LDO current consumption, low voltage mode.

[cocoa]

Hi Nordic guys,

How much is the current consumption of the LDO only (quiescent current), without DC / DC converter, in uA? How much is dropout voltage and PSRR (ripple rejection) ?

When powering nRF51822 in low power mode, LDO has a quiescent current or is true disconnected?

What are the advantages and disadvantages when powering nRF51822 in low voltage mode ?

How much is leakage current of a gpio pin when enabled as output and as input ?

Thanks.

-c

[cocoa]

Hi Håkon, I'm asking 'cause I'm evaluating both LDO and 1.8V mode.

My question is, how can I evaluate an external LDO compared with internal one ?

Does my LDO have better performances compared to nRF51822 LDO ? Impossible to say without electrical characteristic.

Another point of view, LDO ripple reduction, which is better? External or internal one? How much is the maximum admitted VDD ripple for nRF51822?

Thank you.

-cocoa

[Ole Morten]

I'm still not quite sure I understand your point. You have to compare the current consumption of the complete system, not just your external LDO against the internal one, i.e. either external LDO + nRF51822 in low voltage mode or just nRF51822 in internal LDO mode.

For the latter, you must use the values from the PS as is. For the former you must use the current consumption of your external LDO, plus the values from the PS, making sure to add the additional 1 µA consumed in system on and system off.

The general recommendation on ripple voltage when using low-voltage mode is to make sure it's less than 10 mV, which is pretty low, and may be problematic to achieve.

In summary, using an external LDO and low-voltage mode is almost never beneficial in real applications, since you'll have some current consumption from the external LDO in addition to the extra 1 µA, which comes directly on top of the numbers you'll have if you just used the internal one.