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

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

SHDN < 0.6V, the MAX11080 shuts down. For automat-

ic shutdown when the pack is removed from the sys-

tem, connect a 200k

Ω 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-

connection ensures that the next module in the daisy

up. This action propagates up the daisy chain until the

last battery module is enabled. The shutdown of a

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

depends on both the charge-pump capacitor used and

time delay of 10ms can be expected from the time the

reaches its full specified value.

C1 Input Absolute Maximum Rating

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

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

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 the single device application, the device enters the

“level” mode when the TOPSEL is connected to AGND.

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-

12-Channel, High-Voltage Battery-Pack

Fault Monitor

20

______________________________________________________________________________________

TOPSEL

No alarm

alarm

00

0

1

1X

Heartbeat

1