Freescale Semiconductor, Inc
FRDM-K20D50MUM
Page 7 of 17
5
FRDM-K20D50M Hardware Description
5.1.1
Power Supply
There are multiple power supply options on the FRDM-K20D50M. It can be powered from either of the USB
connectors, the V
IN
pin on the I/O header, an on-board coin cell battery, or an off-board 1.71-3.6V supply
from the 3.3V pin on the I/O header. The USB and V
IN
supplies are regulated on-board using a 3.3V linear
regulator to produce the main power supply. The other two sources are not regulated on-board. Table 2
provides the operational details and requirements for the power supplies.
Supply Source Valid Range
OpenSDA
Operational?
Regulated on-
board?
OpenSDA USB 5V
Yes
Yes
K20 USB
5V
No
Yes
V
IN
Pin
4.3-9V
No
Yes
3.3V Pin
1.71-3.6V
No
No
Coin Cell
Battery
1.71-3.6V
No
No
Note that the OpenSDA circuit is only operational when a USB cable is connected and supplying power to
OpenSDA USB. However, protection circuitry is in place to allow multiple sources to be powered at once.