to, usually an R suffices. In fact a C can screw things up. If it's too large the pin may rise too slowly to properly latch a rising edge and the part may not start or respond to ICSP/ICD. On the other hand, the minimum is zero, so... go with zero unless you have a known reason to do otherwise.