13
LTC1482
APPLICATIONS INFORMATION
WUU
U
The supply current does not drop below 20µA immedi-
ately. DE and DI/SHDN must be low for a least 600ns
simultaneously for I
CC
to drop to half its operating value
(driver outputs unloaded) and for t
CDH(SHDN)
before drop-
ping to the 20µA level. Taking either DE or DI/SHDN high
will wake the LTC1482 within 5µs.
In some applications, the A and B lines are pulled to V
CC
or
GND through external resistors to force the line to a high
or low state when all connected drivers are disabled. In
shutdown, the supply current will be higher than 10µA due
to the additional current drawn through the external pull-
up and the 22k input resistance of the LTC1482.
ESD Protection
The ESD performance of the LTC1482 A and B pins is
characterized to meet ±15kV using the Human Body
Model (100pF, 1.5kΩ), IEC-1000-4-2 Level 4 (±8kV)
contact mode and IEC-1000-4-2 Level 3 (±8kV) air dis-
charge mode. This means that external voltage suppres-
sors are not required in many applications, when com-
pared with parts that are only protected to ±2kV. Pins
other than the A and B pins are protected to ±3kV typical
per the Human Body Model.
When powered up, the LTC1482 does not latch up or
sustain damage when the A and B pins are tested using any
of the three conditions listed. The data during the ESD
event may be corrupted, but after the event the LTC1482
continues to operate normally. The additional ESD protec-
tion at the A and B pins is important in applications where
these pins are exposed to the external world via connec-
tions to sockets.
Fault Protection
When shorted to –7V or 10V at room temperature, the
short-circuit current in the driver pins is limited by internal
protection circuitry to 250mA. Over the industrial tem-
perature range, the absolute maximum positive voltage at
any driver pin should be limited to 10V to avoid damage to
the part. At higher ambient temperatures, the rise in die
temperature, due to the short-circuit current, may trip the
thermal shutdown circuit. This circuit protects the part
against prolonged shorts at the driver outputs. If a driver
output is shorted to another output or to V
CC
, the current
will be limited to 250mA. If the die temperature rises above
150°C, the thermal shutdown circuit three-states the
driver outputs to open the current path. When the die cools
down to about 130°C, the driver outputs are taken out of
three-state. If the short persists, the part will heat again
and the cycle will repeat. This thermal oscillation occurs at
about 10Hz and protects the part from excessive power
dissipation. The average fault current drops as the driver
cycles between active and three-state. When the short is
removed, the part will return to normal operation.
When the driver is disabled, the receiver inputs can
withstand the entire –7V to 12V RS485 common mode
range without damage.
