query regarding the value of the Vcap in STM8S microcontroller

piyushispandey07 · ‎2012-05-29

Posted on May 29, 2012 at 09:18

Hello sir

I am using the STM8S103F2P6 microcontroller of the ST microelectronics and when I was studying the power supply section of the microcontroller there it is specified to connect an external capacitor with the value ranging in between the 470 to 3300 nf . the specifications for the external VCAP capacitor are as follows:

Value = 470 to 3300 nf

ESL = 15 nH max.

ESR = .3 ohm at 1 MHz.

But I have connected the 1 uF value capacitor to the Vcap pin of the microcontroller , because I was not getting the microcontroller of that range .

So I want to know that is it ok , or it is going to effect my microcontroller in any way. I mean what will be the effect and how it will effect my whole circuit and the microcontroller.

Please describe me in detail.

Thank you

piyushispandey07 · ‎2012-05-30

Posted on May 30, 2012 at 14:02

I think the experts from the ST microelectronics are not interested in posting the reply to the queries related to their product.

I think I have not asked a question which is simple and need not reply.

as the hitting list of this forum tells the story of that how much activity is going on in htis forum.

Not impressed needs improvement. :(

Viktor POHORELY · ‎2012-05-31

Posted on May 31, 2012 at 09:49

Dear sir,

1 uF capacitor seems to be in the required range. However, you need to check in the datasheet what is the manufacturing variation (e.g. +-10%, sometimes +-20%) and what will be capacity variation within given temperature range - difference from nominal capacity could be in the range of tens percent, depending on the capacitor materials etc.

Last point to be checked is variation with a DC bias - it is important mainly for capacitor in small cases like 0402, where loss of capacity could be up to 50% against the nominal, when 1.8V is connected. A minimum of 470nF capacitance has to be respected over the whole temperature range of your application.

You will find those data in the datasheet from your vendor/supplier of capacitor.

You will find there as well ESL and ESR, however, usual ceramic capacitors has no issue with those parameters.