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User's Manual l MBa335x UM 0202 l © 2018, TQ-Systems GmbH
Page 11
4.1.4
RTC backup supply
The MBa335x does not provide an RTC. On the TQMa335x the following RTCs are available, which are supplied by the MBa335x in
case of a backup:
•
RTC in the CPU AM335x
•
RTC in the PMIC TPS65910
•
RTC DS1339U (optional)
A coin cell on the MBa335x supplies the RTC on the TQMa335x. With jumper X3 the coin cell either supplies the PMIC and with it
the CPU-internal RTC, or the optional RTC DS1339U.
Technical information about the PMIC power modes, as well as the CPU, is provided in the data sheets (see (1), (2), and (3)).
Illustration 6:
RTCs supplies on TQMa335x
The following table shows the electrical characteristics of the RTCs.
Table 10:
Electrical characteristics of RTCs
RTC
Parameter
Min.
Typ.
Max.
Unit
Backup voltage VBACKUP_PMIC
2.2
–
3.0
V
PMIC / AM335x
Current consumption
–
25
–
µA
Backup voltage VBACKUP_RTC
1.3
3.0
3.7
V
DS1339U
Current consumption
–
0.4
1.0
µA
The RTC on the MBa335x is on the bottom side, near the audio codec.
The header for the battery supply is on the top side, next to the SD card holder.
Table 11:
RTC backup supply
Manufacturer / Number
Description
Sony / CR2032
Lithium battery 3.0 V, 220 mAh
RENATA / SMTU2032
CR2032 battery holder
1:
Threshold VBNPR of TPS65910.