AN-1052: Operating the EnerChip™ in High Temp. Environments
EnerChip Charging Duty Cycle
As described, the EnerChip can be charged continuously, or charged and left to float. These modes are
controlled using the digital I/O line ENABLE. A typical charging duty cycle when operating in high temperature
environments is shown in Figure 12.
Figure 12. EnerChip Charging Duty Cycle in High Temperature Operating Environments
Several methods can be used to control the ENABLE line, and therefore the activation of the charge pump that
charges the EnerChip. The simplest approach is to use an I/O line of the system MCU or CPU to activate the
charge pump only when the EnerChip requires charging due to use or to account for the minimal capacity fade
resulting from self-discharge. Or, the MCU/CPU could continuously force the ENABLE pin high and disable it
only when the system reaches an elevated temperature that warrants removing the bias on the EnerChip as
discussed in the previous sections of this Application Note.
Another approach is to use a thermal switch that will automatically drive the CBC31xx ENABLE pin low when
a defined temperature is reached. Such an implementation is shown in Figure 13. The advantage of this
approach is that the activation temperature is relatively tightly controlled and the trip point is user-selectable. A
disadvantage is the parasitic current needed to operate the temperature switch, which has to be factored into
overall power consumption in battery-operated systems. Moreover, the operational voltage range of many of the
thermal switches available, in combination with the voltage level required on the CBC31xx ENABLE pin, limit
this design to 3.3V systems.
Figure 13. EnerChip Bias Control Using a Temperature Switch
Doc AN-72-1052 Rev A
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