CBC915 EnerChip Energy Processor
Electromagnetic generators used for typical energy harvesting applications have an output impedance of several
hundred ohms to several thousand ohms with an impedance of approximately 1kΩ being typical. The output
voltage of an electromagnetic generator will change linearly with input excitation. In most applications, voltages
in the range of 500mV to 2V DC after rectification and filtering are typical.
CBC915 operation with a thermoelectric generator (TEG) transducer (as shown in Figure 3) starts with a
temperature differential across the TEG. This temperature differential causes the TEG to generate a voltage.
When that voltage reaches approximately 400mV, the input charge pump will start, boost the input voltage, and
store the accumulated charge in capacitor Cin. When the accumulated charge voltage reaches approximately
2.4V, the charge will be dumped into the CBC915 power rail, activating the CBC915. Upon activation, the CBC915
outputs are initialized to a known state and the input mode pins will be interrogated in order to recognize the
transducer type. The CBC915 will then pulse-width modulate the LX pin and initiate operation of the boost
converter. When the boost converter voltage rises above 2.4V, power to the input charge pump is removed to
reduce quiescent current. The CBC915 then checks for voltage on the output capacitor (Cout) by setting the EN
VCAP pin high and reading the output capacitor voltage on VCAP pin. If the capacitor is charged, the CBC915 will
leave the capacitor connected to the VOUT pin and EnerChips. If the capacitor has not been charged, the CBC915
will turn off the VOUT connection by setting EN VOUT/ pin high and isolate the capacitor from the EnerChips by
setting EN CAP CHG/ pin high. The CBC915 will then check the boost converter voltage by monitoring the voltage
at the VOUT pin and wait for the voltage to reach 4.06V at which time the CBC915 will enter the maximum peak
power tracking state (MPPT) and pulse the MPPT/ status pin low and start adjusting the boost converter input
impedance to match the output impedance of the TEG. This process can take several minutes. The MPPT state
is only entered at initial power-on and values are subsequently stored. Note the MPPT state can be entered by
five different events:
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•
•
•
•
at initial power up;
when powered up while the Status/ input is held low
by command over the serial interface;
by detection of the input voltage being at a lower level than what it was at the initial MPPT startup while
VOUT is not in regulation (voltage to low);
when the input voltage is at a higher level and VOUT is not in regulation (voltage too high).
Figure 3. CBC915 Energy Processor Application Circuit
In all cases while in the MPPT state, the boost converter is isolated from the EnerChip(s), output capacitor,
and load. During MPPT mode, the load will be operating from the energy stored in the output capacitor and
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DS-72-15 Rev C
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