Low Cost isoSPI Coupling Circuitry for High Voltage High
Capacity Battery Systems
Jon Munson The isoSPIв„ў feature built into the LTC6804 battery
stack monitor, when combined with an LTC6820 isoSPI
communications interface, enables safe and robust
information transfer across a high voltage barrier. isoSPI is
particularly useful in energy storage systems that produce
hundreds of volts via series-connected cells, which require
full dielectric isolation to minimize hazards to personnel.
In a typical isoSPI application (Figure 1)
pulse transformers provide the dielectric isolation and reject common-mode
interference that can be impressed on
the wiring. The isoSPI function operates
with readily available and inexpensive
Ethernet LAN magnetics, which typically
include a common-mode-choke section (as shown in Figure 1) to improve
common-mode line noise, along with the
usual 100Ω line termination resistors and
common-mode decoupling capacitors.
Ordinary signal transformers, including
Ethernet and gate-driver types, are wound with enameled wire that can have pin-hole
sized insulation defects, which expose
the copper to the atmosphere, inherently …