MAX3050/MAX3057
AutoShutdown (MAX3050)
To manage power consumption, AutoShutdown puts
the device into shutdown mode after the device has
been inactive for a period of time. The value of an
external capacitor (C
SHDN
) connected to SHDN deter-
mines the threshold of inactivity time, after which the
AutoShutdown triggers. Floating SHDN allows the
MAX3050 to automatically change from active mode to
shutdown.
Use a 100nF capacitor as C
SHDN
for a typical thresh-
old of 20ms. Change the capacitor value according to
the following equation to change the threshold time
period.
V
SHDN
is the threshold of SHDN guaranteed to be less
than 2V in the Electrical Characteristics table. Drive
SHDN high to turn the MAX3050 on and disable
AutoShutdown.
When the MAX3050 is in shutdown mode, only the
wake-up comparator is active, and normal bus commu-
nication is ignored. The remote master of the CAN sys-
tem wakes up the MAX3050 with a signal greater than
9V on CANH. Internal circuitry in the MAX3050 puts the
device in normal operation by driving SHDN high.
The MAX3057 does not have the AutoShutdown feature.
Driver Output Protection
The MAX3050/MAX3057 have several features that pro-
tect them from damage. Thermal shutdown switches off
the device and puts CANH and CANL into high imped-
ance if the junction temperature exceeds +160°C.
Thermal protection is needed particularly when a bus
line is short circuited. The hysteresis for the thermal
shutdown is approximately 20°C.
Additionally, a current-limiting circuit protects the trans-
mitter output stage against short-circuits to positive and
negative battery voltage. Although the power dissipa-
tion increases during this fault condition, this feature
prevents destruction of the transmitter output stage.
