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Cbuf value of TPS62730

Vipin E
Prodigy 180 points

Hello

We need support in deciding the Cbuf value of TPS62730. In our circuit we interface TPS62730 with CC2541.  We are using Lithium polycarbon monofluoride battery(3V) and our Tx duration is 1sec for each 5sec. We will consume approximately 18mA during Tx. Since the battery chemistry of the coin cell we use doesn't fall under any of the battery chemistry listed in the datasheet (Li-SOCl2, Li-SO2, Li-MnO2) we need help in getting the correct value for Cbuf. Any help is very much appreciated.

  • 0
    TI__Expert 7110 points
    This depends on your specific battery. The less current you get from your battery without a collapsing Cell-Voltage, the more you need to buffer right after the battery. For your dutycycle of 20% it is important to consider the recharge as well.
    The mentioned chemistry types are just examples - this is basically valid for every high impedance battery.
    You need to buffer E = P*t = 54mWs for one cycle, which reflects in a capacitance of C = 2*E/(Vmax²-Vmin²) = 5.8mF if we allow the battery to drop down to 2.7V. This are just assumptions and depend on your system specifications.
    You should carefully check the battery datasheet to check if the impedance is low enough to recharge the capacitor and if the cell voltage behavior is ok for your application.