shorted together, but Cell 1 must always be populated.
The designer can choose which cell inputs to leave
unused. The example application circuits recommended
are the most efficient configurations.
At power-up, the part compares the voltage applied to
each cell input with a nominal cell-detection threshold
voltage of 0.7V. If the cell voltage is less than the cell-
detection threshold, undervoltage detection is disabled
for that cell input. If the voltage at the input is 0.7V or
greater, undervoltage detection is specified by the state
of the UVSEL_ inputs. Overvoltage detection is always
enabled for all cell-voltage inputs. The cell-connection
detection occurs just before the MAX11080/MAX11081
are fully functional as shown in Figure 12 under NUMBER
OF CELLS DETECTED.
TOPSEL Function
The TOPSEL pin is used to indicate to a device whether
it is the top device in the daisy-chain stack. The top
daisy-chain device is responsible for generating the
heartbeat signal at the top of the ALRM_ pin bus. This
heartbeat propagates along the chain toward the host.
To designate a device as the top device, the TOPSEL
pin should be connected to V
AA
. For all other devices
in a daisy-chain, this pin should be connected to
AGND. The TOPSEL pin has a weak internal pulldown
resistor, but this resistor should not be relied upon as
the sole means of setting the TOPSEL logic level. The
logic level of the TOPSEL pin is not latched internally at
startup and is continuously sampled during operation.
The ALRM
U
input should be connected to GND
U
for the
top module as good design practice to prevent noise
pickup even though the input logic level is ignored.
For a single device or DC-coupled daisy-chain applica-
tion, the device can be operated in an alarm level mode
instead of heartbeat mode by tying TOPSEL to AGND for
all devices. In this mode of operation, ALRM
L
passes the
signal of ALRM
U
when the device is not in the alarm state.
ALRM
L
drives high when the device is in the alarm state.
ALRM
U
must be tied to GND
U
for the topmost device for
this application. The following table summarizes the
operation of TOPSEL and ALRM
L
for level mode:
Internal Self-Test
The MAX11080/MAX11081 perform an internal self-test
during power-up according to the linear regulator
power-up flowchart (Figure 12). Each overvoltage com-
parator is tested for the ability to detect an internally
generated overvoltage test condition. This is done by
using the ground voltage level as the threshold refer-
ence in place of the usual threshold level. Figure 8
shows the connection for this test-mode compare level.
If all comparators can detect the internally generated
overvoltage test event, part operation continues. If any
comparator fails to detect the internally generated over-
voltage test event, a fault is signaled using the ALRM
L
pin. The device must be power cycled to retest the
comparators and attempt to clear this fault condition.
Failure Mode and Effects Analysis
High-voltage battery-pack systems can be subjected to
severe stresses during in-service fault conditions and
could experience similar conditions during the manufac-
turing and assembly process. The MAX11080/MAX11081
are designed with high regard to these potential states.
Open and short circuits at the package level must be
readily detected for fault diagnosis and should be toler-
ated whenever possible. A number of circuits are
employed within the MAX11080/MAX11081 specifically
to detect such conditions and progress to a known
device state. Table 3 summarizes other conditions typi-
cal in a normal manufacturing process along with their
effect on the MAX11080/MAX11081 devices.
See Table 4 for the FMEA analysis of the MAX11080/
MAX11081. If the cell voltage is within the monitor
range, the heartbeat signal on ALRM
L
resumes once
the fault condition (either open or short) is removed,
unless otherwise specified.
MAX11080/MAX11081
12-Channel, High-Voltage
Battery-Pack Fault Monitors
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