Decoupling capacitors

BuGless
Posts: 10
Joined: Wed Sep 09, 2015 1:28 am

Decoupling capacitors

Postby BuGless » Wed Sep 09, 2015 2:50 am

I see different recommendations for decoupling capacitors depending on which application/design guide I read.
The following questions come to mind:

a. The VDDPST explicitly does not need a decoupling capacitor. Does that mean that it merely pulls a completely flat DC current? I'd normally say that a decoupling capacitor there is still desirable, but the size depends on the kind of frequency. I'm guessing, but internally the chip seems to be clocked at 80MHz, so I'd normally dimension a decoupling capacitor for that frequency.

b. In some design guides I see a 10uF close to VDD3P3 and a 0.1uF close to VDDA and VDDD. In other guides I see a 10uF and a 0.1F close to VDD3P3 and a 10uF on VDDA and VDDD. And in some guides the last 10uF on VDDA and VDDD is replaced by a 1uF capacitor.
Can someone explain the different design considerations there?

c. What's the difference between VDD3P3, VDDA and VDDD ?

Espressif_Kelly
Posts: 140
Joined: Mon Oct 27, 2014 10:40 am

Re: Decoupling capacitors

Postby Espressif_Kelly » Wed Oct 14, 2015 1:17 pm

Dear BuGless,

1. About the descriptions of power supply pins of ESP8266EX, you can refer to ESP8266EX datasheet for details.
http://bbs.espressif.com/viewtopic.php?f=51&t=818

2.Pin1: Power supply for LNA.
Pin3, Pin4: Power supply for PA
Pin29, Pin30: Power supply for internal PLL

3.PA power supply rail might collapse due to the sudden increase of current when ESP8266EX works in TX mode. Therefore, an additional 10uF capacitor with 0.1uF is needed.
For other power supply pin, we recommend to add 0.1uF to each power supply pin if space of the pcb is enough.

Thanks.

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