Power consumption internal RC 32Khz versus external crystal osc 32Khz

Hi ONSemi,
We are thinking about removing the external 32K osc from our implant design (current osc ll be obsolete, reduced pcba footprint and we do not require fine RTC clock accuracy for our application), with the target to achieve maximum life time duration of our implant device.
From the RSL10 hardware documentation, it is not clear between the RC 32khz or ext 32Khz osc which shall deliver best performance for reduced power consumption.
Is the difference is consequent (in our case, the implant device spend 98% of its time in BLE sleep mode.
Could you provide some infos and quantify the difference?

Section 5.4.2
The 32 kHz crystal oscillator power consumption can be reduced (possibly as low as the level of the RC oscillator consumption) by enabling the following settings in the ACS_XTAL32K_CTRL register:
• EN_AMPL_CTRL = 1 (this regulates the oscillation amplitude to minimize power consumption)
• Set the CLOAD_TRIM register to bring the frequency as close as possible to 32,768 Hz. This register adjusts the crystal load capacitors.
• Leave the other settings at their default values.

Section 6.3.2
Use of the 32 kHz crystal oscillator is recommended over use of the standby RC oscillator due to:
• Improved clock accuracy
• Simplification of system designs
• Lower power consumption

So far i have not been able to update our application to use the internal RC 32Kz, i am not sure to continue the effort if the use of RC 32K worsen the power consumption.
Thanks in advance for your feedback and help provided for all my previous posts,
Best regards


For RSL10, the RC 32KHz maximum current consumption is 60nA (over temperature -40C to +85C).
The typical value is 20nA.
We don’t recommend to use RC 32KHz for a sleep clock in BLE connection mode.

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