VDD decoupling caps maximum values

RE: VDD decoupling caps maximum values

Andreas — Fri, 24 Jul 2020 09:33:45 GMT

Hi John,

There is some derating in the capacitors, see this whitepaper: https://infocenter.nordicsemi.com/topic/nwp_030/WP/nwp_030/intro.html?cp=14_3

Best regards,

Andreas

RE: VDD decoupling caps maximum values

John Man — Fri, 24 Jul 2020 05:27:03 GMT

Hi Andreas,

Per Datasheet, CVDD is requested in the range of 2.7~5.5uF. However, the reference design (configuration No. 5 schematic) shows that the total VDD nominal capacitance is 4.7uF+1uF=5.7uF. This already violates the CVDD requirement. Can you let me know if CVDD requirement is valid or the reference schematic is valid-----they are in contradiction.

Thanks

John

RE: VDD decoupling caps maximum values

Andreas — Thu, 23 Jul 2020 09:25:32 GMT

Hi,

With config 4 both VDD and DEC4 are regulator outputs and inputs, meaning both VDD and DEC4 must be withing the specified range.

Best regards,

Andreas

RE: VDD decoupling caps maximum values

wallance.lin — Thu, 23 Jul 2020 06:48:07 GMT

Hi Andreas

thanks! I would like to check which one or both of them could cause power supply system issue?
Over maximum Effective capacitance in VDD or lower than minimum Effective capacitance in DEC4?

RE: VDD decoupling caps maximum values

Andreas — Mon, 20 Jul 2020 13:13:00 GMT

Hi,

This is outside spec, and could cause the power supply system to not behave according to spec.

Best regards,

Andreas

RE: VDD decoupling caps maximum values

wallance.lin — Thu, 16 Jul 2020 08:15:38 GMT

I'm using nRF52840 and also find the same issue after checking nWP-030, our design follows "7.3.4 Circuit configuration no. 4 from nRF52840 datasheet". after considering tolerance, we find

1. the maximum effective Vdd cap is 7.11uF > 5.5uF(maximum Effective capacitance in VDD),

2. the minimum capacitance of Cdec4 is 0.68uF < 0.7uF (minimum Effective capacitance in DEC4),

do you have any concern for this? and where we need pay attention or check?

RE: VDD decoupling caps maximum values

Andreas — Fri, 12 Jun 2020 07:00:24 GMT

Hi,

This is the capacitive load the REG0 is designed for and is thus only relevant for the power configurations where REG0 is used (supply on VDDH). The capacitance on the main supply pin (VDDH for high-voltage config and VDD+VDDH for normal voltage config) can exceed this.

As for the FEM, note that the REG0 can deliver a maximum of 25mA when nRF52840 TX power < 0 dBm, I would assume your FEM draws a bit more than this. In this case you should not supply the FEM from the VDD rail anyway.

Best regards,

Andreas