High Speed
Connect RS to ground to set the MAX3050/MAX3057 to
high-speed mode. When operating in high-speed
mode, the MAX3050/MAX3057 can achieve transmis-
sion rates of up to 2Mbps. Line drivers are switched on
and off as quickly as possible. However, in this mode,
no measures are taken to limit the rise and fall slope of
the data signal, allowing for potential EMI emissions. If
using the MAX3050/MAX3057 in high-speed mode, use
shielded twisted-pair cable to avoid EMI problems.
Slope Control
Connect a resistor from RS to ground to select slope-
control mode (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 func-
tion for selecting the resistor value is given by:
R
RS
(kΩ) = 12000/speed (in kbps)
See the Slew Rate vs. R
RS
graph in the Typical
Operating Characteristics section.
Receiver
The receiver reads differential input from the bus lines
(CANH, CANL) and transfers this data as 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 > 0.7V), a logic low is
present at the RXD pin. If negative (i.e., ∆V < 0.7V), a
logic high is present.
The receiver always echoes the transmitted data.
The CANH and CANL common-mode range is -7V to
+12V. RXD is logic high when CANH and CANL are
shorted or terminated and undriven. If the differential
receiver input voltage (CANH - CANL) is less than or
equal to 0.5V, RXD is logic high. If (CANH - CANL) is
greater than or equal to 0.9V, RXD is logic low.
Standby
If a logic high level is applied to RS, the MAX3050/
MAX3057 enter a low-current standby mode. In this
mode, the transmitter is switched off and the receiver is
switched to a low-current state. If dominant bits are
detected, RXD switches to a low level. The microcon-
troller should react to this condition by switching the
transceiver back to normal operation (through RS). Due
to the reduced power mode, the receiver is slower in
standby mode, and the first message may be lost at
higher bit rates.
Thermal Shutdown
If the junction temperature exceeds +160°C, the device
is switched off. The hysteresis is approximately 20°C,
disabling thermal shutdown once the temperature
reaches +140°C.
Shutdown (MAX3057)
Drive SHDN low to enter shutdown mode. In shutdown
mode, the device is switched off. The outputs are high
impedance to ±80V. The MAX3057 features a pullup at
SHDN. If shutdown is forced low and then left floating,
the device switches back to normal operating mode.
MAX3050/MAX3057
±80V Fault-Protected, 2Mbps, Low Supply
Current CAN Transceivers
_______________________________________________________________________________________ 9
