MAX11080/MAX11081
12-Channel, High-Voltage
Battery-Pack Fault Monitors
14 ______________________________________________________________________________________
event. Figure 8 summarizes the C
DLY
circuit.
Once the ALRM
L
pin is forced high due to an alarm
(+2.4V minimum as referred to AGND), it transitions
back to a heartbeat signal only after all battery cells
meet the following condition:
(V
OV
- V
HYS
) > V
CELL(ALL)
> (V
UV
+ V
HYS
)
Examples of cell-voltage readings and their effect on
the alarm status are shown in Figures 9 and 10 for sin-
gle- and multiple-cell systems. In the case where an
upper module is forwarding an active alarm condition
down the daisy-chain, that condition continues to be
propagated toward the host regardless of the alarm
state of any lower module. Furthermore, to circumvent
the possibility of a short-circuited capacitor connected
to CD preempting the fault-time validation process, a
redundant built-in delay of 4s nominal is asserted as a
backup. If the V
CD
threshold is not reached within 4s of
an out-of-range event, the alarm becomes active.
Programmable Delay Time
The alarm trigger delay time is calculated according to
the following equations:
t
DLY
= (V
CD
x C
DLY
)/I
CD
C
DLY
= (t
DLY
x I
CD
)/V
CD
The effective I
CD
value of the current source is 6.1µA
typical and the threshold voltage, V
CD,
is 1.23V typical.
The V
CD
threshold is specified at an internal node prior
to the resistor in series with the CD pin as shown in
Figure 8. The threshold voltage seen at the pin is
approximately 1.18V due to the drop associated with
the typical I
CD
value and the 6kΩ resistor. The
MAX11080/MAX11081 can operate with capacitor val-
ues from 15nF (3.0ms) to 16.5µF (3.32s). Each capaci-
tor should have a voltage tolerance of 5V minimum.
Cell-Voltage Threshold Selection
The overvoltage and undervoltage threshold selection
is configured through the OVSEL_ and UVSEL_ inputs.
The overvoltage selection can be configured from 3.3V
to 4.8V in 100mV increments. The undervoltage thresh-
old can be configured from 1.6V to 2.8V in 200mV
increments. The undervoltage detection can also be
disabled. See Tables 1 and 2 for the proper configura-
tion settings.
Immunity to unintended changes in the threshold volt-
age setting (due to accidental pin-to-pin short circuits,
for example) is provided. The customer-programmed
3.3 0 0 0 0
3.4 0 0 0 1
3.5 0 0 1 0
3.6 0 0 1 1
3.7 0 1 0 0
3.8 0 1 0 1
3.9 0 1 1 0
4.0 0 1 1 1
4.1 1 0 0 0
4.2 1 0 0 1
4.3 1 0 1 0
4.4 1 0 1 1
4.5 1 1 0 0
4.6 1 1 0 1
4.7 1 1 1 0
4.8 1 1 1 1
