TQ Ma8XxS, User Manual

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User's Manual l TQMa8XxS UM 0101 l © 2022, TQ-Systems GmbH Page 16
3.2.3 RTC
In addition to the i.MX 8X-internal RTC, the TQMa8XxS provides a discrete RTC PCF85063 as assembly option.
Table 8: RTC variants
TQMa8XxS variant Function
TQMa8XxS without discrete RTC
VDD_RTC supplies via VSNVS controller of the
PMIC the SNVS domain of the i.MX 8X
TQMa8XxS with discrete RTC
(standard)
VDD_RTC supplies external RTC PCF85063.
SNVS domain of i.MX 8X only supplied if module
supply 3.3 V available.
Note: Power supply for i.MX 8X-internal RTC
The i.MX 8X-internal RTC can always be used in ON mode, but resets itself at variants with equipped
PCF85063 when the module supply (3.3 V) fails, since the SNVS domain of the i.MX 8X is then no
longer supplied.
3.2.3.1 i.MX 8X internal RTC
The i.MX 8X has an internal RTC which has to be powered by the power domain (SNVS).
The accuracy of the RTC is primarily determined by the characteristics of the quartz used. The type FC-135 used on the
TQMa8XxS has a standard frequency tolerance of ±20 ppm at +25 °C. (Parabolic coefficient: max.
–
0.04 x 10 –6 / °C 2 )
The RTC power domain SNVS of the CPU is supplied by the PMIC through the internal controller VSNVS. This is supplied either
from the module input voltage V_VDD_IN or from V_VDD_RTC at the PMIC pin LICELL. LICELL supports simple Coin Cells and
SuperCaps. Charging methods and electrical properties of the LICELL pin can be found in the PMIC data sheet (4). Note that the
typical charging current is only 60 µA.
SMARC-Pins PMIC i.MX 8X
LICELL VDD_RTC
VSNVS SNVS
Coin-Cell
Li-Coin-Cell
Super-Cap
(typ. 3 V)
VDD_IN
3…5,25 V
VIN
Figure 8: Block diagram i.MX 8X internal RTC supply (TQMa8XxS without discrete RTC)
Note: SNVS domain supply
For module variants with equipped external RTC, the LICELL pin of the PMIC is not connected to
VDD_RTC. The SNVS domain of the i.MX 8X is therefore only supplied in on-mode.
The following table shows the current consumption at the LICELL pin for TQMa8XxS variants without discrete RTC:
Table 9: Current consumption LICELL with i.MX 8X internal RTC
Voltage LICELL Current consumption LICELL Remark
3.2 V typ. 4,125 µA
VCC5V = typ. 0 V
T
amb
= +25 °C
3.0 V typ. 4,026 µA
2.4 V typ. 3,818 µA
It is recommended to use the RTC PCF85063 due to the high current consumption of the SNVS domain, see section 3.2.3.