Maximum Voltage input to xDot

[Chad Goyette]

I am powering my xDot using two energizer lithium AA batteries with no regulator which produces a fully charged voltage of 3.62V which technically exceeds the 3.57V spec in the developers guide. Will operating at this slightly higher voltage cause any damage to the xDot?

[Chad Goyette]

Is anyone able to answer this for me?

[Darrik Spaude]

Hi Chad,

There isn’t a regulator on the xDot, so your input voltage is routed to all components. Several of the components can accept higher voltages, but some do not. We recommend that you try to add a regulator that can supply 3.3 V. The batteries are going to provide lower voltages over time, so the regulator should also boost the voltage back to 3.3 V. Above 3.6 V the product could be unreliable.

That said, for testing/development, 3.62 V is right on the edge of recommended and would probably work okay. Energizer shows that the lithium AA typically outputs 1.7 V max (but could peak at 1.8 V) while nominal is 1.5 V. Keep in mind that the voltage could be higher or lower depending on the battery. For long term/production application, we still recommend a regulator.

Hope that helps,
Darrik

[Chad Goyette]

Thanks Darrik, I am trying to avoid the regulator to maximize battery life. Currently my setup does not require a constant voltage for reference which lead to the elimination of the regulator and allowed power consumption to be at 25uA during sleep. Do you guys have experience with a regulator that can support the higher load of LoRa transmission while having an extremely low standby current?

[Darrik Spaude]

Hi Chad,

One of the engineers had this suggestion:

Simplest solution would be to use a series Schottky diode to reduce the input voltage. Most Schottky diodes have at least a 250 mV drop across them.

LP5907 is 14 uA quiescent current and drop out is ~50 mV at 100 mA draw.
MIC5501 is 38 uA quiescent current and drop out is ~80 mV at 150 mA draw.

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