Decoupling capacitors for ST25R3911B

[JPehl.1]

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:

I 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

[Travis Palmer]

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.

[JPehl.1]

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]

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

[JPehl.1]

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