User's Manual

System Overview and Functional Block Descriptions
1322x-LPB Reference Manual, Rev. 1.1
Freescale Semiconductor 3-5
3.4.2 Battery Sources
The battery source can be either a AAA battery pack (2 cells) or an optional Lithium coin cell:
• AAA source - as supplied, the 1322x-LPB has a 2-cell AAA battery holder mounted. The typical
usable voltage range for 2 AAA cells is ~3.1V down to 2.2 - 2.0V. Note that a Schottky diode and
a switch MOSFET are in series with the battery pack, and these will impact the lowest usable
voltage for the battery pack.
• Lithium coin cell source - in some very low duty cycle applications where the system mostly
“sleeps” in low power, the use of a Lithium coin cell can be considered. To assist in this design, the
1322x-LPB supports mounting a socket for a coin cell
— The AAA battery holder must first be removed.
— Mount one of two sockets for a Lithium coin cell
– Renata #SMTU2477N-1 - SMD holder for CR2477N cell (950 mAh)
– Renata #SMTU2450N-1 - SMD holder for CR2450N cell (540 mAh)
— The bottom view of the 1322x-LPB is shown in Figure 3-6.
– The mounting pads for the socket are noted (both sockets use the same pads). Be sure to
observe proper polarity.
– The mounting pads for two 100µF tantalum capacitors (C59 & C60) are also provided.
NOTE
Designing with Manganese Dioxide Lithium Coin Cell technology can be
very challenging. It is recommended to consider the following:
• Source impedance is high, typically about 25 ohms. Consider the
fluctuation in source voltage under heavy current load (~20 mA or
more).
• The addition of heavy bulk capacitance (such as C59 & C60) on VCC
can help minimize voltage drop under heavy current.
• High current duty cycle is critical; every effort must be made to
minimize high current activity (primarily TX and RX).
• When developing a coin cell application, it is highly recommended to
use the external DC source for all code development and early testing.
Life of coin cells can be very short with continual and/or heavy load.