VBAT
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
12
NXP Semiconductors
Figure 8. K28F USB port
When the FRDM-K28F board operates in the USB host mode, J13 must be shunted to supply 5 V to
VBUS (J24 pin 1). The 5 V source can be the OpenSDA v2.2 USB port (J6) or the optional 5 V
regulator populated at J25 and supplied by P5-9V_VIN at pin 16 of the J3 connector.
Figure 9. K28F USB port power inputs for host mode
7. VBAT
The Real-Time Clock (RTC) module is powered on its own domain. FRDM-K28F provides a battery
holder for a coin cell battery that can be used as the VBAT supply. The holder supports common 20 mm
diameter 3 V lithium coin cell batteries (for example, 2032 and 2025).
If a coin cell battery is used, add a small amount of solder to the coin cell ground pad before adding the
battery holder.
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