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Decoupling capacitors for ST25R3911B

JPehl.1
Associate III

Hi.

The datasheet of ST25R3911B shows recommended values of capacitors of 1uF (for AGD/VSS) and 2.2uF for others (VSPx-VSNx) plus a 10nF capacitor very close to the pins, according to the the picture:

0693W000005BfuvQAC.pngI just wanted to know if I should use these exact values, or if I can start my custom board project using 4.7uF/0402 for all these 1uF and 2.2uF capacitors. We already have the 4.7uF/0402 in stock. Just wanted to know if I can use them instead of 1uF/2.2uF values recommended on the datasheet. And also if I can use 4.7uF+10nF on VDD pin

1 ACCEPTED SOLUTION

Accepted Solutions
Travis Palmer
ST Employee

Hello JPehl,

The values from the datasheet above are those which we used for our reliability testing of the IC. Only if these values are used, the values in chapter 3 "Electrical characteristics" of the datasheet are guaranteed by ST. AGD for example is the Analog Reference. It is being driven or powered-down during operation and low power mode. Using different capacitor values could cause different rise times and therefore malfunctions.

BR Travis.

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4 REPLIES 4
Travis Palmer
ST Employee

Hello JPehl,

The values from the datasheet above are those which we used for our reliability testing of the IC. Only if these values are used, the values in chapter 3 "Electrical characteristics" of the datasheet are guaranteed by ST. AGD for example is the Analog Reference. It is being driven or powered-down during operation and low power mode. Using different capacitor values could cause different rise times and therefore malfunctions.

BR Travis.

Hi Travis.

Ok, I will use recommended values only.

But on VDD pin, whats the best combination?

  • 100nF + 2.2uF ?
  • 100nF + 1uF ?

Regards,

Jeferson.

Travis Palmer
ST Employee

Hi Jeferson,

on VDD i would also stick to 10nF + 2.2uF. You can also check the schematics of our demo kits. They should have the same decoupling components as mentioned in the datasheet.

br Travis

About the "bulk" capacitor for VDD, there is no indication on the datasheet. The development board uses 1uF, but you recommended 2.2uF, and I would stick to 2.2uF also. So I will use 100nF + 2.2uF.

Thanks and regards,

Jeferson