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

mines the threshold of inactivity time, after which the

AutoShutdown triggers. Floating SHDN allows the

MAX3050 to automatically change from active mode to

shutdown.

old of 20ms. Change the capacitor value according to

the following equation to change the threshold time

period.

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.

CnF

time s

VV

CC

.(

)

=

×µ

−

()

002

SHDN

±80V Fault-Protected, 2Mbps, Low Supply

Current CAN Transceivers

10

______________________________________________________________________________________

FFT

500mV/div

CANH - CANL

1V/div

Figure 5. FFT Dominant Bus at 2Mbps

FFT

200mV/div

CANH - CANL

1V/div

Figure 6. FFT Recessive Bus at 2Mbps

FFT

500mV/div

CANH - CANL

1V/div

Figure 7. FFT Dominant Bus at 500kbps