User's Manual

July 23, 2002 4-27
CreataLink2 XT Hardware Integrator’s Guide Hardware Integration
Battery Selection Criteria
Applying Battery Technologies
Review the following characteristics of packet data products when you consider
different battery technologies:
Inconsistent Current Drain
When battery manufacturers specify the battery discharge profiles, they assume a
constant current drain model. In a packet data system, the constant current drain
model no longer applies. There are three levels of current drain states: sleep, receive,
and transmit. The data transceiver cycles through these different states when
powered and in contact with the network.
To determine the realistic battery life or capacity for the product, contact the battery
manufacturer or experiment by transmitting for different lengths of time.
Peak Currents During Transmissions
Because transmissions are short, view the resulting current drain during
transmissions as current pulses. Consider these pulses when you select the
appropriate battery technology.
Consider the internal impedance of the battery at the peak currents during
transmissions. This is when the largest voltage drop occurs across the battery
terminals. Design an adequate supply guard band to ensure that the data
transceiver and other circuitry in the final product are not reset during
transmissions.
Messaging Model
To determine the product battery capacity, define the messaging model for the
target market:
• Optimal number of hours by day, weeks, or months of use prior to recharge
• Number of messages transmitted per hour
• Number of messages received per hour
• Average length of transmitted messages
Use the information and the current drains of the data transceiver and other
circuitry to define the requirements for battery supply voltage and capacity.