High current consumption during RF sending

[Vicnet]

Hi,

1. I would to know why when the DC/DC is enabled the current is very high (57mA) during RF sending.

2. Why at the end of RF sending the current is higher than previously (15.4mA -> 16.5mA) & 12.3mA -> 57mA)

Test conditions:

• nRF51822 - (Insight 130301)

• RF sending every 90ms

• Payload size: 32bytes

• Supply voltage 2.400V

Thanks you

[Asbjørn]

The additional current during TX is most likely due to the MCU running while sending and the difference between 12.2 mA and 15.4 mA is due to the DC/DC. The peaks at the end are due to the shut down of the internal PA and it's power supply. While running on the DC/DC we have seen that there might be a short but high peak as you measure. To counter this we have recommended to add a larger capacitor on the VDD pin1 as seen in chapter 11.3.3 of the nRF51822 product specification.

[Asbjørn]

@Vicnet, I wasn't able to find a schematic for the ISP130301 with component values. I do however see that C7 is a different component compared to the C7 in Nordics nRF51822 product specification. In the Insight documentation the component I'm referring to is named C9, but without any value specified. I found the datasheet here. (Document named: "DS130301_R4.pdf). So yes, it it could be that the module has one large capacitor on AVDD, but we recommend to also have a 4.7 uF on the VDD pin itself to reduce the peak you see.