MAX11080 Datasheet, PDF (18/27 Pages) Maxim Integrated Products – 12-Channel, High-Voltage Battery-Pack Fault Monitor

12-Channel, High-Voltage Battery-Pack
Fault Monitor
FUSE
TOP OF CELL STACK
C_DCIN
0.1µF
80V
R_DCIN
5kΩ
TO DCIN INPUT
PBMB78AT3
SEE THE APPLICATION CIRCUIT DIAGRAMS (FIGURES 15 AND 16) FOR THE
PROPER CONNECTION LOCATION.
Figure 14. Battery Module Surge and Overvoltage Protection
Circuit
DCIN and GND_U Supply Connections
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
power-up sequence, the ALRM_L output is asserted as a
fault indication. This voltage drop must appear for at
least the delay time set by C_DLY to result in a fault. The
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
forward bias voltage). The diode D_DCIN is used to sup-
ply the transient current demanded at startup by the
decoupling circuit. In parallel with this diode, R_DCIN
provides the supply path during normal operation. It is
selected to be 5kΩ 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-
nected directly to the stack voltage. Finally, GND_U
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
referenced to GND_U. Because the level-shifted supply
VDD_U is referenced to GND_U, the entire upper alarm
communication port glides smoothly on GND_U and it is
effectively immune to noise on GND_U. The upper alarm
signal is internally shifted down to AGND level where it
is processed by the digital logic. There are two connec-
tion methods that can be used for GND_U depending on
application requirements.
For the top module in a system, or where GND_U cannot
be DC-coupled to the next higher module for other rea-
sons, GND_U should be connected to the same location
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.
When GND_U is not DC-coupled to the far side of the
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
that an AC- or DC-coupled version of GND_U is paired
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-
ules is when a DC connection can be made from GND_U
to AGND of the next module. It is again recommended
that the DC-coupled GND_U signal is routed adjacent to
the alarm signal as part of the communication bus for
maximum noise immunity and minimum emissions.
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