Datasheet

LTC6802-1
28
68021fa
APPLICATIONS INFORMATION
FAULT PROTECTION
Overview
Care should always be taken when using high energy
sources such as batteries. There are numerous ways that
systems can be [mis-]configured that might affect a bat-
tery system during its useful lifespan. Table 13 shows the
various situations that should be considered when plan-
ning protection circuitry. The first five scenarios are to be
anticipated during production and appropriate protection
is included within the LTC6802-1 device itself.
Table 13. LTC6802-1 Failure Mechanism Effect Analysis
SCENARIO EFFECT DESIGN MITIGATION
Cell input open-circuit (random) Power-up sequence at IC inputs Clamp diodes at each pin to V
+
& V
–
(within IC) provide
alternate power-path.
Cell input open-circuit (random) Differential input voltage overstress Zener diodes across each cell voltage input pair (within IC)
limits stress.
Top cell input connection loss (V
+
) Power will come from highest connected cell input
or via data port fault current
Clamp diodes at each pin to V
+
& V
–
(within IC) provide
alternate power-path. Diode conduction at data ports will impair
communication with higher-potential units.
Bottom cell input connection loss
(V
–
)
Power will come from lowest connected cell input or
via data port fault current
Clamp diodes at each pin to V
+
& V
–
(within IC) provide
alternate power-path. Diode conduction at data ports will impair
communication with higher-potential units.
Disconnection of a harness
between a group of battery cells
and the IC (in a system of stacked
groups)
Loss of supply connection to the IC Clamp diodes at each pin to V
+
& V
–
(within IC) provide an
alternate power-path if there are other devices (which can
supply power) connected to the LTC6802-1. Diode conduction
at data ports will impair communication with higher-potential
units.
Data link disconnection between
stacked LTC6802-1 units.
Break of "daisy chain" communication (no stress
to ICs). Communication will be lost to devices
above the disconnection. The devices below the
disconnection are still able to communicate and
perform all functions, however, the polling feature is
disabled.
All units above the disconnection will enter standby mode
within 2 seconds of disconnect. Discharge switches are
disabled in standby mode.
Cell-pack integrity, break between
stacked units
Daisy-chain voltage reversal up to full stack potential
during pack discharge
Use series protection diodes with top-port I/O connections
(RS07J for up to 600V). Use isolated data link at bottom-most
data port.
Cell-pack integrity, break between
stacked units
Daisy-chain positive overstress during charging Add redundant current path link
Cell-pack integrity, break within
stacked unit
Cell input reverse overstress during discharge Add parallel Schottky diodes across each cell for load-path
redundancy. Diode and connections must handle full operating
current of stack, will limit stress on IC
Cell-pack integrity, break within
stacked unit
Cell input positive overstress during charge Add SCR across each cell for charge-path redundancy. SCR
and connections must handle full charging current of stack, will
limit stress on IC by selection of trigger Zener
Poll Interrupt Status (Level Polling)
1. Pull CSBI low
2. Send PLINT command byte
3. SDO output from bottom device pulled low if any device has an interrupt condition; otherwise, SDO high
4. Pull CSBI high to exit polling