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

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.

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

this application. The following table summarizes the

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-

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

the fault condition (either open or short) is removed,

unless otherwise specified.

12-Channel, High-Voltage

Battery-Pack Fault Monitors

______________________________________________________________________________________

21

TOPSEL

No alarm

Alarm

00

1

1X

Heartbeat

1