Linear Technology LTC6804-1 - Page 75

LTC6804-1/LTC6804-2
75
680412fc
For more information www.linear.com/LTC6804-1
Interconnecting daisy-chain links between LTC6804-1
devices see <60V stress in typical applications; ordinary
pulse and LAN type transformers will suffice. Multi-drop
connections and connections to the LTC6820, in general,
may need much higher working voltage ratings for good
long-term reliability. Usually, matching the working voltage
to the voltage of the entire battery stack is conservative.
Unfortunately, transformer vendors will often only specify
one-second HV testing, and this is not equal to the long-term
(“permanent”) rating of the part. For example, according
to most safety standards a 1.5kV rated transformer is
expected to handle 230V continuously, and a 3kV device
is capable of 1100V long-term, though manufacturers may
not always certify to those levels (refer to actual vendor
data for specifics). Usually, the higher voltage transformers
are called “high-isolation” or “reinforced insulation” types
by the suppliers. Table48 shows a list of transformers that
have been evaluated in isoSPI links.
In most applications a common mode choke is also
necessary for noise rejection. Table49 includes a list of
suitable CMCs if the CMC is not already integrated into
the transformer being used.
isoSPI Layout Guidelines
Layout of the isoSPI signal lines also plays a significant
role in maximizing the noise immunity of a data link. The
following layout guidelines are recommended:
1. The transformer should be placed as close to the isoSPI
cable connector as possible. The distance should be kept
less than 2cm. The LTC6804 should be placed close to
but at least 1cm to 2cm away from the transformer to
help isolate the IC from magnetic field coupling.
2. A V
–
ground plane should not extend under the trans-
former, the isoSPI connector or in between the trans-
former and the connector.
3. The isoSPI signal traces should be as direct as possible
while isolated from adjacent cir
cuitr
y by ground metal
or space. No traces should cross the isoSPI signal lines,
unless separated by a ground plane on an inner layer.
Table49. Recommended Common Mode Chokes
MANUFACTURER PART NUMBER
TDK ACT45B-101-2P
Murata DLW43SH101XK2