C P 2 4 0 0 / 1 - D K
16
Rev. 0.1
7.2. Target Board Power Options and Current Measurement
The C8051F930 Target Board supports three power options, selectable by the three-way header (J10/J11). The
power options vary based on the configuration (one-cell or two-cell mode) selected by SW4. Power to the MCU
may be switched on/off using the power switch (SW5).
Important Note: The power switch (SW5) must be in the
OFF position prior to switching between one-cell and two-cell mode using SW4.
The power options are
described in the paragraphs below.
7.2.1. Wall Power
When the J10/J11 three-way header is set to WALL_PWR, the C8051F930 Target Board may be powered from the
following power sources:
9 VDC power using the ac to dc power adapter (P2)
5 VDC USB VBUS power from PC via the USB Debug Adapter (J9)
5 VDC USB VBUS power from PC via the CP2103 USB connector (P3)
All the three power sources are ORed together using reverse-biased diodes (D1, D2, D3), eliminating the need for
headers to choose between the sources. The target board will operate as long as any one of the power sources is
present. The ORed power is regulated to a 3.3 V dc voltage using a LDO regulator (U2). The output of the regulator
powers the +3 VD net on the target board.
If SW4 is configured to select two-cell mode, the VBAT supply net on the target board is powered directly from the
+3 VD net. If SW4 is configured to select one-cell mode, the VBAT supply net is powered directly from the +1 VD.
This power supply net takes +3 VD and passes it through a 1.65 V LDO. The LDO’s output voltage is variable and
can be set by changing the value of resistor R32.
7.2.2. AAA Battery
When the J10/J11 three-way header is set to AAA_BAT, the C8051F930 Target Board may be powered from a
single AAA battery inserted in BT1 or from the series combination of the AAA batteries inserted in BT1 and BT2. A
single battery is selected when SW4 is configured to one-cell mode. The two AAA batteries configured in series to
provide a voltage of ~3 V are selected when SW4 is configured to two-cell mode.
7.2.3. Coin Cell Battery
When the J10/J11 three-way header is set to COIN_CELL, the C8051F930 Target Board may be powered from a
single 1.5 V Alkaline (A76) or Silver Oxide (357) button cell inserted in BT4 or from a single 3 V Lithium (CR2032)
coin cell inserted in BT3. The button cell (BT4) is selected when SW4 is configured to one-cell mode, and the coin
cell (BT3) is selected when SW4 is configured to two-cell mode.
J11
J1
0
VBAT
WALL_PWR
AAA_BAT
COIN_CELL
J11
J1
0
VBAT
WALL_PWR
AAA_BAT
COIN_CELL
J11
J1
0
VBAT
WALL_PWR
AAA_BAT
COIN_CELL
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