Silicon Laboratories C8051F500, User Manual

C8051F500DK

10

Rev. 0.1

8.2.  Target Board Power Options and Current Measurement

The C8051F500 target board supports three power options:

1. 12V DC power using the AC to DC power adapter (P4)
2. 5V DC USB VBUS power from PC via the USB Debug Adapter (DEBUG_A)
3. 12V DC power from the LIN external header (TB1)

The two 12V power sources are ORed together using reverse-biased diodes (Z1 and Z2). The ORed power is
regulated to a 5.0V DC voltage using a LDO regulator (U6). To power the board from the USB Debug Adapter
connected to DEBUG_A instead of the 12V sources, move the shorting block on the J7 header to pins 2 and 3 to
select SER_PWR. The output of the regulator powers the +5VD net on the target board, and is also connected to
one end of the header J24 (SIDE A) and J31 (SIDE B). Two shorting blocks can be put on each header to connect
the 5V net to the VREGIN and VIO pins on the two MCUs. With the shorting block removed, a source meter can be
used across the headers to measure the current consumption of the MCU.

Note:

The USB Debug Adapter does not provide the necessary peak power for the CAN transceivers to operate. One of the
12V DC sources is recommended for CAN transceiver operation.

8.3.  System Clock Sources

8.3.1. Internal Oscillators

The C8051F500 and C8051F502 devices installed on the target board feature a factory calibrated programmable
high-frequency internal oscillator (24 MHz base frequency, ±0.5%), which is enabled as the system clock source on
reset. After reset, the internal oscillator operates at a frequency of 187.5 kHz by default but may be configured by
software to operate at other frequencies. The on-chip crystal is accurate for CAN and LIN master communications
and in many applications an external oscillator is not required. However, if you wish to operate the C8051F500
device (SIDE A) at a frequency not available with the internal oscillator, an external crystal may be used. Refer to
the C8051F50x data sheet for more information on configuring the system clock source.

8.3.2. External Oscillator Options

The target board is designed to facilitate the installation of an external crystal. Remove shorting blocks at headers
J9 and J10 and install the crystal at the pads marked Y1. Install a 10 M

Ω

 resistor at R9 and install capacitors at C6

and C7 using values appropriate for the crystal you select. If you wish to operate the external oscillator in capacitor
or RC mode, options to install a capacitor or an RC network are also available on the target board. Populate C6 for
capacitor mode, and populate R3 and C6 for RC mode. Refer to the C8051F50x data sheet for more information on
the use of external oscillators.