Spacelabs qube 91390, Service Manual

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Q U B E
T
H E O R Y
The LTC1960 battery charger IC interfaces with the AO MCU. It is
responsible for load switching between AC and battery or batteries,
and direct communication via SMBUS protocol to the Li-Ion smart
batteries. The IC is also responsible for charging the batteries. Refer
to the battery section for more information on batteries.
For 670-1573-03 CPU PCBAs and higher, a high priority technical
alarm has been added. The AO MCU triggers a technical alarm in the
following events:
• Out of tolerance voltages on the +3.3V, +5V, +12V, and -12V
supplies
• No host CPU MPC8270 response
• If the AO MCU also fails to update the watchdog circuit
The technical alarm is a redundant alarming circuit that does not use
the main CPU audio. This circuit can derive power from the external
power supply, battery, or supercap incorporated in the circuit. The
safety circuit sounds if: the unit is unplugged from AC and no
battery is present, or if the unit is operating on battery and the
battery is depleted.
Li-Ion Batteries
If either the charger or host device fails to function correctly,
electronic circuitry is permanently connected within the battery
pack to prevent damage. If an illegal current source is placed across
the battery terminals or an illegal load is connected, the circuitry
also protects the battery. Redundant levels of protection have been
implemented (the primary protection levels are auto-resettable and
the secondary are non-resettable).
If any cell voltage >=4300
µ
V, the primary protection circuit
prevents the battery from charging. It allows charging again once all
cell voltages are <=4150
µ
V. If any cell voltage >=4.45 V +/-0.05 V
by blowing a power path logic fuse, the secondary protection circuit
prevents the battery from charging. The fuse is non-resettable,
which renders the battery pack nonfunctional.
The primary protection circuit also provides over-temperature
protection and prevents the battery from charging at temperatures
=>54º C. Then, once the battery temperature has cooled to <=45º C,
it again allows charging.
The primary protection circuit also provides continuous over-current
protection and prevents the battery from charging at Current()
=>4.25 A. Then, once the Average Current() <= 200
µ
A for 70 sec,
the battery will retest the overcurrent condition, and again allow
charging.
The primary protection circuit prevents the battery from being
further discharged once any cell voltage reaches <=2500
µ
V. Then,
once all cell voltages are >= 3000
µ
V, it allows discharge again.