We are measuring excessive current draw on the Colibri’s VSS RTC rail when using the Colibri’s Internal RTC option upon power removal. We are using a CR1216 coin cell battery.
When 3.3V is removed from the Colibri, we measure levels of ~70uA, and over the span of a couple minutes the steady state draw is about 50uA. This would make coin cell battery replacement a regular occurrence.
IC manufacturers that offer solutions for RTC applications, including the external option recommended for the Aster, document current draws that are lower by a couple orders of magnitude.
Is there is a register setting that will allow significant reductions in current draw, or is there something else we should consider? Thank you.
The 50 uA internal RTC power consumption is a typical value. Please check Table 8-3 Typical Power Consumption of Colibri iMX6 datasheet. It’s defined by iMX6DL SOC and can not be improved.
From the chapter 5.10.1 Real-Time Clock (RTC) recommendation of the datasheet:
"The RTC on the module is not designed for ultra-low power consumption (typical current
consumption can be found in section 8.2). Therefore, a standard lithium coin cell battery can be
drain faster than required for certain designs. If a rechargeable RTC battery is not a solution, it is
recommended to use an external ultra-low power RTC IC on the carrier board instead. In this case,
add the external RTC to the I2C1 interface of the module and source the VCC_BACKUP pin from
the 3.3V rail that sources also the main module rail. A suitable reference schematic can be found
in the schematic diagram of the Colibri evaluation board. "