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Theory of Operation
• The gauge sets charge* to logic high when the
battery has been charged to 94% (or greater) of the
battery's capacity, this lowers the charge rate to 65
milliampere, or C/25.
• A separate charge control circuit is the voltage
limit for the battery; here a battery voltage moni-
toring circuit in the charger limits the charger to
a voltage limit of 1.55 volts per cell (nominal). The
charger keeps reducing the charge current in order
to remain below this voltage limit. This prevents
damage to the cells from excessive battery voltage.
Charge detector
A charge detector circuit generates the control sig-
nal Charge_Detect to control the illumination of
a battery charge LED indicator and to reset the very
low battery detector circuit located within the battery
pack.
• The main microprocessor does not monitor the
Charge_Detect signal. However, the main
microprocessor communicates with the gauge to
determine charge status.
Battery switchover
A smart switch selects a reliable source of power for
the system power supplies. This switches to internal
battery power when AC power and external DC pow-
er are removed from the pump (or when these sources
are below acceptable thresholds detailed above).
• In normal operation, the battery voltage can be at
a higher voltage than the external DC − especially
during battery charging.
Battery board – schematic level
The battery reports to the "Main" system microproces-
sor present status and controls battery charge from the
Interconnect PCB. The battery PCB has:
• a 3-volt Linear Regulator
• a Gauge IC
• and a Depleted Battery Monitor IC.
The local circuit allows the battery to maintain its cur-
rent capacity regardless of where the battery resides.
The referenced schematic signal nets of the main
board electronics are identified using names in
smallcaps.
52
Battery gauge function
The gauge IC, BQ2012, monitors direction and mag-
nitude of current flowing through the battery.
• The current is sensed by the gauge as a voltage
across R4.
• The gauge computes capacity.
To control charging the battery, the gauge uses battery
temperature and battery voltage to update the battery
capacity − which is a function of current and tempera-
ture.
The charge* signal from the gauge controls the bat-
tery charger, located on the Main PC board, to charge
at different rates depending on the state of the battery.
The gauge terminates standard charge in the event of
the battery temperature exceeding 50°C or if the bat-
tery pack voltage is less than 5.7 volts.
Severely depleted battery monitor
The depleted battery monitor IC senses the battery
voltage to prevent an over-discharged battery. When
the battery pack voltage reaches a nominal voltage
of 5 volts, the IC sets the vlow_battery signal to a
logic low, which disconnects all battery loads with the
exception of the battery monitor circuit.
The battery charger provides the signal charge_de-
tect, which resets this monitor IC reconnecting the
battery back to the system.
40-5648-51B
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Troubleshooting
