MAX3053
±80V Fault-Protected, 2Mbps,
Low Supply Current CAN Transceiver
_______________________________________________________________________________________ 9
Slope Control
Connect a resistor from RS to ground to select slope con-
trol mode (see Table 2). In slope control mode, the gates
of the line drivers are charged with a controlled current,
proportional to the resistor connected to the RS pin.
Transmission speed ranges from 40kbps to 500kbps.
Controlling the rise and fall slope reduces EMI and allows
the use of an unshielded twisted pair or a parallel pair of
wires as bus lines. The transfer function for selecting the
resistor value is given by:
R
RS
(kΩ) = 12000 / speed (in kbps).
See the Typical Operating Characteristics for the Slew
Rate vs. R
RS
graph.
Shutdown
To place the MAX3053 in shutdown, the SHDN pin
should be driven to GND. In shutdown mode, the
device is switched off. The outputs are high impedance
to ±80V.
Receiver
The receiver takes differential input from the bus lines
(CANH, CANL) and converts this data to a single-
ended output (RXD) to the CAN controller. It consists of
a comparator that senses the difference ∆V = (CANH -
CANL) with respect to an internal threshold of 0.7V. If
this difference is positive (i.e., ∆V > 0.9V), a logic low is
present at the RXD pin. If negative (i.e., ∆V < 0.5V), a
logic high is present.
The receiver always echoes the transmitted data.
The CANH and CANL common-mode range is from -7V
to +12V. RXD is logic high when CANH and CANL are
shorted or terminated and undriven.
Thermal Shutdown
If the junction temperature exceeds +160°C, the device
is switched off. The hysteresis is about 20°C, disabling
thermal shutdown once the temperature declines to
+140°C and the device is turned back on.
Autoshutdown
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 determines the
threshold of inactivity time, after which the autoshutdown
triggers (see Typical Operating Characteristics).
Use a 100nF capacitor as C
SHDN
for a typical threshold
of 20ms. Change the capacitor value according to the
following equation to change the threshold time period:
Drive SHDN high to force the MAX3053 on and disable
autoshutdown.
When the MAX3053 is in shutdown mode, only the
wakeup comparator is active, and normal bus commu-
nication is ignored. The remote master of the CAN sys-
tem wakes up the MAX3053 with a signal greater than
9V on CANH. The local CAN controller wakes up the
MAX3053 by driving SHDN high or TXD.
Driver Output Protection
The MAX3053 has several features to protect itself from
damage. Thermal shutdown switches off the device
and puts CANH and CANL into high impedance if the
junction temperature exceeds +160°C. Thermal protec-
tion is needed particularly when a bus line is short cir-
cuited. The hysteresis for the thermal shutdown is
about 20°C.
