DYNAMICALLY SELECTABLE CHARGING CONFIGURATIONS
A wireless device includes an energy harvester configured to convert energy harvested from radio-frequency (RF) signals into a harvested voltage, a storage capacitor to store a voltage, a first port selectively connected to an external USB power source, a second port connected to a battery, a load including a non-volatile memory storing configuration data indicating a plurality of charging configurations, and a power management circuit including a controller and a switcher matrix. The controller is configured to select one of the plurality of charging configurations based on one or more of a presence of a connection with the external USB power source, a type of the battery, an amount of the harvested voltage, or a level of the voltage stored on the storage capacitor. The switcher matrix is configured to charge the battery based on the selected charging configuration.
1 . A wireless device, comprising:
an energy harvester configured to convert energy harvested from radio-frequency (RF) signals into a harvested voltage;
a storage capacitor to store a voltage;
a first port selectively connected to an external USB power source;
a second port connected to a battery;
a load including a non-volatile memory and a plurality of circuits associated with the wireless device, the non-volatile memory storing configuration data indicating a plurality of charging configurations for the wireless device; and
a power management circuit coupled to the energy harvester, the first and second ports, and the load, the power management circuit including:
a controller configured to select one of the plurality of charging configurations based on one or more of a presence of a connection with the external USB power source, a type of the battery, an amount of the harvested voltage, or a level of the voltage stored on the storage capacitor; and
a switcher matrix configured to charge the battery based on the selected charging configuration.
2 . The wireless device of claim 1 , further comprising a low drop-out (LDO) voltage regulator coupled between the USB connection and the switcher matrix, the LDO voltage regulator configured to regulate an output voltage of the external USB power source.
3 . The wireless device of claim 1 , wherein the switcher matrix includes a control input to receive a configuration signal from the controller, the configuration signal indicating a power configuration of the wireless device.
4 . The wireless device of claim 1 , wherein the battery comprises a lithium-ion battery and the configuration data indicates a charging procedure that includes a constant current mode and a constant voltage mode.
5 . The wireless device of claim 4 , wherein the configuration data further indicates:
a maximum charging current to be used for charging the lithium-ion battery during the constant current mode;
a voltage at which the charging procedure transitions from the constant current mode to the constant voltage mode; and
a minimum charging current to be used for charging the lithium-ion battery during the constant voltage mode.
6 . The wireless device of claim 5 , wherein the selected charging configuration causes the wireless device to charge the lithium-ion battery using the external USB power source when the external USB power source is connected to the wireless device.
7 . The wireless device of claim 6 , further comprising a charge circuit coupled between the external USB power source and the lithium-ion battery, the charge circuit configured to:
level-shift an output voltage of the external USB power source to a lower charging voltage; and
limit the charging current to the indicated maximum charging current.
8 . The wireless device of claim 7 , wherein the charge circuit includes one of a low drop-out (LDO) voltage regulator or a programmable current mirror.
9 . The wireless device of claim 7 , wherein the charge circuit includes a control terminal to receive a control signal from the controller, the control signal configured to selectively enable the control circuit and to adjust one or more settings of the control circuit based on the selected charging configuration.
10 . The wireless device of claim 5 , wherein the selected charging configuration causes the switcher matrix to charge the lithium-ion battery using the voltage stored on the storage capacitor when the external USB power source is not connected to the wireless device.
11 . The wireless device of claim 10 , wherein the selected charging configuration further causes the switcher matrix to charge the voltage stored on the storage capacitor using the harvested voltage.
12 . The wireless device of claim 10 , wherein the charge circuit includes one of a voltage rectifier, a pair of clocked diodes, or a DC-to-DC boost converter.
13 . The wireless device of claim 10 , wherein the charge circuit comprises:
a first diode connected between the storage capacitor and a node;
a second diode connected between the node and the lithium-ion battery; and
a clocked capacitor including a first terminal coupled to the node and a second terminal to receive a clock signal.
14 . The wireless device of claim 13 , wherein the charge circuit is configured to:
generate a charging voltage for the lithium-ion battery based on the voltage of the storage capacitor when the clock signal is in a first logic state; and
prevent leakage between the lithium-ion battery and the storage capacitor when the clock signal is in a second logic state.
15 . The wireless device of claim 13 , wherein the first diode, the second diode, and the clocked capacitor are implemented off-chip, the wireless device further comprising a general-purpose input-output (GPIO) pin configured to provide the clock signal to the off-chip capacitor.
16 . The wireless device of claim 10 , wherein the charge circuit comprises:
an inductor connected between the storage capacitor and a node;
a Schottky diode connected between the node and the lithium-ion battery; and
an NMOS transistor coupled between the node and ground, the NMOS transistor including a gate to receive a clock signal.
17 . The wireless device of claim 16 , wherein the inductor, the Schottky diode, and the NMOS transistor are implemented off-chip, the wireless device further comprising a general-purpose input-output (GPIO) pin configured to provide the clock signal to the off-chip NMOS transistor.
18 . The wireless device of claim 10 , wherein the charge circuit comprises:
an inductor connected between the USB power source and a node;
a Schottky diode connected between the node and the lithium-ion battery; and
an NMOS transistor coupled between the node and ground, the NMOS transistor including a gate to receive a clock signal.
19 . The wireless device of claim 18 , wherein the inductor, the Schottky diode, and the NMOS transistor are implemented off-chip, the wireless device further comprising a general-purpose input-output (GPIO) pin configured to provide the clock signal to the off-chip NMOS transistor.
20 . The wireless device of claim 1 , wherein the battery comprises a coin battery and the configuration data indicates an operating voltage of the coin battery, a maximum charge level of the coin battery, and a maximum charging current to be used for charging the coin battery.
21 . The wireless device of claim 20 , wherein the selected charging configuration causes the switcher matrix to charge the coin battery using the harvested energy irrespective of an availability of the external USB power source.
22 . The wireless device of claim 20 , further comprising a charge circuit coupled between the capacitor and the coin battery, the charge circuit comprising one of a low drop-out (LDO) voltage regulator or a programmable current mirror configured to generate a charging voltage by stepping-down the capacitor voltage.