DS-72-40 Datasheet, PDF (9/17 Pages) Cymbet Corporation – EnerChip™ CC Energy Harvester Evaluation Kit

CBC-EVAL-10B EnerChip CC EH Evaluation Kit
Input Circuit Description
The input circuit of the CBC-EVAL-10B consists of input capacitor C8 (12), Power On Reset (POR) circuit U3 and
U5, Diodes D5 and D13, capacitor C11 and resistor R7. The input circuit is designed to allow the CBC-EVAL-10B
to smoothly start up with small solar cells in very low lighting conditions while protecting the CBC- EVAL-10B
circuitry as well as the user load circuitry from overvoltage conditions caused by larger solar cells in direct
sunlight The circuit consists of two section: the input impedance buffer and the overvoltage clamp.
The input impedance buffer is mainly U3 which has a very low input leakage current and, when paired with the
input capacitor C8(C12 optional) provides a very light load to the solar cell on startup. The CBC3150 on the
CBC5100 module can normally be used without this input buffer with large solar cells or use-cases that assure
solar cell output current of over 70uA during startup. The CBC3150 ASIC, like most other ICs, can demand
many times more than its rated 3uA quiescent current as it reaches its internal startup voltage, typically below
2 volts. POR circuit U3 presents a load of under 1uA to the solar cell provided C8 is large enough to prevent
oscillation. When U3 reaches its switching voltage of 2.7 volts it raises its VOUT pin which then powers the rest
of the CBC-EVAL-10B circuitry with as much current as it needs to break through the startup current surge. After
the CBC3150 ASIC has been started, it only draws its rated quiescent current during the rest of the operation.
The overvoltage clamp consists of U5, D13, D5, C11, and R7. The diodes are used to make U5 switch at
a higher voltage simply to avoid using two different voltage POR circuits on the input circuit. The diode
arrangement makes the clamp go off at input voltages above 3.3V. When VOUT of U5 switches high, it shunts
current from the solar cell and the input capacitor C8(C12) to ground until the input voltage drops below 3.3
Volts. The CBC3150 ASIC turns on its charge pump at 3.0 volts with the default setup of R2 and R3. When
the charge pump turns on the current from the input capacitor is boosted and sent to the EnerChips for
charging. Normal operation will show the input voltage to vary between 2.9 and 3.0 volts which presents a 3.0V
operating point for the input solar cell. The solar cell should be selected to have a peak power point at near
3.0V for maximum efficiency.
Output Circuit Description
The output circuit of the CBC-EVAL-10B consists of pulse current output capacitor C5 (C7,C8 optional), Power
On Reset (POR) circuit U4 , diodes D4 and D6, transistor Q3,switch S2, and resistors R9,10,and 11. The output
circuit is designed to allow the pulse current output capacitors to charge up to a minimum output voltage
without the load drawing down the solar cell or EnerChips before switching the output on which presents a very
low impedance power source to the user load to break through any startup current requirements. Without this
circuit, a user load could get stuck drawing so much current from the relatively high impedance solar cell and
EnerChips that it could never break through the voltage level needed to escape the initial startup current pulse.
The circuit operates by monitoring the pulse current output capacitors until they reach a sufficient voltage
determined by U4 where the RESET line of U4 turns on the output transistor Q3B which switches the output on
and Q3A latches the output on. Once the output is on, the RESET output of U4 lowers when the capacitors are
above the threshold voltage and rises when not which, if switch S2 is depressed, will modulate LED D6 for a
visual indication of the output state. The speed that D6 blinks is a measure of how fast the output capacitor is
recharging, which is proportional to the amount of energy coming from the EnerChips and solar cell.
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
immediately turned off can decrease the overall energy consumed. Microcontroller clock frequency can also
have a significant impact on the power budget.
©2014 Cymbet Corporation • Tel: [phone] • www.cymbet.com
DS-72-40 Rev C

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