CBC915 EnerChip Energy Processor

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DS-72-15 Rev F

Page 9 of 16

EnerChip EP Communications Interface and Commands

The CBC915 has seven serial I/O commands to enable the end application to be “energy aware”. The serial I/O

UART is configured as 9600 Bits per second, 8 bits, no parity bit, 1 stop bit. 9600 8N1.

The I/O lines are TXD and RXD, described as follows:

TXD - Serial I/O transmit data out of the Energy Processor. Data rate is 9600 8N1 (0utput from CBC915)

RXD - Serial I/O receive data into the Energy Processor. Data rate is 9600 8N1 (Input to CBC915)

The serial I/O commands are:.

Command 1 (Not available on CBC915-ACA): Power Available. This command returns - in microwatts - the total

power available from the energy harvesting transducer. The application can use this information to change

its performance characteristics depending on the input power available. This command is typically used in

conjunction with command 4 (Find Maximum Peak Power Point)

Command 2 (Not available on CBC915-ACA): State of CBC915. This command returns the current state of the

CBC915. The CBC915 is always in one of five different states:

State 1: Maximum Peak Power Tracking (MPPT). In this mode, the CBC915 adjusts the impedance of the

power conversion stage to match the output impedance of the energy harvesting transducer. While in State

1, the load is not powered from the energy harvester.

State 2: Capacitor Charging. While in State 2, the CBC915 charges the output capacitor. This state is typically

entered only once at initialization or if the EnerChips were to become deeply discharged. While in State 2, the

output capacitor is isolated from the load until the output capacitor has reached full charge.

State 3: EnerChip Charging. This state is entered after the output capacitor charging state is completed and

the system is not in regulation. During State 3 power is applied to the load.

State 4: System in Regulation. This state is entered when the system is in regulation.

State 5 Output Off. This state would typically only be detected and used in a laboratory environment, as power

would normally be turned off to the load and thus prevent serial communications.

Command 3 (Not available on CBC915-ACA): Transducer Type. This command is typically used during production

test to ensure the mode input pins have been set to the correct value for the particular transducer being used.

Command 4: Find Maximum Peak Power Point. To conserve power, the CBC915 only finds the maximum peak

power point once at initialization or anytime the CBC915 falls out of regulation (voltage to high or low) while

at the same time detecting a change in input voltage. If it is desired to reset the maximum peak power point

the host microcontroller can force the CBC915 to find the maximum peak power point. While this command is

being executed power from the energy harvester is cut off to the application and the application system will

get its power while the CBC915 is finding the peak power point from the EnerChip(s) and output capacitor. This

command would typically only be used on systems using PV cells that change impedance with changes in light

level, other transducer types with constant impedance would typically derive little if any benefit from a reset of

the peak power point.

Command 5: EnerChip State of Charge. This command returns the state of charge as a percentage of total

capacity. This indicator is based on a voltage measurement and will not be totally accurate as the EnerChips age,

or with large deviations from room temperature.