Datasheet

SN65HVD255
SN65HVD256, SN65HVD257
SLLSEA2C –DECEMBER 2011–REVISED SEPTEMBER 2013 www.ti.com
SILENT MODE
Activate silent mode (receive only) by setting S high. The CAN driver is turned off while the receiver remains
active and RXD outputs the received bus state.
APPLICATION NOTE: Silent mode may be used to implement babbling idiot protection, to ensure that the
driver does not disrupt the network during a local fault. Silent mode may also be used in redundant systems
to select or de-select the redundant transceiver (driver) when needed.
DRIVER AND RECEIVER FUNCTION TABLES
Table 2. Driver Function Table
INPUTS OUTPUTS
DRIVEN BUS
DEVICE
STATE
S
(1)(2)
TXD
(1)(3)
CANH
(1)
CANL
(1)
L H L Dominant
L or Open
All Devices H or Open Z Z Recessive
H X Z Z Recessive
(1) H = high level, L = low level, X= irrelevant, Z = common mode (recessive) bias to V
CC
/ 2. See
Figure 3 and Figure 4 for bus state and common mode bias information.
(2) Devices have an internal pull down to GND on S pin. If S pin is open the pin will be pulled low and the
device will be in normal mode.
(3) Devices have an internal pull up to V
CC
on TXD pin. If the TXD pin is open the pin will be pulled high
and the transmitter will remain in recessive (non-driven) state.
Table 3. Receiver Function Table
CAN DIFFERENTIAL INPUTS
DEVICE MODE BUS STATE RXD PIN
(1)
V
ID
= V
CANH
– V
CANL
V
ID
≥ 0.9 V Dominant L
(2)
0.5 V < V
ID
< 0.9 V ? ?
Normal or Silent
V
ID
≤ 0.5 V Recessive H
Open (V
ID
≈ 0 V) Open H
(1) H = high level, L = low level, ? = indeterminate.
(2) RXD output remains dominant (low) as long as the bus is dominant. On SN65HVD257 device with
RXD dominant timeout, once the bus has been dominant longer than the dominant timeout, t
RXD_DTO
,
the RXD pin will return recessive (high). See RXD Dominant Timeout (SN65HVD257) for a description
of behavior during receiving a bus stuck dominant condition.
DIGITAL INPUTS AND OUTPUTS
5 V V
CC
Only Devices (SN65HVD255 and SN65HVD257):
The 5V V
CC
device is supplied by a single 5 V rail. The digital inputs are 5 V and 3.3 V compatible. This device
has a 5 V (V
CC
) level RXD output. TXD is internally pulled up to V
CC
and S is internally pulled down to GND.
APPLICATION NOTE: TXD is internally pulled up to V
CC
and the S pin is internally pulled down to GND.
However, the internal bias may only put the device into a known state if the pins float. The internal bias may
be inadequate for system-level biasing. TXD pullup strength and CAN bit timing require special consideration
when the SN65HVD25x devices are used with an open-drain TXD output on the CAN controller. An
adequate external pullup resistor must be used to ensure that the CAN controller output of the μP maintains
adequate bit timing input to the SN65HVD25x.
5 V V
CC
with V
RXD
RXD output Supply Devices (SN65HVD256):
This device is a 5V V
CC
CAN transceiver with a separate supply for the RXD output, V
RXD
. The digital inputs are
5 V and 3.3 V compatible. These devices have a V
RXD
-level RXD output. TXD remains weakly pulled up to V
CC
.
APPLICATION NOTE: On device versions with a V
RXD
supply that shifts the RXD output level, the input pins
of the device remain the same. TXD remains weakly pulled up to V
CC
internally. Thus, a small I
IH
current
flows if the TXD input is used below V
CC
levels.
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Product Folder Links: SN65HVD255 SN65HVD256 SN65HVD257