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

[Locky]

I also see 16.5~17.8mA on TX and 14.5~15.4mA on RX. I do not use the DCDC on my hardware so its inline with your measurements. Not entirely sure of why the deviation from the PS

[Locky]

As for your DCDC measurement, I recall when I used to work with the Ti CC2540 that when using a DCDC, there can be high swing currents at the enable/disable points. This is due to the fact that the Voltage rail switches from Coil Cell level (3.0V) to DCDC level (~2.1V on Nordic) and back during RF events. With this voltage swing you will see an in-rush current when measuring the board with a resistor. Though 57mA seems quite high.

[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.

[Vicnet]

Hi Asbjørn, Thanks for your reply.

During RF sending, the MCU is sleeping. We are using the Insight SIP 130301 and a larger capacitor (C7) is already on VDD pin1 (ver nRF51822 QFAA).

When you said: "larger capacitor on the VDD pin1", add another capacitor in addition to C7?

[Asbjørn]

Yes, you should have a 4.7 uF capacitor at C7. See chapter 24 in chapter 11.3.3.

Do you have anything else running on the chip while you are transmitting? The current consumption if everything is sleeping except the radio, the current number you should see should be in the same as the RX/TX current specified in the product specification with/without the DC/DC.