TM4C129LNCZAD: missing frequency at which ESR and ESL are specified at

Hello John,

We don't have a specification for frequency listed because that is more system dependent. The frequency on the capacitor would be influenced by your actual hardware and if noise is impacting the capacitor etc. The same applies for accounting for the temperature range of your board. Both frequency and temperature on the capacitor will impact ESR and needs to be assessed for each design.

Our System Design Guidelines provide a bit more detail on the LDO cap, see Section 3.4.2: https://www.ti.com/lit/pdf/spma056

Essentially you want capacitors that are low ESR and have better than 10% tolerance. It is strongly recommended to use ceramic caps. Ceramics are recommended over dielectric capacitors due to the wide tolerance over temperature that dielectrics have.

Best Regards,

Ralph Jacobi

Hello Ralph,

The regulator on the chip is a linear regulator whose stability is influenced by the ESR and ESL.  This link 

  https://www.st.com/content/ccc/resource/technical/document/datasheet/21/5a/57/8b/f4/49/4a/12/DM00037613.pdf/files/DM00037613.pdf/jcr:content/translations/en.DM00037613.pdf 

shows on page 46 section 9.3 the conditions under which the ESR and ESL are specified as determined by the internal regulator  (see note 2).  Small capacitors, 0.1, 0.01 µF are effective for system noise.  2.5 to 4.0 µF are not as effective and are for lower frequencies.

I agree temperature is a factor as well as the dielectric material.  You recommended ceramic capacitors over dielectric capacitors.  All capacitors have dielectrics.  What do you mean by dielectric capacitors?

John

Hello John,

John Boecker said:

shows on page 46 section 9.3 the conditions under which the ESR and ESL are specified as determined by the internal regulator  (see note 2).  Small capacitors, 0.1, 0.01 µF are effective for system noise.  2.5 to 4.0 µF are not as effective and are for lower frequencies.

That may be how ST is providing their specs based on their LDO design but we don't have such a specification for TM4C devices.

Section 3.4.2 of the System Design Guidelines discusses which capacitor values to use, you will want 3.3uF or 3.4uF depending on how you want go about add bulk and decoupling caps.

John Boecker said:

I agree temperature is a factor as well as the dielectric material.  You recommended ceramic capacitors over dielectric capacitors.  All capacitors have dielectrics.  What do you mean by dielectric capacitors?

Sorry, it was a specific dielectric that is not recommended. "Z5U dielectric capacitors are not recommended due to wide tolerance over temperature."

Best Regards,

Ralph Jacobi

Hello Ralph,

the first paragraph is section 3.4.2 of the System Design says the voltage regulator requires a capacitor to operate properly.  Nothing about system frequencies.  Our system will have frequencies at 20Kh, 10 MHz and 120 MHz to name a few.  It is going to be very hard to find a capacitor that has an ESR below 100 mΩ over these frequencies.  If you can find one I would like to know its part number.

John

Hello John,

We have capacitors in our BOM for our LaunchPad https://www.ti.com/lit/pdf/spmu365

I had spoken with my colleague earlier and confirmed with him that this is something that is a system concern. 120MHz doesn't seem like a frequency that should be propagating through your system at all. Most customers look in the 1-10MHz range.

Best Regards,

Ralph Jacobi

Also it looks like the Filter Capacitor in particular is where the low ESR is most important as that is specifically called out in the BOM as Low ESR: