EnerChip Solar Energy Harvesting Demo Kit
Connecting CBC-EVAL-08 to the System
The CBC-EVAL-08 board has two control lines that can be connected to a microcontroller (MCU) for the purpose
of conserving available energy, using incoming power efficiently, and extending EnerChip life. The table below
describes the functionality of the J1 and J5 connector pins.
Pin
BATOFF
J1 and J5 Pin Descriptions
Designation
Input control line to the CBC-EVAL-08 for disconnecting the
EnerChips from the CBC-EVAL-08 charging circuit. See the section
Circuit Recommendations to Save Power for additional information.
Active low output from the CBC-EVAL-08 indicating that the Ener-
Chips have been charged or are being charged. This is an open
drain output with an internal 10MΩ pull-up resistor to V
OUT2
. See
the section Circuit Recommendations to Save Power for additional
information.
Connected indirectly to the EnerChips’ positive terminals through
an isolation FET. Voltage is one diode drop above the potential at
V
OUT2.
System power
System ground
CHARGE
(not accessible from the J1 connector)
V
BAT
V
OUT2
GND
• V
OUT2
is the DC output voltage from the CBC-EVAL-08 and is approximately 3.5V depending on load
current. It provides power to the system according to the Operating Characteristics table shown below.
• GND is the ground connection of the CBC-EVAL-08. It is to be connected to the system ground line.
• V
BAT
is normally used for factory test purposes. It is indirectly connected to the on-board EnerChips
through an isolation pass transistor. The voltage on V
BAT
is connected to V
OUT2
by a diode and thus the
voltage at V
OUT2
is one diode drop lower than the voltage on V
BAT
. It is recommended that V
BAT
remain
disconnected from external circuits. In no event should V
BAT
be used for any purpose other than to provide
power to a load.
• BATOFF is typically controlled by a microcontroller I/O line. When driven high, the on-board EnerChips will
be disconnected from the charging source of the CBC-EVAL-08. This feature allows all available power to be
delivered to the load rather than to charging the EnerChips, a useful mode when limited transducer power
is available or when higher operating current is required from the system. When BATOFF is driven low, the
interaction between the charging source and the CBC-EVAL-08 behaves normally. In other words, when
BATOFF is low the EnerChips will always be charging when sufficient input power is available.
• CHARGE is an output signal from the CBC-EVAL-08 that will be forced low under one of two conditions:
»
When transducer output power is very low, a low level on CHARGE indicates that the
EnerChips have been charged.
»
CHARGE will also be driven low when transducer output power is more than sufficient to operate
the boost converter and charge the EnerChips at peak rate, regardless of the state of charge of the
EnerChips. Programming an MCU timer to allow enough charging time to elapse after the assertion
of CHARGE will ensure that the EnerChips are fully charged before using them to deliver power to the
system. The advantage is that the system is then aware of the minimum reservoir of energy available in
the event transducer power goes to zero.
DS-72-08 Rev18
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