MAX11080 Datasheet, PDF (20/27 Pages) Maxim Integrated Products – 12-Channel, High-Voltage Battery-Pack Fault Monitor

12-Channel, High-Voltage Battery-Pack
Fault Monitor
Shutdown Control
The SHDN pin connections of the MAX11080 operate in
a manner that allows the shutdown/wake-up command
to trickle up through the series of daisy-chained packs.
Because the internal linear regulator is powered down
during shutdown, the shutdown function must operate
when V_AA is absent and it, therefore, cannot depend on
a Schmitt trigger input. A special low-current, high-volt-
age circuit is used to detect the state of the SHDN pin.
The shutdown pin has a +1.8V minimum threshold for
the inactive state. When SHDN > 1.8V, the MAX11080
turns on and begins regulating VDD_U and VDD_L. If
SHDN < 0.6V, the MAX11080 shuts down. For automat-
ic shutdown when the pack is removed from the sys-
tem, connect a 200kΩ resistor from SHDN to AGND.
Once SHDN is driven high, the power-up sequence fol-
lows that described for the internal linear regulator. The
SHDN signal of the next higher module should be con-
nected to VDD_U through a 20kΩ resistor pullup. This
connection ensures that the next module in the daisy
chain is enabled as VDD_U of the lower module powers
up. This action propagates up the daisy chain until the
last battery module is enabled. The shutdown of a
VDD_U supply pulls the connected SHDN pin of the
upper module toward GND_L and propagates the shut-
down signal up the daisy chain.
A shutdown signal propagated from the first daisy-
chain device to the last incurs a certain amount of
delay. A deasserted shutdown signal is not propagated
to the next higher module until the charge pump has
regulated the level-shifted upper port supply, VDD_U, to
a value greater than the SHDN V_IH level. This time
depends on both the charge-pump capacitor used and
the value of the VDD_U decoupling capacitor. A typical
time delay of 10ms can be expected from the time the
SHDN pin reaches the deasserted state until VDD_U
reaches its full specified value.
C1 Input Absolute Maximum Rating
The C1 input is limited to V_DCIN - 0.6V above AGND or
a maximum of 20V if the SHDN pin is asserted. If an
application requires that the 20V restriction be removed
during active shutdown, then a 4.0V zener diode can
be added from V_AA to AGND. This protects V_AA and
allows the C1 input to go to V_DCIN - 0.6V regardless of
the SHDN state. It also allows the differential C1 to C0
voltage to range from -0.3V to +80V.
Cell-Connection Detection
An individual MAX11080 can be connected to as many
as 12 series-connected cells. To accommodate configu-
rations with fewer cells, unused cell inputs must be short-
ed together. The designer can choose which cell inputs
to leave unused. The example application circuits in this
document have chosen to populate the uppermost cell
position and group the unused inputs just under this cell.
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-con-
nection detection occurs just before the MAX11080 is
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 the single device application, the device enters the
“level” mode when the TOPSEL is connected to AGND.
The ALRM_L shows the level of AGND for no alarm state
and VAA for alarm state. ALRM_U has to be tied to
GND_U for this mode. The following table summarizes
the operation of TOPSEL and ALRM_L:
TOPSEL
0
1
ALRM_U
0
X
ALRM_L
No alarm
alarm
0
1
Heartbeat
1
Internal Self-Test
The MAX11080 performs an internal self-test during
power-up according to the linear regulator power-up
flowchart (Figure 12). Each overvoltage comparator 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 reference in place
of the usual threshold level. Figure 8 shows the connec-
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