DCDC and SoftDevice

Question

Hi all, 
 What exactly mean "DCDC converter operation controlled by the SoftDevice may interfere with radio function"? Are there increasing of causeless disconnections or decreasing of working range of nRF51822? I was not aware of the existence of this problem and dcdc was always in automatic mode. There was no problems with the tested devices (at least I did not notice any). 
 Best Regards,
Peter

Ole Morten · Accepted Answer

This is kind of a tricky question. The case is that the DC/DC works more or less as it is designed to do, but it is very hard to use correctly in a low-power application. 
 The reason for this is a combination of 
 
 the DC/DC only being effective when the current draw is relatively high, and 
 the DC/DC taking some time to stabilize the output voltage, and 
 unstable DC/DC output voltage reducing the sensitivity of the radio. 
 
 The time it takes to stabilize the voltage is dependent on the current drawn by the chip, and the lower the current draw, the longer time to stabilization. Due to 1. above, it is normally not reasonable to have the DC/DC enabled in between connection events, since the current draw is so low, but if you try to turn it on right before a connection event, you easily hit 3 due to 2. 
 However, if you have an application where the chip is consistently drawing enough current to justify the usage of the DC/DC, you no longer have to turn it on and off, and all problems disappear. This requires the chip's average current consumption to be > 3-6 mA, depending on input voltage. 
 All the information we have, including the above, is currently in the reference manual, section 11.1.1.1. Please have a detailed look at it if something is unclear. 
 If you try to use the automatic mode of the softdevice, which will turn the DC/DC on only for connection events, this will cause reduced radio performance, and may in some cases again cause problems with qualification. Hence, the recommendation is to not use this.