ADS1299: Choosing VCAP1 Capacitor

Helder Oshiro

Part Number: ADS1299

ADS1299 datasheet recommends the use of a 100 µC "nonferroelectric capacitor, such as a tantalum" in VCAP1.

I was looking for a small capacitor and I found a 0603 tantalum one, but it is polarized, 4VDC rated (less than the analog voltage used) and 10 Ohms @ 100 kHz.

I saw in the datasheet that the capacitor will be charged to more than 1.1V, but I don't know the upper limit. Is there any problem using this capacitor, and considering it is polarized and 4VDC rated?

Thanks

over 3 years ago

0 Praveen Aroul over 3 years ago

TI__Mastermind 49906 points

Hello Helder,

Due to the Thanksgiving holidays in the US, our response is delayed. We shall get back to you by next week.

0 TCT over 3 years ago in reply to Praveen Aroul

TI__Genius 11550 points

Hi Helder,

Welcome to the E2E forum !!!

The typical voltage for VCAP1 will be 1.2V, so it is acceptable to use 4VDC rated capacitors for VCAP1. However, it is recommended to use low ESR for the decoupling capacitors. In addition, there are multiple options for 100uF ceramic capacitors for the 0805 package size available.

Thanks

-TC

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/408488/ads1299-using-aluminium-electrolytic-capacitors-for-vcap1-vcap3-and-vrefp-vrefn

0 Helder Oshiro over 3 years ago in reply to TCT

Prodigy 40 points

Thanks, TC!

Is there a maximum ESR value for this capacitor?

I saw in the page you linked that 1 Ohm or less is recommended for aluminium capacitors. The 0603 capacitor I found is 10 Ohms at 100 kHz. In practice, it will affect filtering, correct? What about the electrolytic tantalum polymer capacitors? Can they be used? I found one model with 150 mOhms ESR.

+1 TCT over 3 years ago in reply to Helder Oshiro

TI__Genius 11550 points

Hi Helder,

We do not specify any maximum ESR value for this capacitor. The VCAP1 is mainly used as an external band-limiting capacitor to limit the reference noise in the system. It should be fine to use the electrolytic tantalum polymer capacitors.

Thanks

-TC

0 Helder Oshiro over 3 years ago in reply to TCT

Prodigy 40 points

Thank you very much for explaining, TCT!

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ADS1299: Choosing VCAP1 Capacitor