BACKGROUND

Advances in microelectronic circuits have allowed for creation of electronic devices having smaller and smaller footprints with ever increasing computational and communication capabilities. These advances have allowed for creation of new classes of electronic devices. Various challenges exist in providing power to such devices. It is generally desirable to power small portable or personal electronic devices with batteries. Much attention has been focused on high energy density rechargeable cells/batteries, such as lithium ion cells/batteries, for applications such as laptop and notebook computers, tablet computers, smartphones, and the like. However, for some applications, other battery chemistries may provide a better solution.

As an example, for applications in which the average power requirement is very low, it may be preferable to use a lithium metal cell/battery. Lithium metal cells are designed to have relatively long lifetimes as compared to many other battery chemistries. This may be advantageous from a user perspective, because it reduces the frequency with which the user must change the cells/batteries. Additionally, lithium metal cells are widely available in a “coin cell” form factor, including the CR20xx series, which makes sourcing replacement cells/batteries easy for the user. However, lithium metal cells may be somewhat limited in their instantaneous power delivery capabilities with respect to other battery chemistries. As a result, even if the average power requirements of an electronic device are sufficiently low, some transient power requirements of a device may be such that use of a lithium metal cell (or other long-life optimized cell) compromises operation of the device in situations calling for high but transient instantaneous power delivery.

Thus, what is needed in the art are circuits and techniques for adapting long-life optimized cells/batteries for use in devices that have relatively low average power requirements, but which may have relatively high, but transient, instantaneous power requirements.

SUMMARY

An electronic device can include a battery bus configured to be powered by a battery and at least one load having a transient instantaneous power requirement. The device can further include a transient power management circuit coupled between the battery bus and the at least one load. The transient power management circuit may be configured to meet the transient instantaneous power requirement of the at least one load while maintaining a minimum voltage on the battery bus. The electronic device may further include at least one load coupled to the battery bus, and the minimum voltage on the battery bus may be selected to prevent interrupting operation of the at least one load coupled to the battery bus.

The transient power management circuit can include a boost converter having an input coupled to the battery bus and an output coupled to a capacitor bank. The at least one load having a transient instantaneous power requirement may be coupled to the capacitor bank. The transient power management circuit may further include a control circuit configured to operate the boost converter to charge the capacitor bank. The boost converter may be a buck-boost converter. The transient power management circuit may further include a control switch coupled between the boost converter and the capacitor bank, and the control circuit may be further configured to limit inrush current into the capacitor bank to maintain a minimum voltage on the battery bus.

A transient power management circuit can include a boost converter having an input coupled to a battery bus and an output coupled to a capacitor bank and a control circuit configured to operate the boost converter to charge the capacitor bank while maintaining a minimum voltage on the battery bus. The minimum voltage on the battery bus may be selected to prevent interrupting operation of at least one load coupled to the battery bus. The boost converter may be a buck-boost converter. The transient power management circuit can further include a control switch coupled between the boost converter and the capacitor bank, and the control circuit is further configured to limit inrush current into the capacitor bank to maintain a minimum voltage on the battery bus.

The transient power management circuit can further include an operational amplifier configured to receive a battery bus voltage and a setpoint voltage and to generate therefrom an output signal to control the control switch and the boost converter. A bias supply of the operational amplifier may be coupled to the battery bus by a first diode and to the boost converter output via a second diode. At least one of the first and second diodes may be low forward voltage drop diodes.

A method of operating an electronic device comprising a transient power management circuit can include, responsive to an enabling of the transient power management circuit, operating the transient power management circuit to charge a capacitor bank while maintaining a minimum voltage on a battery bus and, responsive to the capacitor bank reaching a target voltage, operating a load coupled to the capacitor bank. Operating the transient power management circuit to charge a capacitor bank while maintaining a minimum voltage on the battery bus can include determining whether an output voltage of a boost converter coupled between the battery bus and the capacitor bank is greater than an input voltage of the boost converter. Responsive to a determination that the output voltage is less than the input voltage, the method can include operating a control switch as a linear regulator to regulate current flow from the battery bus to the capacitor bank. Responsive to a determination that the output voltage is greater than the input voltage, the method can include operating the boost converter to boost a voltage of the battery bus to a voltage of the capacitor bank.

The method of operating an electronic device comprising a transient power management circuit can further include determining whether continued operation of the load coupled to the capacitor bank is required. Responsive to a determination that continued operation of the load coupled to the capacitor bank is required, the method can further include operating the transient power management circuit to charge a capacitor bank while maintaining a minimum voltage on a battery bus. Responsive to a determination that continued operation of the load coupled to the capacitor bank is not required, the method can further include disabling the transient power management circuit.

A method of estimating battery state of charge from operation of a transient power management circuit configured to charge a capacitor bank while maintaining a minimum voltage on a battery bus can include measuring a time to charge the capacitor bank while maintaining a minimum voltage on the battery bus and comparing the measured time to a threshold to determine a battery state of charge. The method can further include performing a temperature compensation on the measured time before comparing the measured time to the threshold. Measuring the time to charge the capacitor bank while maintaining a minimum voltage on the battery bus can include making a plurality of charging time measurements and comparing the measured time to a threshold comprises comparing a moving average of the measurements to the threshold. The threshold may be stored in a lookup table. The threshold can include a plurality of time measurements correlated with a plurality of states of charge.

