User's Manual l TQMa8XxS UM 0101 l © 2022, TQ-Systems GmbH
Page 32
3.8.1.2
V_VDD_RTC
The SMARC pin VDD_RTC allows the connection of a coin cell. Depending on the module variant, either the SNVS domain of the
i.MX 8X or the external RTC is supplied via the V_VDD_RTC voltage connected to it.
Note: Functional scope of RTC
Depending on the TQMa8XxS variant, the range of functions in battery mode (only VDD_RTC
supplied) is reduced, since no SNVS function of the i.MX 8X is available when using the PCF85063.
For TQMa8XxS variants without external RTC, the voltage range of the SMARC pin is limited to 2.4 V to
3.25 V by the VSNVS rail of the PMIC. The SMARC standard, however, requires 2.0 V to 3.25 V and is
therefore not met.
3.8.1.3
USB_OTG[2:1]_VBUS
The voltage inputs USB_OTG1_VBUS and USB_OTG2_VBUS are used to detect the USB-VBUS voltage. While USB_OTG1_VBUS is 5
V tolerant, USB_OTG2_VBUS has only a 3.3 V level.
3.8.2
Voltage monitoring
The 3.3 V input voltage is monitored on the TQMa8XxS.
If the input voltage is too low, a reset is triggered until the input voltage is within the defined range again.
Attention: Malfunction or destruction
The voltage monitoring does not detect an exceedance of the maximum permitted input voltage.
An excessively high supply voltage can lead to malfunctions, untimely aging or destruction of the
TQMa8XxS.
3.8.3
Power-Up sequence TQMa8XxS / carrier board
Since the TQMa8XxS can be operated with a supply voltage of 3.0 V to 5.25 V and all voltages of the CPU signals are generated
on the TQMa8XxS, there are requirements for the mainboard design concerning the time behavior of the voltages generated on
the mainboard. The mainboard voltages are to be released exclusively by the SMARC pin CARRIER_PWRON. This is connected to
the PMIC signal PGOOD.
The following figure shows the voltage regulator control of a carrier board:
Mainboard
TQMa8XxS
VDD_IN
CARRIER_PWR_ON
ENABLE
VIN
VOUT
VIN
3,0...5,25 V
3,3V / 1,8V / ...
Figure 30: Block diagram power supply carrier board
