TWR-KL28Z Hardware Description
TWR-
KL28Z User’s Guide, Rev. 0, 06/2016
4
NXP Semiconductors
4. TWR-KL28Z Hardware Description
4.1. Power supply
The TWR-KL28Z offers a design with multiple power supply options. It can be powered from the USB
connector, the VIN pin on the I/O header, or an off-board 1.71-3.6 V supply from the 3.3 V pin on the
I/O header. The USB and VIN supplies are regulated on-board using a 3.3 V linear regulator to produce
the main power supply. The other sources are not regulated on-board.
The following table provides the operational details and requirements for the power supplies.
Table 1.
Tags Power supply requirements
Supply Source & Location
Valid Range
CMSIS-DAP Operational?
Regulated on-board?
CMSIS-DAP USB (J10)
5 V
Yes
Yes
KL28Z USB (J29)
5 V
No
Yes
P3V3 Pin
（
J34 PIN2
）
1.71-3.6 V
No
No
Figure 3
shows the schematic drawing for the power supply inputs and the on-board voltage regulator.
Figure 3. Power supply schematic
NOTE
The CMSIS-DAP circuit is operational only when a USB cable is
connected and supplying power to J10. However, the protection circuitry
is in place to allow multiple sources to be powered at once.
Table 2.
FRDM-KL28Z power supplies
Power Supply Name
Description
P5V_miniUSB
Primary input power. Filtered from miniUSB connector
P5V_microUSB
Secondary input power. Filtered from microUSB connector
P5V_ELEV
Third input power from primary elevator connector.
P5V_TRG_USB
Output from USB power switch, which is controlled by the K20's VTRG_EN and elevator's
ELE_PS_SENSE.
V_BRD
Output from jumper header, to select 1.8 V, 3.3 V. Also could be supplied externally via
header pins
MCU_PWR
Output from jumper header, to select V_BRD, VREGOUT_KL28. Also could be supplied
externally via header pin
VDDA
Output from jumper header to select MCU_PWR. Also could be supplied externally via
header pin.