TJA1052I All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2018. All rights reserved.
Product data sheet Rev. 5 — 29 January 2018 5 of 27
NXP Semiconductors
TJA1052i
Galvanically isolated high-speed CAN transceiver
7. Functional description
7.1 Operation
7.1.1 Normal mode
During normal operation, the TJA1052i transceiver transmits and receives data via bus
lines CANH and CANL (see Figure 1
for the block diagram). The differential receiver
converts the analog data on the bus lines into digital data, which is output on pin RXD.
The slopes of the output signals on the bus lines are controlled internally and are
optimized in a way that guarantees the lowest possible EME.
The isolator used in the TJA1052i is an AC device that employs on-off keying to
guarantee the DC output state at all times. The states of TXD, RXD and the CAN bus at
start-up, shut-down and during normal operation are described in Table 5
.
Care should be taken regarding power sequencing if the device is used in networks that
support remote wake-up (see Section 12 “
Application information”).
7.1.2 Standby mode
The TJA1052i cannot transmit or receive regular CAN messages in Standby mode. Only
the isolator and low-power CAN receiver are active, monitoring the bus lines for activity.
The bus wake-up filter ensures that only bus dominant and bus recessive states that
persist longer than t
fltr(wake)bus
are reflected on the RXD pin (see Figure 3). To reduce
current consumption, the CAN bus is terminated to GND and not biased to V
DD2
/2 as in
Normal mode.
Standby mode is selected by setting pin STB HIGH. The TJA1052i also switches to
Standby mode when an undervoltage is detected on V
DD2
(V
uvd(swoff)(VDD2)
< V
DD2
<
V
uvd(stb)(VDD2)
; Section 7.2.3). An internal pull-up ensures that Standby mode is selected
by default when pin STB is not connected.
In Standby mode:
• The CAN transmitter if off
• The normal CAN receiver is off
• The low-power CAN receiver is active
• CANH and CANL are biased to GND
• The signal received at the low-power CAN receiver is reflected on pin RXD
• V
DD2
undervoltage detection is active
Table 5. Input/output states at start-up, shut-down and during normal operation
TXD RXD V
DD1
V
DD2
CAN Comments
HH>V
uvd(VDD1)
>V
uvd(stb)VDD2)
recessive Normal mode operation
LL>V
uvd(VDD1)
>V
uvd(stb)VDD2)
dominant Normal mode with TXD dominant time-out active
X X unpowered >V
uvd(stb)VDD2)
dominant dominant after V
DD1
power loss until TXD dominant
timeout; recessive while V
DD2
is ramping up from
an unpowered state
XL>V
uvd(VDD1)
unpowered disconnected RXD transitions L-to-H when V
DD2
restored
