BeagleBoard XM C2, Reference Manual

Page: 55 / 163

REF: BB_SRM_xM
BeagleBoard-xM System
Reference Manual
Revision C2
Page 55 of 163
7.6 VBAT Power Conditioning
This circuitry regulates the DC input to a nominal 4.2VDC level. This is required in order
to meet the maximum DC voltage level as specified by the
TPS65950 Power
Management device which is 4.7V. Using 4.2V gives us some margin and meets the
nominal 4.2V rating of the
TPS65950 .
Figure 25 is the power conditioning section of the BeagleBoard.
VBAT_FB
VBAT
R14
56.2K,1%
R15
22.6K,1%
C5
10uF,CER,0805,6.3V
DC_5V
4.2V
VBAT_MAIN
R13 .1,0805
C7
0.1uF,10V
+
J2
HDR2_.1x.1
1 2
U3
TL1963A
IN
2
SHDN
1
OUT
4
ADJ
5
GND
3
GND
6
Figure 24. VBAT Power Conditioning
The
TPS65950 provides the main power rails to the board and has a maximum limit of
4.7V on its VBAT input and a nominal of 4.2V. U3 , the TL1963A , is used to convert the
DC_5V, which can come from a DC wall supply or the USB, to 4.2V to meet this
requirement. The
TL1963A is a linear low-dropout (LDO) voltage regulator and is
thermal shutdown and current limit protected. It has the ability to deliver 1A of current,
although this is far and above the requirements of the board. By adjusting the values of
R14 and R15 , the actual voltage can be adjusted if needed.
7.7 TPS65950 Reset and Power Management
The
TPS65950 supplies several key functions on the BeagleBoard. This section covers a
portion of those functions centered on the power and reset functions. Included in this
section are:
o
Main Core Voltages
o
Peripheral Voltages
o
Power Sequencing
o
Reset