CBC-EVAL-09 EnerChip EP Universal EH Eval Kit
to replenish the energy storage device. If the power budget is not exceeded during this phase, the system
can continue with its initialization. Next, the main initialization of the system, radio links, analog circuits, and
so forth, can begin. Care should be taken to ensure that the time the system is on during this phase does
not exceed the power budget. Several sleep cycles might be needed to ‘stair step’ the system up to its main
operational state. The EnerChip EP CBC915-ACA Energy Processor has a serial port to communicate to a
microcontroller when energy is available.
Circuit Recommendations to Save Power
In most system power budgets, the peak power required is not as critical as the length of time the power
is required. Careful selection of the message protocol for the RF link can have a significant impact on the
overall power budget. In many cases, using higher power analog circuits that can be turned on, settle quickly,
and be turned off can decrease the overall energy consumed. Microcontroller clock frequency can also have
a significant impact on the power budget. In some applications it might be advantageous to use a higher
microcontroller clock frequency to reduce the time the microcontroller and peripheral circuits are active. Avoid
using circuits that bias microcontroller digital inputs to mid-level voltages; this can cause significant amounts
of parasitic currents to flow. Use 10MΩ to 22MΩ pull-up/down resistors where possible. However, be aware
that high circuit impedances coupled with parasitic capacitance can make for a slow rise/fall time that can
place the voltage on the microcontroller inputs at mid-levels, resulting in parasitic current flow. One solution to
the problem is to enable the internal pull-up/down resistor of the microcontroller input to force the input to a
known state, then disable the resistor when it’s time to check the state of the line. If using the microcontroller’s
internal pull-up/down resistors on the inputs to bias push-button switches in a polled system, leave the pull-up/
down resistor disabled and enable the resistor only while checking the state of the input port. Alternatively, in
an interrupt-driven system, disable the pull-up/down resistor within the first few instructions in the interrupt
service routine. Enable the pull-up/down resistor only after checking that the switch has been opened.
Microcontroller pull-up/down resistors are typically less than 100kΩ and will be a huge load on the system if
left on continuously while a button is being pressed or if held for any significant length of time. For even greater
reduction in power, use external pull-up/down resistors in the 10MΩ to 22MΩ range. Bias the external resistor
not with the power rail but with a microcontroller port. The same algorithm used for internal pull-up/down
resistors can then be used to save power. The CHARGE line on the CBC5301 has a 10MΩ pull-up resistor with
a very slow rise time. Use an internal microcontroller pull-down resistor to force the CHARGE line low all of the
time and then disable the pull-down resistor to check the state of the line. This will keep the CHARGE line from
biasing the input at mid level for long periods of time which could case large parasitic currents to flow.
Using the CBC915 Serial Communications Port on the EVAL-09
One of the key features on the CBC915 Energy Processor is the ability to communicate between the CBC915
and the system-level Microcontroller. The information provided over this serial communications port enables
systems to become “Energy Aware”. The Commands/Responses and data fields are detailed in the CBC915
datasheet DS-72-15. The CBC915 serial port on the EVAL-09 as shown in the schematic, is accessible either
on J9 Pin 1 is RXD, pin 6 is TXD, or on J10 Pin 2 is RXD, pin 1 is TXD. The serial I/O UART is configured as 9600
Bits per second, 8 bits, no parity bit, 1 stop bit. 9600 8N1.
To connect the EVAL-09 serial port to a newer version PC that does not have a serial port, a USB to TTL adapter
should be used. There are versions of these adapters available at many electronics distributors such as the
Pololu USB-to-serial adapter. Please note that there are 10 MΩ resistors R18 and R19 on the RXD and TXD
lines to protect the CBC915 from ESD damage. In order to use some USB to TTL adapters, these resistors may
need to be shorted for proper communications operation.
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DS-72-13 Rev G
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