Device Description; Power Supply; Main Power Supply; Backup Power Supply - u-blox EVK-M8BZOE User Manual

4 Device description

4.1 Power supply

4.1.1 5V main power supply
The EVK-M8BZOE board must be supplied either by the micro USB connector or by an external 4.5 V – 5.5 V power
supply connected to digital connector pin 2 and GND to pin 18, see Figure 1.
The interface circuitry and other logic on the board relies on the 5 V power supply to always work properly.
In the default setup this 5 V main power supply is connected to the low-dropout linear voltage regulators (LDOs)
that provide the 1.8 V VCC voltage of ZOE-M8B.
Power consumption of a ZOE-M8B based design can however be easily calculated by measuring the voltage drop
over the VCC current measurement shunt resistor and then multiplying the resulting values by the 1.8 V power
supply voltage. For more information about current measurement of ZOE-M8B, see section 6.1.

4.1.2 Backup power supply

The backup supply (V_BCKP) of ZOE-M8B is used to supply the ZOE-M8B and the optional RTC crystal during
hardware backup mode (main supply removed). This enables hot start and warm start capabilities.
The EVK-M8BZOE includes a super capacitor to supply the V_BCKP of ZOE-M8B.
In normal operation, when the main supply of ZOE-M8B (VCC) is present, the backup domain in ZOE-M8B is
supplied by the main supply. V_BCKP supplies the backup domain of ZOE-M8B only when the main supply VCC
is removed.
4.1.2.1 Super Capacitor
The capacity of the super capacitor is 1 F and provides backup power over a 100 Ω shunt resistor to the ZOE-M8B
(V_BCKP). When this 1 F capacitor is fully charged to 3.3 V, it can provide backup power for about 35 hours
(t=C*U/I=1*(3.3-1.4)/15uA=126'666 sec. -> ~35 hours).
As soon as the EVK-M8BZOE is supplied, the super capacitor gets charged.
When evaluating very long backup periods, the backup supply can be supplied by the digital connector J1 pin 1
(2.5 V...3.6 V).

4.2 Interfaces

The EVK-M8BZOE supports all three communication interfaces of ZOE-M8B: UART, DDC(I
SiP itself does not have a USB interface. There is a USB to UART converter on EVK-M8BZOE which allows
communication to ZOE-M8B by USB.
The UART interface of ZOE-M8B is available on USB, RS232 and on digital connector J1. Only use one of them to
communicate. The SPI and the DDC (I

4.2.1 Interface Switch

The Interface Switch has to be set according if either the UART (RS232/USB) and DDC (I²C) or the SPI interface is
used. See Figure 1 for location of interface switch.
Only if SPI communication interface on digital connector is used, the interface switch has to be switched to
SPI marking. For all other communication interfaces it has to be set at RS-232 / USB marking.

4.2.2 USB 2.0 micro connector

The USB 2.0 micro B connector on the evaluation board can be used for both power supply and communication.
On the EVK-M8BZOE there is a USB to UART converter to UART interface of ZOE-M8B.
The easiest way to evaluate the EVK-M8BZOE operation is to connect the board to a PC by a micro USB cable and
then to use the u-center to configure and monitor the GNSS function.
UBX-17053592 - R03
2
C) interface are only supported on digital connector J1, see section 4.4.
Early Production Information
EVK-M8BZOE User Guide
2
C) and SPI. The ZOE-M8B
Device description
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