A surge voltage is produced by the electric motor dur-

ing regenerative braking conditions. The MAX11080 is

designed to tolerate an absolute maximum of 80V

under this condition. The MAX11080 should be protect-

ed against higher voltages with an external voltage

suppressor such as the PBMB78AT3 on the DCIN con-

nection point. This protection circuit also helps to

reduce power spikes that can occur during the inser-

tion of the battery cells. During negative voltage excur-

sions, the protection circuit stores enough charge to

power the regulator through the transient. Figure 14

shows the clamp configuration to protect the DCIN sup-

ply input.

The DCIN input contains a comparator circuit to detect

an open circuit on this pin for fault-management pur-

poses. Whenever a nominal voltage of two silicon diode

drops appears between C12 and DCIN following the

fault indication. This voltage drop must appear for at

voltage drop from C12 to DCIN during normal operation

should be kept at no more than 0.5V to prevent erro-

neous tripping of the DCIN open-circuit comparator

under worst-case circumstances (lowest silicon diode

ply the transient current demanded at startup by the

provides the supply path during normal operation. It is

selected to be 5k

Ω so that the maximum voltage drop

between C12 and DCIN is about 0.25V with nominal

supply currents.

High-power batteries are often used in noisy environ-

ments subject to high dV/dt or dI/dt supply noise and

EMI noise. For example, the supply noise of a power

inverter driving a high horse-power motor produces a

large square wave at the battery terminals, even though

the battery is also a high-power battery. Typically, the

battery dominates the task of absorbing this noise,

since it is impractical to put hundreds of farads at the

inverter.

The MAX11080 is designed with several mechanisms to

deal with extremely noisy environments. First, the major

power-supply inputs that see the full battery-stack volt-

age are 80V tolerant. This is high enough to handle the

large voltage changes on the battery stack that can

occur when the batteries transition between charge and

discharge conditions. Next, the linear regulator has

high PSRR to produce a clean low-voltage power sup-

ply for the internal circuitry. This allows DCIN to be con-

serves two purposes. It supplies the internal charge

pump with its power and acts as the reference ground

for the upper alarm communication port. The charge

pump creates a secondary low-voltage supply that is

signal is internally shifted down to AGND level where it

is processed by the digital logic. There are two connec-

application requirements.

be DC-coupled to the next higher module for other rea-

as DCIN. This connection is valid as long as the voltage

difference between the top of Stack(n) and the bottom

of Stack(n+1) during worst-case conditions does not

exceed the margin of the alarm pin signaling levels.

bus bar, it can be AC-coupled to the far side to main-

tain alarm communication when the bus bar is open-cir-

cuit. In that case, the two sides of the AC-coupling

capacitor can be at different DC potentials, but the

alarm communication signal continues to be passed

across the capacitor connection. It is recommended

with the alarm signal through the communication bus

wiring, possibly by twisted pair wire, for maximum noise

immunity and minimum emissions.

The preferred connection to reject noise between mod-

to AGND of the next module. It is again recommended

the alarm signal as part of the communication bus for

maximum noise immunity and minimum emissions.

12-Channel, High-Voltage Battery-Pack

Fault Monitor

18

______________________________________________________________________________________

TO DCIN INPUT

5k

Ω

0.1

µF

80V

PBMB78AT3

FUSE

TOP OF CELL STACK

SEE THE APPLICATION CIRCUIT DIAGRAMS (FIGURES 15 AND 16) FOR THE

PROPER CONNECTION LOCATION.

Figure 14. Battery Module Surge and Overvoltage Protection

Circuit