MAX3051(2004) データシートの表示（PDF） - Maxim Integrated
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MAX3051 Datasheet PDF : 13 Pages
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+3.3V, 1Mbps, Low-Supply-Current
CAN Transceiver
Detailed Description
The MAX3051 interfaces between the CAN protocol
controller and the physical wires of the bus lines in a
CAN. It provides differential transmit capability to the
bus and differential receive capability to the CAN con-
troller. It is primarily intended for +3.3V single-supply
applications that do not require the stringent fault pro-
tection specified by the automotive industry (ISO 11898)
The MAX3051 features four different modes of opera-
tion: high-speed, slope-control, standby, and shutdown
mode. High-speed mode allows data rates up to
1Mbps. The slope-control mode can be used to pro-
gram the slew rate of the transmitter for data rates of up
to 500kbps. This reduces the effects of EMI, thus allow-
ing the use of unshielded twisted or parallel cable. In
standby mode, the transmitter is shut off and the
receiver is pulled high, placing the MAX3051 in low-
current mode. In shutdown mode, the transmitter and
receiver are switched off.
The MAX3051 input common-mode range is from -7V to
+12V, exceeding the ISO 11898 specification of -2V to
+7V. These features, and the programmable slew-rate
limiting, make the part ideal for nonautomotive, harsh
environments.
The transceivers operate from a single +3.3V supply
and draw 35µA of supply current in dominant state and
2µA in recessive state. In standby mode, supply cur-
rent is reduced to 8µA. In shutdown mode, supply cur-
rent is less than 1µA.
CANH and CANL are output short-circuit current limited
and are protected against excessive power dissipation
by thermal-shutdown circuitry that places the driver
outputs into a high-impedance state.
Receiver
The receiver reads differential inputs 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 VDIFF = (CANH
- CANL) with respect to an internal threshold of +0.75V.
If this VDIFF is greater than 0.75, a logic-low is present at
RXD. If VDIFF is less than 0.75V, a logic-high is present.
The receiver always echoes the CAN BUS 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.
Mode Selection
High-Speed Mode
Connect RS to ground to set the MAX3051 to high-
speed mode. When operating in high-speed mode, the
MAX3051 can achieve transmission rates of up to
1Mbps. In high-speed mode, use shielded twisted pair
cable to avoid EMI problems.
Slope-Control Mode
Connect a resistor from RS to ground to select slope-
control mode (Table 2). In slope-control mode, CANH
and CANL slew rates are controlled by the resistor con-
nected to the RS pin. Maximum transmission speeds
are controlled by RRS and range from 40kbps to
500kbps. Controlling the rise and fall slopes reduces
EMI and allows the use of an unshielded twisted pair or
a parallel pair of wires as bus lines. The equation for
selecting the resistor value is given by:
RRS (kΩ) ≈ 12000 / (maximum speed in kbps)
Transmitter
The transmitter converts a single-ended input (TXD)
from the CAN controller to differential outputs for the
bus lines (CANH, CANL). The truth table for the trans-
mitter and receiver is given in Table 1.
See the Slew Rate vs. RRS graph in the Typical
Operating Characteristics.
Standby Mode
If a logic-high is applied to RS, the MAX3051 enters a
low-current standby mode. In this mode, the transmitter
Table 1. Transmitter and Receiver Truth Table When Not Connected to The Bus
TXD
Low
High or float
X
X
RS
VRS < 0.75 x
VCC
VRS < 0.75 x
VCC
VRS > 0.75 x
VCC
X
SHDN
Low
Low
Low
High
CANH
CANL
High
Low
5kΩ to 25kΩ to
VCC / 2
5kΩ to 25kΩ to
GND
Floating
5kΩ to 25kΩ to
VCC / 2
5kΩ to 25kΩ to
GND
Floating
BUS STATE
Dominant
Recessive
Recessive
Floating
RXD
Low
High
High
High
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