User's Manual l TQMa7x UM 0203 l © 2022, TQ-Systems GmbH
Page 20
On account of the high power consumption of the i.MX7-internal RTC the optional RTC on the TQMa7x is recommended for long
term bridging.
Note: Current consumption of i.MX7-internal RTC
A coin cell is not suitable for long term bridging on account of the high current consumption of the
i.MX7-internal RTC. A Lithium coin cell or a SuperCap might be an option depending on the use case.
It is to be taken note of that the typical charging current is only 60 µA.
For long term bridging an external RTC connected at the I
2
C bus on the carrier board or the optional
RTC DS1339U on the TQMa7x is recommended.
3.2.3.2
RTC DS1339U
In addition to the i.MX7-internal RTC, an optional I
2
C RTC type Maxim DS1339U-33+ is available.
The accuracy of the RTC is mainly determined by the characteristics of the quartz used. The type CM7V used on the TQMa7x
has a standard frequency tolerance of ±20 ppm @ +25 °C. (Parabolic coefficient: max. –0.04 × 10
–6
/ °C
2
).
Connector
TQMa7x
PMIC
i.MX7
LICELL
DS1339U
VCC
V33
I2C
I2C1
VBACKUP
VCC5V
5 V
4.2 V
VIN
Coin Cell
Li-Coin Cell
SuperCap
(typ. 3 V)
Figure 9:
Block diagram DS1339U RTC on TQMa7x
The I
2
C address of the RTC is
0x68 / 110 1000b
The following table shows the current consumption of the DS1339U RTC assembled on the TQMa7x.
Table 16:
Current consumption DS1339U on TQMa7x at LICELL
Voltage LICELL
Current consumption LICELL
Remark
3.2 V
0.44 µA typical; 0.7 µA maximal (10)
VCC5V = 0 V
Tamb = +25 °C
3.0 V
0.44 µA typical; 0.7 µA maximal (10
2.1 V
0.4 µA typical; 0.7 µA maximal (10
Note: Assembled DS1339U
If the DS1339U is assembled, the SNVS voltage domain is not supplied by LICELL. The i.MX7 SNVS
functions are therefore only available when the TQMa7x is supplied with 5 V.
Coin cells cannot be charged at LICELL, when the DS1339U is assembled.
The RTC DS1339U is directly supplied by LICELL. The PMIC supplies the RTC when the TQMa7x is
powered with 5 V.
10:
See Data Sheet DS1339U (9).